Gamma-ray Burst 210104A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:27:12 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1015873,   Seg_Num: 0
GRB_RA:          103.705d {+06h 54m 49s} (J2000),
                 104.213d {+06h 56m 51s} (current),
                 102.491d {+06h 49m 58s} (1950)
GRB_DEC:         +64.661d {+64d 39' 39"} (J2000),
                 +64.632d {+64d 37' 57"} (current),
                 +64.724d {+64d 43' 26"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       2033 [cnts]    Image_Peak=197 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   121     E_range: 15-50 keV
BKG_INTEN:       18719 [cnts]
BKG_TIME:        41205.72 SOD {11:26:45.72} UT
BKG_DUR:         8 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.10 SOD {11:26:59.10} UT
GRB_PHI:         -49.88 [deg]
GRB_THETA:        20.01 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     23.38 [sigma]
IMAGE_SIGNIF:    11.40 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +1  +1  +0  +0 +74  +0 
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        138.02 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.37d {+11h 29m 30s}   +9.02d {+09d 01' 14"}
MOON_DIST:        72.60 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.03, 24.69 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       97.79, 41.59 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 150.99,3.62 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=631452424).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:27:23 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     631452424
GRB_RA:           86.467d {+05h 45m 52s} (J2000),
                  87.144d {+05h 48m 34s} (current),
                  84.858d {+05h 39m 26s} (1950)
GRB_DEC:         +74.017d {+74d 01' 00"} (J2000),
                 +74.023d {+74d 01' 24"} (current),
                 +73.996d {+73d 59' 44"} (1950)
GRB_ERROR:       10.08 [deg radius, statistical plus systematic]
GRB_INTEN:       230 [cnts/sec]
DATA_SIGNIF:     7.10 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         158.00 [deg]
GRB_THETA:       145.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      1.08
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       0,0,0, 0,0,0, 1,0,0, 0,1,0, 0,0,
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        127.69 [deg]   Sun_angle= -10.8 [hr] (East of Sun)
MOON_POSTN:      172.37d {+11h 29m 30s}   +9.02d {+09d 01' 12"}
MOON_DIST:        80.02 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      139.45, 21.67 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       88.47, 50.60 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 212.10,-17.97 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=1015873).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:27:33 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     631452424
GRB_RA:           86.067d {+05h 44m 16s} (J2000),
                  86.742d {+05h 46m 58s} (current),
                  84.462d {+05h 37m 51s} (1950)
GRB_DEC:         +73.950d {+73d 57' 00"} (J2000),
                 +73.957d {+73d 57' 26"} (current),
                 +73.927d {+73d 55' 37"} (1950)
GRB_ERROR:       7.02 [deg radius, statistical plus systematic]
GRB_INTEN:       304 [cnts/sec]
DATA_SIGNIF:     14.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         158.00 [deg]
GRB_THETA:       145.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.93
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 1,0,0, 0,1,0, 0,0,
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        127.71 [deg]   Sun_angle= -10.7 [hr] (East of Sun)
MOON_POSTN:      172.38d {+11h 29m 30s}   +9.02d {+09d 01' 10"}
MOON_DIST:        80.13 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      139.46, 21.54 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       88.29, 50.53 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 212.10,-17.97 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=1015873).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:27:45 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      68
TRIGGER_NUM:     631452424
GRB_RA:           74.983d {+04h 59m 56s} (J2000),
                  75.555d {+05h 02m 13s} (current),
                  73.627d {+04h 54m 31s} (1950)
GRB_DEC:         +69.500d {+69d 30' 00"} (J2000),
                 +69.530d {+69d 31' 47"} (current),
                 +69.425d {+69d 25' 29"} (1950)
GRB_ERROR:       4.25 [deg radius, statistical plus systematic]
GRB_INTEN:       1032 [cnts/sec]
DATA_SIGNIF:     22.40 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         167.00 [deg]
GRB_THETA:       145.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.60
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      93%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 1,0,0, 0,1,0, 0,0,
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        129.83 [deg]   Sun_angle= -10.0 [hr] (East of Sun)
MOON_POSTN:      172.38d {+11h 29m 31s}   +9.02d {+09d 01' 07"}
MOON_DIST:        83.93 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      141.75, 16.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       82.43, 46.45 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 212.10,-17.97 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=1015873).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:27:44 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     631452424
GRB_RA:           99.860d {+06h 39m 26s} (J2000),
                 100.421d {+06h 41m 41s} (current),
                  98.522d {+06h 34m 05s} (1950)
GRB_DEC:         +68.460d {+68d 27' 36"} (J2000),
                 +68.439d {+68d 26' 22"} (current),
                 +68.504d {+68d 30' 16"} (1950)
GRB_ERROR:       2.67 [deg radius, statistical only]
DATA_SIGNIF:     19.70 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         159.00 [deg]
GRB_THETA:       138.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        134.12 [deg]   Sun_angle= -11.7 [hr] (East of Sun)
MOON_POSTN:      172.38d {+11h 29m 31s}   +9.02d {+09d 01' 07"}
MOON_DIST:        75.04 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      146.60, 24.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       95.12, 45.20 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_631452424.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=1015873).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:28:55 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     631452424
GRB_RA:          110.770d {+07h 23m 05s} (J2000),
                 111.319d {+07h 25m 17s} (current),
                 109.457d {+07h 17m 50s} (1950)
GRB_DEC:         +68.720d {+68d 43' 12"} (J2000),
                 +68.678d {+68d 40' 41"} (current),
                 +68.816d {+68d 48' 57"} (1950)
GRB_ERROR:       2.53 [deg radius, statistical only]
DATA_SIGNIF:     21.40 [sigma]
DATA_INTERVAL:   11.264 [sec]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         154.00 [deg]
GRB_THETA:       136.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        133.85 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      172.39d {+11h 29m 33s}   +9.01d {+09d 00' 51"}
MOON_DIST:        71.36 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      146.95, 27.99 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      100.69, 46.05 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_631452424.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the CALET_GBM event (trignum=1293794541).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:36:16 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     631452424
GRB_RA:          107.940d {+07h 11m 46s} (J2000),
                 108.472d {+07h 13m 53s} (current),
                 106.669d {+07h 06m 41s} (1950)
GRB_DEC:         +67.090d {+67d 05' 24"} (J2000),
                 +67.053d {+67d 03' 12"} (current),
                 +67.173d {+67d 10' 22"} (1950)
GRB_ERROR:       2.88 [deg radius, statistical only]
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.87 SOD {11:26:59.87} UT
GRB_PHI:         156.00 [deg]
GRB_THETA:       135.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       285.56d {+19h 02m 15s}  -22.66d {-22d 39' 52"}
SUN_DIST:        135.57 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      172.45d {+11h 29m 49s}   +8.99d {+08d 59' 11"}
MOON_DIST:        71.77 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      148.68, 26.79 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       99.64, 44.25 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_locplot_all_bn210104477.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(3.0<100sec) coincident with the CALET_GBM event (trignum=1293794541).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:28:38 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
GRB_RA:          103.7707d {+06h 55m 04.9s} (J2000),
                 104.2795d {+06h 57m 07.0s} (current),
                 102.5565d {+06h 50m 13.5s} (1950)
GRB_DEC:         +64.6743d {+64d 40' 27.4"} (J2000),
                 +64.6460d {+64d 38' 45.4"} (current),
                 +64.7377d {+64d 44' 15.7"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       57 [cnts]
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41281.82 SOD {11:28:01.82} UT,   62.7 [sec] since BAT Trigger Time
CENTROID_X:      253.41,  raw= 253  [pixels]
CENTROID_Y:      242.75,  raw= 243  [pixels]
ROLL:            357.42 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -130.47
GRB_POS_XRT_Z:   -127.26
IMAGE_URL:       sw01015873000msxps_rw.img
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        138.01 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.39d {+11h 29m 33s}   +9.02d {+09d 00' 55"}
MOON_DIST:        72.58 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.02, 24.72 [deg] galactic lon,lat of the burst
ECL_COORDS:       97.83, 41.61 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:28:40 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
GRB_RA:          103.7707d {+06h 55m 04.9s} (J2000),
                 104.2795d {+06h 57m 07.0s} (current),
                 102.5565d {+06h 50m 13.5s} (1950)
GRB_DEC:         +64.6743d {+64d 40' 27.4"} (J2000),
                 +64.6460d {+64d 38' 45.4"} (current),
                 +64.7377d {+64d 44' 15.7"} (1950)
GRB_ERROR:       5.0 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       57 [cnts]
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41281.82 SOD {11:28:01.82} UT,   62.7 [sec] since BAT Trigger Time
CENTROID_X:      253.41,  raw= 253  [pixels]
CENTROID_Y:      242.75,  raw= 243  [pixels]
ROLL:            357.42 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -130.47
GRB_POS_XRT_Z:   -127.26
IMAGE_URL:       sw01015873000msxps_rw.img
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        138.01 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.39d {+11h 29m 33s}   +9.02d {+09d 00' 54"}
MOON_DIST:        72.58 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.02, 24.72 [deg] galactic lon,lat of the burst
ECL_COORDS:       97.83, 41.61 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:28:28 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1015873,   Seg_Num: 0
GRB_RA:          103.7707d {+06h 55m 04.96s} (J2000),
                 104.2795d {+06h 57m 07.09s} (current),
                 102.5565d {+06h 50m 13.56s} (1950)
GRB_DEC:         +64.6743d {+64d 40' 27.4"} (J2000),
                 +64.6460d {+64d 38' 45.4"} (current),
                 +64.7377d {+64d 44' 15.7"} (1950)
GRB_ERROR:       5.3 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.41e-09 [erg/cm2/sec]
GRB_SIGNIF:      7.54 [sigma]
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41281.82 SOD {11:28:01.82} UT,   62.7 [sec] since BAT Trigger Time
TAM[0-3]:        327.65 237.22 261.61 243.50
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 54"}
SUN_DIST:        138.01 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.38d {+11h 29m 32s}   +9.02d {+09d 00' 57"}
MOON_DIST:        72.58 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.02, 24.72 [deg] galactic lon,lat of the burst
ECL_COORDS:       97.83, 41.61 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.88 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:30:25 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1015873,   Seg_Num: 0
GRB_RA:          103.705d {+06h 54m 49s} (J2000),
                 104.213d {+06h 56m 51s} (current),
                 102.491d {+06h 49m 58s} (1950)
GRB_DEC:         +64.661d {+64d 39' 39"} (J2000),
                 +64.632d {+64d 37' 57"} (current),
                 +64.724d {+64d 43' 26"} (1950)
GRB_DATE:        19218 TJD;     4 DOY;   21/01/04
GRB_TIME:        41219.10 SOD {11:26:59.10} UT
TRIGGER_INDEX:   121
GRB_PHI:         -49.88 [deg]
GRB_THETA:        20.01 [deg]
DELTA_TIME:      -57.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     23.38 [sigma]
IMAGE_SIGNIF:    11.40 [sigma]
LC_URL:          sw01015873000msb.lc
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 53"}
SUN_DIST:        138.02 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.40d {+11h 29m 36s}   +9.01d {+09d 00' 31"}
MOON_DIST:        72.62 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.03, 24.69 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       97.79, 41.59 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 150.99,3.62 [deg].

GCN Circular #29232
The Fermi GBM team reports the detection of a likely LONG GRB
At 11:26:59 UT on 4 Jan 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210104A (trigger 631452424.865632 / 210104477).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 107.9, Dec = 67.1 (J2000 degrees, equivalent to J2000 07h 11m, 67d 05'), with a statistical uncertainty of 2.9 degrees.
The angle from the Fermi LAT boresight is 135.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_skymap_all_bn210104477.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_healpix_all_bn210104477.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210104477/quicklook/glg_lc_medres34_bn210104477.gif

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:38:35 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
ROLL:            357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41501.93 SOD {11:31:41.93} UT,   282.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     631452728
X_OFFSET:        1158 [pixels]
Y_OFFSET:        982 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1318
Y_GRB_POS:       1142
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0309.fits
SUN_POSTN:       285.57d {+19h 02m 16s}  -22.66d {-22d 39' 51"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.47d {+11h 29m 54s}   +8.98d {+08d 58' 40"}
MOON_DIST:        72.68 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:38:48 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
ROLL:            357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41501.93 SOD {11:31:41.93} UT,   282.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     631452728
X_OFFSET:        1158 [pixels]
Y_OFFSET:        982 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1318
Y_GRB_POS:       1142
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0309.fits
SUN_POSTN:       285.57d {+19h 02m 16s}  -22.66d {-22d 39' 51"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.48d {+11h 29m 54s}   +8.98d {+08d 58' 37"}
MOON_DIST:        72.68 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #29233
E. Troja (NASA/GSFC/UMCP), M. G. Bernardini (INAF-OAB), A. A. Breeveld (UCL-MSSL), P. D'Avanzo (INAF-OAB), P. A. Evans (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB), K. L. Page (U Leicester) and T. Sbarrato (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team:
At 11:26:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210104A (trigger=1015873). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 103.705, +64.661 which is
```
   RA(J2000) = 06h 54m 49s
   Dec(J2000) = +64d 39' 39"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 40 sec. The peak count rate was ~16000 counts/sec (15-350 keV), at ~21 sec after the trigger.
The XRT began observing the field at 11:28:01.8 UT, 62.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 103.7707, 64.6743 which is equivalent to:
```
   RA(J2000)  = 06h 55m 4.97s
   Dec(J2000) = +64d 40' 27.5"
```
with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 111 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 1.41e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of nominal 150.0 seconds with the White filter starting 70 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at
```
RA(J2000) = 06:55:05.25 = 103.77188
DEC(J2000) = +64:40:34.0 = 64.67611
```
with a 90%-confidence error radius of about 1.10 arc sec. This position is 6.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 15.52. No correction has been made for the expected extinction corresponding to E(B-V) of 0.04.
Burst Advocate for this burst is E. Troja (eleonora.troja AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:44:11 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
POINT_ROLL:      357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  42079.77 SOD {11:41:19.77} UT,   860.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.705
N_STARS:         190
X_OFFSET:        598 [pixels]
Y_OFFSET:        422 [pixels]
X_MAX:           2037 [pixels]
Y_MAX:           1861 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01015873000msufc0860.fits
SUN_POSTN:       285.57d {+19h 02m 17s}  -22.66d {-22d 39' 50"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.52d {+11h 30m 06s}   +8.96d {+08d 57' 24"}
MOON_DIST:        72.72 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:44:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
POINT_ROLL:      357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  42079.77 SOD {11:41:19.77} UT,   860.7 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.705
N_STARS:         190
X_OFFSET:        598 [pixels]
Y_OFFSET:        422 [pixels]
X_MAX:           2037 [pixels]
Y_MAX:           1861 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01015873000msufc0860.fits
SUN_POSTN:       285.57d {+19h 02m 17s}  -22.66d {-22d 39' 50"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.53d {+11h 30m 06s}   +8.96d {+08d 57' 21"}
MOON_DIST:        72.72 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:45:35 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
ROLL:            357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  42079.77 SOD {11:41:19.77} UT,   860.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     631453306
X_OFFSET:        1157 [pixels]
Y_OFFSET:        981 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1317
Y_GRB_POS:       1141
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0887.fits
SUN_POSTN:       285.57d {+19h 02m 17s}  -22.66d {-22d 39' 49"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.54d {+11h 30m 09s}   +8.95d {+08d 57' 05"}
MOON_DIST:        72.73 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:45:48 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
ROLL:            357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  42079.77 SOD {11:41:19.77} UT,   860.7 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     631453306
X_OFFSET:        1157 [pixels]
Y_OFFSET:        981 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1317
Y_GRB_POS:       1141
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0887.fits
SUN_POSTN:       285.57d {+19h 02m 17s}  -22.66d {-22d 39' 49"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.54d {+11h 30m 09s}   +8.95d {+08d 57' 02"}
MOON_DIST:        72.73 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #29234
B. Biltzinger, F. Kunzweiler, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 631452424 at 11:26:59 on 04 Jan. 2021 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60).
The best-fit position (1 sigma statistical errors) is:
```
RA(2000.0) = 102.7+/-5.4 deg
Decl.(2000.0) = 69.8+/-1.3 deg
```
We estimate an additional systematic error of 1 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB210104477/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB210104477/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB210104477/json
GCN Circular #29235
L. P. Xin(NAOC), J. Wang(GXU), X. H. Han(NAOC), J. Y. Wei(NAOC), G. W. LI(NAOC), L. H. Li(NAOC), C. Wu(NAOC), X. G. Wang(GXU), E. W. Liang (GXU), R. S. Zhang(NAOC), Y. L. Qiu(NAOC), and J. S. Deng(NAOC) report:
We began to observe GRB 210104A (Troja et al., GCN 29233) with Xinglong GWAC-F60A telescope, China, at 11:28:00 (UT), 4th. Jan. 2021, about 61 sec after the burst.
A series of R, I, and B band images were obtained. The optical afterglow (Troja et al., GCN 29233) was clear detected in our images.
The brightness is about 14.5 mag in R band at 71 sec after the burst, calibrated to the USNO B1.0 catalog.
The observations are continuing
GCN Circular #29236
Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), S. Guziy (Univ. of Nikolaev) and D. R. Xiong, Y.F. Fan, J.M. Bai, C. J. Wang, Y.X. Xin, X. H. Zhao (Yunnan Observatories of CAS) on behalf of a larger collaboration, report:
"Following the detection of GRB 210104A by Swift (Troja et al. GCNC 29233) and Fermi (Fermi GBM team GCNC 29232, Biltzinger et al. GCNC 29234), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) started to gather images in clear filter starting at 2021-01-04 11:27:52 UT (~53 s after trigger). The optical afterglow reported by Swift/UVOT (Troja et al. GCNC 29233) is detected with a magnitude of 15.15+-0.15 in the first 5 s exposure image. Additional observations are ongoing."
We thank the staff at Lijiang observatory for their excellent support.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:37:28 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
POINT_ROLL:      357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41501.93 SOD {11:31:41.93} UT,   282.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.549
N_STARS:         70
X_OFFSET:        838 [pixels]
Y_OFFSET:        662 [pixels]
X_MAX:           1797 [pixels]
Y_MAX:           1621 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01015873000msufc0282.fits
SUN_POSTN:       285.56d {+19h 02m 16s}  -22.66d {-22d 39' 52"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.46d {+11h 29m 51s}   +8.98d {+08d 58' 55"}
MOON_DIST:        72.67 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:30:59 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.691d {+06h 54m 46s} (J2000)
POINT_DEC:       +64.638d {+64d 38' 17"} (J2000)
POINT_ROLL:      357.423d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41289.96 SOD {11:28:09.96} UT,   70.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.696
N_STARS:         90
X_OFFSET:        664 [pixels]
Y_OFFSET:        528 [pixels]
X_MAX:           1623 [pixels]
Y_MAX:           1487 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01015873000msufc0070.fits
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 53"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.41d {+11h 29m 38s}   +9.01d {+09d 00' 23"}
MOON_DIST:        72.62 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.05, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:32:24 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.691d {+06h 54m 46s} (J2000)
POINT_DEC:       +64.638d {+64d 38' 17"} (J2000)
ROLL:            357.423d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41289.96 SOD {11:28:09.96} UT,   70.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     631452516
X_OFFSET:        1158 [pixels]
Y_OFFSET:        982 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1318
Y_GRB_POS:       1142
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0097.fits
SUN_POSTN:       285.56d {+19h 02m 15s}  -22.66d {-22d 39' 53"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.42d {+11h 29m 41s}   +9.00d {+09d 00' 04"}
MOON_DIST:        72.63 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.05, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:32:35 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.691d {+06h 54m 46s} (J2000)
POINT_DEC:       +64.638d {+64d 38' 17"} (J2000)
ROLL:            357.423d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41289.96 SOD {11:28:09.96} UT,   70.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     631452516
X_OFFSET:        1158 [pixels]
Y_OFFSET:        982 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1318
Y_GRB_POS:       1142
BINNING_INDEX:   1
IM_URL:          sw01015873000msuni0097.fits
SUN_POSTN:       285.56d {+19h 02m 15s}  -22.66d {-22d 39' 53"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.42d {+11h 29m 41s}   +9.00d {+09d 00' 01"}
MOON_DIST:        72.64 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.05, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:37:42 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.688d {+06h 54m 45s} (J2000)
POINT_DEC:       +64.636d {+64d 38' 10"} (J2000)
POINT_ROLL:      357.418d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41501.93 SOD {11:31:41.93} UT,   282.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.549
N_STARS:         70
X_OFFSET:        838 [pixels]
Y_OFFSET:        662 [pixels]
X_MAX:           1797 [pixels]
Y_MAX:           1621 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01015873000msufc0282.fits
SUN_POSTN:       285.57d {+19h 02m 16s}  -22.66d {-22d 39' 51"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.47d {+11h 29m 52s}   +8.98d {+08d 58' 52"}
MOON_DIST:        72.67 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.06, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 04 Jan 21 11:31:16 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1015873,   Seg_Num: 0
POINT_RA:        103.691d {+06h 54m 46s} (J2000)
POINT_DEC:       +64.638d {+64d 38' 17"} (J2000)
POINT_ROLL:      357.423d
IMG_START_DATE:  19218 TJD;     4 DOY;   21/01/04
IMG_START_TIME:  41289.96 SOD {11:28:09.96} UT,   70.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.696
N_STARS:         90
X_OFFSET:        664 [pixels]
Y_OFFSET:        528 [pixels]
X_MAX:           1623 [pixels]
Y_MAX:           1487 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw01015873000msufc0070.fits
SUN_POSTN:       285.56d {+19h 02m 14s}  -22.67d {-22d 39' 53"}
SUN_DIST:        138.05 [deg]   Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN:      172.41d {+11h 29m 38s}   +9.01d {+09d 00' 19"}
MOON_DIST:        72.63 [deg]
MOON_ILLUM:      71 [%]
GAL_COORDS:      151.05, 24.68 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       97.79, 41.57 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN Circular #29237
R. Hosokawa, R. Adachi, M. Niwano, K. L. Murata, F. Ogawa, N. Nakamura, N. Ito, S. Ogata, H. Takamatsu, H. Hara, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210104A (The Fermi GBM team , GCN 29232, E. Troja et al., GCN 29233, B. Biltzinger et al., GCN 29234) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started at 2021-01-04 11:27:54 UT (55s after Swift BAT trigger). We detected the point source at the position consistent with the afterglow detected previously(E. Troja et al., GCN 29233, L. P. Xin et al., GCN 29235, Y.-D. Hu et al., GCN 29236). We measured the magnitudes as follows.
```
T0+[sec] MID-UT T-EXP[sec] measured magnitudes
------------------------------------------------------------------------------------------------
55 11:28:24 60 g'=14.6+/-0.1, Rc=14.2+/-0.1, Ic=13.8+/-0.1
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
```
We used PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al., https://doi.org/10.1093/pasj/psaa091, https://arxiv.org/abs/2008.11486; https://github.com/MNiwano/Eclaire).
GCN Circular #29238
V. Kim (FAI, Pulkovo Observatory), A. Pozanenko (IKI), M. Krugov (FAI), S. Belkin (IKI) report on behalf of GRB-IKI-FuN:
We observed the GRB 210104A (Fermi GBM team, GCN 29232; Troja et al., GCN 29233) with AZT-20 telescope of Assy-Turgen observatory starting on Jan. 04 (UT) 12:55:33 in r'-filter. We detect the optical afterglow (Troja et al., GCN 29233; Xin et al., GCN 29235; Hu et al., GCN 29236; Hosokawa et al., GCN 29237).
Preliminary photometry of the afterglow obtained in a few initial imaging is following
```
Date       UT start  t-T0    Filter  Exp.   OT    Err.   UL (3sigma)
                      (mid, days)        (s)

2021-04-01 12:55:33  0.0632  r'(AB)  5*60   17.97 0.06   22.7
```
The photometry is based on nearby stars of PanSTARRS-PS1. Observations is continuing.
GCN Circular #29239
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University)
MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 210104A ( Fermi GBM team, GCN 29232) errorbox 13896 sec after notice time and 13949 sec after trigger time at 2021-01-04 15:19:29 UT, with upper limit up to 18.0 mag. Observations started at twilight. The observations began at zenith distance = 51 deg. The sun altitude is -10.7 deg.
The galactic latitude b = 27 deg., longitude l = 149 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1518462
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   13980 | 2021-01-04 15:19:29 |      MASTER-Tavrida | (06h 52m 09.73s , +68d 11m 37.6s) |   C |    60 | 17.7 |        
   13980 | 2021-01-04 15:19:29 |      MASTER-Tavrida | (07h 08m 11.29s , +68d 09m 51.0s) |   C |    60 | 17.9 |        
   14060 | 2021-01-04 15:20:49 |      MASTER-Tavrida | (06h 59m 02.10s , +66d 11m 00.3s) |   C |    60 | 17.7 |        
   14060 | 2021-01-04 15:20:49 |      MASTER-Tavrida | (07h 13m 46.16s , +66d 09m 08.7s) |   C |    60 | 18.0 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #29241
Takashi Horiuchi, Hidekazu Hanayama (NAOJ), Katsuhiro L. Murata, Yoichi Yatsu, Nobuyuki Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210104A (The Fermi GBM team, GCN 29232, E. Troja et al., GCN 29233) with the optical three color (g', Rc, and Ic) CCD cameras attached to the 105 cm Murikabushi telescope of Ishigakijima Astronomical Observatory, Okinawa, Japan.
The observation with a series of 60 sec exposures started on 2021-01-04 13:58:34 UT (150 min after Swift BAT trigger). We detected the point source at the position consistent with the afterglow reported by Swift UVOT and obtained the magnitudes as follows.
```
T0+[min] MID-UT T-EXP[sec] measured magnitudes
------------------------------------------------------------------------------------------------
150 2021-01-04T14:14:02 1500  g'=19.17+/-0.08, Rc=18.12+/-0.04, Ic=17.96+/-0.09
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
```
The SDSS catalog (DR16) is used for flux calibration.
GCN Circular #29245
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 2419 s of XRT Photon Counting mode data and 4 UVOT images for GRB 210104A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 103.77281, +64.67604 which is equivalent to:
```
RA (J2000): 06h 55m 5.47s
Dec (J2000): +64d 40' 33.8"
```
with an uncertainty of 1.4 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #29246
C. Malacaria (NASA-MSFC/USRA), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 11:26:59.87 UT on 04 January 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210104A (trigger 631452424 / 210104477). which was also detected by the Swift/BAT (Troja et al. 2021, GCN 29233) The Fermi GBM Final Real-time Localization (GCN 29232) is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 134 degrees.
The GBM light curve roughly consists of three separated peaks with a duration (T90) of about 32 s (50-300 keV). The time-averaged spectrum of each peak is best fit by a power law function with an exponential high-energy cutoff. For the first peak, from T0-3.1 s to T0+9.2 s, the power law index is -1.2 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 155 +/- 21 keV. For the second peak, from T0+16.4 s to T0+22.5 s, the power law index is -0.92 +/- 0.1 and Epeak is 245 +/- 23 keV. For the third peak, from T0+24.6 s to T0+33.8 s, the power law index is -1.1 +/- 0.1 and Epeak is 199 +/- 14 keV.
The event fluence values (10-1000 keV) in the first, second and third time interval are (4.004 +/- 0.270)E-06, (5.350 +/- 0.246)E-06 and (8.266 +/- 0.276)E-06 erg/cm^2, respectively. The 1-sec peak photon flux measured starting from T0+19.7 s in the 10-1000 keV band is 17.2 +/- 0.6 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #29247
A. A. Breeveld (UCL-MSSL) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210104A 71 s after the BAT trigger (Troja et al., GCN Circ. 29233). A fading source is detected in all UVOT filters in the initial exposures, at the position given in Troja et al., (GCN Circ. 29233), and also seen by others (Xin et al., GCN Circ. 29235; Hosokawa et al., GCN Circ. 29237; Kim et al., GCN Circ. 29238; Lipunov et al., GCN Circ. 29239 and Horiuchi et al., GCN Circ. 29241).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white_FC            71          221          147         14.61 � 0.02
white              562          582           20         16.23 � 0.05
white             1512         1706           39         17.02 � 0.05

b                  538          558           20         16.59 � 0.10
u_FC               283          533          246         15.28 � 0.03
v                  613          632           20         16.36 � 0.16
uvw1               662          682           20         16.12 � 0.16
uvm2               637          657           20         16.58 � 0.25
uvw2               588          608           20         17.09 � 0.26
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #29248
V. Lipunov, V.Kornilov, E.Gorbovskoy, N.Tiurina,P.Balanutsa,F.Balakin, V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, A.Chasovnikov,A.Pozdnyakov,V.Topolev, D.Cheryasov(Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov, Yu. Sergienko (Blagoveschensk Educational StateUniversity)
MASTER-Tavrida robotic telescope (Global MASTER-Net http://observ.pereplet.ru, Lipunov et al. 2010, Advances in Astronomy,v.2010,30L) started (Lipunov et al. GCN 29239) inspect of Fermi and Swift GRB 210104A (Fermi GCN 29232, 29246;Ttrig=11:26:59; Swift GCN Troja et al. GCN 29233,Beardmore et al. GCN 29245, Breeveld et al. GCN 29247 ; Barthelmy https://gcn.gsfc.nasa.gov/other/210104A.gcn3 ) at sunset at Lomonosov MSU Crimean observatory at 2021-01-04 15:19:29 UT.
We detect rebrightening of OT (discovered by Swift GCN 29233 and observed by Xin et al., GCN Circ. 29235; Hosokawa etal. GCN 29237; Kim et al. GCN 29238; Lipunov et al. GCN 29239, Horiuchi et al. GCN 29241, Breeveld et al. GCN 29247) MASTER OT J065505.45+644035.0 at 2021-01-04 15:48:32UT with unfiltered m_OT=17.3.
The message may be cited.
GCN Circular #29251
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU), E. Troja (NASA/GSFC/UMCP), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210104A (trigger #1015873) (Troja et al., GCN Circ. 29233). The BAT ground-calculated position is RA, Dec = 103.771, 64.675 deg which is
```
   RA(J2000)  =  06h 55m 04.9s
   Dec(J2000) = +64d 40' 30.6"
```
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 82%.
The mask-weighted light curve shows a multi-peaked structure that starts at ~T-1 s and ends at ~T+45 s. Several prominent peaks occur at ~T+4 s, ~T+21 s, ~T+27 s, and ~T+34 s, respectively. T90 (15-350 keV) is 32.06 +- 0.49 sec (estimated error including systematics).
The time-averaged spectrum from T-1.00 to T+45.39 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.55 +- 0.04. The fluence in the 15-150 keV band is 8.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+26.78 sec in the 15-150 keV band is 12.1 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1015873/BA/
GCN Circular #29252
Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of GRB 210104A (Troja et al., GCN 29233) using the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. Observations started at 11:59:19 UT (i.e., 0.538 hr post-burst) on 2021-01-04 and ended at 22:34:07 UT (i.e., 11.11 hr post-burst) on 2021-01-04, and a series of 120 s, 200 s, 300 s Sloan r-band frames were obtained.
Preliminary analysis of the data shows that afterglow is decaying as F_rband ~ t^(-\alpha), where \alpha = 0.73 since the very beginning of our observations.
If the afterglow continues to decay in this way, it would be of r ~ 20.3 mag at 1 day post-burst, and still bright enough for optical spectroscopy.
GCN Circular #29254
Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Taewoo Kim, and Wonseok Kang (DOAO) on behalf of a larger collaboration
We observed the optical counterpart of GRB 210104A (E. Troja et al., GCN #29233) with the 1-m class telescope in Deokheung Optical Astronomy Observatory (DOAO). We calibrated flux with the SDSS catalog and used an AB magnitude system.
```
----------------------------------------------------------
Filter Date-obs[UT]            Exp.time[s] Mag   Mag Error
----------------------------------------------------------
R      2021-01-04T13:37:29.100 300*4       18.34  0.07
I      2021-01-04T13:42:37.050 300*4       18.04  0.05
----------------------------------------------------------
```
The magnitudes are not corrected for galactic extinction.
GCN Circular #29257
Amit Kumar (ARIES), Rahul Gupta (ARIES), Dimple (ARIES), Ankur Ghosh (ARIES), Nikita Rawat (ARIES), Brajesh Kumar (ARIES), Vibhore Negi (ARIES), Amar Aryan (ARIES), Shashi B. Pandey (ARIES), and Kuntal Misra (ARIES) report:
We observed the optical afterglow of the Fermi (Fermi GBM team GCNC 29232, Biltzinger et al. GCNC 29234) and Swift detected GRB 210104A (Troja et al. GCNC 29233) with the 1.3m Devsthal Fast Optical Telescope (DFOT) at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (India), from 2021-01-04 17:50:11 to 2021-01-04 18:35:28 UTC (from ~6.386 to 7.141 hours after the burst). We observed 10 frames each of 240 seconds in the Bessell R filter. We clearly detected the optical afterglow of GRB 210104A in all individual frames within the Swift XRT enhanced error circle (Beardmore et al. 29245) as reported by Xin et al. GCN 29235 and later by Hu et al. GCN 29236, Hosokawa et al. GCN 29237, Kim et al. GCN 29238, Takashi et al. GCN 29241, Lipunov et al. GCN 29248, Zhu et al. GCN 29252 and Gregory et al. GCN 29254.
The estimated preliminary magnitude for the first R-band image is as follows:
```
T_start-T0 (hours) Start Date (UTC) Filter Magnitude (mag)

-----------------------------------------------------------
-----------------------------------------------------------
6.386 2021-01-04T17:50:11 R 18.95 +- 0.07
```
Photometry is done based on the USNO-B1.0 catalog. The quoted magnitude is not corrected for the Galactic extinction in the direction of GRB 210104A.
This message may be cited.
GCN Circular #29258
D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 210104A (Swift detection: Troja et al., GCN 29233; Fermi GBM detection: Malacaria et al., GCN 29246) triggered Konus-Wind (KW) at T0=41224.536 s UT (11:27:04.536).
The burst light curve shows multiple partly overlapped peaks in the interval from ~T0-2 s to ~T0+33 s. The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB210104_T41224/
As observed by Konus-Wind, the burst had a fluence of (2.15 � 0.35)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+26.624, of (1.13 � 0.19)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.00 (-0.16,+0.18), the high energy photon index beta = -2.52 (-0.52,+0.24), the peak energy Ep = 157 (-18,+23) keV, chi2 = 90/97 dof.
The spectrum near the peak count rate (measured from T0+16.640 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.95 (-0.11,+0.11), the high energy photon index beta = -2.47 (-1.10,+0.24), the peak energy Ep = 176 (-24,+37) keV, chi2 = 83/97 dof.
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #29260
J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU) and E. Troja report on behalf of the Swift-XRT team:
We have analysed 5.9 ks of XRT data for GRB 210104A (Troja et al. GCN Circ. 29233), from 69 s to 76.7 ks after the BAT trigger. The data comprise 1.8 ks in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 29245).
The late-time light curve (from T0+6.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.35 (+0.08, -0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.012 (+/-0.028). The best-fitting absorption column is 1.10 (+/-0.08) x 10^21 cm^-2, in excess of the Galactic value of 5.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.92 (+0.11, -0.10) and a best-fitting absorption column of 1.24 (+0.31, -0.29) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.24 (+0.31, -0.29) x 10^21 cm^-2
Galactic foreground: 5.1 x 10^20 cm^-2
Excess significance: 4.1 sigma
Photon index:	     1.92 (+0.11, -0.10)
```
If the light curve continues to decay with a power-law decay index of 1.35, the count rate at T+24 hours will be 0.047 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x 10^-12 (1.8 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01015873.
This circular is an official product of the Swift-XRT team.
GCN Circular #29262
S. J. Smartt, K. W. Smith (QUB), S. Srivastav,, D. R. Young, M. Fulton, (QUB) L. Denneau, A. Heinze, J. Tonry, H. Weiland (IfA, Univ. Hawaii), A. Rest (STScI), B. Stalder (LSST), C. Stubbs (Harvard), O. McBrien, J. Gillanders, L. Shingles (QUB), T.-W. Chen (MPE)
We report serendipitous observations of GRB210104A (Troja et al. GCN 29233) by ATLAS, the twin telescope system on Haleakala and Mauna Loa that surveys the whole northern sky every 2 days (see Tonry et al. 2018, PASP, 130f4505). Optical transients are automatically detected on the difference images and discoveries (Smith et al. 2020, PASP, 132h5002) are made public through the IAU Transient Name Server.
During the course of its survey, ATLAS happened to be observing the field of GRB210104A starting 1min 47sec after the Swift BAT trigger at 2021-01-04 11:26:59 UT (Troja et al. GCN 29233). This was a fortunate coincidence in normal survey mode and not a triggered pointing.
We detect the bright UVOT afterglow as initially reported in (Troja et al. GCN 29233), and appear to have the caught it early and bright at o = 13.9 along with rapid fading (see also Xin et al, GCN29235, Hu et al. 29236, Hosokawa et al. GCN 29237, Kim et al. GCN 29238, Lipunov et al. 29239),
It was detected at a position :
RA = 06:55:05.37 (103.77240) DEC = +64:40:34.2 (+64.67618)
The expoures were 30sec long in the o-band (an r+i composite), with start time and magnitudes as follows :
```
###MJD              UTC                                         m      dm  
59218.478319  2021-01-04 11:28:46.762 UTC 13.94  0.01
59218.481544  2021-01-04 11:33:25.402 UTC 15.56  0.01
59218.487080  2021-01-04 11:41:23.712 UTC 16.43  0.02
59218.497226  2021-01-04 11:56:00.326 UTC 16.96  0.03
59218.670448  2021-01-04 16:05:26.707 UTC >18.4  (3 sigma limit) 
```
GCN Circular #29265
V. Kim (FAI, Pulkovo Observatory), A. Pozanenko (IKI), M. Krugov (FAI), S. Belkin (IKI), Y. Aimuratov (FAI) report on behalf of GRB IKI FuN:
We continued observations of the GRB 210104A (Fermi GBM team, GCN 29232; Troja et al., GCN 29233; Frederiks et al., GCN 29258) with AZT-20 telescope of Assy-Turgen observatory starting on Jan. 05 (UT) 12:55:33 in r'-filter. We detect the optical afterglow (Troja et al., GCN 29233; Xin et al., GCN 29235; Hu et al., GCN 29236; Hosokawa et al., GCN 29237; Kim et al., GCN 29238; Lipunov et al., GCN 29239; Horiuchi et al., GCN 29241; Breeveld et al., GCN 29247; Zhu et al., GCN 29252; Paek et al., GCN 29254; Kumar et al., GCN 29257; Smartt et al., GCN 29262).
Preliminary photometry obtained in images in the beginning of observations on Jan. 05 is following
```
Date       UT start     Filter  Exp.    OT    Err.
                                 (s)

2021-01-04 15:35:27     r'(AB)  20*60   20.85 0.07
2021-01-04 16:20:20     r'(AB)  20*60   21.23 0.10
2021-01-04 17:05:11     r'(AB)  20*60   21.19 0.06
```
The photometry is based on nearby stars of PanSTARRS-PS1. Observations are continuing.
GCN Circular #29268
M. L. Cherry (LSU), A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:
The long bright GRB 210104A (Swift detection: Troja et al., GCN Circ. 29233, Palmer et al., GCN Circ. 29251; Fermi GBM detection: Malacaria et al., GCN Circ. 29246; Konus-Wind detection: Frederiks et al., GCN Circ. 29258; https://gcn.gsfc.nasa.gov/other/210104A.gcn3) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 11:26:56.318 UTC on 4 January 2021 (http://cgbm.calet.jp/cgbm_trigger/flight/1293794541/). The burst signal was seen by all CGBM detectors.
The burst light curve shows multiple partially overlapped pulses which start at T+2.5 sec and end at T+36.5 sec. The T90 and T50 durations measured by the SGM data are 31.2 +- 2.0 sec and 11.6 +- 9.4 sec (40-1000 keV), respectively.
The ground processed light curve is available at
http://cgbm.calet.jp/cgbm_trigger/ground/1293794541/
The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
GCN Circular #29269
```
TITLE:   GCN CIRCULAR
NUMBER:  29269
SUBJECT: GRB 210104A: iTelescope optical upper limit
DATE:    21/01/06 10:19:18 GMT
FROM:    Filipp Dmitrievich Romanov at Amateur astronomer  
```
I observed the field of GRB 210104A (Troja et al., GCN Circ. 29233) with remote telescope T11 (0.50-m f/6.8 reflector + CCD + f/4.5 focal reducer) of iTelescope.Net in New Mexico Observatory. Three images with AstroDon Luminance filter and with 300 seconds exposure time were obtained on 2021-01-05. Start time of exposures: 06:46:48 UT (~19.3 h. after trigger; Binx1), 06:52:21 UT (Binx2) and 06:57:44 UT (Binx1). I did not detect any optical transients (magnitude limit of about 21.0 in stacked image).
GCN Circular #29273
S. Anandagoda, S. Geier, K. Pellegrin and D. Hartmann report:
We observed the field of GRB 20210104A (Fermi GBM Team, GCN 29232; Troja et al., GCN 29233; Biltzinger et al., GCN 29234) using the SARA 0.9m optical telescope located at Kitt Peak, AZ, USA, equipped with the Alta-E6-1105 camera. Observation started at 06:20:04 UTC on 2021-01-05 and ended at 09:34:43 UTC (~ 18 to 21 hours after the detection of the burst by the Fermi GBM Team). We obtained a series of 120s exposure frames in the Bessell R filter. We clearly detect the optical afterglow of GRB 20210104A at the enhanced Swift-XRT position (Beardmore et al., GCN 29245).
The estimated magnitude of the GRB afterglow was 20.61 found by stacking 20 images of 120s each in the Bessell R band filter.
```
T_start-T0 (hrs)   T_end-T0 (hrs)     Start Date (UTC) 	  Filter 	Magnitude (mag)
-------------------------
----------------------------------------------------------------------------------------------------------------
18:53		      19:33	         2021-01-05T06:20:04       R 	   20.61
```
Photometry is done based on the USNO-B1.0 catalog.
The Southeastern Association for Research in Astronomy (SARA) consortium operates three telescopes: the 0.9-m SARA-KP at Kitt Peak in Arizona, and the 0.6-m SARA-CT at Cerro Tololo in Chile, and the 1.0-m SARA-RM (formerly the JKT) telescope at Roque de los Muchachos Observatory in the Canary Islands. For more information see: Keel et al. (2016): https://iopscience.iop.org/article/10.1088/1538-3873/129/971/015002
GCN Circular #29274
We observed the field of GRB210104A (The Fermi GBM team, GCN 29232, Troja et al., GCN 29233) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 01-05-2021 starting at 23:44:00 UT with a midpoint of observation of T+40 hrs. We performed a series of exposures in R filter with a total exposure of ~10ks. The weather conditions were clear during the hours of observation with an average airmass of 1.7.
We detect a source consistent with the UVOT position (Troja et al., GCN 29233) and optical transient identified by others (e.g., Bilitzinger et al., GCN 29234, Xin et al., GCN 29235, Hu et al., GCN 29236) with magnitude:
R= 20.8 +/- 0.3
This magnitude is consistent with the powerlaw decay rate of alpha = 0.73 reported by Zhu et al, GCN 29252.
The magnitude is estimated from comparison to nearby USNO B1 stars and is not corrected for Galactic extinction. Further analysis is in progress. The VIRT is still in the commissioning phase.
This work is supported by NASA-MUREP-MIRO grant NNX15AP95A, NSF EiR AST Award 1901296, and NSF HBCU-UP AST Award 1831682. This message can be cited.
GCN Circular #29275
J. Mao, X. Ding, X.-L. Zhang, and J.-M. Bai (YNAO) report:
We observed the field of GRB 210104A (Troja et al. GCN 29233) with the 2.4-meter optical telescope at Gao-Mei-Gu (GMG) station of Yunnan Observatories. The observation began at UT 13:00:11, 4, Jan. 2021, about 1.5 hours after the trigger. We clearly detected the source, and the preliminary magnitude was measured to be R~17.6. Further analysis of the observations during the night is ongoing.
GCN Circular #29277
A. S. Moskvitin, V. V. Vlasyuk (SAO RAS) on behalf of GRB follow-up team report.
We observed the field of the GRB 210104A (Fermi GBM Team, GCN #29232; Troja et al., GCN #29233; Biltzinger et al., GCN #29234) with the 0.5m Astrosib RC500-2 telescope of SAO RAS equipped with the Rc filter and FLI Proline PL16801 camera. The observations carried out on 2021 Jan. 4, 0.32--0.38 days after the trigger (T_mid - T0 = 0.35d).
In the 37 x 20 sec. stacked image we clearly detect the GRB OT (Troja et al., GCN #29233; Xin et al., GCN #29235; Hu et al., GCN #29236; Hosokawa et al., GCN #29237; Kim et al., GCN #29238; Lipunov et al., GCN #29239; Horiuchi et al., GCN #29241; Breeveld et al., GCN #29247; Zhu et al., GCN #29252; Paek et al., GCN #29254; Kumar et al., GCN #29257; Smartt et al., GCN #29262; V. Kim, GCN #29265; S. Anandagoda, GCN #29273; P. Gokuldass, GCN #29274; J. Mao, GCN #29275) with the brightness of R = 19.4 +/- 0.1. The preliminary photometry is based on R2 magnitudes of nearby USNO-B1 stars.
GCN Circular #29283
V. Kim (FAI, Pulkovo Observatory), S. Belkin (IKI), A. Pozanenko (IKI), M. Krugov (FAI), Y. Aimuratov (FAI) report on behalf of GRB IKI FuN:
We continued observations of the GRB 210104A (Fermi GBM team, GCN 29232; Troja et al., GCN 29233; Frederiks et al., GCN 29258; Cherry et al., GCN 29268) with AZT-20 telescope of Assy-Turgen observatory starting on Jan. 05 (UT) 12:55:33 in r'-filter. We detect the optical afterglow (Troja et al., GCN 29233; Xin et al., GCN 29235; Hu et al., GCN 29236; Hosokawa et al., GCN 29237; Kim et al., GCN 29238, 29265; Lipunov et al., GCN 29239; Horiuchi et al., GCN 29241; Breeveld et al., GCN 29247; Zhu et al., GCN 29252; Paek et al., GCN 29254; Kumar et al., GCN 29257; Smartt et al., GCN 29262; Romanov, GCN 29269; Anandagoda et al., GCN 29273; Gokuldass, GCN 29274; Mao et al., GCN 29275; Moskvitin et al., GCN 29277).
Preliminary photometry is following
```
Date       UT start     Filter  Exp.   OT(AB)  Err. UL(3 sigma)
                                 (s)

2021-01-06 15:18:17     r'     82*60   22.00   0.08 23.0
2021-01-09 17:22:22     r'    136*60   22.88   0.19 24.1
```
The photometry is based on nearby stars of PanSTARRS-PS1. Observations are continuing.
We also report corrected date of observation reported in the GCN 29265. The correct table of the GCN 29265 should be as follows
```
Date       UT start     Filter  Exp.   OT(AB)  Err.
2021-01-05 15:35:27     r'      20*60   20.85 0.07
2021-01-05 16:20:20     r'      20*60   21.23 0.10
2021-01-05 17:05:11     r'      20*60   21.19 0.06
```
GCN Circular #29286
S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), V. Kim (FAI, Pulkovo Observatory), Y. Aimuratov (FAI), M. Krugov (FAI) report on behalf of GRB IKI FuN:
We observed GRB 210104A (Fermi GBM team, GCN 29232; Troja et al., GCN 29233; Frederiks et al., GCN 29258; Cherry et al., GCN 29268) with AZT-33IK telescope of Sayan observatory (Mondy). We detect the optical afterglow (Troja et al., GCN 29233; Xin et al., GCN 29235; Hu et al., GCN 29236; Hosokawa et al., GCN 29237; Kim et al., GCN 29238, 29265; Lipunov et al., GCN 29239; Horiuchi et al., GCN 29241; Breeveld et al., GCN 29247; Zhu et al., GCN 29252; Paek et al., GCN 29254; Kumar et al., GCN 29257; Smartt et al., GCN 29262; Romanov, GCN 29269; Anandagoda et al., GCN 29273; Gokuldass, GCN 29274; Mao et al., GCN 29275; Moskvitin et al., GCN 29277).
Preliminary photometry of the afterglow is following
```
Date       UT start   t-T0     Filter Exp.   OT       Err. UL(3 sigma)
                       (mid, days)     (s)

2021-01-07 15:10:23   3.19681  R      80*90   n/d     n/d 22.1
2021-01-08 15:22:18   4.20438  R      59*120  22.2    0.2 22.9
2021-01-09 11:51:54   5.07980  R      90*120  22.7    0.3 22.7
```
The photometry is based on nearby stars of USNO-B1.0
```
USNO-B1.0_id R2
1546-0139059 15.53
1546-0139029 14.82
```
A light curve of the afterglow based on our observations including reported early (Kim et al., GCN 29238, 29265, 29283) can be found in
http://grb.rssi.ru/GRB210104A/GRB210104A_LC.png
GCN Circular #29291
M. Nakamura, K. Hasuda, T. Sakamoto (AGU)
We observed the field of GRB 210104A (Troja et al., GCN Circ. 29233; Malacaria et al., GCN Circ. 29246; Frederiks et al., GCN Circ. 29258; Cherry et al., GCN Circ. 29268) with the 14-inch AGU Robotic Optical Monitor for Astrophysical object - Narrow (AROMA-N) located at the Sagamihara campus of Aoyama Gakuin University.
60 images of 60 sec exposures were taken in the R filter starting from January 4 11:29:50 (UT) about 171 seconds after the trigger and stopped on January 4 12:45:20 (UT). We detected the optical afterglow at the consistent position previously reported (Troja et al., GCN Circ. 29233; Xin et al., GCN Circ. 29235; Hu et al., GCN Circ. 29236; Hosokawa et al., GCN Circ. 29237; Kim et al., GCN Circ. 29238, 29265; Lipunov et al., GCN Circ. 29239; Horiuchi et al., GCN Circ. 29241; Breeveld et al., GCN Circ. 29247; Zhu et al., GCN Circ. 29252; Paek et al., GCN Circ. 29254; Kumar et al., GCN Circ. 29257; Smartt et al., GCN Circ. 29262; Romanov, GCN Circ. 29269; Anandagoda et al., GCN Circ. 29273; Gokuldass, GCN Circ. 29274; Mao et al., GCN Circ. 29275; Moskvitin et al., GCN Circ. 29277; Belkin et al., GCN Circ. 29286). The clear decay signature was visible in our images. The magnitudes of the initial 60 s image and the combined image from T+2915 sec to T+3577 sec images (total exposure of 540 sec) were 14.3 mag and 17.1 mag. The afterglow light curve of our data showed the initial temporal decay of -1.4 following by the shallow decay of -0.6 at the break around T+650 sec. Our reported magnitudes are calibrated using the USNO-B1 catalog.
GCN Circular #29299
D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 2020, arxiv:2011.07067) showed detection of a bright long GRB 210104A, which was also detected by Fermi-GBM (GCN #29232), Swift-BAT (GCN #29233), Konus-Wind (GCN #29258) and CALET-CGBM (GCN #29268).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-01-04 11:27:17.5 UT. The measured peak count rate associated with the burst is 867 (+60, -56) cts/s above the background in the combined data of four quadrants, with a total of 7003 (+407, -394) cts. The local mean background count rate was 555 (+2, -2) cts/s. Using cumulative rates, we measure a T90 of 33 (+7, -1) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-01-04 11:27:17 UT. The measured peak count rate is 606 (+86, -55) cts/s above the background in the combined Veto data of four quadrants, with a total of 4520 (+693, -789) cts. The local mean background count rate was 2009 (+4, -5) cts/s. We measure a T90 of 35 (+7, -14) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
GCN Circular #29304
I.A. Smith (Rice U.), D.A. Perley (LJMU), and N.R. Tanvir (U. of Leicester) report:
We observed the Swift UVOT location of GRB 210104A (Troja et al., GCN Circ. 29233) using the SCUBA-2 sub-millimeter continuum camera on the James Clerk Maxwell Telescope. The observation started at 08:23 UT on 2021-01-05, with the mid-point of the run at 0.894 days after the burst trigger. Exposures totaling 1.0 hours were made in very good weather conditions. No source was detected, with the RMS background noise being 1.7 mJy/beam at 850 microns and 14.5 mJy/beam at 450 microns.
We thank Kevin Silva, Mark Rawlings, and the JCMT staff for the prompt support of these observations that were taken under project M20BP026.
GCN Circular #29318
D. A. Kann (HETH/IAA-CSIC), A. Rossi (INAF-OAS), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui Fernandez (both HETH/IAA-CSIC), and J. I. Vico Linares (CAHA) report:
We observed the afterglow position (Troja et al., GCN #29233) of the bright Swift/Fermi GRB 210104A (Swift detection: Troja et al., GCN #29233; GBM detection: Fermi GBM Team, GCN #29232; Biltzinger et al., GCN #29234; Konus-Wind detection: Frederiks et al., GCN #29258; CALET detection: Cherry et al., GCN #29268; AstroSat CZTI detection: Nadella et al., GCN #29299) with CAFOS at the 2.2m telescope at Calar Alto, Almeria, Spain, in the Rc band. We obtained 6 x 600 s exposures, centered at 11.4624 days after the GRB, under good conditions but mediocre seeing.
After removing the halo of a nearby star, the afterglow (Xin et al., GCN #29235; Hu et al., GCN #29236; Hosokawa et al., GCN #29237; Kim et al., GCNs #29238,29265,29283; Horiuchi et al., GCN #29241; Breeveld et al., GCN #29247; Lipunov et al., GCN #29248; Zhu et al., GCN #29252; Paek et al., GCN #29254; Kumar et al., GCN #29257; Smartt et al., GCN #29262; Anandagoda et al., GCN #29273; Gokuldass et al., GCN #29274; Mao et al., GCN #29275; Moskvitin et al., GCN #29277; Belkin et al., GCN #29286; Nakamura et al., GCN #292291) is faintly but clearly detected.
Against three SDSS comparison stars (transformed to Rc band using the Lupton 2005 equations, then transformed back to AB magnitude), we measure Rc = 23.67 +/- 0.14 mag. This value is in agreement with the extrapolation of the light curve decay reported by Belkin et al., GCN #29286 (A. Pozanenko, priv. comm.). This implies there is no significant evidence for a supernova rise, and therefore the redshift of GRB 210104A is conservatively estimated to be z > 0.4 (e.g., SN 2012eb associated with GRB 120714B at z ~ 0.4 peaks at r' ~ 22.2 mag 12 days after trigger, Klose et al. 2019, A&A, 622, A138).
We thank Alexei Pozanenko for discussions.
GCN Circular #29337
Dimple (ARIES), K. Misra (ARIES), A. Ghosh (ARIES), R. Gupta (ARIES), A. Kumar (ARIES), S.B. Pandey (ARIES) report:
We observed the field of GRB 210104A (Troja et al. GCN #29233) with Aries Devasthal Faint Object Spectrograph and Camera (ADFOSC) mounted on the 3.6m Devasthal Optical Telescope (DOT). The observations started on 2021-01-13 at 19:52:50 UT (9.374 days after the burst). We obtained a set of consecutive images with short exposure times to avoid saturation from the nearby bright star. We do not detect any optical counterpart upto a magnitude limit of 23.2 in the stacked image.
GCN Circular #29440
A. Melandri (INAF-OAB), and A Rossi (INAF-OAS) report on behalf of the CIBO collaboration:
We observed the field of GRB 210104A (Troja et al., GCN 29233; Malacaria et al., GCN 29246) simultaneously in the r' and z' bands with the LBC imager mounted on LBT (Mt Graham, AZ, USA). We obtained 20min of imaging on 2021-02-05, 31.8 days after the burst trigger. Observations were performed under poor seeing (~1.7") conditions but reached a depth of r~25.5 mag.
At the position of the afterglow (Xin et al., GCN 29235; Hu et al., GCN 29236; Kim et al., GCNs 29238, 29265, 29283; Lipunov et al., GCNs 29239, 29248; Horiuchi et al., GCN 29241; Breeveld et al., GCN 29247; Paek et al., GCN 29254; Smartt et al., GCN 29262; Anandagoda et al., GCN 29273; Mao et al., GCN 29275; Moskvitin & Vlasyuk, GCN 29277; Belikin et al., GCN 29286; Nakamura et al., GCN 29291; Kann et al., GCN 29318), we clearly detect the host galaxy in both filters (RA,DEC = 06:55:05.18,+64:40:33.7; J2000).
After removing the halo of a nearby star, we measure the following AB magnitudes:
```
r = 24.2 +/- 0.3
z = 22.1 +/- 0.2
```
calibrated against SDSS field stars.
We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly B. Rothberg, F. Cusano, and D. Paris, in obtaining these observations.
Redshift z=0.46
from afterglow spectroscopy: Zhang L.L. et al. 2022, ApJ 941, 63

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