Gamma-ray Burst 210731A

(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:     Sat 31 Jul 21 22:22:49 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1062336,   Seg_Num: 0
GRB_RA:          300.314d {+20h 01m 15s} (J2000),
                 300.645d {+20h 02m 35s} (current),
                 299.544d {+19h 58m 11s} (1950)
GRB_DEC:         -28.042d {-28d 02' 30"} (J2000),
                 -27.981d {-27d 58' 51"} (current),
                 -28.181d {-28d 10' 50"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=1633 [image_cnts]
TRIGGER_DUR:     88.000 [sec] 
TRIGGER_INDEX:   20000     E_range: 15-50 keV
BKG_INTEN:       0 [cnts]
BKG_TIME:        0.00 SOD {00:00:00.00} UT
BKG_DUR:         0 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80468.53 SOD {22:21:08.53} UT
GRB_PHI:         112.84 [deg]
GRB_THETA:        29.78 [deg]
SOLN_STATUS:     0x20000013
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    9.45 [sigma]
MERIT_PARAMS:     +1  +0  +0  +6  +1  +0  +0  +0 +96  +0 
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 30"}
SUN_DIST:        166.01 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.40d {+02h 45m 35s}  +13.64d {+13d 38' 29"}
MOON_DIST:       105.71 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.46,-26.74 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      296.69, -7.37 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)  
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 = 288.34,1.37 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=649462872).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:21:31 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     649462872
GRB_RA:          302.467d {+20h 09m 52s} (J2000),
                 302.793d {+20h 11m 10s} (current),
                 301.709d {+20h 06m 50s} (1950)
GRB_DEC:         -26.433d {-26d 25' 59"} (J2000),
                 -26.369d {-26d 22' 06"} (current),
                 -26.581d {-26d 34' 51"} (1950)
GRB_ERROR:       20.80 [deg radius, statistical plus systematic]
GRB_INTEN:       111 [cnts/sec]
DATA_SIGNIF:     6.30 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         175.00 [deg]
GRB_THETA:       100.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.16
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   3%  Cyg X-1
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,1,1, 0,0,
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.03d {+18d 01' 30"}
SUN_DIST:        168.50 [deg]   Sun_angle= -11.4 [hr] (East of Sun)
MOON_POSTN:       41.39d {+02h 45m 33s}  +13.64d {+13d 38' 15"}
MOON_DIST:       103.58 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       15.85,-28.06 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      298.91, -6.19 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 40.00,18.92 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:21:40 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     649462872
GRB_RA:          302.433d {+20h 09m 44s} (J2000),
                 302.760d {+20h 11m 02s} (current),
                 301.675d {+20h 06m 42s} (1950)
GRB_DEC:         -26.400d {-26d 23' 59"} (J2000),
                 -26.335d {-26d 20' 06"} (current),
                 -26.548d {-26d 32' 51"} (1950)
GRB_ERROR:       10.05 [deg radius, statistical plus systematic]
GRB_INTEN:       171 [cnts/sec]
DATA_SIGNIF:     12.90 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         175.00 [deg]
GRB_THETA:       100.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.34
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,1, 0,1,1, 0,0,
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.03d {+18d 01' 30"}
SUN_DIST:        168.50 [deg]   Sun_angle= -11.4 [hr] (East of Sun)
MOON_POSTN:       41.39d {+02h 45m 33s}  +13.64d {+13d 38' 17"}
MOON_DIST:       103.61 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       15.88,-28.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      298.89, -6.16 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 40.00,18.92 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:21:50 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     649462872
GRB_RA:          299.730d {+19h 58m 55s} (J2000),
                 300.066d {+20h 00m 16s} (current),
                 298.950d {+19h 55m 48s} (1950)
GRB_DEC:         -29.770d {-29d 46' 11"} (J2000),
                 -29.710d {-29d 42' 35"} (current),
                 -29.906d {-29d 54' 22"} (1950)
GRB_ERROR:       5.79 [deg radius, statistical only]
DATA_SIGNIF:     13.30 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         174.00 [deg]
GRB_THETA:       104.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.03d {+18d 01' 30"}
SUN_DIST:        164.43 [deg]   Sun_angle= -11.2 [hr] (East of Sun)
MOON_POSTN:       41.39d {+02h 45m 34s}  +13.64d {+13d 38' 18"}
MOON_DIST:       106.42 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       11.44,-26.78 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      295.84, -8.96 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_649462872.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:22:28 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     649462872
GRB_RA:          299.580d {+19h 58m 19s} (J2000),
                 299.911d {+19h 59m 39s} (current),
                 298.812d {+19h 55m 15s} (1950)
GRB_DEC:         -27.550d {-27d 33' 00"} (J2000),
                 -27.490d {-27d 29' 24"} (current),
                 -27.686d {-27d 41' 08"} (1950)
GRB_ERROR:       3.70 [deg radius, statistical only]
DATA_SIGNIF:     17.50 [sigma]
DATA_INTERVAL:   6.144 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         173.00 [deg]
GRB_THETA:       102.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 30"}
SUN_DIST:        165.84 [deg]   Sun_angle= -11.2 [hr] (East of Sun)
MOON_POSTN:       41.39d {+02h 45m 35s}  +13.64d {+13d 38' 25"}
MOON_DIST:       106.29 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.75,-25.97 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      296.15, -6.76 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_649462872.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:22:38 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     649462872
GRB_RA:          299.570d {+19h 58m 17s} (J2000),
                 299.901d {+19h 59m 36s} (current),
                 298.802d {+19h 55m 13s} (1950)
GRB_DEC:         -27.530d {-27d 31' 47"} (J2000),
                 -27.470d {-27d 28' 12"} (current),
                 -27.666d {-27d 39' 56"} (1950)
GRB_ERROR:       3.46 [deg radius, statistical only]
DATA_SIGNIF:     21.00 [sigma]
DATA_INTERVAL:   10.240 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         173.00 [deg]
GRB_THETA:       102.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 30"}
SUN_DIST:        165.85 [deg]   Sun_angle= -11.2 [hr] (East of Sun)
MOON_POSTN:       41.40d {+02h 45m 35s}  +13.64d {+13d 38' 27"}
MOON_DIST:       106.30 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.77,-25.96 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      296.15, -6.74 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_649462872.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.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:22:52 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     649462872
GRB_RA:          301.420d {+20h 05m 41s} (J2000),
                 301.746d {+20h 06m 59s} (current),
                 300.663d {+20h 02m 39s} (1950)
GRB_DEC:         -26.030d {-26d 01' 47"} (J2000),
                 -25.967d {-25d 58' 00"} (current),
                 -26.174d {-26d 10' 24"} (1950)
GRB_ERROR:       2.76 [deg radius, statistical only]
DATA_SIGNIF:     26.40 [sigma]
DATA_INTERVAL:   15.360 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         174.00 [deg]
GRB_THETA:       100.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 30"}
SUN_DIST:        168.08 [deg]   Sun_angle= -11.4 [hr] (East of Sun)
MOON_POSTN:       41.40d {+02h 45m 36s}  +13.64d {+13d 38' 30"}
MOON_DIST:       104.46 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       15.95,-27.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      298.08, -5.60 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_649462872.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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1062336).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:23:02 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      3
TRIGGER_NUM:     649462872
GRB_RA:          299.970d {+19h 59m 53s} (J2000),
                 300.298d {+20h 01m 12s} (current),
                 299.208d {+19h 56m 50s} (1950)
GRB_DEC:         -26.560d {-26d 33' 35"} (J2000),
                 -26.500d {-26d 29' 58"} (current),
                 -26.697d {-26d 41' 50"} (1950)
GRB_ERROR:       2.22 [deg radius, statistical only]
DATA_SIGNIF:     28.30 [sigma]
DATA_INTERVAL:   19.456 [sec]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         173.00 [deg]
GRB_THETA:       101.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 29"}
SUN_DIST:        166.73 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.40d {+02h 45m 36s}  +13.64d {+13d 38' 32"}
MOON_DIST:       105.82 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       14.92,-25.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      296.69, -5.86 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_649462872.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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1062336).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:30:25 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     649462872
GRB_RA:          302.020d {+20h 08m 05s} (J2000),
                 302.349d {+20h 09m 24s} (current),
                 301.257d {+20h 05m 02s} (1950)
GRB_DEC:         -27.320d {-27d 19' 11"} (J2000),
                 -27.256d {-27d 15' 21"} (current),
                 -27.466d {-27d 27' 57"} (1950)
GRB_ERROR:       2.50 [deg radius, statistical only]
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80467.20 SOD {22:21:07.20} UT
GRB_PHI:         175.00 [deg]
GRB_THETA:       101.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       131.36d {+08h 45m 26s}  +18.02d {+18d 01' 25"}
SUN_DIST:        167.59 [deg]   Sun_angle= -11.4 [hr] (East of Sun)
MOON_POSTN:       41.46d {+02h 45m 50s}  +13.66d {+13d 39' 53"}
MOON_DIST:       104.18 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       14.76,-27.96 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      298.33, -6.98 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_lc_medres34_bn210731931.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210731931/quicklook/glg_locplot_all_bn210731931.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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1062336).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:25:10 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1062336,   Seg_Num: 0
GRB_RA:          300.3036d {+20h 01m 12.8s} (J2000),
                 300.6352d {+20h 02m 32.4s} (current),
                 299.5341d {+19h 58m 08.1s} (1950)
GRB_DEC:         -28.0595d {-28d 03' 34.1"} (J2000),
                 -27.9986d {-27d 59' 54.8"} (current),
                 -28.1984d {-28d 11' 54.1"} (1950)
GRB_ERROR:       5.8 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       44 [cnts]
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80669.42 SOD {22:24:29.42} UT,   200.9 [sec] since BAT Trigger Time
CENTROID_X:      333.47,  raw= 333  [pixels]
CENTROID_Y:      305.27,  raw= 305  [pixels]
ROLL:            227.73 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   16.92
GRB_POS_XRT_Z:   61.46
IMAGE_URL:       sw01062336000msxps_rw.img
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 28"}
SUN_DIST:        165.99 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.42d {+02h 45m 40s}  +13.65d {+13d 38' 55"}
MOON_DIST:       105.74 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.44,-26.74 [deg] galactic lon,lat of the burst
ECL_COORDS:      296.68, -7.38 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:25:18 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1062336,   Seg_Num: 0
GRB_RA:          300.3036d {+20h 01m 12.8s} (J2000),
                 300.6352d {+20h 02m 32.4s} (current),
                 299.5341d {+19h 58m 08.1s} (1950)
GRB_DEC:         -28.0595d {-28d 03' 34.1"} (J2000),
                 -27.9986d {-27d 59' 54.8"} (current),
                 -28.1984d {-28d 11' 54.1"} (1950)
GRB_ERROR:       5.8 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       44 [cnts]
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80669.42 SOD {22:24:29.42} UT,   200.9 [sec] since BAT Trigger Time
CENTROID_X:      333.47,  raw= 333  [pixels]
CENTROID_Y:      305.27,  raw= 305  [pixels]
ROLL:            227.73 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   16.92
GRB_POS_XRT_Z:   61.46
IMAGE_URL:       sw01062336000msxps_rw.img
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 28"}
SUN_DIST:        165.99 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.42d {+02h 45m 40s}  +13.65d {+13d 38' 57"}
MOON_DIST:       105.74 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.44,-26.74 [deg] galactic lon,lat of the burst
ECL_COORDS:      296.68, -7.38 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:26:53 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1062336,   Seg_Num: 0
POINT_RA:        300.286d {+20h 01m 09s} (J2000)
POINT_DEC:       -28.067d {-28d 04' 02"} (J2000)
POINT_ROLL:      227.732d
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80678.89 SOD {22:24:38.89} UT,   210.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.254
N_STARS:         84
X_OFFSET:        248 [pixels]
Y_OFFSET:        688 [pixels]
X_MAX:           1207 [pixels]
Y_MAX:           1647 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01062336000msufc0210.fits
SUN_POSTN:       131.36d {+08h 45m 25s}  +18.02d {+18d 01' 27"}
SUN_DIST:        165.97 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.43d {+02h 45m 43s}  +13.65d {+13d 39' 14"}
MOON_DIST:       105.77 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.42,-26.73 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      296.66, -7.39 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:28:15 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1062336,   Seg_Num: 0
POINT_RA:        300.286d {+20h 01m 09s} (J2000)
POINT_DEC:       -28.067d {-28d 04' 02"} (J2000)
ROLL:            227.732d
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80678.89 SOD {22:24:38.89} UT,   210.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649463106
X_OFFSET:        656 [pixels]
Y_OFFSET:        905 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       816
Y_GRB_POS:       1065
BINNING_INDEX:   1
IM_URL:          sw01062336000msuni0238.fits
SUN_POSTN:       131.36d {+08h 45m 26s}  +18.02d {+18d 01' 26"}
SUN_DIST:        165.97 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.44d {+02h 45m 46s}  +13.66d {+13d 39' 29"}
MOON_DIST:       105.78 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.42,-26.73 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      296.66, -7.39 [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:     Sat 31 Jul 21 22:25:47 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1062336,   Seg_Num: 0
GRB_RA:          300.314d {+20h 01m 15s} (J2000),
                 300.645d {+20h 02m 35s} (current),
                 299.544d {+19h 58m 11s} (1950)
GRB_DEC:         -28.042d {-28d 02' 30"} (J2000),
                 -27.981d {-27d 58' 51"} (current),
                 -28.181d {-28d 10' 50"} (1950)
GRB_DATE:        19426 TJD;   212 DOY;   21/07/31
GRB_TIME:        80468.53 SOD {22:21:08.53} UT
TRIGGER_INDEX:   20000
GRB_PHI:         112.84 [deg]
GRB_THETA:        29.78 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     88.000 [sec] 
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    9.45 [sigma]
LC_URL:          sw01062336000msb.lc
SUN_POSTN:       131.36d {+08h 45m 25s}  +18.02d {+18d 01' 28"}
SUN_DIST:        166.00 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.42d {+02h 45m 41s}  +13.65d {+13d 39' 02"}
MOON_DIST:       105.73 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.46,-26.74 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      296.69, -7.37 [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 an image 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 = 288.34,1.37 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 31 Jul 21 22:28:28 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1062336,   Seg_Num: 0
POINT_RA:        300.286d {+20h 01m 09s} (J2000)
POINT_DEC:       -28.067d {-28d 04' 02"} (J2000)
ROLL:            227.732d
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80678.89 SOD {22:24:38.89} UT,   210.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649463106
X_OFFSET:        656 [pixels]
Y_OFFSET:        905 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       816
Y_GRB_POS:       1065
BINNING_INDEX:   1
IM_URL:          sw01062336000msuni0238.fits
SUN_POSTN:       131.36d {+08h 45m 26s}  +18.02d {+18d 01' 26"}
SUN_DIST:        165.97 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.44d {+02h 45m 46s}  +13.66d {+13d 39' 32"}
MOON_DIST:       105.78 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.42,-26.73 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      296.66, -7.39 [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:     Sat 31 Jul 21 22:27:07 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1062336,   Seg_Num: 0
POINT_RA:        300.286d {+20h 01m 09s} (J2000)
POINT_DEC:       -28.067d {-28d 04' 02"} (J2000)
POINT_ROLL:      227.732d
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80678.89 SOD {22:24:38.89} UT,   210.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.254
N_STARS:         84
X_OFFSET:        248 [pixels]
Y_OFFSET:        688 [pixels]
X_MAX:           1207 [pixels]
Y_MAX:           1647 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw01062336000msufc0210.fits
SUN_POSTN:       131.36d {+08h 45m 25s}  +18.02d {+18d 01' 27"}
SUN_DIST:        165.97 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.43d {+02h 45m 44s}  +13.65d {+13d 39' 17"}
MOON_DIST:       105.77 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.42,-26.73 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      296.66, -7.39 [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:     Sat 31 Jul 21 22:25:00 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1062336,   Seg_Num: 0
GRB_RA:          300.3036d {+20h 01m 12.86s} (J2000),
                 300.6352d {+20h 02m 32.45s} (current),
                 299.5341d {+19h 58m 08.17s} (1950)
GRB_DEC:         -28.0595d {-28d 03' 34.1"} (J2000),
                 -27.9986d {-27d 59' 54.8"} (current),
                 -28.1984d {-28d 11' 54.1"} (1950)
GRB_ERROR:       5.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       7.96e-10 [erg/cm2/sec]
GRB_SIGNIF:      6.63 [sigma]
IMG_START_DATE:  19426 TJD;   212 DOY;   21/07/31
IMG_START_TIME:  80669.42 SOD {22:24:29.42} UT,   200.9 [sec] since BAT Trigger Time
TAM[0-3]:        327.67 237.17 261.78 243.57
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       131.35d {+08h 45m 25s}  +18.02d {+18d 01' 28"}
SUN_DIST:        165.99 [deg]   Sun_angle= -11.3 [hr] (East of Sun)
MOON_POSTN:       41.41d {+02h 45m 40s}  +13.65d {+13d 38' 53"}
MOON_DIST:       105.74 [deg]
MOON_ILLUM:      46 [%]
GAL_COORDS:       13.44,-26.74 [deg] galactic lon,lat of the burst
ECL_COORDS:      296.68, -7.38 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.18 arcmin from the BAT position.

GCN Circular #30567
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB210731.93 (trigger No 1062336,20h 01m 15.36s , -28d 02m 31.2s, R=0.05) errorbox 67 sec after trigger time at 2021-07-31 22:22:16 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 5 deg. The sun altitude is -75.2 deg.
MASTER-IAC robotic telescope located in Spain (IAC Teide Observatory) was pointed to the Swift GRB210731.93 errorbox 108 sec after trigger time at 2021-07-31 22:22:57 UT, with upper limit up to 16.2 mag. The observations began at zenith distance = 64 deg. The sun altitude is -28.8 deg.
The galactic latitude b = -27 deg., longitude l = 14 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1677220
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      73 |         MASTER-SAAO |   C |    10 | 17.4 |        
     107 |         MASTER-SAAO |   C |    20 | 17.8 |        
     119 |          MASTER-IAC |  P| |    20 | 14.2 |        
     119 |          MASTER-IAC |  P- |    20 | 15.1 |        
     152 |         MASTER-SAAO |   C |    30 | 18.4 |        
     164 |          MASTER-IAC |  P| |    30 | 16.2 |        
     164 |          MASTER-IAC |  P- |    30 | 15.8 |        
     206 |         MASTER-SAAO |   C |    40 | 18.7 |        
     218 |          MASTER-IAC |  P| |    40 | 15.8 |        
     266 |         MASTER-SAAO | P\  |    10 | 16.7 |        
     292 |         MASTER-SAAO | P\  |    20 | 17.5 |        
     324 |         MASTER-SAAO | P\  |    20 | 16.5 |        
     362 |         MASTER-SAAO | P\  |    30 | 17.6 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #30568
E. Troja (NASA/GSFC/UMCP), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), B. Sbarufatti (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 22:21:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210731A (trigger=1062336). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 300.314, -28.042 which is
```
   RA(J2000) = 20h 01m 15s
   Dec(J2000) = -28d 02' 30"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 22:24:29.4 UT, 200.9 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 300.3036, -28.0595 which is equivalent to:
```
   RA(J2000)  = 20h 01m 12.86s
   Dec(J2000) = -28d 03' 34.2"
```
with an uncertainty of 5.8 arcseconds (radius, 90% containment). 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 7.96e-10 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 63 seconds with the White filter starting 210 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.092.
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 Circular #30569
Antonino D'Ai (INAF-iASFPA), P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team:
Using 963 s of XRT Photon Counting mode data and 4 UVOT images, 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 = 300.30500, -28.06105 which is equivalent to:
```
RA (J2000):  20 01 13.20
Dec (J2000): -28 03 39.8
```
with an uncertainty of 2.6 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 is an official product of the Swift-XRT team.
GCN Circular #30570
S. de Wet (UCT), A.J. Levan (Radboud), P.J. Groot (Radboud/UCT/SAAO) P.M. Vreeswijk (Radboud) report on behalf of the MeerLICHT consortium:
Following the detection of GRB210731A by Swift and its X-ray counterpart (Troja et al., GCN30568), the 0.6m MeerLICHT telescope, located at Sutherland, South Africa obtained a repeating series of 60s images in the q,u,q,g,q,r,q,i,q,z bands. Observations began at 2021-07-31, 22:25:54 UT, 5 minutes after the Swift detection, and 3 minutes after the distribution of the BAT alert, and continued until 2021-08-01, 02:40:21 UT.
We find a new transient candidate in our first q-band exposure (318 seconds post-trigger) with magnitude q = 19.50 +/- 0.09 at coordinates:
```
RA (J2000) = 20:01:13.19 (300.30494d)
Dec (J2000) = -28:03:40.10 (-28.06114d)
```
calibrated against Gaia DR2. This position is 0.3" from the updated XRT position, and which we regard as the optical afterglow to GRB210731A. We note that no credible afterglow candidate was reported by UVOT at ~210s post burst (Troja et al., GCN30568).
We detect the afterglow in further observations in the q,g,r and i bands but not in u and z. Our q-band light curve shows a complex shape with a steep rise and drop of ~0.7 mag within the first 2000s, then a gradual rise of 0.7 mag for a further 3000s and a plateau until ~10000s post-trigger. The final q-band magnitude of the source was q=18.95 +/- 0.07 at 2021-08-01, 01:06:47 UT. Our first g,r and i source detections and u and z non-detections are, at:
```
g = 18.93 +/- 0.06 at 22:31:29 UT
r = 18.63 +/- 0.06 at 22:34:59 UT
i = 18.34 +/- 0.09 at 22:38:33 UT
u > 19.40 at 22:28:06 UT
z > 18.57 at 22:41:58 UT
```
Reference images of the field show no underlying host galaxy down to the 5-sigma limiting magnitude, at the position of the afterglow, at: q > 20.95. There is also no source identified at this location in archival PanSTARRS images of the field.
MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam.
GCN Circular #30572
N. P. M. Kuin (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 210731A 210 s after the BAT trigger (Troja et al., GCN Circ. 30568). An optical afterglow consistent with the XRT position (D'Ai et al. GCN Circ. 30569) and discovered by Meerlicht (de Wet ert al, GCN Circ. 30570) is also detected in the initial UVOT exposures. Interestingly, the initial rise to peak is slow.
Preliminary 3-sigma magnitudes using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              210          273           62         20.2  +/- 0.38
b                17547        18204          587         19.02 +/- 0.08
u                29863        30504          624         18.66 +/- 0.09
v                11787        12145          348         18.60 +/- 0.17
uvw1             28956        29857          886         19.33 +/- 0.14
uvw2             34767        35667          886         20.41 +/- 0.27
uvm2             23308        23846          530         19.40 +/- 0.21
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.092 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #30573
S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 22:21:07 UT on 31 July 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210731A (trigger 649462872/210731931) which was also detected by Swift BAT (E. Troja et al. 2021, GCN 30568). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 102 degrees.
The GBM light curve consists of a single emission episode with a duration (T90) of about 26 s (10-1000 keV). The time-averaged spectrum from T0+0.003 to T0+19.968 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.1 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 175 +/- 11 keV.
The event fluence (10-1000 keV) in this time interval is (4.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10.3 s in the 10-1000 keV band is 2.9 +/- 0.3 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 #30574
A. Nicuesa Guelbenzu, S. Klose, S. Schmidl (all TLS Tautenburg) and A. Rau (MPE Garching) report:
We observed the field of GRB 210731A (Swift trigger 1062336; Troja et al., GCN 30568) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile).
Observations started on 01-AUG-2021 at 02:33 UT, about 4.2 hours after the GRB trigger. They were performed at an average seeing of 1.0 arcsec and at an average airmass of 1.1.
At a meantime of 2:46 UT, for the GRB afterglow (de Wet et al, GCN 30570; Kuin et al., GCN 30572) we measure the following AB magnitudes:
```
g' = 18.71 +/- 0.01 mag,
r' = 18.44 +/- 0.01 mag,
i' = 18.19 +/- 0.01 mag,
z' = 18.01 +/- 0.01 mag,
J  = 17.66 +/- 0.02 mag,
H  = 17.38 +/- 0.02 mag, and
K  = 17.14 +/- 0.15 mag.
```
Optical magnitudes are calibrated against the Pan-STARRS catalog, NIR magnitudes against 2MASS stars in the field.
After correcting for a Galactic foreground reddening of E(B-V)=0.09 mag (Schlegel et al. 1998), the SED is a power-law with no evidence for extinction by dust in the GRB host galaxy.
We thank Sam Kim for excellent support and for performing the observations.
GCN Circular #30576
A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU) and E. Troja report on behalf of the Swift-XRT team:
We have analysed 7.9 ks of XRT data for GRB 210731A (Troja et al. GCN Circ. 30568), from 191 s to 60.1 ks after the BAT trigger. The data comprise 62 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. Using 3002 s of PC mode data and 8 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 300.30466, -28.06096 which is equivalent to:
```
RA (J2000): 20h 01m 13.12s
Dec(J2000): -28d 03' 39.4"
```
with an uncertainty of 2.2 arcsec (radius, 90% confidence).
The light curve can be modelled with an initial power-law decay with an index of alpha=3.6 (+/-0.5), followed by a break at T+424 s to an alpha of 0.86 (+0.18, -0.19).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 3.07 (+0.29, -0.21). The best-fitting absorption column is 1.36 (+0.47, -0.21) x 10^21 cm^-2, consistent with the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.97 (+0.26, -0.19) and a best-fitting absorption column of 1.35 (+0.77, -0.20) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.35 (+0.77, -0.20) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.97 (+0.26, -0.19)
```
If the light curve continues to decay with a power-law decay index of 0.86, the count rate at T+24 hours will be 0.022 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.3 x 10^-13 (9.3 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01062336.
This circular is an official product of the Swift-XRT team.
GCN Circular #30578
V. Lipunov, E. Gorbovskoy, N.Tyurina, K.Minkina, I.Gorbunov, P.Balanutsa,V.Vladimirov, A.Kuznetsov, D.Cheryasov (Lomonosov Moscow State University,SAI, Physics Department), O.A. Gres, N.M. Budnev (Irkutsk State University, API), R. Podesta, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra, N. Lodiu (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
R. Podesta, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
Three MASTER robotic telescopes (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) in Spain (IAC, Canary) and South Africa (SAAO observatory) automatically observed Swift GRB 210801A (Troja et al., GCN 30568) started 60-70s after trigger (Lipunov ) up to 2021-08-01 09:16:46 (Lipunov et al., GCN 30567).
MASTER-OAFA auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 20h 01m 13.07s , -28d 03m 39s.6 (err = +-0".9).
The OT magnitude in 'clear' filter is 18.3m (mlim = 19.8) at plato ( see detection de Wet et al., GCN 30570).
The OT is seen in dozeens images. There is no minor planet at this place.
We have reference image on 2017-08-22.12663 UT with 'clear' filter 19.7m.
GCN Circular #30580
M. Stamatikos (OSU), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), E. Troja (NASA/GSFC/UMCP) T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+409 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210731A (trigger #1062336) (Troja et al., GCN Circ. 30568). The BAT ground-calculated position is RA, Dec = 300.311, -28.056 deg which is
```
   RA(J2000)  =  20h 01m 14.5s
   Dec(J2000) = -28d 03' 20.0"
```
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 39%.
The mask-weighted light curve shows a single-pulse structure that starts at ~T-1 s, peaks at ~T+11 s, and ends at ~T+30 s. T90 (15-350 keV) is 22.51 +- 2.79 sec (estimated error including systematics).
The time-averaged spectrum from T-0.78 to T+25.50 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index -0.25 +- 0.59, and Epeak of 106.5 +- 26.8 keV (chi squared 50.28 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.2 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+11.28 sec in the 15-150 keV band is 1.6 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.01 +- 0.11 (chi squared 67.96 for 57 d.o.f.). 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/1062336/BA/
GCN Circular #30582
WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to the Swift GRB 210731A (Troja et al., GCN 30568) starting at ~9.04 hours after the Swift trigger. A total of 30x60s images were obtained in the clear (roughly R) filter. The optical afterglow (de Wet et al., GCN 30571; Kuin et al., GCN 30572; Guelbenzu et al., GCN 30574; Lipunov et al., GCN 30578;) was clearly detected in each single image. We measured its brightness of 18.6 +/- 0.1 mag at 9.26 hours after burst, calibrated to the Pan-STARRS1 catalog.
GCN Circular #30583
D.A. Kann (HETH/IAA-CSIC), L. Izzo (DARK/NBI), A.J. Levan (Radboud), D.B. Malesani (DTU Space), S. de Wet (UCT) report for the STARGATE collaboration:
"We observed the afterglow of GRB 210731A (Troja et al. GCN 30568, de Wet et al. GCN 30570) with the ESO VLT UT3 equipped with the X-shooter spectrograph on 1 Aug 2021. A total of 4800 s (4x1200 s) of spectra were obtained starting at 02:45 UT (approximately 28.5 hours after the burst).
The afterglow is well detected in the acquisition imaging with r=20.7+/- 0.1, and a continuum is visible across the X-shooter spectral range. The spectra contain several prominent absorption features of Fe II, Al III, Mg II and Mg I, at a common redshift z=1.2525. This is consistent with the detection of the afterglow in all the UVOT filters (Kuin & Troja GCN 30572), and we suggest it to be the redshift of GRB 210731A.
We thank the Paranal staff for the excellent assistance in securing these observations."
GCN Circular #30584
A. Nicuesa Guelbenzu, S. Klose, S. Schmidl (all TLS Tautenburg), A. Rau (MPE Garching), and D. A. Kann (HETH/IAA-CSIC) report:
Using GROND mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile), we continued to observe the bright afterglow of GRB 210731A (Swift trigger 1062336; Troja et al., GCN 30568).
A comparison of our first-epoch optical data (Nicuesa Guelbenzu et al., GCN 30574) with those from de Wet et al. (GCN 30570) indicated that the optical afterglow underwent a relatively long-lasting plateau phase (see also Zhen & Filippenko, GCN 30582). Our 2nd epoch GROND observations now reveal that this plateau phase has finished and the afterglow has entered a declining phase.
At a mean time of 1.22 days post burst we measure (AB magnitudes)
r' = 20.74 +/- 0.02 mag,
calibrated against the Pan-STARRS catalog. This is in good agreement with the VLT X-shooter result at 1.19 d (Kann et al., GCN 30583).
We thank Sam Kim for excellent support and for performing the observations.

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Jochen Greiner, last update: 02-Aug-2021 [Disclaimer]