Gamma-ray Burst 210402A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:04:23 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     639093861
GRB_RA:          202.033d {+13h 28m 08s} (J2000),
                 202.255d {+13h 29m 01s} (current),
                 201.511d {+13h 26m 03s} (1950)
GRB_DEC:         +48.800d {+48d 47' 60"} (J2000),
                 +48.690d {+48d 41' 25"} (current),
                 +49.059d {+49d 03' 31"} (1950)
GRB_ERROR:       27.68 [deg radius, statistical plus systematic]
GRB_INTEN:       50 [cnts/sec]
DATA_SIGNIF:     4.90 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19306 TJD;    92 DOY;   21/04/02
GRB_TIME:        79456.98 SOD {22:04:16.98} UT
GRB_PHI:         238.00 [deg]
GRB_THETA:        45.00 [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, 1,1,0, 0,0,0, 0,0,
SUN_POSTN:        12.32d {+00h 49m 16s}   +5.28d {+05d 16' 57"}
SUN_DIST:        125.33 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
MOON_POSTN:      263.35d {+17h 33m 25s}  -24.17d {-24d 10' 15"}
MOON_DIST:        90.95 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      107.21, 67.19 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      173.22, 52.06 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210402920/quicklook/glg_lc_medres34_bn210402920.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 304.15,0.95 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:04:39 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     639093861
GRB_RA:          196.680d {+13h 06m 43s} (J2000),
                 196.918d {+13h 07m 40s} (current),
                 196.119d {+13h 04m 28s} (1950)
GRB_DEC:         +45.040d {+45d 02' 24"} (J2000),
                 +44.927d {+44d 55' 36"} (current),
                 +45.307d {+45d 18' 25"} (1950)
GRB_ERROR:       10.41 [deg radius, statistical only]
DATA_SIGNIF:     5.50 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19306 TJD;    92 DOY;   21/04/02
GRB_TIME:        79456.98 SOD {22:04:16.98} UT
GRB_PHI:         231.00 [deg]
GRB_THETA:        43.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        12.32d {+00h 49m 16s}   +5.28d {+05d 16' 57"}
SUN_DIST:        129.62 [deg]   Sun_angle= 11.7 [hr] (West of Sun)
MOON_POSTN:      263.36d {+17h 33m 26s}  -24.17d {-24d 10' 16"}
MOON_DIST:        91.77 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      114.25, 71.83 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      171.98, 46.88 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210402920/quicklook/glg_lc_medres34_bn210402920.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_639093861.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:09:56 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1040123,   Seg_Num: 0
GRB_RA:          198.2584d {+13h 13m 02.01s} (J2000),
                 198.4941d {+13h 13m 58.58s} (current),
                 197.7028d {+13h 10m 48.66s} (1950)
GRB_DEC:         +44.5125d {+44d 30' 45.0"} (J2000),
                 +44.4002d {+44d 24' 00.7"} (current),
                 +44.7773d {+44d 46' 38.3"} (1950)
GRB_ERROR:       4.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.31e-08 [erg/cm2/sec]
GRB_SIGNIF:      15.23 [sigma]
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79551.52 SOD {22:05:51.52} UT
TAM[0-3]:        327.65 237.17 261.61 243.57
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 02"}
SUN_DIST:        130.01 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.41d {+17h 33m 39s}  -24.18d {-24d 10' 42"}
MOON_DIST:        90.59 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.33, 72.08 [deg] galactic lon,lat of the burst
ECL_COORDS:      173.77, 47.06 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:           
COMMENTS:        WARNING: No BAT_Position TDRSS message was received for this trigger_number!  
COMMENTS:           
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:10:06 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
GRB_RA:          198.2584d {+13h 13m 02.0s} (J2000),
                 198.4941d {+13h 13m 58.5s} (current),
                 197.7028d {+13h 10m 48.6s} (1950)
GRB_DEC:         +44.5125d {+44d 30' 45.0"} (J2000),
                 +44.4002d {+44d 24' 00.7"} (current),
                 +44.7773d {+44d 46' 38.3"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       232 [cnts]
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79551.52 SOD {22:05:51.52} UT
CENTROID_X:      285.38,  raw= 285  [pixels]
CENTROID_Y:      225.72,  raw= 226  [pixels]
ROLL:            7.69 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -170.60
GRB_POS_XRT_Z:   -51.89
IMAGE_URL:       sw01040123000msxps_rw.img
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 02"}
SUN_DIST:        130.01 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.42d {+17h 33m 40s}  -24.18d {-24d 10' 42"}
MOON_DIST:        90.59 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.33, 72.08 [deg] galactic lon,lat of the burst
ECL_COORDS:      173.77, 47.06 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:10:09 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
GRB_RA:          198.2584d {+13h 13m 02.0s} (J2000),
                 198.4941d {+13h 13m 58.5s} (current),
                 197.7028d {+13h 10m 48.6s} (1950)
GRB_DEC:         +44.5125d {+44d 30' 45.0"} (J2000),
                 +44.4002d {+44d 24' 00.7"} (current),
                 +44.7773d {+44d 46' 38.3"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       232 [cnts]
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79551.52 SOD {22:05:51.52} UT
CENTROID_X:      285.38,  raw= 285  [pixels]
CENTROID_Y:      225.72,  raw= 226  [pixels]
ROLL:            7.69 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -170.60
GRB_POS_XRT_Z:   -51.89
IMAGE_URL:       sw01040123000msxps_rw.img
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 02"}
SUN_DIST:        130.01 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.42d {+17h 33m 40s}  -24.18d {-24d 10' 43"}
MOON_DIST:        90.59 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.33, 72.08 [deg] galactic lon,lat of the burst
ECL_COORDS:      173.77, 47.06 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:10:51 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.191d {+13h 12m 46s} (J2000)
POINT_DEC:       +44.505d {+44d 30' 16"} (J2000)
POINT_ROLL:      7.695d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79560.05 SOD {22:06:00.05} UT
FILTER:          10, White
BKG_MEAN:        1.507
N_STARS:         23
X_OFFSET:        744 [pixels]
Y_OFFSET:        816 [pixels]
X_MAX:           1703 [pixels]
Y_MAX:           1775 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01040123000msufc639093960.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 03"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.42d {+17h 33m 42s}  -24.18d {-24d 10' 46"}
MOON_DIST:        90.63 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:11:10 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.191d {+13h 12m 46s} (J2000)
POINT_DEC:       +44.505d {+44d 30' 16"} (J2000)
ROLL:            7.695d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79560.05 SOD {22:06:00.05} UT
FILTER:          10, White
EXPOSURE_ID:     639093986
X_OFFSET:        1059 [pixels]
Y_OFFSET:        1130 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1219
Y_GRB_POS:       1290
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639093987.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 03"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.43d {+17h 33m 42s}  -24.18d {-24d 10' 47"}
MOON_DIST:        90.63 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:11:16 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.191d {+13h 12m 46s} (J2000)
POINT_DEC:       +44.505d {+44d 30' 16"} (J2000)
ROLL:            7.695d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79560.05 SOD {22:06:00.05} UT
FILTER:          10, White
EXPOSURE_ID:     639093986
X_OFFSET:        1059 [pixels]
Y_OFFSET:        1130 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1219
Y_GRB_POS:       1290
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639093987.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 03"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.43d {+17h 33m 43s}  -24.18d {-24d 10' 48"}
MOON_DIST:        90.63 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:11:05 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.191d {+13h 12m 46s} (J2000)
POINT_DEC:       +44.505d {+44d 30' 16"} (J2000)
POINT_ROLL:      7.695d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79560.05 SOD {22:06:00.05} UT
FILTER:          10, White
BKG_MEAN:        1.507
N_STARS:         23
X_OFFSET:        744 [pixels]
Y_OFFSET:        816 [pixels]
X_MAX:           1703 [pixels]
Y_MAX:           1775 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01040123000msufc639093960.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 03"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.43d {+17h 33m 42s}  -24.18d {-24d 10' 47"}
MOON_DIST:        90.63 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:13:04 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.189d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
POINT_ROLL:      7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79718.51 SOD {22:08:38.51} UT
FILTER:          7, U
BKG_MEAN:        0.391
N_STARS:         23
X_OFFSET:        739 [pixels]
Y_OFFSET:        810 [pixels]
X_MAX:           1698 [pixels]
Y_MAX:           1769 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw01040123000msufc639094118.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 05"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.45d {+17h 33m 47s}  -24.18d {-24d 10' 57"}
MOON_DIST:        90.65 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:14:11 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.189d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
ROLL:            7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79718.51 SOD {22:08:38.51} UT
FILTER:          7, U
EXPOSURE_ID:     639094145
X_OFFSET:        1059 [pixels]
Y_OFFSET:        1130 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1219
Y_GRB_POS:       1290
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639094145.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 06"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.46d {+17h 33m 50s}  -24.18d {-24d 11' 02"}
MOON_DIST:        90.66 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:13:17 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.189d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
POINT_ROLL:      7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79718.51 SOD {22:08:38.51} UT
FILTER:          7, U
BKG_MEAN:        0.391
N_STARS:         23
X_OFFSET:        739 [pixels]
Y_OFFSET:        810 [pixels]
X_MAX:           1698 [pixels]
Y_MAX:           1769 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw01040123000msufc639094118.fits
SUN_POSTN:        12.32d {+00h 49m 17s}   +5.28d {+05d 17' 05"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.45d {+17h 33m 48s}  -24.18d {-24d 10' 58"}
MOON_DIST:        90.65 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:14:24 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.189d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
ROLL:            7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  79718.51 SOD {22:08:38.51} UT
FILTER:          7, U
EXPOSURE_ID:     639094145
X_OFFSET:        1059 [pixels]
Y_OFFSET:        1130 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1219
Y_GRB_POS:       1290
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639094145.fits
SUN_POSTN:        12.32d {+00h 49m 18s}   +5.29d {+05d 17' 06"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.46d {+17h 33m 51s}  -24.18d {-24d 11' 03"}
MOON_DIST:        90.66 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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 #29741
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-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) was pointed to the Swift GRB210402.92 (trigger No 1040123,13h 13m 01.92s , +44d 30m 46.8s, R=0.00130556) errorbox 108 sec after trigger time at 2021-04-02 22:07:40 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 42 deg. The sun altitude is -35.7 deg.
MASTER-Tavrida robotic telescope located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB210402.92 errorbox 123 sec after trigger time at 2021-04-02 22:07:55 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 0 deg. The sun altitude is -40.6 deg.
The galactic latitude b = 72 deg., longitude l = 109 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1582249
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

     139 |          MASTER-IAC |   C |    60 | 19.1 |        
     154 |      MASTER-Tavrida |   C |    60 | 18.8 |        
     292 |          MASTER-IAC |  P| |    50 | 18.1 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #29742
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 GRB210402.92 (trigger No 639093861,13h 06m 43.20s , +45d 02m 24.0s, R=10.41) errorbox 120 sec after notice time and 138 sec after trigger time at 2021-04-02 22:06:35 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 3 deg. The sun altitude is -40.6 deg.
MASTER-IAC robotic telescope located in Spain (IAC Teide Observatory) started inspect of the Fermi GRB210402.92 errorbox 185 sec after notice time and 203 sec after trigger time at 2021-04-02 22:07:40 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 42 deg. The sun altitude is -35.7 deg.
MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB210402.92 errorbox 344 sec after notice time and 361 sec after trigger time at 2021-04-02 22:10:18 UT, with upper limit up to 16.0 mag. The observations began at zenith distance = 78 deg. The sun altitude is -62.1 deg.
The galactic latitude b = 72 deg., longitude l = 113 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1582244
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

     169 | 2021-04-02 22:06:35 |      MASTER-Tavrida | (12h 53m 56.10s , +46d 16m 08.2s) |   C |    60 | 18.8 |        
     233 | 2021-04-02 22:07:40 |          MASTER-IAC | (13h 02m 48.24s , +44d 08m 22.0s) |   C |    60 | 19.1 |        
     233 | 2021-04-02 22:07:40 |          MASTER-IAC | (12h 51m 27.91s , +44d 13m 49.5s) |   C |    60 | 18.9 |        
     249 | 2021-04-02 22:07:55 |      MASTER-Tavrida | (13h 11m 59.89s , +44d 16m 23.4s) |   C |    60 | 18.8 |        
     386 | 2021-04-02 22:10:18 |          MASTER-IAC | (13h 12m 20.00s , +44d 37m 33.9s) |  P| |    50 | 18.1 |        
     387 | 2021-04-02 22:10:18 |         MASTER-SAAO | (13h 14m 02.65s , +44d 32m 46.0s) | P\  |    50 | 16.0 |        
     467 | 2021-04-02 22:11:28 |         MASTER-SAAO | (13h 14m 04.20s , +44d 31m 15.3s) | P\  |    70 | 15.7 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:20:48 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.188d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
POINT_ROLL:      7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  80275.74 SOD {22:17:55.74} UT
FILTER:          10, White
BKG_MEAN:        1.542
N_STARS:         159
X_OFFSET:        499 [pixels]
Y_OFFSET:        570 [pixels]
X_MAX:           1938 [pixels]
Y_MAX:           2009 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01040123000msufc639094675.fits
SUN_POSTN:        12.33d {+00h 49m 18s}   +5.29d {+05d 17' 12"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.53d {+17h 34m 07s}  -24.19d {-24d 11' 33"}
MOON_DIST:        90.71 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 02 Apr 21 22:21:00 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.188d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
POINT_ROLL:      7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  80275.74 SOD {22:17:55.74} UT
FILTER:          10, White
BKG_MEAN:        1.542
N_STARS:         159
X_OFFSET:        499 [pixels]
Y_OFFSET:        570 [pixels]
X_MAX:           1938 [pixels]
Y_MAX:           2009 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01040123000msufc639094675.fits
SUN_POSTN:        12.33d {+00h 49m 19s}   +5.29d {+05d 17' 12"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.53d {+17h 34m 08s}  -24.19d {-24d 11' 34"}
MOON_DIST:        90.71 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:22:09 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.188d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
ROLL:            7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  80275.74 SOD {22:17:55.74} UT
FILTER:          10, White
EXPOSURE_ID:     639094702
X_OFFSET:        1058 [pixels]
Y_OFFSET:        1129 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1218
Y_GRB_POS:       1289
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639094702.fits
SUN_POSTN:        12.33d {+00h 49m 19s}   +5.29d {+05d 17' 14"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.54d {+17h 34m 11s}  -24.19d {-24d 11' 40"}
MOON_DIST:        90.72 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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:     Fri 02 Apr 21 22:22:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1040123,   Seg_Num: 0
POINT_RA:        198.188d {+13h 12m 45s} (J2000)
POINT_DEC:       +44.504d {+44d 30' 15"} (J2000)
ROLL:            7.692d
IMG_START_DATE:  19306 TJD;    92 DOY;   21/04/02
IMG_START_TIME:  80275.74 SOD {22:17:55.74} UT
FILTER:          10, White
EXPOSURE_ID:     639094702
X_OFFSET:        1058 [pixels]
Y_OFFSET:        1129 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1218
Y_GRB_POS:       1289
BINNING_INDEX:   1
IM_URL:          sw01040123000msuni639094702.fits
SUN_POSTN:        12.33d {+00h 49m 19s}   +5.29d {+05d 17' 14"}
SUN_DIST:        130.02 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      263.55d {+17h 34m 11s}  -24.19d {-24d 11' 40"}
MOON_DIST:        90.72 [deg]
MOON_ILLUM:      67 [%]
GAL_COORDS:      110.48, 72.11 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      173.72, 47.03 [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 #29743
K. L. Page (U Leicester), S. D. Barthelmy (GSFC), F. E. Marshall (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team:
BAT has triggered on a new GRB 210402A (Trigger #1040123) causing Swift to slew to the location and make follow-up observations. Due to a ground pass at the time of the GRB, no precise trigger time, location, or light curve data is immediately available. These details will be given in a later circular.
We note that Fermi triggered on a GRB at around the same time at a consistent location (Fermi Trigger #639093861) confirming its GRB status.
Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 198.25866, 44.51291 which is equivalent to:
```
   RA(J2000)  = 13h 13m 02.08s
   Dec(J2000) = +44d 30' 46.5"
```
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.51 x 10^20 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 1.31e-08 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of nominal 150 seconds with the White filter. 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. No correction has been made for the extinction in the Milky Way.
Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 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 #29745
Z.P. Zhu (NAOC, HUST), D. Xu (NAOC), L. Izzo (DARK/NBI), J. Martikainen (NOT) report on behalf of a larger collaboration:
We observed the field of GRB 210402A (Page et al., GCN 29743) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 00:19:22 UT on 2021-04-03, i.e., 2.23 hr after the burst, and we obtained 3x300 s and 5x200 s frames in the SDSS r- and z- filters, respectively.
Preliminary analysis reveals that no optical transient is detected in our stacked images within or at the edge of the current XRT error circle (3.5 arcsec; Page et al., GCN 29743), down to limiting magnitudes of r ~ 24.6 and z ~ 23.2, calibrated with nearby PanSTARRS stars.
Compared with the bright X-ray afterglow and no much X-ray column density excess, it may indicate that the burst is a high-redshift one.
NIR follow-ups are strongly encouraged.
GCN Circular #29747
Simone Leonini, M. Conti, P. Rosi and L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy) report:
We observed the field of GRB210402A (Swift trigger 1040123, Fermi trigger 639093861, K.L. Page et al., GCN Circ. 29743) with the automatic 0.53m RC telescope + U47 detector at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2021-04-02 22:48:18 UT (18 minutes post-burst) stacking 4 unfiltered CCD exposures of 40s each.
We have not found optical transient within the error-box given. Mag. upper limit R = 20.10+/-0.19
Magnitudes were obtained using Astrometrica software using USNO-B1 catalogue and are not corrected for galactic extinction.
GCN Circular #29750
P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), J.P. Osborne (U. Leicester) and K.L. Page report on behalf of the Swift-XRT team:
We have analysed 6.0 ks of XRT data for GRB 210402A (Page et al. GCN Circ. 29743), from 160 s to 46.0 ks after the BAT trigger. The data comprise 1.1 ks in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. Using 1629 s of PC mode data and 3 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 = 198.25927, +44.51454 which is equivalent to:
```
RA (J2000): 13h 13m 02.22s
Dec(J2000): +44d 30' 52.3"
```
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
The late-time light curve (from T0+5.4 ks) can be modelled with a power-law decay with a decay index of alpha=1.03 (+0.21, -0.27).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.811 (+0.027, -0.026). The best-fitting absorption column is 3.25 (+/-0.13) x 10^21 cm^-2, in excess of the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.09 (+0.20, -0.19) and a best-fitting absorption column of 3.2 (+/-0.8) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.2 (+/-0.8) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: 6.5 sigma
Photon index:	     2.09 (+0.20, -0.19)
```
If the light curve continues to decay with a power-law decay index of 1.03, the count rate at T+24 hours will be 0.017 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x 10^-13 (9.4 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/01040123.
This circular is an official product of the Swift-XRT team.
GCN Circular #29752
Nat Butler (ASU), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Oc�lotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report:
We observed the field of the Swift/BAT GRB 210402A (Page et al., GCN Circ. 29743) with the DDOTI wide-field imager at the Observatorio Astron�mico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-03 02:52 UTC to 2021-04-03 12:18 UTC (from 4.8 to 14.2 hours after the trigger).
We observed a region covering aproximately 7 degrees in RA and 10 degrees in declination (about 70 square degrees), including the XRT position in the w filter, and obtained 23ks of exposure. We calibrated our images against the APASS catalog.
Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we do not detect a source at the X-ray position to a 3-sigma limiting magnitude of w = 23.2.
Our non-detection is consistent with the non-detections reported by Zhu et al. (GCN Circ. 29745) and Leonini et al. (GCN Circ. 29747).
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
GCN Circular #29753
A Rossi (INAF-OAS) report on behalf of the CIBO collaboration:
We observed the field of GRB 210402A (Page et al., GCN 29743) simultaneously in the r' and z' bands with the LBC imager mounted on LBT (Mt Graham, AZ, USA). We obtained 20min of imaging on 2021-04-03 at mid-time 05:33:00 UT, 0.305 days days after the swift GCN. Observations were performed under an average seeing of ~1.4".
Within the refined XRT position (Evans etal., GCN 29750) we detect an extended source in both bands at position (J2000)
```
RA =13:13:02.04
DEC=+44:30:52.7
```
and preliminary magnitudes (AB system),
```
r=23.9+-0.2
z=23.1+-0.3
```
calibrated against SDSS field stars.
We note that a second source with r=23.4+-0.1 lies at position (J2000)
```
RA =13:13:02.46
DEC=+44:30:50.3
```
which is at south-east and outside the XRT error circle, and thus unlikely associated eith the GRB.
Moreover, this second source is already present (but it is very faint) in archival Pan-STARRS images, while the first one is beyond the survey limits. We note that, assuming that both are galaxies, the first one is more likely to be the host galaxy because of its brightness and distance which result in a smaller probability of chance association.
In both cases we cannot exclude that the afterglow is still contributing to the brightness of this sources. Further observations are necessary to assess their variability.
We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly B. Rothberg, J. Williams, and F. Cusano, in obtaining these observations.
GCN Circular #29755
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), R. Fernandez-Munoz (IHSM/UMA-CSIC), M. Jelinek (ASU-CAS), 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 210402A by Swift (Page et al. GCNC 29743), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically followed up this event at 22:10:15 UT (~ 19 s after notice) gathering images (60 s exposure time, clear filter). Furthermore, the 0.6 m BOOTES-2/TELMA robotic telescope at IHSM La Mayora (UMA-CSIC) in Algarrobo Costa (Malaga, Spain) also responded to this event, with the first image (60 s exposure, clear filter) obtained at 22:12:04 UT on April 2 (~ 2 min after notice).
In any case, no optical transient is detected down to 19.2 and 18.9 mag respectively within the Swift/XRT error region (Evans et al, GCNC 29750). These two non-detections are consistent with the limits reported by MASTER (Lipunov et al, GCNC 29741), Swift/UVOT (Page et al. GCNC 29743), Montarrenti (Leonini et al. GCNC 29747), NOT (Zhu et al, GCNC 29745) and DDOTI (Butler et al, GCNC 29752).
We thank the staff at both La Mayora and Lijiang Astronomical Observatory for their excellent support.
GCN Circular #29757
D. Xu (NAOC), Z.P. Zhu (NAOC,HUST), D. B. Malesani (DTU Space) report on behalf of a larger collaboration:
We reanalysed our previously reported NOT data (Zhu et al., GCN 29745), given that the position of the Swift/XRT error circle has significantly changed (Page et al., GCN 29743; Evans et al., GCN 29750).
An optical source, S1, is detected at the western edge of the refined XRT error circle (Evans et al., GCN 29750) at coordinates: R.A.(J2000) =13:13:02.04 and Dec.(J2000)=+44:30:52.69, with r = 24.0 +/- 0.2 and z = 22.6 +/- 0.3, calibrated with nearby PanSTAR stars. S1 is also detected by the LBT observations (Rossi, GCN 29753), and the magnitudes are consistent with each other with 1sigma error. In addition, the GRB field is covered by the Legacy Survey, and forced aperture photometry of the S1 position gives r ~ 24.5 and z ~ 23.3, both fainter than the NOT measurements. Thus, S1 is the optical afterglow candidate of the burst.
A second source, S2, is detected at the south-east and outside of the refined XRT error circle at coordinates: R.A.(J2000) =13:13:02.45 and Dec.(J2000)=+44:30:50.31, as pointed by the LBT observations. It has r = 23.5 +/- 0.1 and z = 23.0 +/- 0.2 from the NOT images, and again no r-band variability between the NOT and LBT epochs. Moreover, forced aperture photometry of the S2 position from the Legacy Survey gives r ~ 23.6 and z ~ 23.0, being consistent with the NOT measurements. Thus, we're inclined to conclude that S2 is unlikely the optical afterglow of the burst.
Further observations are planned to asses the brightness variability.
GCN Circular #29761
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210402A (trigger #1040123) (Page et al., GCN Circ. 29743). The BAT ground-calculated position is RA, Dec = 198.265, 44.510 deg which is
```
   RA(J2000)  =  13h 13m 03.7s
   Dec(J2000) = +44d 30' 36.1"
```
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 69%.
The mask-weighted light curve shows a multi-peaked structure that starts at ~T-50 s and ends at ~T+310 s. The main peak occurs at ~T+174 s. T90 (15-350 keV) is 238.7 +- 18.8 sec (estimated error including systematics).
The time-averaged spectrum from T-51.60 to T+310.20 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.49 +- 0.27, and Epeak of 63.6 +- 22.9 keV (chi squared 58.82 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 8.6 +- 0.4 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+173.53 sec in the 15-150 keV band is 1.6 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.87 +- 0.06 (chi squared 65.10 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/1040123/BA/
GCN Circular #29762
Z.P. Zhu (NAOC,HUST), D. Xu (NAOC), D. B. Malesani (DTU Space) report on behalf of a larger collaboration:
We continued to observe the field of GRB 210402A (Page et al., GCN 29743) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 9x360 s frames in the Sloan r-filter, starting at 23:04:56 UT on 2021-04-04, i.e., 2.04 days after the burst.
The optical afterglow candidate, S1, (Xu et al. GCN 29757, see also Rossi et al., GCN 29753) is still detected in the stacked image. S1 now has r = 24.3 +/- 0.1, calibrated with nearby Pan-STARRS stars, while it had r = 24.0 +/- 0.2 in the last NOT epoch. The magnitudes are basically consistent with each other within 1\sigma error, although there might be slight decay, which indicates that S1 has been dominated by the potential host galaxy since the first NOT epoch.
Meanwhile, the unlikely optical afterglow source, S2, is well detected in the stacked image with r= 23.5 +/- 0.1, the same as the last NOT epoch. We thus conclude that S2 is not associated to the GRB.
GCN Circular #29763
O.J. Roberts (USRA/MSFC) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 22:04:16.98 UT on the 2nd April 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210402A (trigger 639093861 / 210402920), which was also detected by the Swift/BAT (Page et al. 2021, GCN 29743). The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 44 degrees.
The GBM light curve consists of several broad, faint peaks, including emission about 60 s prior to the trigger time. The T90 duration of the event is about 76 s (50-300 keV). The time-averaged spectrum from T0-60 s to T0+16 s is adequately fit by a simple power law function with index -1.34 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is (1.699 +/- 0.008)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0-52.7 s in the 10-1000 keV band is 1.5 +/- 0.2 ph/s/cm^2.
Due to the powering down of Fermi-GBM detectors because of SAA entry about 19 s after the trigger time (note T90), the T90 duration, peak fluxes and fluences are lower limits only.
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 #29764
GRB 210402A: Swift/UVOT Upper Limits
S. J. LaPorte (PSU) and K. L. Page (U Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210402A 73 s after the BAT trigger (Page et al., GCN Circ. 29743). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 29750) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           163          313          147         >20.8
u_FC               321          571          246         >20.3
white              163         1718          411         >21.4
v                  653         5581          229         >19.6
b                  578         1694          117         >20.2
u                  321         1669          304         >20.2
w1                1108         1644           78         >19.2
w2                1207         1227           19         >18.4
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.018 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #29765
K.Zhirkov, V. Lipunov, V.Kornilov, E.Gorbovskoy,P.Balanutsa,V.Vladimirov, A.Kuznetsov, D. Vlasenko, N.Tiurina, I.Gorbunov, A.Chasovnikov, D.Zimnukhov, V.Senik, V.Topolev, F.Balakin, D.Cheryasov (Lomonosov Moscow State University,SAI, Physics Department), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev (Irkutsk State University, API), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L) observed GRB 210402A (Swift trigger 1040123 Page et al. GCN 29743, Evans et al. GCN 29750, Laha et al. 29761, Ttrigger=2021-04-02T22:03:17.22, also Fermi trigger #639093861 T_trigger(Fermi) = 22 04 17 Roberts et al. GCN 29763) at MASTER-IAC, -Tavrida, -SAAO, -Kislovodsk, -OAFA, -Tunka (Lipunov et al. GCN 29741) by MASTER-VWF cameras (two 24.3x16.2sq.deg.) with mlim=13 and by MASTER-II (two 4sq.deg.) with mlims at MASTER cover map https://master.sai.msu.ru/site/master2/observ.php?id=1582249
We observed this field with the MASTER-VWFC of MASTER-IAC, covering the Swift/XRT position from 2021-04-02 22:04:21 to 2021-04-02 22:07:17, i.e. during the prompt emission. Frames were taken with the exposure time of 5s and with no filter .
Calibrated with NOMAD V-filter, we marginally see optical source inside T90 at 2 images: started at 2021-04-02 22:05:36(79 from Fermi trigger time) and at 2021-04-02 22:05:46(89 from Fermi trigger) with m_OT~11 at XRT position, but the pixel of this camera is 21".
Comparing to the GAIA EDR3, we see no optical counterpart down to the magnitude of 10.5 at other images. It puts the upper limit on the flux of the prompt optical emission at ~5e-10 erg cm^-2 s^-1. Considering that the x-ray flux was ~1e-08 erg cm^-2 s^-1, we constrain the relation between optical flux and x-ray flux at ~10^-2.

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Jochen Greiner, last update: 06-Apr-2021 [Disclaimer]