Gamma-ray Burst 210207B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 21:52:20 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.582d {+18h 02m 20s} (J2000),
                 270.693d {+18h 02m 46s} (current),
                 270.321d {+18h 01m 17s} (1950)
GRB_DEC:         +53.694d {+53d 41' 39"} (J2000),
                 +53.695d {+53d 41' 43"} (current),
                 +53.692d {+53d 41' 31"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1889 [cnts]    Image_Peak=143 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   124     E_range: 25-100 keV
BKG_INTEN:       19427 [cnts]
BKG_TIME:        78717.53 SOD {21:51:57.53} UT
BKG_DUR:         8 [sec]
GRB_DATE:        19252 TJD;    38 DOY;   21/02/07
GRB_TIME:        78728.15 SOD {21:52:08.15} UT
GRB_PHI:          17.13 [deg]
GRB_THETA:        32.95 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     17.74 [sigma]
IMAGE_SIGNIF:    9.59 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +2  +0  +0  +0 -14  +0 
SUN_POSTN:       321.77d {+21h 27m 05s}  -15.02d {-15d 00' 56"}
SUN_DIST:         81.35 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.65d {+18h 02m 36s}  -24.61d {-24d 36' 53"}
MOON_DIST:        78.31 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.69, 28.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      271.55, 77.13 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 221.37,10.01 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 21:53:58 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.6356d {+18h 02m 32.5s} (J2000),
                 270.7462d {+18h 02m 59.0s} (current),
                 270.3738d {+18h 01m 29.7s} (1950)
GRB_DEC:         +53.6836d {+53d 41' 00.9"} (J2000),
                 +53.6850d {+53d 41' 06.0"} (current),
                 +53.6811d {+53d 40' 52.1"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       227 [cnts]
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78802.03 SOD {21:53:22.03} UT,   73.9 [sec] since BAT Trigger Time
CENTROID_X:      295.55,  raw= 296  [pixels]
CENTROID_Y:      321.38,  raw= 321  [pixels]
ROLL:            130.46 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   54.89
GRB_POS_XRT_Z:   -27.91
IMAGE_URL:       sw01031297000msxps_rw.img
SUN_POSTN:       321.77d {+21h 27m 06s}  -15.02d {-15d 00' 54"}
SUN_DIST:         81.31 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.67d {+18h 02m 41s}  -24.62d {-24d 36' 57"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.68, 28.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      271.69, 77.12 [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 .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 21:54:04 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.6356d {+18h 02m 32.5s} (J2000),
                 270.7462d {+18h 02m 59.0s} (current),
                 270.3738d {+18h 01m 29.7s} (1950)
GRB_DEC:         +53.6836d {+53d 41' 00.9"} (J2000),
                 +53.6850d {+53d 41' 06.0"} (current),
                 +53.6811d {+53d 40' 52.1"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       227 [cnts]
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78802.03 SOD {21:53:22.03} UT,   73.9 [sec] since BAT Trigger Time
CENTROID_X:      295.55,  raw= 296  [pixels]
CENTROID_Y:      321.38,  raw= 321  [pixels]
ROLL:            130.46 [deg]
GAIN:            4
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   54.89
GRB_POS_XRT_Z:   -27.91
IMAGE_URL:       sw01031297000msxps_rw.img
SUN_POSTN:       321.77d {+21h 27m 06s}  -15.02d {-15d 00' 54"}
SUN_DIST:         81.31 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.67d {+18h 02m 41s}  -24.62d {-24d 36' 58"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.68, 28.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      271.69, 77.12 [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:     Sun 07 Feb 21 21:53:48 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.6356d {+18h 02m 32.54s} (J2000),
                 270.7462d {+18h 02m 59.08s} (current),
                 270.3738d {+18h 01m 29.71s} (1950)
GRB_DEC:         +53.6836d {+53d 41' 00.9"} (J2000),
                 +53.6850d {+53d 41' 06.0"} (current),
                 +53.6811d {+53d 40' 52.1"} (1950)
GRB_ERROR:       4.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.09e-08 [erg/cm2/sec]
GRB_SIGNIF:      15.06 [sigma]
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78802.03 SOD {21:53:22.03} UT,   73.9 [sec] since BAT Trigger Time
TAM[0-3]:        327.65 237.15 261.68 243.53
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       321.77d {+21h 27m 06s}  -15.02d {-15d 00' 54"}
SUN_DIST:         81.31 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.67d {+18h 02m 40s}  -24.62d {-24d 36' 57"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.68, 28.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      271.69, 77.12 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 2.00 arcmin from the BAT position.  
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:     Sun 07 Feb 21 21:56:34 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.582d {+18h 02m 20s} (J2000),
                 270.693d {+18h 02m 46s} (current),
                 270.321d {+18h 01m 17s} (1950)
GRB_DEC:         +53.694d {+53d 41' 39"} (J2000),
                 +53.695d {+53d 41' 43"} (current),
                 +53.692d {+53d 41' 31"} (1950)
GRB_DATE:        19252 TJD;    38 DOY;   21/02/07
GRB_TIME:        78728.15 SOD {21:52:08.15} UT
TRIGGER_INDEX:   124
GRB_PHI:          17.13 [deg]
GRB_THETA:        32.95 [deg]
DELTA_TIME:      58.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     17.74 [sigma]
IMAGE_SIGNIF:    9.59 [sigma]
LC_URL:          sw01031297000msb.lc
SUN_POSTN:       321.78d {+21h 27m 06s}  -15.01d {-15d 00' 52"}
SUN_DIST:         81.35 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.70d {+18h 02m 47s}  -24.62d {-24d 37' 05"}
MOON_DIST:        78.31 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.69, 28.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      271.55, 77.13 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 221.37,10.01 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 21:57:51 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
POINT_ROLL:      130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78810.60 SOD {21:53:30.60} UT,   82.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        5.891
N_STARS:         31
X_OFFSET:        328 [pixels]
Y_OFFSET:        632 [pixels]
X_MAX:           1287 [pixels]
Y_MAX:           1591 [pixels]
DET_THRESH:      21
PHOTO_THRESH:    12
SL_URL:          sw01031297000msufc0082.fits
SUN_POSTN:       321.78d {+21h 27m 06s}  -15.01d {-15d 00' 51"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.71d {+18h 02m 50s}  -24.62d {-24d 37' 09"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 21:58:06 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
POINT_ROLL:      130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78810.60 SOD {21:53:30.60} UT,   82.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        5.891
N_STARS:         31
X_OFFSET:        328 [pixels]
Y_OFFSET:        632 [pixels]
X_MAX:           1287 [pixels]
Y_MAX:           1591 [pixels]
DET_THRESH:      21
PHOTO_THRESH:    12
SL_URL:          sw01031297000msufc0082.fits
SUN_POSTN:       321.78d {+21h 27m 06s}  -15.01d {-15d 00' 51"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.71d {+18h 02m 51s}  -24.62d {-24d 37' 09"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [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:     Sun 07 Feb 21 22:00:00 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
ROLL:            130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78810.60 SOD {21:53:30.60} UT,   82.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     634427637
X_OFFSET:        796 [pixels]
Y_OFFSET:        765 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       956
Y_GRB_POS:       925
BINNING_INDEX:   1
IM_URL:          sw01031297000msuni0109.fits
SUN_POSTN:       321.78d {+21h 27m 07s}  -15.01d {-15d 00' 49"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.73d {+18h 02m 56s}  -24.62d {-24d 37' 15"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [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:     Sun 07 Feb 21 22:00:07 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
ROLL:            130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78810.60 SOD {21:53:30.60} UT,   82.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     634427637
X_OFFSET:        796 [pixels]
Y_OFFSET:        765 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       956
Y_GRB_POS:       925
BINNING_INDEX:   1
IM_URL:          sw01031297000msuni0109.fits
SUN_POSTN:       321.78d {+21h 27m 07s}  -15.01d {-15d 00' 49"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.73d {+18h 02m 56s}  -24.62d {-24d 37' 15"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [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:     Sun 07 Feb 21 22:02:09 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     1031297,   Seg_Num: 0
GRB_RA:          270.6350d {+18h 02m 32.39s} (J2000),
                 270.7456d {+18h 02m 58.93s} (current),
                 270.3732d {+18h 01m 29.56s} (1950)
GRB_DEC:         +53.6822d {+53d 40' 55.9"} (J2000),
                 +53.6836d {+53d 41' 01.0"} (current),
                 +53.6798d {+53d 40' 47.1"} (1950)
GRB_ERROR:       0.7 [arcsec radius, statistical only]
GRB_MAG:         13.72 +/- 0.14 [mag]
FILTER:          10, White
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  78807.00 SOD {21:53:27.00} UT,   78.9 [sec] since BAT Trigger Time
SUN_POSTN:       321.78d {+21h 27m 07s}  -15.01d {-15d 00' 48"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.76d {+18h 03m 01s}  -24.62d {-24d 37' 21"}
MOON_DIST:        78.31 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.68, 28.62 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      271.69, 77.12 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The UVOT position is 5.0 arcsec from the XRT position.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 22:05:08 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
POINT_ROLL:      130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  79022.59 SOD {21:57:02.59} UT,   294.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.531
N_STARS:         16
X_OFFSET:        476 [pixels]
Y_OFFSET:        445 [pixels]
X_MAX:           1435 [pixels]
Y_MAX:           1404 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01031297000msufc0294.fits
SUN_POSTN:       321.78d {+21h 27m 07s}  -15.01d {-15d 00' 45"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.79d {+18h 03m 09s}  -24.63d {-24d 37' 30"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.  
COMMENTS:        The Pointing RA,Dec,Roll values came from the 1st SrcList Notice.

GCN Circular #29420
A. Y. Lien (GSFC/UMBC), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC), J.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), S. Laha (GSFC/UMBC/CRESST), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), A. Tohuvavohu (U Toronto) and E. Troja (NASA/GSFC/UMCP) report on behalf of the Neil Gehrels Swift Observatory Team:
At 21:52:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210207B (trigger=1031297). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 270.582, +53.694 which is
```
   RA(J2000) = 18h 02m 20s
   Dec(J2000) = +53d 41' 39"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 100 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~45 sec after the trigger.
The XRT began observing the field at 21:53:22.0 UT, 73.9 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 270.6356, 53.6836 which is equivalent to:
```
   RA(J2000)  = 18h 02m 32.54s
   Dec(J2000) = +53d 41' 01.0"
```
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 120 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 1.09e-08 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 82 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
  RA(J2000)  =	18:02:32.40 = 270.63501
  DEC(J2000) = +53:40:56.0  =  53.68223
```
with a 90%-confidence error radius of about 0.74 arc sec. This position is 5.1 arc sec. from the center of the XRT error circle. The estimated magnitude is 13.72 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.041.
Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 07 Feb 21 22:05:26 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
POINT_ROLL:      130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  79022.59 SOD {21:57:02.59} UT,   294.4 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.531
N_STARS:         16
X_OFFSET:        476 [pixels]
Y_OFFSET:        445 [pixels]
X_MAX:           1435 [pixels]
Y_MAX:           1404 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01031297000msufc0294.fits
SUN_POSTN:       321.78d {+21h 27m 07s}  -15.01d {-15d 00' 45"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.79d {+18h 03m 10s}  -24.63d {-24d 37' 30"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [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:     Sun 07 Feb 21 22:06:28 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
ROLL:            130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  79022.59 SOD {21:57:02.59} UT,   294.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     634427849
X_OFFSET:        796 [pixels]
Y_OFFSET:        765 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       956
Y_GRB_POS:       925
BINNING_INDEX:   1
IM_URL:          sw01031297000msuni0321.fits
SUN_POSTN:       321.78d {+21h 27m 08s}  -15.01d {-15d 00' 44"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.80d {+18h 03m 12s}  -24.63d {-24d 37' 33"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The Pointing RA,Dec,Roll values came from the 1st Image Notice.  
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:     Sun 07 Feb 21 22:06:43 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1031297,   Seg_Num: 0
POINT_RA:        270.608d {+18h 02m 26s} (J2000)
POINT_DEC:       +53.676d {+53d 40' 35"} (J2000)
ROLL:            130.455d
IMG_START_DATE:  19252 TJD;    38 DOY;   21/02/07
IMG_START_TIME:  79022.59 SOD {21:57:02.59} UT,   294.4 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     634427849
X_OFFSET:        796 [pixels]
Y_OFFSET:        765 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       956
Y_GRB_POS:       925
BINNING_INDEX:   1
IM_URL:          sw01031297000msuni0321.fits
SUN_POSTN:       321.78d {+21h 27m 08s}  -15.01d {-15d 00' 44"}
SUN_DIST:         81.32 [deg]   Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN:      270.80d {+18h 03m 13s}  -24.63d {-24d 37' 34"}
MOON_DIST:        78.30 [deg]
MOON_ILLUM:      17 [%]
GAL_COORDS:       81.67, 28.64 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      271.61, 77.11 [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 #29421
Amit Kumar (ARIES), Shashi B. Pandey (ARIES), Rahul Gupta (ARIES), Ankur Ghosh (ARIES), Dimple (ARIES), Amar Aryan (ARIES), Brajesh Kumar (ARIES), and Kuntal Misra (ARIES) report:
We observed the Swift detected GRB 210207B (Lien et al., GCN 29420) using the 4Kx4K CCD Imager (Pandey et al. 2018, 2018BSRSL..87...42P) mounted at the axial port of the 3.6m Devasthal Optical Telescope (DOT) of ARIES Nainital. The observations were carried out on 2021-02-07 in Bessel UBVRI-bands starting from UT 22:32:31.875 (corresponding to 40.38 minutes after the burst). We clearly detect the optical transient reported by Lien et al., GCN 29420. In the first I band image the afterglow has a I band magnitude of 15.61+/-0.01 mag. Further processing of the data is in progress.
The quoted magnitude is calibrated with the nearby USNO-B1 stars and not corrected for Galactic extinction in the direction of the GRB. 3.6m Devasthal Optical Telescope (DOT) is a recently commissioned facility in the Northern Himalayan region of India (long:79 41 04E, lat:29 21 40N, alt:2540m) owned and operated by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital (https://www.aries.res.in). Authors of this GCN circular thankfully acknowledge consistent support from the staff members to run and maintain the 3.6m DOT. This circular may be cited.
GCN Circular #29422
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 1993 s of XRT Photon Counting mode data and 5 UVOT images for GRB 210207B, 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 = 270.63474, +53.68210 which is equivalent to:
```
RA (J2000): 18h 02m 32.34s
Dec (J2000): +53d 40' 55.5"
```
with an uncertainty of 1.7 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #29423
S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V. R. Ayvazian (AbAO), G. V. Kapanadze (AbAO), N. Pankov (HSE, IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 210207B (Lien et al., GCN 29420) with AS-32 telescope of Abastumani observatory (AbAO) in R-filter starting on 2021-02-08 (UT) 02:14:17. The optical afterglow (Lien et al., GCN 29420; Kumar et al., GCN 29421) is not detected in stacked image.
```
Date       UT start   t-T0    Filter  Exp.   OT    Err.  UL(3sigma)
                        (mid, days)     (s)

2021-02-08 02:14:17   0.19837  R      47*60   n/d  n/d   18.7
```
The photometry is based on nearby USNO-B1.0 stars
```
USNO-B1.0_id R2
1436-0267956 15.29
1436-0268040 15.52
```
The non-detection of the afterglow implies a jet break somewhere before of our observations, or the source of the GRB 210207B is highly redshifted.
GCN Circular #29426
D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:
The long GRB 210207B (Swift detection: Lien et al., GCN 29420) triggered Konus-Wind (KW) at T0=78768.813 s UT (21:52:48.813).
The burst light shows a multi-peaked emission complex, which starts at ~T0-50 s, peaks at ~T0, and has the total duration of ~110 s. The emission in is seen up to ~2.5 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB210207_T78768/
As observed by Konus-Wind, the burst had a fluence of (2.4 � 0.8)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+1.472, of (4.5 � 0.8)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum (measured from T0 to T0+65.792 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.85(-0.34,+0.44) and Ep = 334(-97,+237) keV (chi2 = 91/97 dof). Fitting this spectrum by a Band function yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.15 (chi2 =67/97 dof).
The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by the CPL model with alpha = -0.46(-0.22,+0.25) and Ep = 497(-84,+120) keV (chi2 = 76/97 dof). Fitting this spectrum by a Band function yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.33 (chi2 =76/96 dof).
All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.
GCN Circular #29427
K.L. Page (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and A.Y. Lien report on behalf of the Swift-XRT team:
We have analysed 6.8 ks of XRT data for GRB 210207B (Lien et al. GCN Circ. 29420), from 80 s to 45.6 ks after the BAT trigger. The data comprise 329 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 29422).
The late-time light curve (from T0+3.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.37 (+0.07, -0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.99 (+/-0.04). The best-fitting absorption column is 1.38 (+/-0.13) x 10^21 cm^-2, in excess of the Galactic value of 3.5 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.78 (+0.11, -0.10) and a best-fitting absorption column of 7.2 (+2.9, -2.6) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     7.2 (+2.9, -2.6) x 10^20 cm^-2
Galactic foreground: 3.5 x 10^20 cm^-2
Excess significance: 2.3 sigma
Photon index:	     1.78 (+0.11, -0.10)
```
If the light curve continues to decay with a power-law decay index of 1.37, the count rate at T+24 hours will be 0.021 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7 x 10^-13 (8.7 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/01031297.
This circular is an official product of the Swift-XRT team.
GCN Circular #29428
A. Ursi (INAF/IAPS), F. Longo (Univ. Trieste and INFN Trieste), C. Pittori, F. Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan, M. Cardillo, C. Casentini, Y. Evangelista, G. Piano (INAF/IAPS), F. Lucarelli (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, F. Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi (INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois (INAF/OA-Cagliari), I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:
The AGILE satellite detected GRB 210207B, reported by Swift (GCNs #29420, #29422, #29427) and Konus-Wind (GCN #29426) at T0 = 2021-02-07 21:52:08 (UT).
The AGILE Mini-CALorimeter (MCAL; 0.4-100 MeV) scientific ratemeters clearly detected the main peak of the burst, which occurred at T0 + 40 s, as reported by Swift/BAT. The episode lasted ~4 s and released 7950 counts in the MCAL detector, above a background rate of 1250 Hz. The AGILE ratemeters light curve can be found at: http://www.agilescienceapp.it/notices/GRB210207B_AGILE_RM.png . The event was 160� off-axis.
Additional analysis of AGILE data is in progress.
GCN Circular #29430
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 210207B (Lien et al., GCN 29420) starting at ~0.657 days after the trigger.
A total of 20x60s images were obtained in the clear (roughly R) filters.
We marginally detect the optical afterglow (Lien et al., GCN 29420; Kumar et al., GCN 29421) in the coadd image with a mag of 20.3 +/- 0.3, calibrated to the Pan-STARRS1 catalog.
GCN Circular #29431
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB 210207B (Lien, GCN 29420) with the LCO 1-m Sinistro instrument at the McDonald Observatory, Texas, USA site, on February 8, from 11:23 to 11:34 UT (corresponding to 13.30 to 13.48 hours from the GRB trigger time) with the Bessel R and I filters.
We performed a series of 5x60s exposures in R and I. We clearly detect an optical source in R and I band in stacked images at a location consistent the initial UVOT detection (Lien, GCN 29420). Using the USNO-B.1 catalog as reference, we calculate the following magnitudes:
R = 20.24 +/- 0.13
I = 20.56 +/- 0.24
These magnitudes are not corrected for galactic extinction. A quick catalog search found no galaxies at this brightness at this location. Further observations are encouraged.
R.S. is funded by NSF AST grant #1831682
GCN Circular #29434
C. Zheng, C. Cai, J. C. Liu, Q. Luo, S. Xiao, W. C. Xue, Q. B. Yi, Y. Q. Zhang, Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, X. Y. Song, S. L. Xiong, C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:
At 2021-02-07T21:52:49.600 (T0), Insight-HXMT/HE detected GRB 210207B (trigger ID: HEB210207911) in a routine search of the data, which also triggered Swift/BAT (A. Y. Lien et al. , GCN #29420).
The Insight-HXMT/HE light curve mainly consists of a single pulse with a duration (T90) of 2.03 s measured from T0+0.24 s. The 1-ms peak rate, measured from T0+1.829 s, is 3687 cnts/sec. The total counts from this burst is 5247 counts. URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB210207911_lc.jpg
All measurements above are made with the CsI detectors operating in the GRB mode with the energy range of about 250-3000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
GCN Circular #29435
H. A. Krimm (NSF), S. D. Barthelmy (GSFC), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210207B (trigger #1031297) (Lien et al., GCN Circ. 29420). The BAT ground-calculated position is RA, Dec = 270.614, 53.700 deg which is
```
   RA(J2000)  =  18h 02m 27.3s
   Dec(J2000) = +53d 42' 01.1"
```
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 56%.
The mask-weighted light curve shows a multi-peaked structure that starts at ~T0 and ends at ~T+106 s. The main peak occurs at ~T+43 s. T90 (15-350 keV) is 95.69 +- 4.52 sec (estimated error including systematics).
The time-averaged spectrum from T-0.25 to T+106.40 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.20 +- 0.07. The fluence in the 15-150 keV band is 4.3 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+43.16 sec in the 15-150 keV band is 3.1 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1031297/BA/

GCN Circular #29436
M. H. Siegel (PSU) and A. Y. Lien (GSFC/UMBC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210207B 82 s after the BAT trigger (Lien et al., GCN Circ. 29420). A source consistent with the XRT position (Lien et al. GCN Circ. 29420) is detected in the initial UVOT exposures, as reported in the initial circular and confirmed by ARIES (Kumar et al., GCN Circ. 29421), KAIT (Zheng & Filippenko, GCN Circ. 29430) and LCO (Strausbaugh & Cucchiara, GCN Circ. 294311). We note that the lack of detection in the two bluer NUV passbands is suggestive of a redshift in the 1.4-1.9 range.
The preliminary UVOT position is:

    RA  (J2000) =  18:02:32.40 = 270.63500 (deg.)
    Dec (J2000) = +53:40:55.8  =  53.68217 (deg.)

with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag
white (fc)          83          233          147      13.66+/-1.13
white             4081         5717          393      17.91+/-0.04
white            61938        62307          361      21.06+/-0.32
v                 4492         4692          196      17.61+/-0.10
v                 9433        10341          885      18.54+/-0.09
v                56912        74907         1297     >19.84
b                 3876         5512          393      17.95+/-0.05
b                44686        45593          885     >20.99
b                61025        79012         1770      20.79+/-0.18
u (fc)             295          410          113      14.42+/-0.03
u                 5106         5306          196      17.80+/-0.09
u                43773        44680          885      20.47+/-0.26
u                51795        69087          612     >19.80
uvw1              4901         5101          196      18.23+/-0.18
uvw1             11254        11428          171     >18.90
uvw1             39917        40544          616     >19.72
uvw1             50889        68646         1771     >20.53
uvm2              4697         4896          196     >19.12
uvm2             10346        11246          885     >20.23
uvw2              4287         5871          342     >19.39
uvw2             56005        74346         1771     >20.68

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.041 in the direction of the burst (Schlegel et al. 1998).

GCN Circular #29437
G. Waratkar (IITB), D. Nadella (NITK), V. Shenoy (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 2020, arxiv:2011.07067) showed detection of a bright long GRB 210207B, which was also detected by Swift (BAT - GCN #29420, #29435, XRT - #29422, #29427) Konus-Wind (GCN #29426), AGILE-MCAL (GCN #29428) and Insight-HXMT/HE (GCN #29434).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-02-07 21:52:49 UT in all four quadrants. The measured peak count rate associated with the burst is 517 (+52, -57) cts/s above the background in the combined data of four quadrants, with a total of 3408 (+384, -451) cts. The local mean background count rate was 560 (+3, -3) cts/s. Using cumulative rates, we measure a T90 of 42 (+10, -2) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-02-07 21:52:48 UT. The measured peak count rate is 994 (+88, -93) cts/s above the background in the combined Veto data of four quadrants, with a total of 6364 (+849, -894) cts. The local mean background count rate was 1931.8 (+5, -5) cts/s. We measure a T90 of 44 (+9, -4) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
GCN Circular #29441
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We performed a second set of observations on Swift GRB 210207B (Lien, GCN 29420) with the LCO 1-m Sinistro instrument at the McDonald Observatory, Texas, USA site, on February 9, from 11:19 to 11:24 UT (corresponding to 37.23 to 37.31 hours from the GRB trigger time) with the Bessel R filter.
We performed a second series of 4x60s exposures in R band. We no longer detect a source at the location consistent with other optical detections (Lien, GCN 29420; Kumar, GCN ; Zheng, GCN 29430; Strausbaugh, GCN 29431). Using the USNO-B.1 catalog as reference, we calculate the following upper limit:
R > 21.42
These magnitudes are not corrected for galactic extinction. This lack of a detection provides further evidence for the transient nature of this source. As a correction to GCN 29431, the series of exposures in R and I bands were 4x60s, not the originally reported 5x60s.
R.S. is funded by NSF AST grant #1831682
GCN Circular #29486
Y. Zhao, X. Y. Song, S. Xiao, C. Cai, S. L. Xiong, Y. Huang, C. Y. Li, J. J. He, Q. B. Yi, B. X. Zhang, Y. Q. Zhang, S. Y. Zhao, C. Zheng, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, B. Li, C. Li, J. H. Li, Q. X. Li, X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu, X. J. Liu, Y. Q. Liu, F. J. Lu, Q. Luo, X. Ma, G. Ou, W. X. Peng, R. Qiao, D. L. Shi, J. Y. Shi, L. M. Song, J. C. Liu, G. X. Sun, X. L. Sun, Y. L. Tuo, C. W. Wang, J. Z. Wang, P. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, W. C. Xue, S. Yang, M. Yao, C. Y. Zhang,D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Z. Zhang, X. Y. Zhao, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team:
During the commissioning phase, the ground search of GECAM-B data found a long burst, GRB 210207B, at 2021-02-07T21:52:14.050 UTC (T0), which was also reported by Swift/BAT (GCN #29420, #29435), Konus/Wind (GCN #29426), AGILE (GCN #29428) and Insight-HXMT/HE (GCN #29434). The later bright pulse also triggered GECAM-B in-flight.
According to the GECAM-B light curves in about 8 keV-4 MeV, this burst mainly consists of multiple pulses with a duration (T90) of 45.0 +/- 4.5 s starting from T0 - 1.8 s. The 1-s peak counts rate is about 1300 cps while the total counts is about 4600 counts.
Although the in-flight calibration of energy response and localization has not been finalized yet, GECAM-B localized this burst to the following position (J2000):
```
Ra: 275.00 deg Dec: 51.57 deg
Err: 8.23 deg (1-sigma, statistical only)
```
The current systematic error of location is estimated to be several degrees which could be minimized by the ongoing calibration.
This position is consistent with Swift (GCN #29420) within the error.
The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GECAM-B-tn210207_215215.pdf
Please note that all GECAM results here are preliminary. The final analysis will be published in journal papers or GECAM online catalog.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time), which was funded by the Chinese Academy of Sciences (CAS).
GCN Circular #29759
F. Sutaria (IIA, Bangalore, India) and A. Ray (TIFR /HBCSE, Mumbai, India) report on the observations of the optical counterpart of GRB 210207B (Lien et al., GCN #29420; Strausbaugh, R, GCN #29441 and references therein) taken with the Himalyan Chandra telescope (HCT) on two epochs.
The first observation was on MJD 59254.91163194 -- i.e 48.0103 hr after the Swift/BAT trigger. The field of the GRB was observed in the Bessel R filter. We stacked 12 frames to achieve a total exposure time of 570 s. The photometry was carried out using standard IRAF utilities for faint objects in relatively uncrowded fields. The instrumental magnitudes were calibrated against photometric standards in the field of PG0918+029, taken on the same and on the previous night, resulting in an average atmospheric extinction coefficient of 0.087(\pm 0.0208) /mag in this filter. At the position of the GRB (18:02:32.40 +53:40:56.0) we find a faint optical source with apparent magnitude R=22.0 \pm 0.1, uncorrected for galactic extinction.
We observed the same field once again on 17th Mar. 2021 (MJD 59290.91730324), in the same filter. A stacked exposure of 10 frames leading to a total exposure time of 600s did not reveal any source at the location of the GRB, down to a 3-sigma limiting magnitude of R= 23.66. We thus conclude that there was no contribution from the host galaxy in the previous detection. Our results are also tabulated below.
```
-------------------------------------------------------------------------------
MJD            Filter  Detected?         Magnitude
                                          (uncorrected for galactic 
extinction)
-------------------------------------------------------------------------------
59254.9116        R        Yes           22.0 \pm 0.1
59290.9173        R        No.           < 23.66 (3-sigma)
-------------------------------------------------------------------------------
```
We note that the galactic extinction for the CTIO R filter in this direction is estimated at A_R = 0.087 mag [Schlafly E. F. & Finkbeiner D., 2011, ApJ, 737, 103], based on a SDSS dust map. However, the IRAS and COBE/DIRBE survey [D.J. Schlegel, D.P. Finkbeiner, & M. Davis, 1998, ApJ, 500, 525] sets it at A_R=0.109 mag.
This GCN may be cited.
We thank the staff of IAO, Hanle and CREST, Hosakote, that made these observations possible. The facilities at IAO and CREST are operated by the Indian Institute of Astrophysics, Bangalore.

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Jochen Greiner, last update: 04-Apr-2021 [Disclaimer]