Gamma-ray Burst 210820A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:39:07 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.629d {+01h 22m 31s} (J2000),
                  20.910d {+01h 23m 38s} (current),
                  19.981d {+01h 19m 55s} (1950)
GRB_DEC:          +4.632d {+04d 37' 55"} (J2000),
                  +4.745d {+04d 44' 41"} (current),
                  +4.371d {+04d 22' 15"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       46084 [cnts]    Image_Peak=592 [image_cnts]
TRIGGER_DUR:     16.384 [sec] 
TRIGGER_INDEX:   460     E_range: 15-50 keV
BKG_INTEN:       170822 [cnts]
BKG_TIME:        63380.41 SOD {17:36:20.41} UT
BKG_DUR:         64 [sec]
GRB_DATE:        19446 TJD;   232 DOY;   21/08/20
GRB_TIME:        63480.70 SOD {17:38:00.70} UT
GRB_PHI:         -80.70 [deg]
GRB_THETA:        28.69 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     8.54 [sigma]
IMAGE_SIGNIF:    7.81 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +1  -2  +0  +0 +60  +0 
SUN_POSTN:       150.10d {+10h 00m 23s}  +12.19d {+12d 11' 39"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.61d {+20h 34m 27s}  -23.16d {-23d 09' 30"}
MOON_DIST:        75.75 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.40,-57.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       20.80, -3.76 [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 = 108.36,20.32 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:40:31 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.6376d {+01h 22m 33.02s} (J2000),
                  20.9183d {+01h 23m 40.39s} (current),
                  19.9895d {+01h 19m 57.48s} (1950)
GRB_DEC:          +4.6071d {+04d 36' 25.5"} (J2000),
                  +4.7197d {+04d 43' 10.9"} (current),
                  +4.3460d {+04d 20' 45.6"} (1950)
GRB_ERROR:       4.9 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       3.75e-09 [erg/cm2/sec]
GRB_SIGNIF:      11.35 [sigma]
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63605.71 SOD {17:40:05.71} UT,   125.0 [sec] since BAT Trigger Time
TAM[0-3]:        327.67 237.23 261.67 243.54
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 38"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.63d {+20h 34m 30s}  -23.16d {-23d 09' 20"}
MOON_DIST:        75.74 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.43,-57.39 [deg] galactic lon,lat of the burst
ECL_COORDS:       20.80, -3.79 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 1.57 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:40:41 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.6376d {+01h 22m 33.0s} (J2000),
                  20.9183d {+01h 23m 40.3s} (current),
                  19.9895d {+01h 19m 57.4s} (1950)
GRB_DEC:          +4.6071d {+04d 36' 25.5"} (J2000),
                  +4.7197d {+04d 43' 10.9"} (current),
                  +4.3460d {+04d 20' 45.6"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       129 [cnts]
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63605.71 SOD {17:40:05.71} UT,   125.0 [sec] since BAT Trigger Time
CENTROID_X:      264.27,  raw= 264  [pixels]
CENTROID_Y:      259.21,  raw= 259  [pixels]
ROLL:            70.93 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -91.66
GRB_POS_XRT_Z:   -101.64
IMAGE_URL:       sw01069551000msxps_rw.img
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 38"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.63d {+20h 34m 31s}  -23.16d {-23d 09' 19"}
MOON_DIST:        75.74 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.43,-57.39 [deg] galactic lon,lat of the burst
ECL_COORDS:       20.80, -3.79 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:40:45 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.6376d {+01h 22m 33.0s} (J2000),
                  20.9183d {+01h 23m 40.3s} (current),
                  19.9895d {+01h 19m 57.4s} (1950)
GRB_DEC:          +4.6071d {+04d 36' 25.5"} (J2000),
                  +4.7197d {+04d 43' 10.9"} (current),
                  +4.3460d {+04d 20' 45.6"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       129 [cnts]
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63605.71 SOD {17:40:05.71} UT,   125.0 [sec] since BAT Trigger Time
CENTROID_X:      264.27,  raw= 264  [pixels]
CENTROID_Y:      259.21,  raw= 259  [pixels]
ROLL:            70.93 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -91.66
GRB_POS_XRT_Z:   -101.64
IMAGE_URL:       sw01069551000msxps_rw.img
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 38"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.63d {+20h 34m 31s}  -23.16d {-23d 09' 18"}
MOON_DIST:        75.74 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.43,-57.39 [deg] galactic lon,lat of the burst
ECL_COORDS:       20.80, -3.79 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:41:44 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.629d {+01h 22m 31s} (J2000),
                  20.910d {+01h 23m 38s} (current),
                  19.981d {+01h 19m 55s} (1950)
GRB_DEC:          +4.632d {+04d 37' 55"} (J2000),
                  +4.745d {+04d 44' 41"} (current),
                  +4.371d {+04d 22' 15"} (1950)
GRB_DATE:        19446 TJD;   232 DOY;   21/08/20
GRB_TIME:        63480.70 SOD {17:38:00.70} UT
TRIGGER_INDEX:   460
GRB_PHI:         -80.70 [deg]
GRB_THETA:        28.69 [deg]
DELTA_TIME:      51.00 [sec]
TRIGGER_DUR:     16.384 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     8.54 [sigma]
IMAGE_SIGNIF:    7.81 [sigma]
LC_URL:          sw01069551000msb.lc
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 37"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.64d {+20h 34m 33s}  -23.15d {-23d 09' 11"}
MOON_DIST:        75.73 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.40,-57.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       20.80, -3.76 [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 = 108.36,20.32 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:44:50 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.603d {+01h 22m 25s} (J2000)
POINT_DEC:        +4.622d {+04d 37' 21"} (J2000)
POINT_ROLL:      70.926d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63611.36 SOD {17:40:11.36} UT,   130.7 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.682
N_STARS:         34
X_OFFSET:        432 [pixels]
Y_OFFSET:        208 [pixels]
X_MAX:           1871 [pixels]
Y_MAX:           1647 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01069551000msufc0130.fits
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 35"}
SUN_DIST:        126.76 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.67d {+20h 34m 41s}  -23.15d {-23d 08' 49"}
MOON_DIST:        75.67 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.36,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:45:10 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.603d {+01h 22m 25s} (J2000)
POINT_DEC:        +4.622d {+04d 37' 21"} (J2000)
POINT_ROLL:      70.926d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63611.36 SOD {17:40:11.36} UT,   130.7 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.682
N_STARS:         34
X_OFFSET:        432 [pixels]
Y_OFFSET:        208 [pixels]
X_MAX:           1871 [pixels]
Y_MAX:           1647 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01069551000msufc0130.fits
SUN_POSTN:       150.10d {+10h 00m 24s}  +12.19d {+12d 11' 34"}
SUN_DIST:        126.76 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.67d {+20h 34m 42s}  -23.15d {-23d 08' 47"}
MOON_DIST:        75.67 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.36,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [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 20 Aug 21 17:48:05 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.6395d {+01h 22m 33.48s} (J2000),
                  20.9202d {+01h 23m 40.84s} (current),
                  19.9914d {+01h 19m 57.93s} (1950)
GRB_DEC:          +4.6078d {+04d 36' 28.0"} (J2000),
                  +4.7204d {+04d 43' 13.4"} (current),
                  +4.3467d {+04d 20' 48.1"} (1950)
GRB_ERROR:       0.8 [arcsec radius, statistical only]
GRB_MAG:         17.53 +/- 0.14 [mag]
FILTER:          7, U
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63608.00 SOD {17:40:08.00} UT,   127.3 [sec] since BAT Trigger Time
SUN_POSTN:       150.10d {+10h 00m 25s}  +12.19d {+12d 11' 32"}
SUN_DIST:        126.73 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.70d {+20h 34m 49s}  -23.14d {-23d 08' 26"}
MOON_DIST:        75.67 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.43,-57.39 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       20.80, -3.79 [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 7.2 arcsec from the XRT position.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN Circular #30664
A. P. Beardmore (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 17:38:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210820A (trigger=1069551). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 20.629, +4.632 which is
```
   RA(J2000) = 01h 22m 31s
   Dec(J2000) = +04d 37' 55"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~8 sec after the trigger.
The XRT began observing the field at 17:40:05.7 UT, 125.0 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 20.6376, 4.6071 which is equivalent to:
```
   RA(J2000)  = 01h 22m 33.02s
   Dec(J2000) = +04d 36' 25.6"
```
with an uncertainty of 11.1 arcseconds (radius, 90% containment). This location is 94 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 3.75e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 250 seconds with the U filter starting 130 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at
```
  RA(J2000)  =	01:22:33.48 =  20.63952
  DEC(J2000) = +04:36:28.2  =	4.60783
```
with a 90%-confidence error radius of about 0.76 arc sec. This position is 7.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.53 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.031.
Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:57:05 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.601d {+01h 22m 24s} (J2000)
POINT_DEC:        +4.621d {+04d 37' 16"} (J2000)
POINT_ROLL:      70.925d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  64341.90 SOD {17:52:21.90} UT,   861.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.384
N_STARS:         15
X_OFFSET:        518 [pixels]
Y_OFFSET:        369 [pixels]
X_MAX:           1957 [pixels]
Y_MAX:           1808 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw01069551000msufc0861.fits
SUN_POSTN:       150.11d {+10h 00m 26s}  +12.19d {+12d 11' 24"}
SUN_DIST:        126.77 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.80d {+20h 35m 11s}  -23.12d {-23d 07' 21"}
MOON_DIST:        75.55 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.35,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:57:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.601d {+01h 22m 24s} (J2000)
POINT_DEC:        +4.621d {+04d 37' 16"} (J2000)
POINT_ROLL:      70.925d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  64341.90 SOD {17:52:21.90} UT,   861.2 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.384
N_STARS:         15
X_OFFSET:        518 [pixels]
Y_OFFSET:        369 [pixels]
X_MAX:           1957 [pixels]
Y_MAX:           1808 [pixels]
DET_THRESH:      6
PHOTO_THRESH:    2
SL_URL:          sw01069551000msufc0861.fits
SUN_POSTN:       150.11d {+10h 00m 26s}  +12.19d {+12d 11' 24"}
SUN_DIST:        126.77 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.80d {+20h 35m 12s}  -23.12d {-23d 07' 19"}
MOON_DIST:        75.55 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.35,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [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 20 Aug 21 17:58:32 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.601d {+01h 22m 24s} (J2000)
POINT_DEC:        +4.621d {+04d 37' 16"} (J2000)
ROLL:            70.925d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  64341.90 SOD {17:52:21.90} UT,   861.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     651174769
X_OFFSET:        1077 [pixels]
Y_OFFSET:        928 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1237
Y_GRB_POS:       1088
BINNING_INDEX:   1
IM_URL:          sw01069551000msuni0889.fits
SUN_POSTN:       150.11d {+10h 00m 26s}  +12.19d {+12d 11' 23"}
SUN_DIST:        126.77 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.81d {+20h 35m 15s}  -23.12d {-23d 07' 11"}
MOON_DIST:        75.54 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.35,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [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 20 Aug 21 17:57:29 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1069551,   Seg_Num: 0
GRB_RA:           20.6392d {+01h 22m 33.40s} (J2000),
                  20.9199d {+01h 23m 40.77s} (current),
                  19.9911d {+01h 19m 57.86s} (1950)
GRB_DEC:          +4.6078d {+04d 36' 28.0"} (J2000),
                  +4.7204d {+04d 43' 13.4"} (current),
                  +4.3467d {+04d 20' 48.1"} (1950)
GRB_ERROR:       1.9 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  63952.00 SOD {17:45:52.00} UT,   471.3 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       150.11d {+10h 00m 26s}  +12.19d {+12d 11' 24"}
SUN_DIST:        126.74 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.80d {+20h 35m 12s}  -23.12d {-23d 07' 18"}
MOON_DIST:        75.57 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.43,-57.39 [deg] galactic lon,lat of the burst
ECL_COORDS:       20.80, -3.79 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 20 Aug 21 17:58:47 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1069551,   Seg_Num: 0
POINT_RA:         20.601d {+01h 22m 24s} (J2000)
POINT_DEC:        +4.621d {+04d 37' 16"} (J2000)
ROLL:            70.925d
IMG_START_DATE:  19446 TJD;   232 DOY;   21/08/20
IMG_START_TIME:  64341.90 SOD {17:52:21.90} UT,   861.2 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     651174769
X_OFFSET:        1077 [pixels]
Y_OFFSET:        928 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1237
Y_GRB_POS:       1088
BINNING_INDEX:   1
IM_URL:          sw01069551000msuni0889.fits
SUN_POSTN:       150.11d {+10h 00m 26s}  +12.19d {+12d 11' 23"}
SUN_DIST:        126.77 [deg]   Sun_angle= 8.6 [hr] (West of Sun)
MOON_POSTN:      308.82d {+20h 35m 16s}  -23.12d {-23d 07' 09"}
MOON_DIST:        75.53 [deg]
MOON_ILLUM:      96 [%]
GAL_COORDS:      137.35,-57.38 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       20.77, -3.76 [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 #30666
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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 210820A ( A. P. Beardmore et al., GCN 30664) errorbox 4451 sec after notice time and 4532 sec after trigger time at 2021-08-20 18:53:33 UT, with upper limit up to 15.2 mag. The observations began at zenith distance = 84 deg. The sun altitude is -26.1 deg.
The galactic latitude b = -57 deg., longitude l = 138 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1695760
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________


    4622 |   MASTER-Kislovodsk |   C |   180 | 14.5 |        
    4622 |   MASTER-Kislovodsk |   C |   180 | 15.2 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #30667
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 2824 s of XRT Photon Counting mode data and 3 UVOT images for GRB 210820A, 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 = 20.63963, +4.60764 which is equivalent to:
```
RA (J2000): 01h 22m 33.51s
Dec (J2000): +04d 36' 27.5"
```
with an uncertainty of 2.5 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 #30668
J.P. Osborne (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), K.L. Page (U. Leicester) and A.P. Beardmore report on behalf of the Swift-XRT team:
We have analysed 6.5 ks of XRT data for GRB 210820A (Beardmore et al. GCN Circ. 30664), from 131 s to 18.2 ks after the BAT trigger. The data comprise 339 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. 30667).
The late-time light curve (from T0+5.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.9 (+0.6, -0.5).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.77 (+/-0.03). The best-fitting absorption column is 1.20 (+/-0.11) x 10^21 cm^-2, in excess of the Galactic value of 3.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.28 (+0.25, -0.13) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.9 x 10^-11 (3.3 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.6 (+4.3, -0.0) x 10^20 cm^-2
Galactic foreground: 3.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.28 (+0.25, -0.13)
```
If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 2.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x 10^-15 (9.6 x 10^-15) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01069551.
This circular is an official product of the Swift-XRT team.
GCN Circular #30669
S.Y. Fu (NAOC), Z.P. Zhu (NAOC,HUST), X. Liu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of GRB 210820A (Beardmore et al., GCN 30664) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained 10x200 s frames in the Sloan r-band, starting at 21:17:58 UT on 2021-08-20, i.e., 3.67 hr after the BAT trigger.
No optical source is detected in our stacked image at the Swift/UVOT position (Beardmore et al., GCN 30664), down to a limiting magnitude of r~21.3, calibrated with the nearby PanSTARRS field.
GCN Circular #30670
Z.P. Zhu (NAOC, HUST), D. B. Malesani (DTU space), L. Izzo (DARK/NBI), J.P.U. Fynbo (DAWN/NBI), D. Xu (NAOC), R. Clavero (NOT) report on behalf of a larger collaboration:
We observed the field of GRB210820A (Beardmore et al., GCN30664) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3x200s frames in the Sloan r- filter, starting at 00:49:56 UT on 2021-08-21 (i.e., ~ 7.29 hr after the BAT trigger).
No optical source is detected in our stacked image at the Swift/UVOT position (Beardmore et al., GCN 30664), down to a limiting magnitude of r~22.2, calibrated with the nearby PanSTARRS field.
GCN Circular #30672
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Eleonora Troja (GSFC), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Enrico Ramirez-Ruiz (UCSC), Jes�s Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Harvey Moseley (GSFC), Rosa L. Becerra (UNAM), Simone Dichiara (UMD), and Oc�lotl L�pez (UNAM) report:
We observed the field of GRB 210820A (Beardmore, et al., GCN 30664) with the Reionization and Transients Infrared Camera (RATIR) on the 1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on Sierra San Pedro M�rtir from 2021/08 21.27 to 2021/08 21.50 UTC (12.47 to 17.96 hours after the BAT trigger), obtaining a total of 3.70 hours exposure in the r and i bands.
We detect one source within the Swift-XRT error circle (Beardmore, et al., GCN 30667). In comparison with the SDSS DR9 and 2MASS catalogs, we obtain:
```
  r = 22.84 +/- 0.22
  i = 22.66 +/- 0.18
```
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
The source is located at RA, Dec = 1:22:33.47, +4:36:28.1 (J2000, +/-0.5"). This is 0.2 arcsec away from the UVOT OT (GCN 30664).
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro M�rtir.
GCN Circular #30673
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 210820A (Beardmore, et al., GCN 30664) with the LCO 1-m Sinistro instrument at the Teide Observatory, Tenerife site, on August 21, from 01:20 to 01:51 UT (corresponding to 7.7 to 8.5 hours from the GRB trigger time) with the Bessel R and I filters.
We performed a series of 5x120s exposures in R and I. In the UVOT detection region (Beardmore, et al., GCN 30664) no optical counterpart could be detected down to the following upper limits, calculated using the USNO-B.1 catalog as reference:
R>20.16
I>19.17
These magnitudes are not corrected for galactic extinction.
R.S. is funded by NSF AST grant #1831682
GCN Circular #30674
M. Blazek, D. A. Kann (both HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/ IAA-CSIC, DARK/NBI), C. C. Thoene, J. F. Agui Fernandez (both HETH/IAA-CSIC) report:
We observed the location of the Swift GRB 210820A (Beardmore et al., GCN #30664) with 2-m Liverpool Telescope located in La Palma, Canary Isands, Spain. We obtained 15 x 60 s images beginning 2021-08-21 03:29:30 UT. In a stack of all images, centered at 0.4175 days after the GRB, no source is detected at the UVOT position. Measured against three nearby SDSS stars, we derive an upper limit of r' > 21.1 mag. This agrees with the non-detections reported by Lipunov et al. (GCN #30666), Fu et al. (GCN #30669)., and Zhu et al. (GCN #30670).
GCN Circular #30675
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), H. A. Krimm (NSF), A. Y. Lien (U Tampa), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210820A (trigger #1069551) (Beardmore et al., GCN Circ. 30664). The BAT ground-calculated position is RA, Dec = 20.622, 4.642 deg which is
```
   RA(J2000)  =  01h 22m 29.4s
   Dec(J2000) = +04d 38' 30.6"
```
with an uncertainty of 3.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%.
The mask-weighted light curve shows many weak overlapping pulses that start at ~T0 and end at ~T+260 s. T90 (15-350 keV) is 196.8 +- 51.4 sec (estimated error including systematics).
The time-averaged spectrum from T+0.78 to T+258.97 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.26 +- 0.22. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+10.92 sec in the 15-150 keV band is 0.8 +- 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/1069551/BA/
GCN Circular #30686
GRB 210820A: Swift/UVOT Detection
S. J. LaPorte (PSU) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210820A 131 s after the BAT trigger (Beardmore et al., GCN Circ. 30664). A source consistent with the XRT position (Beardmore et al., GCN Circ. 30664) is detected in the initial UVOT exposures.
The preliminary UVOT position is:
```
    RA  (J2000) =  01:22:33.48 =  20.63952 (deg.)
    Dec (J2000) = +04:36:28.3  =   4.60786 (deg.)
```
with an estimated uncertainty of 0.45 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits 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

v                  437         1684          156         18.86 +/- 0.24
b                  387          555           39         18.57 +/- 0.19
u                  131          381          246         17.60 +/- 0.06
w1                 784         1733           58        >19.0
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.030 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #30688
T. Komesh (NU), B. Grossan (UCB, NU), Z. Maksut (NU), A. Kim (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Linder (UCB, NU), E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) observed the field of GRB 210820A on receipt of an automated GCN / BAT position alert, observing in Sloan g', r' and i' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).
We received the alert at 17:39:26 UT (85 seconds between GRB time and notification time) and started observations at 17:39:32 UT on 2021-08-20, 6.5 s after receipt, 91 s after the BAT trigger. Observations were made under 95+% moon illumination and cloudy conditions starting at only about 20 deg. target altitude. No source consistent with the XRT or UVOT position was detected. The observations fully cover the UVOT U detection observation time (Palmer 2021, GCN 30664) and some additional UVOT observations (LaPorte 2021, GCN 30686). Note that these observations provide essentially full-time coverage, simultaneous in all three bands. We report the following results:
```
start time        end time        UL g'    UL r'        ULi'       exposure_time (s)
------------        -----------        ------    ------        	------      --------------------
17:39:32        17:40:32        17.0    15.1         	16.4		60 
17:40:57        17:56:42        17.9    15.9  	16.8         135 
```
UL g', r', i', gives the 5 sigma upper limit sensitivity in magnitudes in the respective filter, for images co-added to the given exposure time. The first row in the table corresponds to co-adds of an initial short exposure image sequence of 7.5 s each, the second row corresponds to co-adds from a continuing series of 15 s exposures, uninterrupted for the entire interval. No uncatalogued sources near the XRT location were found up to the co-add times indicated. Calibration was done with the few bright Pan-STARRS catalog stars on our images.
We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate. We anticipate improved analysis in 15-30 days posted at http://ecl.nu.edu.kz/gamma-ray-burst/grb210820a.
```
----------------------------------
NU = Nazarbayev University, Nur-Sultan, Kazakhstan
UCB = University of California, Berkeley, USA
HKUST = Hong Kong University of Science and Technology
FAI = Fesenkov Astrophysical Institute, Kazakhstan
```
The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
GCN Circular #30695
A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg) and A. Rau (MPE Garching) report:
We observed the field of GRB 210820A (Swift trigger 1069551); Beardmore et al., GCN 30664) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2 m MPG/ESO telescope at La Silla Observatory (Chile).
Observations were performed at 9:03 UT (midtime) on August 21, 2021, about 15.5 hours after the GRB trigger. They were executed at an average seeing of 1.3 arcsec and at an average airmass of 1.2.
We detect a source within the XRT error circle (Beardmore, et al., GCN 30667) in the i' band with the following preliminary AB magnitude
i'=22.46 +/- 0.28
in agreement with the RATIR detection (Butler et al., GCN 30672).
We do not detect the source in the other bands down to the following limiting AB magnitudes:
g' > 22.6,
r' > 22.9,
z' > 22.3,
J > 20.9,
H > 20.4, and
K > 17.4.
The given limits and magnitude are derived based on calibrating the images against SDSS in g'r'i'z' and 2MASS field stars in JHK.
We thank Paul Eigenthaler for excellent support and for performing the observations.
GCN Circular #30731
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), A. Fernandez, and I. Hermelo (all CAHA) report:
We observed GRB 210820A (Swift detection: Beardmore et al., GCN #30664) with CAFOS mounted on the 2.2m CAHA telescope at Calar Alto, Alemria, Spain, under inclement conditions (bright moonlight, passing clouds, low transparency). We obtained 10 x 90 s each in filters B, V, Rc. Stacks reveal no detection of the afterglow in B (very shallow because of moonlight) and Rc (shallow because of incoming clouds which also prevented further observations). However, the afterglow (Beardmore et al., GCN #30664; Butler et al., GCN #30672; LaPorte & Beardmore, GCN #30686; Nicuesa Guelbenzu et al., GCN #30695) is clearly detected in V, somewhat north of a source also seen in Pan-STARRS and in SDSS.
We find the afterglow to be V = 22.43 +/- 0.15 mag (AB mag, derived from two SDSS field stars transformed to V via the equations of Lupton 2005) at 0.43868 days after the GRB.
GCN Circular #30757
S. Belkin (IKI), I. Reva (FAP), A. Kusakin (FAP), A. Pozanenko (IKI), N.Pankov (HSE), V. Kim (FAP) report on behalf of GRB-IKI-FuN:
We observed GRB 210820A (Beardmore et al., GCN 30664) with Zeiss-1000 telescope of Tien Shan Astronomical Observatory starting on Aug. 21 (UT) 21:32:02.
The optical afterglow (Beardmore et al., GCN 30664; Lipunov et al., GCN 30666; Fu et al., GCN 30669; Zhu et al., GCN 30670; Butler et al., GCN 30672; Strausbaugh et al., GCN 30673; Blazek et al., GCN 30674; Laha et al., GCN 30675; LaPorte and Beardmore, GCN 30686; Komesh et al., GCN 30688; Guelbenzu et al., GCN 30695; Kann et al., GCN 30731) was not detected in the stacked image down to a limiting magnitude of 21.8 in R filter. Preliminary photometry of the field in a stacked image is following.
```
Date       UT start t-T0    Filter  Exp.  OT  Err. UL(3 sigma)
                      (mid, days)     (s)
2021-08-21 21:32:02 1.17659  R      27*90 n/d n/d  21.8
```
The photometry is based on nearby USNO-B1.0 stars.
```
USNO-B1.0
RA Dec R2
01:22:01.52088 +04:35:30.2028 17.48
01:22:14.95944 +04:43:31.2204 17.89
```

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Jochen Greiner, last update: 03-Sep-2021 [Disclaimer]