Gamma-ray Burst 210421A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:27:55 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.908d {+06h 59m 38s} (J2000),
                 105.191d {+07h 00m 46s} (current),
                 104.244d {+06h 56m 59s} (1950)
GRB_DEC:          +4.934d {+04d 56' 03"} (J2000),
                  +4.903d {+04d 54' 12"} (current),
                  +5.004d {+05d 00' 15"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       6363 [cnts]    Image_Peak=280 [image_cnts]
TRIGGER_DUR:     2.048 [sec] 
TRIGGER_INDEX:   253     E_range: 15-50 keV
BKG_INTEN:       60653 [cnts]
BKG_TIME:        1613.11 SOD {00:26:53.11} UT
BKG_DUR:         24 [sec]
GRB_DATE:        19325 TJD;   111 DOY;   21/04/21
GRB_TIME:        1650.30 SOD {00:27:30.30} UT
GRB_PHI:          24.95 [deg]
GRB_THETA:        34.19 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     11.44 [sigma]
IMAGE_SIGNIF:    10.17 [sigma]
MERIT_PARAMS:     +1  +0  +0  +1  +1  +0  +0  +1 -25  +0 
SUN_POSTN:        29.00d {+01h 56m 00s}  +11.87d {+11d 52' 07"}
SUN_DIST:         75.50 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.34d {+08h 53m 23s}  +22.15d {+22d 08' 53"}
MOON_DIST:        32.23 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.47,  4.07 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      105.61,-17.70 [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 = 211.05,12.46 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:29:29 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.8744d {+06h 59m 29.8s} (J2000),
                 105.1572d {+07h 00m 37.7s} (current),
                 104.2105d {+06h 56m 50.5s} (1950)
GRB_DEC:          +4.9202d {+04d 55' 12.7"} (J2000),
                  +4.8895d {+04d 53' 22.1"} (current),
                  +4.9901d {+04d 59' 24.3"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       28 [cnts]
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1738.11 SOD {00:28:58.11} UT,   87.8 [sec] since BAT Trigger Time
CENTROID_X:      292.17,  raw= 292  [pixels]
CENTROID_Y:      309.25,  raw= 309  [pixels]
ROLL:            280.99 [deg]
GAIN:            1
MODE:            2, Short Image mode
WAVEFORM:        134
EXPO_TIME:       0.10 [sec]
GRB_POS_XRT_Y:   26.30
GRB_POS_XRT_Z:   -35.88
IMAGE_URL:       sw01044426000msxps_rw.img
SUN_POSTN:        29.00d {+01h 56m 00s}  +11.87d {+11d 52' 08"}
SUN_DIST:         75.47 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.36d {+08h 53m 26s}  +22.14d {+22d 08' 41"}
MOON_DIST:        32.28 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.03 [deg] galactic lon,lat of the burst
ECL_COORDS:      105.57,-17.72 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:29:32 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.8744d {+06h 59m 29.8s} (J2000),
                 105.1572d {+07h 00m 37.7s} (current),
                 104.2105d {+06h 56m 50.5s} (1950)
GRB_DEC:          +4.9202d {+04d 55' 12.7"} (J2000),
                  +4.8895d {+04d 53' 22.1"} (current),
                  +4.9901d {+04d 59' 24.3"} (1950)
GRB_ERROR:       6.1 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       28 [cnts]
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1738.11 SOD {00:28:58.11} UT,   87.8 [sec] since BAT Trigger Time
CENTROID_X:      292.17,  raw= 292  [pixels]
CENTROID_Y:      309.25,  raw= 309  [pixels]
ROLL:            280.99 [deg]
GAIN:            1
MODE:            2, Short Image mode
WAVEFORM:        134
EXPO_TIME:       0.10 [sec]
GRB_POS_XRT_Y:   26.30
GRB_POS_XRT_Z:   -35.88
IMAGE_URL:       sw01044426000msxps_rw.img
SUN_POSTN:        29.00d {+01h 56m 00s}  +11.87d {+11d 52' 08"}
SUN_DIST:         75.47 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.36d {+08h 53m 26s}  +22.14d {+22d 08' 41"}
MOON_DIST:        32.28 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.03 [deg] galactic lon,lat of the burst
ECL_COORDS:      105.57,-17.72 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:29:19 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.8744d {+06h 59m 29.85s} (J2000),
                 105.1572d {+07h 00m 37.72s} (current),
                 104.2105d {+06h 56m 50.52s} (1950)
GRB_DEC:          +4.9202d {+04d 55' 12.7"} (J2000),
                  +4.8895d {+04d 53' 22.1"} (current),
                  +4.9901d {+04d 59' 24.3"} (1950)
GRB_ERROR:       6.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.51e-08 [erg/cm2/sec]
GRB_SIGNIF:      5.29 [sigma]
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1738.11 SOD {00:28:58.11} UT,   87.8 [sec] since BAT Trigger Time
TAM[0-3]:        327.61 237.19 261.64 243.62
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:        29.00d {+01h 56m 00s}  +11.87d {+11d 52' 08"}
SUN_DIST:         75.47 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.36d {+08h 53m 26s}  +22.15d {+22d 08' 42"}
MOON_DIST:        32.28 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.03 [deg] galactic lon,lat of the burst
ECL_COORDS:      105.57,-17.72 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 2.19 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:31:10 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.908d {+06h 59m 38s} (J2000),
                 105.191d {+07h 00m 46s} (current),
                 104.244d {+06h 56m 59s} (1950)
GRB_DEC:          +4.934d {+04d 56' 03"} (J2000),
                  +4.903d {+04d 54' 12"} (current),
                  +5.004d {+05d 00' 15"} (1950)
GRB_DATE:        19325 TJD;   111 DOY;   21/04/21
GRB_TIME:        1650.30 SOD {00:27:30.30} UT
TRIGGER_INDEX:   253
GRB_PHI:          24.95 [deg]
GRB_THETA:        34.19 [deg]
DELTA_TIME:      -38.00 [sec]
TRIGGER_DUR:     2.048 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     11.44 [sigma]
IMAGE_SIGNIF:    10.17 [sigma]
LC_URL:          sw01044426000msb.lc
SUN_POSTN:        29.00d {+01h 56m 01s}  +11.87d {+11d 52' 10"}
SUN_DIST:         75.50 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.37d {+08h 53m 30s}  +22.14d {+22d 08' 29"}
MOON_DIST:        32.26 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.47,  4.07 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      105.61,-17.70 [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 = 211.05,12.46 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:32:20 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1044426,   Seg_Num: 0
POINT_RA:        104.886d {+06h 59m 33s} (J2000)
POINT_DEC:        +4.928d {+04d 55' 40"} (J2000)
POINT_ROLL:      280.987d
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1746.71 SOD {00:29:06.71} UT,   96.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.695
N_STARS:         190
X_OFFSET:        392 [pixels]
Y_OFFSET:        704 [pixels]
X_MAX:           1351 [pixels]
Y_MAX:           1663 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw01044426000msufc0096.fits
SUN_POSTN:        29.00d {+01h 56m 01s}  +11.87d {+11d 52' 11"}
SUN_DIST:         75.48 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.39d {+08h 53m 33s}  +22.14d {+22d 08' 20"}
MOON_DIST:        32.29 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.04 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      105.59,-17.71 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 21 Apr 21 00:32:34 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1044426,   Seg_Num: 0
POINT_RA:        104.886d {+06h 59m 33s} (J2000)
POINT_DEC:        +4.928d {+04d 55' 40"} (J2000)
POINT_ROLL:      280.987d
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1746.71 SOD {00:29:06.71} UT,   96.4 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.695
N_STARS:         190
X_OFFSET:        392 [pixels]
Y_OFFSET:        704 [pixels]
X_MAX:           1351 [pixels]
Y_MAX:           1663 [pixels]
DET_THRESH:      16
PHOTO_THRESH:    9
SL_URL:          sw01044426000msufc0096.fits
SUN_POSTN:        29.00d {+01h 56m 01s}  +11.87d {+11d 52' 11"}
SUN_DIST:         75.48 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.39d {+08h 53m 33s}  +22.14d {+22d 08' 18"}
MOON_DIST:        32.29 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.04 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      105.59,-17.71 [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:     Wed 21 Apr 21 00:35:11 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1044426,   Seg_Num: 0
POINT_RA:        104.886d {+06h 59m 33s} (J2000)
POINT_DEC:        +4.928d {+04d 55' 40"} (J2000)
ROLL:            280.987d
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1746.71 SOD {00:29:06.71} UT,   96.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     640657773
X_OFFSET:        833 [pixels]
Y_OFFSET:        794 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       993
Y_GRB_POS:       954
BINNING_INDEX:   1
IM_URL:          sw01044426000msuni0123.fits
SUN_POSTN:        29.01d {+01h 56m 01s}  +11.87d {+11d 52' 13"}
SUN_DIST:         75.48 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.41d {+08h 53m 39s}  +22.13d {+22d 07' 59"}
MOON_DIST:        32.31 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.04 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      105.59,-17.71 [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:     Wed 21 Apr 21 00:35:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1044426,   Seg_Num: 0
POINT_RA:        104.886d {+06h 59m 33s} (J2000)
POINT_DEC:        +4.928d {+04d 55' 40"} (J2000)
ROLL:            280.987d
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1746.71 SOD {00:29:06.71} UT,   96.4 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     640657773
X_OFFSET:        833 [pixels]
Y_OFFSET:        794 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       993
Y_GRB_POS:       954
BINNING_INDEX:   1
IM_URL:          sw01044426000msuni0123.fits
SUN_POSTN:        29.01d {+01h 56m 01s}  +11.87d {+11d 52' 13"}
SUN_DIST:         75.48 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.41d {+08h 53m 39s}  +22.13d {+22d 07' 58"}
MOON_DIST:        32.31 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.04 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      105.59,-17.71 [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 #29849
M. J. Moss (GWU), S. D. Barthelmy (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 00:27:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210421A (trigger=1044426). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 104.908, +4.934, which is
```
   RA(J2000)  =  06h 59m 38s
   Dec(J2000) = +04d 56' 03"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 00:28:58.1 UT, 87.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 104.87569, 4.92168 which is equivalent to:
```
   RA(J2000)  = 06h 59m 30.17s
   Dec(J2000) = +04d 55' 18.0"
```
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 124 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density.
The initial flux in the 0.1 s image was 1.51e-08 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 96 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected.
Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). 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 #29850
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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 210421A ( M. J. Moss et al., GCN 29849) errorbox 13 sec after notice time and 47 sec after trigger time at 2021-04-21 00:28:17 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 54 deg. The sun altitude is -30.5 deg.
The galactic latitude b = 5 deg., longitude l = 210 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1597889
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      52 |         MASTER-OAFA |   C |    10 | 16.4 |        
      82 |         MASTER-OAFA |   C |    10 | 16.4 |        
     116 |         MASTER-OAFA |   C |    20 | 16.8 |        
     160 |         MASTER-OAFA |   C |    30 | 17.0 |        
     215 |         MASTER-OAFA |   C |    40 | 17.1 |        
```
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:     Wed 21 Apr 21 00:48:07 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1044426,   Seg_Num: 0
GRB_RA:          104.8756d {+06h 59m 30.14s} (J2000),
                 105.1584d {+07h 00m 38.01s} (current),
                 104.2117d {+06h 56m 50.81s} (1950)
GRB_DEC:          +4.9216d {+04d 55' 17.7"} (J2000),
                  +4.8909d {+04d 53' 27.1"} (current),
                  +4.9915d {+04d 59' 29.4"} (1950)
GRB_ERROR:       3.7 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19325 TJD;   111 DOY;   21/04/21
IMG_START_TIME:  1873.00 SOD {00:31:13.00} UT,   222.7 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        29.01d {+01h 56m 03s}  +11.87d {+11d 52' 24"}
SUN_DIST:         75.46 [deg]   Sun_angle= -5.1 [hr] (East of Sun)
MOON_POSTN:      133.53d {+08h 54m 08s}  +22.11d {+22d 06' 22"}
MOON_DIST:        32.40 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      209.46,  4.03 [deg] galactic lon,lat of the burst
ECL_COORDS:      105.58,-17.72 [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:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.11% < P(seren) < 0.58%.

GCN Circular #29857
Alan M. Watson (UNAM), Nat Butler (ASU), 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 210421A (Moss et al., GCN Circ. 29849) with the DDOTI wide-field imager at the Observatorio Astron�mico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-21 03:05 to 04:33 UTC (from 2.6 to 4.1 hours after the trigger) and obtained 4320 seconds of exposure in the w filter.
We observed a region covering aproximately 7 degrees in RA and 10 degrees in declination (about 70 square degrees), including the XRT position. We calibrated our images against the APASS catalog.
We do not detect any source in the XRT region to a 3-sigma limiting AB magnitude of w = 21.1.
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
GCN Circular #29865
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 1675 s of XRT Photon Counting mode data and 1 UVOT images for GRB 210421A, 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 = 104.87443, +4.92232 which is equivalent to:
```
RA (J2000): 06h 59m 29.86s
Dec (J2000): +04d 55' 20.4"
```
with an uncertainty of 2.4 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #29875
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester) and M.J. Moss report on behalf of the Swift-XRT team:
We have analysed 6.4 ks of XRT data for GRB 210421A (Moss et al. GCN Circ. 29849), from 91 s to 68.9 ks after the BAT trigger. The data comprise 130 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 29865).
The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=2.6 (+0.8, -0.9). At T+109 s the decay steepens to an alpha of 4.96 (+0.17, -0.15) before breaking again at T+397 s to a final decay with index alpha=0.59 (+0.22, -0.14).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.74 (+/-0.08). The best-fitting absorption column is 5.3 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 4.6 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.17 (+0.19, -0.14) 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 3.7 x 10^-11 (6.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     4.6 (+0.8, -0.0) x 10^21 cm^-2
Galactic foreground: 4.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.17 (+0.19, -0.14)
```
If the light curve continues to decay with a power-law decay index of 0.59, the count rate at T+24 hours will be 0.011 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x 10^-13 (7.4 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/01044426.
This circular is an official product of the Swift-XRT team.
GCN Circular #29882
N. Ito, K. L. Murata, R. Hosokawa, M. Niwano, H. Takamatsu, Y. Yatsu, and N.Kawai (TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210421A (M. J. Moss et al. GCN Circular #29849, V. Lipunov et al. GCN Circular #29850, Alan M. Watson et al. GCN Circular #29857, P.A. Evans et al. GCN Circular #29865, P.A. Evans et al. GCN Circular #29875) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation with a series of 60 sec exposures started at 2021-04-21 09:51:58 UT (9.4 hours after the Swift BAT trigger) We stacked the images with good conditions. We did not detect any sources within the enhanced XRT error region (P.A. Evans et al. GCN Circular #29865) in all three bands. We obtained the 5-sigma limits of the stacked images as follows.
```
T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
9.8 11:25 7020 g'>18.8, Rc>18.8, Ic>18.4
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
```
We used the PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).
GCN Circular #29885
S. R. Oates (U.Birmingham) and M. J. Moss (GWU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210421A 96 s after the BAT trigger (Moss et al., GCN Circ. 29849). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 29865). 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              96           246          147         >20.4
white  	             96          1912          191         >20.6
v      	         1608          1800           39         >17.9
b      	         1534          1899           58         >19.2
u_FC                  308           484          173         >19.5
u      	           308          1874          211         >19.6
uvw1   	         1658          1850           39         >18.1
uvm2   	         1633          1825           39         >17.9
uvw2   	         1584          1776           39         >18.3
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.318 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #29889
S. L. Xie, X. Y. Song, Q. B. Yi, X. Y. Zhao, Y. Huang, S. L. Xiong, S. Xiao, C. Cai, Y. Zhao, J. C. Liu, Y. Q. Zhang, W. C. Xue, C. Zheng, Z. W. Guo, C. W. Wang, D. Y. Guo, P. Wang, X. B. Li, W. X. Peng, R. Qiao, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He, B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. 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, D. L. Shi, J. Y. Shi, L. M. Song, G. X. Sun, X. L. Sun, Y. L. Tuo, J. Z. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, S. Yang, M. Yao, B. X. Zhang, C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Z. Zhang, S. Y. Zhao, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team:
During the commissioning phase, GECAM-B triggered a long burst, GRB 210421A, at 2021-04-21T00:27:32.000 UTC (denoted as T0), which was also detected by Swift/BAT(GCN #29849).
According to the GECAM-B light curves in about 8 keV - 115 keV, this burst mainly consists of multiple pulses with duration of about 20 s.
Although in-flight calibration has not been finalized yet, GECAM-B localized this burst to the following position (J2000):
```
Ra: 103.56 deg 
Dec: 2.26 deg 
Err: 3.46 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.
GECAM location is consistent with the Swift/BAT(GCN #29849) position within the error.
The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/multiLCvsE_2021-04-21T003A273A32.950_.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 #29893
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), (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 210421A (trigger #1044426) (Moss et al., GCN Circ. 29849). The BAT ground-calculated position is RA, Dec = 104.882, 4.928 deg which is
```
   RA(J2000)  =  06h 59m 31.7s
   Dec(J2000) = +04d 55' 41.2"
```
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 44%.
The BAT light curve showed a complex structure with a duration of about ~60 sec. T90 (15-350 keV) is 79.52 +- 26.78 sec (estimated error including systematics).
The time-averaged spectrum from T-21.74 to T+73.22 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.10 +- 0.72, and Epeak of 35.2 +- 8.5 keV (chi squared 61.93 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+2.47 sec in the 15-150 keV band is 2.0 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.10 +- 0.13 (chi squared 69.44 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/BATbursts/1044426/bascript/top.html

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Jochen Greiner, last update: 23-Apr-2021 [Disclaimer]