Gamma-ray Burst 210321A

(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 21 Mar 21 07:14:19 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.874d {+05h 51m 30s} (J2000),
                  88.472d {+05h 53m 53s} (current),
                  86.465d {+05h 45m 51s} (1950)
GRB_DEC:         +70.119d {+70d 07' 09"} (J2000),
                 +70.123d {+70d 07' 23"} (current),
                 +70.106d {+70d 06' 20"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       4930 [cnts]    Image_Peak=165 [image_cnts]
TRIGGER_DUR:     2.048 [sec] 
TRIGGER_INDEX:   255     E_range: 15-50 keV
BKG_INTEN:       47356 [cnts]
BKG_TIME:        25997.29 SOD {07:13:17.29} UT
BKG_DUR:         24 [sec]
GRB_DATE:        19294 TJD;    80 DOY;   21/03/21
GRB_TIME:        26031.02 SOD {07:13:51.02} UT
GRB_PHI:         -109.54 [deg]
GRB_THETA:        35.04 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     15.81 [sigma]
IMAGE_SIGNIF:    7.40 [sigma]
MERIT_PARAMS:     +1  +0  +0  +1  +1  -3  +0  +0  -2  +0 
SUN_POSTN:         0.82d {+00h 03m 18s}   +0.36d {+00d 21' 25"}
SUN_DIST:         88.87 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.07d {+05h 48m 17s}  +24.66d {+24d 39' 34"}
MOON_DIST:        45.47 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.47, 20.52 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       88.95, 46.69 [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 = 226.61,-20.42 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 07:17:37 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.874d {+05h 51m 30s} (J2000),
                  88.472d {+05h 53m 53s} (current),
                  86.465d {+05h 45m 51s} (1950)
GRB_DEC:         +70.119d {+70d 07' 09"} (J2000),
                 +70.123d {+70d 07' 23"} (current),
                 +70.106d {+70d 06' 20"} (1950)
GRB_DATE:        19294 TJD;    80 DOY;   21/03/21
GRB_TIME:        26031.02 SOD {07:13:51.02} UT
TRIGGER_INDEX:   255
GRB_PHI:         -109.54 [deg]
GRB_THETA:        35.04 [deg]
DELTA_TIME:      -11.00 [sec]
TRIGGER_DUR:     2.048 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     15.81 [sigma]
IMAGE_SIGNIF:    7.40 [sigma]
LC_URL:          sw01037828000msb.lc
SUN_POSTN:         0.83d {+00h 03m 18s}   +0.36d {+00d 21' 28"}
SUN_DIST:         88.86 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.10d {+05h 48m 24s}  +24.66d {+24d 39' 44"}
MOON_DIST:        45.47 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.47, 20.52 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       88.95, 46.69 [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 = 226.61,-20.42 [deg].

GCN Circular #29677
S. Dichiara (NASA/GSFC/UMCP), C. Gronwall (PSU), H. A. Krimm (NSF), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 07:13:51 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210321A (trigger=1037828). Swift did not immediately slew due to an observing constraint. The BAT on-board calculated location is RA, Dec 87.874, +70.119 which is
```
   RA(J2000) = 05h 51m 30s
   Dec(J2000) = +70d 07' 09"
```
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 15 sec. The peak count rate was ~1300 counts/sec (15-350 keV), at ~1 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+43.3 minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). 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 21 Mar 21 07:59:39 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1037828,   Seg_Num: 0
POINT_RA:         87.783d {+05h 51m 08s} (J2000)
POINT_DEC:       +70.115d {+70d 06' 55"} (J2000)
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28761.62 SOD {07:59:21.62} UT,   2730.6 [sec] since BAT Trigger Time
COUNTS:          2    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        1    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:04:37 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1037828,   Seg_Num: 0
POINT_RA:         87.782d {+05h 51m 08s} (J2000)
POINT_DEC:       +70.115d {+70d 06' 55"} (J2000)
POINT_ROLL:      267.236d
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28766.18 SOD {07:59:26.18} UT,   2735.2 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        7.258
N_STARS:         55
X_OFFSET:        278 [pixels]
Y_OFFSET:        661 [pixels]
X_MAX:           1237 [pixels]
Y_MAX:           1620 [pixels]
DET_THRESH:      23
PHOTO_THRESH:    14
SL_URL:          sw01037828000msufc2735.fits
SUN_POSTN:         0.86d {+00h 03m 25s}   +0.37d {+00d 22' 15"}
SUN_DIST:         88.81 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.53d {+05h 50m 08s}  +24.70d {+24d 42' 12"}
MOON_DIST:        45.42 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.49 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       88.90, 46.68 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:04:50 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1037828,   Seg_Num: 0
POINT_RA:         87.782d {+05h 51m 08s} (J2000)
POINT_DEC:       +70.115d {+70d 06' 55"} (J2000)
POINT_ROLL:      267.236d
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28766.18 SOD {07:59:26.18} UT,   2735.2 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        7.258
N_STARS:         55
X_OFFSET:        278 [pixels]
Y_OFFSET:        661 [pixels]
X_MAX:           1237 [pixels]
Y_MAX:           1620 [pixels]
DET_THRESH:      23
PHOTO_THRESH:    14
SL_URL:          sw01037828000msufc2735.fits
SUN_POSTN:         0.86d {+00h 03m 25s}   +0.37d {+00d 22' 15"}
SUN_DIST:         88.81 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.54d {+05h 50m 09s}  +24.70d {+24d 42' 13"}
MOON_DIST:        45.42 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.49 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       88.90, 46.68 [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 21 Mar 21 08:06:11 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1037828,   Seg_Num: 0
POINT_RA:         87.782d {+05h 51m 08s} (J2000)
POINT_DEC:       +70.115d {+70d 06' 55"} (J2000)
ROLL:            267.236d
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28766.18 SOD {07:59:26.18} UT,   2735.2 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     638006392
X_OFFSET:        597 [pixels]
Y_OFFSET:        980 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       757
Y_GRB_POS:       1140
BINNING_INDEX:   1
IM_URL:          sw01037828000msuni2762.fits
SUN_POSTN:         0.86d {+00h 03m 26s}   +0.37d {+00d 22' 16"}
SUN_DIST:         88.81 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.55d {+05h 50m 12s}  +24.70d {+24d 42' 17"}
MOON_DIST:        45.42 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.49 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       88.90, 46.68 [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:     Sun 21 Mar 21 08:06:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1037828,   Seg_Num: 0
POINT_RA:         87.782d {+05h 51m 08s} (J2000)
POINT_DEC:       +70.115d {+70d 06' 55"} (J2000)
ROLL:            267.236d
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28766.18 SOD {07:59:26.18} UT,   2735.2 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     638006392
X_OFFSET:        597 [pixels]
Y_OFFSET:        980 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       757
Y_GRB_POS:       1140
BINNING_INDEX:   1
IM_URL:          sw01037828000msuni2762.fits
SUN_POSTN:         0.86d {+00h 03m 26s}   +0.37d {+00d 22' 16"}
SUN_DIST:         88.81 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.55d {+05h 50m 12s}  +24.70d {+24d 42' 18"}
MOON_DIST:        45.42 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.49 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       88.90, 46.68 [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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:06:39 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.8969d {+05h 51m 35.25s} (J2000),
                  88.4955d {+05h 53m 58.91s} (current),
                  86.4873d {+05h 45m 56.94s} (1950)
GRB_DEC:         +70.1295d {+70d 07' 46.1"} (J2000),
                 +70.1332d {+70d 07' 59.5"} (current),
                 +70.1159d {+70d 06' 57.0"} (1950)
GRB_ERROR:       4.5 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28887.00 SOD {08:01:27.00} UT,   2856.0 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:         0.86d {+00h 03m 26s}   +0.37d {+00d 22' 17"}
SUN_DIST:         88.85 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.55d {+05h 50m 13s}  +24.71d {+24d 42' 19"}
MOON_DIST:        45.43 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.53 [deg] galactic lon,lat of the burst
ECL_COORDS:       88.96, 46.70 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
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 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:09:02 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.8947d {+05h 51m 34.72s} (J2000),
                  88.4933d {+05h 53m 58.39s} (current),
                  86.4850d {+05h 45m 56.40s} (1950)
GRB_DEC:         +70.1305d {+70d 07' 49.7"} (J2000),
                 +70.1342d {+70d 08' 03.2"} (current),
                 +70.1168d {+70d 07' 00.6"} (1950)
GRB_ERROR:       0.6 [arcsec radius, statistical only]
GRB_MAG:         18.51 +/- 0.14 [mag]
FILTER:          10, White
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28763.00 SOD {07:59:23.00} UT,   2732.0 [sec] since BAT Trigger Time
SUN_POSTN:         0.86d {+00h 03m 26s}   +0.37d {+00d 22' 19"}
SUN_DIST:         88.85 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.57d {+05h 50m 18s}  +24.71d {+24d 42' 26"}
MOON_DIST:        45.43 [deg]
MOON_ILLUM:      47 [%]
GAL_COORDS:      143.46, 20.53 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       88.96, 46.70 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        Result based on Genie data.  
COMMENTS:        Notice generated automatically.

GCN Circular #29678
M. Perri (SSDC & INAF-OAR), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU) and G. Cusumano (INAF-IASF PA) report on behalf of the Swift-XRT team:
The XRT began observing the field of GRB 210321A at 07:59:21.6 UT, 2730.6 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 87.89627, 70.13042 which is equivalent to:
```
   RA(J2000)  = 05h 51m 35.10s
   Dec(J2000) = +70d 07' 49.5"
```
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 49 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.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.13 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 4 (+3.35/-2.86) x 10^21 cm^-2 (90% confidence).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:24:06 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.8959d {+05h 51m 35.01s} (J2000),
                  88.4945d {+05h 53m 58.67s} (current),
                  86.4862d {+05h 45m 56.69s} (1950)
GRB_DEC:         +70.1304d {+70d 07' 49.4"} (J2000),
                 +70.1341d {+70d 08' 02.8"} (current),
                 +70.1168d {+70d 07' 00.3"} (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:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28887.00 SOD {08:01:27.00} UT,   2856.0 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:         0.87d {+00h 03m 28s}   +0.38d {+00d 22' 34"}
SUN_DIST:         88.84 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.71d {+05h 50m 51s}  +24.72d {+24d 43' 12"}
MOON_DIST:        45.42 [deg]
MOON_ILLUM:      48 [%]
GAL_COORDS:      143.46, 20.53 [deg] galactic lon,lat of the burst
ECL_COORDS:       88.96, 46.70 [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 0.58% < P(seren) < 1.1%.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 21 Mar 21 08:45:13 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1037828,   Seg_Num: 0
GRB_RA:           87.8960d {+05h 51m 35.04s} (J2000),
                  88.4946d {+05h 53m 58.70s} (current),
                  86.4863d {+05h 45m 56.71s} (1950)
GRB_DEC:         +70.1306d {+70d 07' 50.1"} (J2000),
                 +70.1343d {+70d 08' 03.5"} (current),
                 +70.1170d {+70d 07' 01.0"} (1950)
GRB_ERROR:       3.6 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19294 TJD;    80 DOY;   21/03/21
IMG_START_TIME:  28887.00 SOD {08:01:27.00} UT,   2856.0 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:         0.88d {+00h 03m 31s}   +0.38d {+00d 22' 55"}
SUN_DIST:         88.83 [deg]   Sun_angle= -5.8 [hr] (East of Sun)
MOON_POSTN:       87.91d {+05h 51m 38s}  +24.74d {+24d 44' 17"}
MOON_DIST:        45.40 [deg]
MOON_ILLUM:      48 [%]
GAL_COORDS:      143.46, 20.53 [deg] galactic lon,lat of the burst
ECL_COORDS:       88.96, 46.70 [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 0.58% < P(seren) < 1.1%.

GCN Circular #29679
M.. H. Siegel (PSU) and S. Dichiara (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210321A 2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677). A source consistent with the XRT position (Perri et al., GCN Circ. 29678) is detected in the initial UVOT exposures.
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 2735 2837 100 18.76 +/- 0.11
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.116 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #29680
Nat Butler (ASU), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Oc�lotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report:
We observed the field of the Swift/BAT GRB 210321A (Dichiara et al., GCN Circ. 29677) with the DDOTI wide-field imager at the Observatorio Astron�mico Nacional on Sierra San Pedro Martir ( http://ddoti.astroscu.unam.mx) starting at 2021-03-21 08:56 UTC (from 1.7 hours after the trigger).
We observed a region covering approximately 7 degrees in RA and 10 degrees in declination (about 70 square degrees) centered on the XRT position (Perri et al., GCN 29678) in the w filter.
Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we detect a bright source at 08:39:50.04 +60:12:18.9 (J2000) fading from about w = 18. This confirms the afterglow reported in UVOT observations by Siegel et al. (GCN Circ. 29679).
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
GCN Circular #29681
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 1720 s of XRT Photon Counting mode data and 5 UVOT images for GRB 210321A, 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 = 87.89579, +70.13057 which is equivalent to:
```
RA (J2000): 05h 51m 34.99s
Dec (J2000): +70d 07' 50.1"
```
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 #29683
V. Lipunov, V.Kornilov, E.Gorbovskoy,N.Tiurina,P.Balanutsa,F.Balakin, V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, A.Chasovnikov,A.Pozdnyakov,V.Topolev, D.Cheryasov(Lomonosov Moscow State University, SAI, Physics Department), D. Buckley (South African Astronomical Observatory), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L) started Swift GRB 210321A (BAT:Dichiara et al. GCN 29677,Ttrig=07:13:51; XRT:Perri et al. GCN 29678,Beardmore et al. GCN29681; UVOT: Siegel GCN29679), optical observations at MASTER-Tavrida at 2021-03-21 16:55:20UT, ~9.7h after trigger time, with mlim=20.8m. Swift optical counterpart (87.8947 +70.1305) isn't visible yet.
This message may be cited.
GCN Circular #29684
Kasper E. Heintz (Univ. of Iceland, DAWN/NBI), Johan P. U. Fynbo (DAWN/NBI), and Tapio Pursimo (NOT), report on behalf of a larger collaboration:
We observed the field of the Swift/BAT-detected GRB 210321A (Dichiara et al., GCN #29677), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Starting at 20:26:25.6 UTC on March 21, we obtained 3x300 sec exposures in the Sloan r-band. The observations were carried out under good conditions, with seeing around 0.8". We confirm the optical afterglow reported by Siegel et al. (GCN #29679), and measure r = 21.6 +/- 0.15 mag at 13.5 hr post-burst, calibrated against nearby field stars in the Pan-STARRS catalog.
Following the imaging sequence, we obtained spectroscopy of the afterglow with ALFOSC using grism 4 (320 to 960 nm) and for 4x1200 sec total integration. A faint trace is detected but we do not identify any particular absorption or emission features to infer the redshift from. However, since the continuum is detected down to 380 nm, we put a limit on the redshift of z < 2.
GCN Circular #29685
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D.A. Kann, C. Thoene, M. Blazek, J.F. Agui Fernandez (all HETH/IAA-CSIC), S. Geier (GTC, IAC), A. Tejero (GTC) report:
We observed the afterglow of GRB 210321A (Dichiara et al. GCN 29677; Perri et al. GCN 29678; Siegel et al. GCN 29679; Butler et al. GCN 29680; Heintz et al. GCN 29684) with OSIRIS at the 10.4m GTC telescope at Roque de los Muchachos Observatory, in La Palma (Spain). The observation started at 20:28 UT (0.5517 days after the burst), and consisted in 3x900s with grism R1000B, covering the spectral range from 3700 to 7800 AA.
The 30s acquisition image, with a seeing of 0.75'', shows the afterglow at a magnitude of r' = 21.39+/-0.03, using a nearby PanSTARRS field star as photometric reference.
The spectral continuum is well detected above 3900 AA, and shows very weak lines consistent with several features of FeII, MgII and MgI at a common redshift of z = 1.487, which we assume to be the likely redshift of the GRB. However, we note that strictly speaking this would be a lower limit, with the upper limit being z ~< 2, as already noted by the NOT spectroscopy (Heintz et al. GCN 29684).
GCN Circular #29686
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU) and S. Dichiara report on behalf of the Swift-XRT team:
We have analysed 6.7 ks of XRT data for GRB 210321A (Dichiara et al. GCN Circ. 29677), from 2.7 ks to 44.2 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 29681).
The light curve can be modelled with a power-law decay with a decay index of alpha=1.59 (+0.13, -0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.99 (+0.20, -0.19). The best-fitting absorption column is 2.3 (+0.8, -0.7) x 10^21 cm^-2, in excess of the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     2.3 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 2.9 sigma
Photon index:	     1.99 (+0.20, -0.19)
```
If the light curve continues to decay with a power-law decay index of 1.59, the count rate at T+24 hours will be 2.2 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x 10^-14 (1.1 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/01037828.
This circular is an official product of the Swift-XRT team.
GCN Circular #29687
L. P. Xin(NAOC), C. Gao(GXU), X. H. Han(NAOC), J. Y. Wei(NAOC), J. Wang(GXU), G. W. LI(NAOC), L. H. Li(NAOC), C. Wu(NAOC), X. G. Wang(GXU), E. W. Liang (GXU), Y. L. Qiu(NAOC), and J. S. Deng(NAOC) report:
We began to observe GRB 210321A (Dichiara et al. GCN 29677; Perri et al. GCN 29678; Siegel et al. GCN 29679; Butler et al. GCN 29680; Heintz et al. GCN 29684; Ugarte Postigo et al., GCN 29685) with Xinglong GWAC-F60A telescope, China, at 11:30:49 (UT), 21th. Mar. 2021, about 4.28 hours after the burst.
A series of R, I images were obtained. The optical counterpart ( Siegel et al. GCN 29679; Butler et al. GCN 29680; Heintz et al. GCN 29684; Ugarte Postigo et al., GCN 29685) was clearly detected in the stacked R-band image observed during 11:30:49 and 12:48:17 UT. The brightness was estimated to be 18.98 +/-0.13 mag at the mean time of 4.88 hours after the burst, calibrated to USNO B1.0 R2 mag,
This result is consistent with the previous report (Zhu et al., GCN 29530).
GCN Circular #29689
N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We observed the field of GRB 210321A (Dichiara et al., GCN 29677) with AZT-33IK telescope of Sayan observatory (Mondy) starting on 2021-03-21 (UT) 14:20:37. The optical afterglow (Siegel et al., GCN 29679; Butler et al., GCN 29680; Lipunov et al., GCN 29683; Heintz et al., GCN 29684; de Ugarte Postigo et al., GCN 29685; Xin et al. GCN 29687) is clearly detected in a combined image. Preliminary photometry of the afterglow in the combined image is following
```
Date       UT start   t-T0       Filter Exp.   OT   Err.  UL(3sigma)
                       (mid, days)        (s)

2021-03-21 14:20:37   0.31199    R      45*60  20.1 0.14  20.5
```
The photometry is based on the nearby USNO-B1.0 stars
```
USNO-B1.0_id R2
1601-0068003 15.84
1600-0068970 16.18
1601-0068018 16.54
1601-0067995 16.23
```
GCN Circular #29691
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), S. Dichiara (NASA/GSFC/UMCP), 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-240 to T+700 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210321A (trigger #1037828) (Dichiara, et al., GCN Circ. 29677). The BAT ground-calculated position is RA, Dec = 87.887, 70.109 deg which is
```
  RA(J2000)  =  05h 51m 32.8s 
  Dec(J2000) = +70d 06' 33.4" 
```
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 30%.
The mask-weighted light curve shows a single, fairly symmetrical peak from approximately T-8 to T+4 sec. T90 (15-350 keV) is 8.21 +- 0.50 sec (estimated error including systematics).
The time-averaged spectrum from T-7.00 to T+1.84 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.15 +- 0.20. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-6.99 sec in the 15-150 keV band is 1.7 +- 0.4 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/1037828/BA/
GCN Circular #29692
N. Pankov (HSE), S. Nazarov (CrAO), A. Pozanenko (IKI), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We observed the field of GRB 210321A (Dichiara et al., GCN 29677) with AZT-8 telescope of CrAO observatory starting on 2021-03-21 (UT) 19:04:11. The optical afterglow (Siegel et al., GCN 29679; Butler et al., GCN 29680; Lipunov et al., GCN 29683; Heintz et al., GCN 29684; de Ugarte Postigo et al., GCN 29685; Xin et al. GCN 29687; Pankov et al., GCN 29689) is not detected in a combined image. Preliminary photometry of the field is following
```
Date       UT start   t-T0       Filter Exp.   OT   Err.  UL(3sigma)
                       (mid, days)        (s)

2021-03-21 19:04:11   0.51238    R      55*60  n/d  n/d   20.8
```
The photometry is based on the nearby USNO-B1.0 stars
```
USNO-B1.0_id R2
1601-0068003 15.84
1600-0068970 16.18
1601-0068018 16.54
1601-0067995 16.23
```
GCN Circular #29694
The afterglow position quoted by Butler et al. (GCN 29680) was typed incorrectly. The correct position is 05:51:34.82, +70:07:50.4 (J2000).
GCN Circular #29696
D. Frederiks, S. Golenetskii, A.Lysenko, D. Svinkin, A. Ridnaya, A. Tsvetkova, M. Ulanov, and T. Cline, report:
The long GRB 210321A (Swift-BAT trigger #1037828, T0(BAT)= 07:13:51.023 UT: Dichiara, et al., GCN 29677; Ukwatta, et al., GCN 29691) was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~10 sigma count rate increase over background in the interval from ~T0(BAT)-6.430 s to ~T0(BAT)+2.402 s.
A fit to the KW 3-cannel waiting mode spectrum with by a power law with an exponential cutoff (CPL) yields alpha~-2 and doesn't constrain Ep. A fit with a simple power law (PL) gives a photon index of (2.19 � 0.17), chi^2 = 0.78/ 1 dof. This result is consistent with the Swift-BAT refined analysis (GCN 29691).
In the 10 keV-10 MeV band, standard for the KW spectral analysis, the total burst fluence, estimated from the PL model, is (1.6 � 0.3)x10^-6 erg/cm^2, and the 2.944 s peak energy flux is (2.2 � 0.4)x10^-7 erg/cm^2.
Assuming the redshift z=1.487 (de Ugarte Postigo, et al., GCN 29685) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to ~9.7x10^51 erg and the isotropic luminosity L_iso to ~3.2x10^51 erg/s.
The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB210321A/
GCN Circular #29697
GRB 210321A: Swift/UVOT Detection
S. J. Laporte (PSU) and S. Dichiara (NASA/GSFC/UMCP) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210321A 2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677). A source consistent with the XRT position (Beardmore et al. GCN Circ. 29681) is detected in the initial UVOT exposures.
The preliminary UVOT position is:
```
    RA  (J2000) =  05:51:34.75 =  87.89479 (deg.)
    Dec (J2000) = +70:07:49.8  =  70.13051 (deg.)
```
with an estimated uncertainty of 0.49 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

white             2735         2885          147         18.69 +/- 0.09
v                 2892         4465          331         18.44 +/- 0.16
b                 3713         3913          197         18.64 +/- 0.11
u                 3507         3706          197         18.29 +/- 0.12
w1                3302         3502          197         18.48 +/- 0.17
m2                3097         3296          197        >18.9
w2                4124         4324          197        >19.8
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.118 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #29725
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and F. Aceituno (IAA-CSIC) report:
We observed the optical afterglow (Perri et al. GCN #29678; Siegel et al. GCN #29679; Butler et al. GCN #29680; Heintz et al. GCN #29684; Xin et al., GCN #29687; Pankov et al., GCNs #29689, #29692; Laporte et al., GCN #29697) of GRB 210321A (Swift detection: Dichiara et al., GCN #29677) with the 1.5m T150 telescope of the Observatorio de Sierra Nevada (OSN), Granada, Spain. Observations could not be taken due to high winds in the first night after the GRB. We obtained 11 x 180 s exposures in Rc starting at 2021-03-22 19:59:44.93 UT, before high winds shut the telescope down again. The afterglow is not detected in the combined image.
We determine an upper limit Rc > 23.3 mag (AB mag, vs. a nearby Pan-STARRS star converted to Rc following the Lupton transformations, then transformed back to AB mag) at 1.5437 days after the GRB.

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Jochen Greiner, last update: 25-Mar-2021 [Disclaimer]