Gamma-ray Burst 210726A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:19:21 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1061687,   Seg_Num: 0
GRB_RA:          193.342d {+12h 53m 22s} (J2000),
                 193.608d {+12h 54m 26s} (current),
                 192.723d {+12h 50m 54s} (1950)
GRB_DEC:         +19.185d {+19d 11' 05"} (J2000),
                 +19.068d {+19d 04' 04"} (current),
                 +19.456d {+19d 27' 21"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       1308 [cnts]    Image_Peak=88 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   124     E_range: 25-100 keV
BKG_INTEN:       13930 [cnts]
BKG_TIME:        69532.56 SOD {19:18:52.56} UT
BKG_DUR:         8 [sec]
GRB_DATE:        19421 TJD;   207 DOY;   21/07/26
GRB_TIME:        69543.69 SOD {19:19:03.69} UT
GRB_PHI:         -13.10 [deg]
GRB_THETA:         2.08 [deg]
SOLN_STATUS:     0x83
RATE_SIGNIF:     13.45 [sigma]
IMAGE_SIGNIF:    6.71 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +2  -3  +0  +0 -45  +0 
SUN_POSTN:       126.34d {+08h 25m 22s}  +19.25d {+19d 14' 51"}
SUN_DIST:         63.09 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.50d {+22h 50m 00s}  -12.92d {-12d 55' 03"}
MOON_DIST:       149.52 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.23, 82.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      184.31, 22.84 [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:        Since the IMAGE_SIGNIF is less than 7 sigma, this is a questionable detection.  
COMMENTS:        This trigger occurred at longitude,latitude = 246.56,15.63 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:20:22 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.335d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 21"} (J2000)
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69603.67 SOD {19:20:03.67} UT,   60.0 [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:     Mon 26 Jul 21 19:24:27 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.335d {+12h 53m 20s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 21"} (J2000)
POINT_ROLL:      282.351d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69608.62 SOD {19:20:08.62} UT,   64.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        5.998
N_STARS:         4
X_OFFSET:        427 [pixels]
Y_OFFSET:        558 [pixels]
X_MAX:           1386 [pixels]
Y_MAX:           1517 [pixels]
DET_THRESH:      21
PHOTO_THRESH:    12
SL_URL:          sw01061687000msufc0064.fits
SUN_POSTN:       126.35d {+08h 25m 23s}  +19.25d {+19d 14' 48"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.55d {+22h 50m 11s}  -12.90d {-12d 53' 58"}
MOON_DIST:       149.56 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.18, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.  
COMMENTS:        There is a bright star (mag=6.15) 10.45 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:24:28 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1061687,   Seg_Num: 0
GRB_RA:          193.2921d {+12h 53m 10.10s} (J2000),
                 193.5588d {+12h 54m 14.10s} (current),
                 192.6735d {+12h 50m 41.64s} (1950)
GRB_DEC:         +19.1903d {+19d 11' 25.0"} (J2000),
                 +19.0735d {+19d 04' 24.6"} (current),
                 +19.4616d {+19d 27' 41.7"} (1950)
GRB_ERROR:       7.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69622.00 SOD {19:20:22.00} UT,   78.3 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       126.35d {+08h 25m 23s}  +19.25d {+19d 14' 48"}
SUN_DIST:         63.04 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.55d {+22h 50m 11s}  -12.90d {-12d 53' 58"}
MOON_DIST:       149.60 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      305.89, 82.05 [deg] galactic lon,lat of the burst
ECL_COORDS:      184.26, 22.83 [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 Circular #30522
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University)
MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the Swift GRB210726.80 (trigger No 1061687,12h 53m 22.08s , +19d 11m 06.0s, R=0.05) errorbox 31 sec after notice time and 54 sec after trigger time at 2021-07-26 19:19:58 UT, with upper limit up to 15.0 mag. The observations began at zenith distance = 66 deg. The sun altitude is -18.0 deg.
The galactic latitude b = 82 deg., longitude l = 310 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1671119
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      59 |      MASTER-Tavrida |  P\ |    10 | 14.1 |        
      94 |      MASTER-Tavrida |  P\ |    20 | 15.0 |        
```
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:26:40 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.335d {+12h 53m 20s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 21"} (J2000)
ROLL:            282.351d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69608.62 SOD {19:20:08.62} UT,   64.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649020036
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0092.fits
SUN_POSTN:       126.35d {+08h 25m 23s}  +19.25d {+19d 14' 47"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.57d {+22h 50m 16s}  -12.89d {-12d 53' 30"}
MOON_DIST:       149.58 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.18, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:     Mon 26 Jul 21 19:26:47 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.335d {+12h 53m 20s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 21"} (J2000)
ROLL:            282.351d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69608.62 SOD {19:20:08.62} UT,   64.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649020036
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0092.fits
SUN_POSTN:       126.35d {+08h 25m 23s}  +19.25d {+19d 14' 47"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.57d {+22h 50m 16s}  -12.89d {-12d 53' 28"}
MOON_DIST:       149.58 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.18, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:32:56 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 19"} (J2000)
POINT_ROLL:      282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69820.52 SOD {19:23:40.52} UT,   276.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.404
N_STARS:         8
X_OFFSET:        187 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1626 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01061687000msufc0276.fits
SUN_POSTN:       126.35d {+08h 25m 24s}  +19.25d {+19d 14' 43"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.62d {+22h 50m 29s}  -12.87d {-12d 52' 10"}
MOON_DIST:       149.62 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:33:23 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1061687,   Seg_Num: 0
GRB_RA:          193.2908d {+12h 53m 09.79s} (J2000),
                 193.5575d {+12h 54m 13.79s} (current),
                 192.6722d {+12h 50m 41.33s} (1950)
GRB_DEC:         +19.1898d {+19d 11' 23.2"} (J2000),
                 +19.0730d {+19d 04' 22.8"} (current),
                 +19.4611d {+19d 27' 39.9"} (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:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69622.00 SOD {19:20:22.00} UT,   78.3 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       126.35d {+08h 25m 25s}  +19.25d {+19d 14' 43"}
SUN_DIST:         63.04 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.62d {+22h 50m 30s}  -12.87d {-12d 52' 04"}
MOON_DIST:       149.67 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      305.88, 82.05 [deg] galactic lon,lat of the burst
ECL_COORDS:      184.26, 22.83 [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:     Mon 26 Jul 21 19:33:14 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 19"} (J2000)
POINT_ROLL:      282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69820.52 SOD {19:23:40.52} UT,   276.8 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.404
N_STARS:         8
X_OFFSET:        187 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1626 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      10
PHOTO_THRESH:    5
SL_URL:          sw01061687000msufc0276.fits
SUN_POSTN:       126.35d {+08h 25m 25s}  +19.25d {+19d 14' 43"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.62d {+22h 50m 30s}  -12.87d {-12d 52' 06"}
MOON_DIST:       149.62 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:     Mon 26 Jul 21 19:34:19 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 19"} (J2000)
ROLL:            282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69820.52 SOD {19:23:40.52} UT,   276.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     649020247
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0304.fits
SUN_POSTN:       126.35d {+08h 25m 25s}  +19.25d {+19d 14' 43"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.63d {+22h 50m 32s}  -12.86d {-12d 51' 52"}
MOON_DIST:       149.63 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:     Mon 26 Jul 21 19:34:33 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 19"} (J2000)
ROLL:            282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  69820.52 SOD {19:23:40.52} UT,   276.8 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     649020247
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0304.fits
SUN_POSTN:       126.35d {+08h 25m 25s}  +19.25d {+19d 14' 43"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.63d {+22h 50m 32s}  -12.86d {-12d 51' 49"}
MOON_DIST:       149.63 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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 #30523
M. G. Bernardini (INAF-OAB), M. A. Baer (PSU), P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), S. Laha (GSFC/UMBC/CRESST), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), M. J. Moss (GWU), K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team:
At 19:19:03 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210726A (trigger=1061687). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 193.342, +19.185 which is
```
   RA(J2000) = 12h 53m 22s
   Dec(J2000) = +19d 11' 05"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short spike with a tail with a total duration of about ~3 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. This may be a short GRB.
The XRT began observing the field at 19:20:03.6 UT, 60.0 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 193.2909, 19.1898 which is equivalent to:
```
   RA(J2000)  = 12h 53m 09.81s
   Dec(J2000) = +19d 11' 23.2"
```
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 174 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 (1.73 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.4 (+2.93/-2.51) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 250 seconds with the U filter starting 276 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 none of the XRT error circle. 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.020.
Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.inaf.it). 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:     Mon 26 Jul 21 19:40:42 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 20"} (J2000)
POINT_ROLL:      282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  70420.81 SOD {19:33:40.81} UT,   877.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.092
N_STARS:         23
X_OFFSET:        187 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1626 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      15
PHOTO_THRESH:    8
SL_URL:          sw01061687000msufc0877.fits
SUN_POSTN:       126.36d {+08h 25m 26s}  +19.24d {+19d 14' 39"}
SUN_DIST:         63.08 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.69d {+22h 50m 45s}  -12.84d {-12d 50' 31"}
MOON_DIST:       149.68 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 26 Jul 21 19:40:59 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 20"} (J2000)
POINT_ROLL:      282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  70420.81 SOD {19:33:40.81} UT,   877.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        3.092
N_STARS:         23
X_OFFSET:        187 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1626 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      15
PHOTO_THRESH:    8
SL_URL:          sw01061687000msufc0877.fits
SUN_POSTN:       126.36d {+08h 25m 26s}  +19.24d {+19d 14' 39"}
SUN_DIST:         63.07 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.69d {+22h 50m 46s}  -12.84d {-12d 50' 27"}
MOON_DIST:       149.68 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:     Mon 26 Jul 21 19:42:18 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 20"} (J2000)
ROLL:            282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  70420.81 SOD {19:33:40.81} UT,   877.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649020848
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0905.fits
SUN_POSTN:       126.36d {+08h 25m 26s}  +19.24d {+19d 14' 38"}
SUN_DIST:         63.07 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.70d {+22h 50m 49s}  -12.84d {-12d 50' 10"}
MOON_DIST:       149.69 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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:     Mon 26 Jul 21 19:42:28 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1061687,   Seg_Num: 0
POINT_RA:        193.336d {+12h 53m 21s} (J2000)
POINT_DEC:       +19.189d {+19d 11' 20"} (J2000)
ROLL:            282.354d
IMG_START_DATE:  19421 TJD;   207 DOY;   21/07/26
IMG_START_TIME:  70420.81 SOD {19:33:40.81} UT,   877.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     649020848
X_OFFSET:        746 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       906
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01061687000msuni0905.fits
SUN_POSTN:       126.36d {+08h 25m 26s}  +19.24d {+19d 14' 38"}
SUN_DIST:         63.07 [deg]   Sun_angle= -4.5 [hr] (East of Sun)
MOON_POSTN:      342.70d {+22h 50m 49s}  -12.84d {-12d 50' 08"}
MOON_DIST:       149.69 [deg]
MOON_ILLUM:      91 [%]
GAL_COORDS:      306.19, 82.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      184.30, 22.84 [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 #30524
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 1692 s of XRT Photon Counting mode data and 1 UVOT images for GRB 210726A, 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 = 193.29093, +19.19030 which is equivalent to:
```
RA (J2000): 12h 53m 9.82s
Dec (J2000): +19d 11' 25.1"
```
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 #30525
Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado M. D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), A. Gardini and I. Hermelo (CAHA) on behalf of a larger collaboration, report:
Following the detection of GRB210726A by Swift (Bernardini et al. GCNC 30523), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). A series of i-band images were gathered starting on July 26, 20:23 UT (i.e. 1.07 h post trigger). On the co-added image (15 x 60s), no optical object is detected down to 21.9 mag at the X-ray afterglow position reported by Swift/XRT (Osborne et al. GCNC 30524).
We thank the staff at Calar Alto observatory for their excellent support.
GCN Circular #30534
Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H. Lee (UNAM), 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 candidate short GRB 210726A (Bernardini et al., GCN Circ., 30523) 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 2021/07 27.16 to 2021/07 27.22 UTC (8.24 to 9.65 hours after the BAT trigger), obtaining a total of 1.09 hours exposure in the r and i bands.
For a source within the enhanced Swift-XRT error circle (Osborne et al., GCN Circ., 30524), in comparison with the SDSS DR9 catalog, we obtain the following upper limits (3-sigma):
```
  r	> 23.0
  i	> 22.7
```
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.
We note that the SDSS galaxy J125309.63+191127.2 is 3.1 arcsec from the enhanced XRT position and just outside the error circle. In our observations, it has r = 22.2 +/- 0.2 and i = 22.2 +/- 0.2, in agreement with the cataloged values. The cataloged photometric redshift is z = 0.35 +/- 0.15. The probability of a chance alignment is approximately 3%. Given this low probability, we suggest that this source might be the host galaxy.
Since this GRB appears to be potentially both short and low-redshift, we encourage further observations.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro M�rtir.
GCN Circular #30535
```
TITLE:   GCN CIRCULAR
NUMBER:  30535
SUBJECT: GRB 210726A: Likely a short burst
DATE:    21/07/27 16:59:24 GMT
FROM:    Aaron Tohuvavohu at U Toronto      
```
GRB 210726A, detected by Swift BAT and XRT (GCN 30523) appears likely to be a short burst, despite the real time duration estimate (~3s) reported in the discovery circular using limited data products. The T90 estimate derived from the full downlinked Swift/BAT event data is less than 0.5 seconds. Follow-up is encouraged.
GCN Circular #30536
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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 210726A (trigger #1061687) (Bernardini et al., GCN Circ. 30523). The BAT ground-calculated position is RA, Dec = 193.333, 19.211 deg which is
```
   RA(J2000)  =  12h 53m 19.9s
   Dec(J2000) = +19d 12' 38.9"
```
with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%.
The mask-weighted light curve shows a short spike that starts at ~T0, peaks at ~T+0.2 s, and ends at ~T+0.4 s. Some tail emission from the raw light curves was mentioned in the original circular (Bernardini et al., GCN Circ. 30523), and this potential weak tail can be seen in the 1-s binned light curve (15-350 keV) as well. However, image analyses from ~T+0.5 s to ~T+2 s do not find any significant detections that are >~ 2 sigma. Therefore, this signal is also consistent with noise fluctuation. T90 (15-350 keV) is 0.39 +- 0.11 sec (estimated error including systematics).
The time-averaged spectrum from T-0.00 to T+0.42 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.47. The fluence in the 15-150 keV band is 4.5 +- 1.1 x 10^-8 erg/cm2. The 1-sec peak photon flux measured from T-0.29 sec in the 15-150 keV band is 0.7 +- 0.3 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/1061687/BA/
GCN Circular #30537
A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and M.G. Bernardini report on behalf of the Swift-XRT team:
We have analysed 5.9 ks of XRT data for GRB 210726A (Bernardini et al. GCN Circ. 30523), from 79 s to 75.9 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 30524).
The light curve can be modelled with a power-law decay with a decay index of alpha=1.49 (+0.22, -0.26).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+/-0.3). The best-fitting absorption column is 3.3 (+1.3, -1.2) x 10^21 cm^-2, in excess of the Galactic value of 1.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     3.3 (+1.3, -1.2) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 4.5 sigma
Photon index:	     2.2 (+/-0.3)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01061687.
This circular is an official product of the Swift-XRT team.
GCN Circular #30540
P. Veres (UAH) reports on behalf of the Fermi-GBM Team:
"Swift-BAT detected GRB 210726A at 19:19:03 UT (GCN 30523). There was no Fermi-GBM onboard trigger around the event.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals was run from +/-30 s around the BAT trigger time. A transient source was identified whose most significant timescale according to the search is 512 ms, and a location consistent with the Swift-BAT event. The GBM targeted search event was found with the highest significance with a "soft" spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7).
The GBM light curve consists of a single peak. The time-averaged spectrum from T0+0.6 s to T0+1.4 s is best fit by a power law function with index -2.03 +/- 0.3 (T0 is 2021-07-26 19:19:03 UT). A power law function with an exponential high-energy cutoff fits equally well, but it is not statistically preferred over the power law; the fit measures the power law index 0.23 +/- 1.67 and the cutoff energy, parameterized as Epeak, is 41 +/- 10 keV.
The event fluence (10-1000 keV) in this time interval for the power law with the exponential cutoff is (6.4 +/- 1.7)E-08 erg/cm^2. Using the photometric redshift z=0.35 reported by Watson et al. (GCN 30534), we derive an isotropic equivalent energy in the 1-10,000 keV range of (2.1 +/- 0.5)E+49 erg.
This analysis is preliminary.
[1] Goldstein et al. 2019 arXiv:1903.12597 "
GCN Circular #30542
G. Schroeder, W. Fong, A. Rouco Escorial, (Northwestern), T. Laskar (U. of Bath), E. Berger (Harvard) report:
"We observed the position of short GRB 210726A (Bernardini et al., GCN 30523; Veres et al., GCN 30540; Palmer et al., GCN 30536; Tohuvavohu et al., GCN 30535) with the Karl G. Jansky Very Large Array (VLA) under program 20B-057 (PI: Fong) beginning on 2021 July 27.81 UT (1.00 days post-burst) at a mean frequency of 6 GHz.
Based on preliminary analysis, in 1 hour of observations we do not detect any radio emission at or near the position of the XRT afterglow (Osborne et al., GCN 30524) to a 3-sigma limit of 15 microJy. Additional, detailed analysis is ongoing.
We thank the VLA staff for quickly approving and executing these observations."
GCN Circular #30543
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. Gardini, and I. Hermelo (both CAHA) report:
We observed the XRT afterglow position (Osborne et al., GCN #30524) of GRB 210726A (Bernardini et al., GCN #30523), classified as a short GRB (Tohuvavohu, GCN #30535; Palmer et al., GCN #30536; Veres, GCN #30540) with CAFOS mounted at the 2.2m Calar Alto telescope (Almeria, Spain), under good conditions but at high airmass, starting July 26, 20:52:13 UT, 1.553 h after the GRB. We obtained 15 x 180 s images in r'.
Within the XRT error circle, we do not detect any source down to r' > 24.2 mag (AB magnitude) at 0.081518 d (1.956 h) after the burst, in agreement with but deeper than limits presented by Hu et al., GCN #30525; Watson et al., GCN #30534.
Watson et al. suggest an object about 3" away as a possible host-galaxy candidate. We clearly detect this object and measure r' = 22.26 +/- 0.06 mag. This value is in agreement with detections from the PanSTARRS and SDSS surveys, and therefore there is no evidence of excess emission that could be an afterglow superposed on the host galaxy.
GCN Circular #30545
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), J. P. U. Fynbo (DAWN/NBI), L. Izzo (DARK/NBI), N. R. Tanvir (U. Leicester), and G. Gomez Velarde (GRANTECAN) report:
We observed the XRT afterglow position (Osborne et al., GCN #30524) of GRB 210726A (Bernardini et al., GCN #30523), classified as a short GRB (Tohuvavohu, GCN #30535; Palmer et al., GCN #30536; Veres, GCN #30540) with OSIRIS mounted on the 10.4m Gran Telescopio Canarias (Observatorio Astrof�isco Roque de Los Muchachos, La Palma, Canary Islands, Spain), under mediocre conditions and at high airmass, starting July 26, 21:21:31 UT, 2.041 h after the GRB. We obtained a sequence of 30, 30, 60, 30 s images in r' for a total integration time of 150 s.
Within the XRT error circle, we do not detect any source down to r' > 24.4 mag (AB magnitude), measured against a nearby PanSTARRS fiel star, at 0.088533 d (2.125 h) after the burst, in agreement with Kann et al., GCN #30543.
The possible host galaxy (Watson et al., GCN #30534, Kann et al., GCN #30543) is found at r' = 22.04 +/- 0.05 mag, again in agreement with detections from the PanSTARRS and SDSS surveys.
GCN Circular #30558
A. Rouco Escorial, W. Fong, K. Paterson (Northwestern University), R. Margutti (UC Berkeley) and E. Berger (Harvard University) report:
“We initiated observations with the Chandra X-ray Observatory of the short-duration GRB 210726A (Bernardini et al., GCN 30523; Tohuvavohu, GCN 30535; Palmer, GCN 30536) starting on 2021 July 29 16:04:38 UT, with a median observation time of ~3 days post-trigger. We obtained one ACIS-S observation under the Proposal 22400461 (ObsID 23445; PI: Fong), with an effective exposure time of ~24.6 ks.
We obtain a ~7sigma detection of GRB 210726A with a total net source counts of 76+/-10 (0.5-7 keV). The Chandra position of the short GRB is fully consistent with the enhanced Swift-XRT position (90% confidence; XRT GRB catalogue, Evans et al., 2009). The Chandra position is:
```
RA(J2000)= 12h53m09.7s
Dec(J2000)=19d11m24.6s
```
with a total positional uncertainty of 0.81 arcsec (largely dominated by Chandra's absolute astrometric uncertainty).
Based on our MCMC modeling, the XRT and Chandra afterglow flux, starting at ~120.89 s post-burst, can be modeled with a broken power-law decline characterized by a second segment with a decay index (F~t^alpha) of alpha2=-0.62 (-0.05,+0.04) starting at ~418 s post-burst. In particular, the Chandra detection roughly follows the latest decline rate based on XRT data alone..
Further Chandra observations are planned. We thank the Chandra Director, Pat Slane, and staff for the rapid planning and scheduling of these observations.”
GCN Circular #30658
G. Schroeder, K. D. Alexander, W. Fong, A. Rouco Escorial, (Northwestern), T. Laskar (U. of Bath), E. Berger (Harvard) report:
"We re-observed the position of short GRB 210726A (Bernardini et al., GCN 30523; Veres et al., GCN 30540; Palmer et al., GCN 30536; Tohuvavohu et al., GCN 30535) with the Karl G. Jansky Very Large Array (VLA) under program 20B-057 (PI: Fong) beginning on 2021 August 07.02 UT (11.21 days post-burst) at a mean frequency of 6 GHz.
In 1.5 hour of observations we detect a radio source with a preliminary flux density of ~40 uJy. The position of this radio source is fully consistent with the position of the X-ray afterglow (Osborne et al., GCN 30524; Rouco Escorial et al., GCN 30558) at:
```
RA(J2000): 12:53:09.8
Dec(J2000): +19:11:25.1
```
with an uncertainty of 0.6 arcsec in each coordinate.
We obtained further VLA observations at 6 GHz and 10 GHz beginning on 2021 August 14.75 UT (18.94 days post-burst) and detect the source at both frequencies. We find a significant brightening at 6 GHz, confirming this source as the radio afterglow of GRB210726A. We note that this radio afterglow is among the brightest ever detected for a short GRB to date.
Further observations are planned. We thank the VLA staff for quickly approving and executing these observations."
photometric redshift z = 0.37 +0.32 -0.17
of host-galaxy: A. E. Nugent et al. 2022, ApJ, 940, 57

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