Gamma-ray Burst 210905A

(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:     Sun 05 Sep 21 00:19:12 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.062d {+20h 36m 15s} (J2000),
                 309.431d {+20h 37m 43s} (current),
                 308.207d {+20h 32m 50s} (1950)
GRB_DEC:         -44.431d {-44d 25' 50"} (J2000),
                 -44.354d {-44d 21' 15"} (current),
                 -44.605d {-44d 36' 16"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       5412 [cnts]    Image_Peak=210 [image_cnts]
TRIGGER_DUR:     2.048 [sec] 
TRIGGER_INDEX:   263     E_range: 25-100 keV
BKG_INTEN:       52014 [cnts]
BKG_TIME:        724.32 SOD {00:12:04.32} UT
BKG_DUR:         24 [sec]
GRB_DATE:        19462 TJD;   248 DOY;   21/09/05
GRB_TIME:        761.32 SOD {00:12:41.32} UT
GRB_PHI:          54.49 [deg]
GRB_THETA:        32.96 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     14.17 [sigma]
IMAGE_SIGNIF:    9.35 [sigma]
MERIT_PARAMS:     +1  +0  +0  +1  +2  +0  +0  +0 +66  +0 
SUN_POSTN:       164.03d {+10h 56m 07s}   +6.80d {+06d 48' 03"}
SUN_DIST:        131.85 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.30d {+09h 25m 13s}  +20.14d {+20d 08' 14"}
MOON_DIST:       153.85 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.14,-36.86 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      299.75,-24.94 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This Notice was delayed by more than 60 sec past the end of the trigger integration interval;  
COMMENTS:        probably due to it occurring during a Malindi downlink session.  
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 = 12.68,-9.77 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:19:45 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.0459d {+20h 36m 11.01s} (J2000),
                 309.4152d {+20h 37m 39.64s} (current),
                 308.1914d {+20h 32m 45.94s} (1950)
GRB_DEC:         -44.4392d {-44d 26' 21.1"} (J2000),
                 -44.3629d {-44d 21' 46.3"} (current),
                 -44.6130d {-44d 36' 46.6"} (1950)
GRB_ERROR:       5.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.23e-09 [erg/cm2/sec]
GRB_SIGNIF:      7.68 [sigma]
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  853.02 SOD {00:14:13.02} UT,   91.7 [sec] since BAT Trigger Time
TAM[0-3]:        327.60 237.22 261.66 243.62
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       164.03d {+10h 56m 07s}   +6.80d {+06d 48' 03"}
SUN_DIST:        131.84 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.31d {+09h 25m 14s}  +20.14d {+20d 08' 09"}
MOON_DIST:       153.83 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.12,-36.85 [deg] galactic lon,lat of the burst
ECL_COORDS:      299.74,-24.95 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 0.84 arcmin from the BAT position.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:19:55 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.0459d {+20h 36m 11.0s} (J2000),
                 309.4152d {+20h 37m 39.6s} (current),
                 308.1914d {+20h 32m 45.9s} (1950)
GRB_DEC:         -44.4392d {-44d 26' 21.1"} (J2000),
                 -44.3629d {-44d 21' 46.3"} (current),
                 -44.6130d {-44d 36' 46.6"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       59 [cnts]
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  853.02 SOD {00:14:13.02} UT,   91.7 [sec] since BAT Trigger Time
CENTROID_X:      319.92,  raw= 320  [pixels]
CENTROID_Y:      272.59,  raw= 273  [pixels]
ROLL:            229.59 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -60.12
GRB_POS_XRT_Z:   29.53
IMAGE_URL:       sw01071993000msxps_rw.img
SUN_POSTN:       164.03d {+10h 56m 07s}   +6.80d {+06d 48' 03"}
SUN_DIST:        131.84 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.31d {+09h 25m 14s}  +20.14d {+20d 08' 07"}
MOON_DIST:       153.83 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.12,-36.85 [deg] galactic lon,lat of the burst
ECL_COORDS:      299.74,-24.95 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:19:58 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.0459d {+20h 36m 11.0s} (J2000),
                 309.4152d {+20h 37m 39.6s} (current),
                 308.1914d {+20h 32m 45.9s} (1950)
GRB_DEC:         -44.4392d {-44d 26' 21.1"} (J2000),
                 -44.3629d {-44d 21' 46.3"} (current),
                 -44.6130d {-44d 36' 46.6"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       59 [cnts]
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  853.02 SOD {00:14:13.02} UT,   91.7 [sec] since BAT Trigger Time
CENTROID_X:      319.92,  raw= 320  [pixels]
CENTROID_Y:      272.59,  raw= 273  [pixels]
ROLL:            229.59 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -60.12
GRB_POS_XRT_Z:   29.53
IMAGE_URL:       sw01071993000msxps_rw.img
SUN_POSTN:       164.03d {+10h 56m 07s}   +6.80d {+06d 48' 03"}
SUN_DIST:        131.84 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.31d {+09h 25m 15s}  +20.14d {+20d 08' 07"}
MOON_DIST:       153.83 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.12,-36.85 [deg] galactic lon,lat of the burst
ECL_COORDS:      299.74,-24.95 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:20:12 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.062d {+20h 36m 15s} (J2000),
                 309.431d {+20h 37m 43s} (current),
                 308.207d {+20h 32m 50s} (1950)
GRB_DEC:         -44.431d {-44d 25' 50"} (J2000),
                 -44.354d {-44d 21' 15"} (current),
                 -44.605d {-44d 36' 16"} (1950)
GRB_DATE:        19462 TJD;   248 DOY;   21/09/05
GRB_TIME:        761.32 SOD {00:12:41.32} UT
TRIGGER_INDEX:   263
GRB_PHI:          54.49 [deg]
GRB_THETA:        32.96 [deg]
DELTA_TIME:      -18.00 [sec]
TRIGGER_DUR:     2.048 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     14.17 [sigma]
IMAGE_SIGNIF:    9.35 [sigma]
LC_URL:          sw01071993000msb.lc
SUN_POSTN:       164.03d {+10h 56m 07s}   +6.80d {+06d 48' 02"}
SUN_DIST:        131.85 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.31d {+09h 25m 15s}  +20.13d {+20d 08' 05"}
MOON_DIST:       153.84 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.14,-36.86 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      299.75,-24.94 [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 = 12.68,-9.77 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:22:21 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1071993,   Seg_Num: 0
POINT_RA:        309.052d {+20h 36m 12s} (J2000)
POINT_DEC:       -44.459d {-44d 27' 33"} (J2000)
POINT_ROLL:      229.590d
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  918.29 SOD {00:15:18.29} UT,   157.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.295
N_STARS:         190
X_OFFSET:        0 [pixels]
Y_OFFSET:        0 [pixels]
X_MAX:           2047 [pixels]
Y_MAX:           2047 [pixels]
DET_THRESH:      5
PHOTO_THRESH:    2
SL_URL:          sw01071993000msufc0156.fits
SUN_POSTN:       164.03d {+10h 56m 08s}   +6.80d {+06d 48' 00"}
SUN_DIST:        131.83 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.33d {+09h 25m 20s}  +20.13d {+20d 07' 45"}
MOON_DIST:       153.80 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.10,-36.85 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      299.74,-24.97 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:22:34 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1071993,   Seg_Num: 0
POINT_RA:        309.052d {+20h 36m 12s} (J2000)
POINT_DEC:       -44.459d {-44d 27' 33"} (J2000)
POINT_ROLL:      229.590d
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  918.29 SOD {00:15:18.29} UT,   157.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.295
N_STARS:         190
X_OFFSET:        0 [pixels]
Y_OFFSET:        0 [pixels]
X_MAX:           2047 [pixels]
Y_MAX:           2047 [pixels]
DET_THRESH:      5
PHOTO_THRESH:    2
SL_URL:          sw01071993000msufc0156.fits
SUN_POSTN:       164.03d {+10h 56m 08s}   +6.80d {+06d 48' 00"}
SUN_DIST:        131.83 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.33d {+09h 25m 20s}  +20.13d {+20d 07' 43"}
MOON_DIST:       153.80 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.10,-36.85 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      299.74,-24.97 [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 05 Sep 21 00:25:32 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1071993,   Seg_Num: 0
POINT_RA:        309.052d {+20h 36m 12s} (J2000)
POINT_DEC:       -44.459d {-44d 27' 33"} (J2000)
ROLL:            229.590d
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  918.29 SOD {00:15:18.29} UT,   157.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     652493745
X_OFFSET:        797 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       957
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01071993000msuni0184.fits
SUN_POSTN:       164.03d {+10h 56m 08s}   +6.80d {+06d 47' 57"}
SUN_DIST:        131.83 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.36d {+09h 25m 27s}  +20.12d {+20d 07' 15"}
MOON_DIST:       153.79 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.10,-36.85 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      299.74,-24.97 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:25:40 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1071993,   Seg_Num: 0
POINT_RA:        309.052d {+20h 36m 12s} (J2000)
POINT_DEC:       -44.459d {-44d 27' 33"} (J2000)
ROLL:            229.590d
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  918.29 SOD {00:15:18.29} UT,   157.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     652493745
X_OFFSET:        797 [pixels]
Y_OFFSET:        1022 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       957
Y_GRB_POS:       1182
BINNING_INDEX:   1
IM_URL:          sw01071993000msuni0184.fits
SUN_POSTN:       164.03d {+10h 56m 08s}   +6.80d {+06d 47' 57"}
SUN_DIST:        131.83 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.36d {+09h 25m 27s}  +20.12d {+20d 07' 14"}
MOON_DIST:       153.79 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.10,-36.85 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      299.74,-24.97 [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 #30765
E. Sonbas (Adiyaman Univ.), E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), C. Gronwall (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (U Tampa), F. E. Marshall (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team:
At 00:12:41 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210905A (trigger=1071993). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 309.062, -44.431 which is
```
   RA(J2000) = 20h 36m 15s
   Dec(J2000) = -44d 25' 50"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of at least 30 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 00:14:13.0 UT, 91.7 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 309.04815, -44.43959 which is equivalent to:
```
   RA(J2000)  = 20h 36m 11.56s
   Dec(J2000) = -44d 26' 22.5"
```
with an uncertainty of 7.0 arcseconds (radius, 90% containment). This location is 47 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. No spectrum from the promptly downlinked event data is yet available to determine the column density.
The initial flux in the 2.5 s image was 1.23e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of 250 seconds with the U filter starting 156 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 19.2 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.034.
Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.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 #30766
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 210905A ( E. Sonbas et al., GCN 30765) errorbox 6 sec after notice time and 414 sec after trigger time at 2021-09-05 00:19:36 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 48 deg. The sun altitude is -55.5 deg.
The galactic latitude b = -37 deg., longitude l = 356 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1709881
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

     455 |         MASTER-SAAO | P\  |    80 | 18.2 |        
     565 |         MASTER-SAAO | P\  |   300 | 19.1 |  Coadd 
     556 |         MASTER-SAAO | P\  |   100 | 18.3 |        
     678 |         MASTER-SAAO | P\  |   120 | 18.5 |        
     826 |         MASTER-SAAO | P\  |   150 | 18.5 |        
```
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 05 Sep 21 00:33:45 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1071993,   Seg_Num: 0
GRB_RA:          309.0481d {+20h 36m 11.54s} (J2000),
                 309.4174d {+20h 37m 40.17s} (current),
                 308.1936d {+20h 32m 46.47s} (1950)
GRB_DEC:         -44.4395d {-44d 26' 22.2"} (J2000),
                 -44.3632d {-44d 21' 47.4"} (current),
                 -44.6133d {-44d 36' 47.7"} (1950)
GRB_ERROR:       7.0 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  19462 TJD;   248 DOY;   21/09/05
IMG_START_TIME:  1010.00 SOD {00:16:50.00} UT,   248.7 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       164.04d {+10h 56m 09s}   +6.80d {+06d 47' 50"}
SUN_DIST:        131.83 [deg]   Sun_angle= -9.7 [hr] (East of Sun)
MOON_POSTN:      141.44d {+09h 25m 45s}  +20.10d {+20d 05' 58"}
MOON_DIST:       153.76 [deg]
MOON_ILLUM:      5 [%]
GAL_COORDS:      356.12,-36.85 [deg] galactic lon,lat of the burst
ECL_COORDS:      299.74,-24.95 [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 #30768
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team.
Using 97 s of XRT Photon Counting mode data and 1 UVOT images for GRB 210905A, 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 = 309.04826, -44.43956 which is equivalent to:
```
RA (J2000): 20h 36m 11.58s
Dec (J2000): -44d 26' 22.4"
```
with an uncertainty of 2.6 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 #30769
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB 210905A (Sonbas, et al., GCN 30765) with the LCO 1-m Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on September 5, from 01:09 to 01:36 UT (corresponding to 0.95 to 1.40 hours from the GRB trigger time) with the Bessel R and I filters.
We performed a series of 3x300s exposures in R and I. In the XRT detection region (Sonbas, et al., GCN 30765) we detect an uncatalogued source in I band at the following coordinates (309.0481637, -44.4402618). Using the USNO-B.1 catalog as reference, we calculate the following magnitudes and upper limits:
R>22.44
I=19.52+/-0.09
These magnitudes are not corrected for galactic extinction. The detection in I and the lack of detection in R is suggestive of a high-z source. As such additional follow-up is encouraged. Additional LCO measurements are underway.
R.S. is funded by NSF AST grant #1831682
GCN Circular #30770
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB 210905A (Sonbas, et al., GCN 30765) with the LCO 1-m Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on September 5, from 02:32 to 02:53 UT (corresponding to 2.37 to 2.72 hours from the GRB trigger time) with the Bessel I filter.
We performed a series of 5x300s exposures in I band. We detect the same uncataloged source (Strausbaugh, et al., GCN 30769) at the following coordinates (309.0481637, -44.4402618). Using the USNO-B.1 catalog as reference, we calculate the following magnitude:
I=20.4+/-0.1
These magnitudes are not corrected for galactic extinction. There is clear evidence of fading from the first epoch (I=19.52+/-0.09) providing strong evidence that this is the afterglow of this burst.
R.S. is funded by NSF AST grant #1831682
GCN Circular #30771
N. Tanvir (Univ. Leicester), A. Rossi (INAF-OAS), D. Xu (NAOC), Z.P. Zhu (NAOC,HUST), L. Izzo (DARK/NBI), D. A. Kann (HETH/IAA-CSIC), and A.J. Levan (Radboud) report on behalf of the Stargate collaboration:
We observed the location of the afterglow (Strausbaugh & Cucchiara, GCN 30769, 30770) of GRB 210905A (Sonbas et al., GCN 30765) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures by 1200 s each. Our observations started on 2021 September 05 at 02:44 UT, ~2.53 hours after the GRB detection.
In the acquisition image obtained between 2.53 and 2.73 hours after the burst, the afterglow is well detected at I and z-bands, but not in the r-band, confirming the red color already noted by Strausbaugh & Cucchiara. We measure the following AB magnitudes:
```
r>23.5
I=20.3+-0.1
z=19.4+-0.1
```
Spectroscopy of the source reveals a continuum well detected in the red part of visible arm. A clear break is detected around 9000AA which we interpret as the Lyman-alpha break at z = 6.318, and explains the strong r-z color as due to Lyman dropout. Other lines such as Fe II, Al II, C IV and Si II are visible and display a double absorption profile, which is possibly due to different intervening systems at z1 = 6.312 and z2 = 6.318. We thus conclude that z=6.318 is the redshift of GRB 210905A. Further analysis is undergoing.
We acknowledge support from the ESO observing staff at Paranal, in particular Israel Blanchard, Michael Abdul-Masih, and Matias Jones.
GCN Circular #30772
P. D'Avanzo, A. Melandri, S. Covino, D. Fugazza (INAF-OAB), on behalf of the REM team, report:
We observed the field of GRB 210905A (Sonbas, et al., GCN 30765) with the REM 60cm robotic telescope located at the ESO premise of La Silla (Chile). The observations were carried in the g, r, i, z, J, H and K bands, starting on 2021 September 05 at 00:19:49 UT (i.e. 428 seconds after the burst) and lasting for about three hours.
At the position of the optical afterglow (Strausbaugh & Cucchiara, GCN Circ. 30769) we detected an uncatalogued source in all NIR bands. From preliminary photometry we derive the following magnitude:
H = 14.82 +/- 0.15 (Vega; calibrated against the 2MASS catalogue)
at a mid time of t-t0 = 469 seconds.
GCN Circular #30773
J. Cooke (Swinburne), S. Webb (Swinburne), D. Dobie (Swinburne), J. Zhang (Swinburne), S. Hegarty (Swinburne), A. Moller (Swinburne), S. Goode (Swinburne), R. Strausbaugh (U. of the Virgin Islands), Tim Abbott (NOIRLab), Vivek Gupta (Swinburne), Mark Suhr (Swinburne)
We observed Swift GRB 210905A (Sonbas, et al., GCN 30765) with the Dark Energy Camera (DECam) at Cerro Tololo Inter-American Observatory. We performed 3x60s exposures with the i filter on September 5, from 04:46:10 to 04:50:09 UT.
We make a marginal detection of a source at the position reported by Strausbaugh et al. (GCN 30769) with i=23.6. This measurement is not corrected for galactic extinction.
GCN Circular #30776
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), P.A. Evans (U. Leicester) and E. Sonbas report on behalf of the Swift-XRT team:
We have analysed 5.7 ks of XRT data for GRB 210905A (Sonbas et al. GCN Circ. 30765), from 82 s to 84.8 ks after the BAT trigger. The data comprise 209 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 30768).
The late-time light curve (from T0+3.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.19 (+0.26, -0.27).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.44 (+0.05, -0.04). The best-fitting absorption column is 3.8 (+1.8, -1.7) x 10^22 cm^-2, at a redshift of 6.318, in addition to the Galactic value of 3.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.90 (+/-0.13) and a best-fitting absorption column of 2.9 (+3.7, -2.9) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Galactic foreground: 3.4 x 10^20 cm^-2
Intrinsic column:    2.9 (+3.7, -2.9) x 10^22 cm^-2 at z=6.318
Photon index:	     1.90 (+/-0.13)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01071993.
This circular is an official product of the Swift-XRT team.
GCN Circular #30779
P. Veres (UAH) and O. J. Roberts (USRA) report on behalf of the Fermi-GBM Team:
"Swift-BAT detected GRB 210905A at 00:12:41 UT (GCN 30765). 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 8.192 s with a false alarm rate of 1.3e-5 Hz, and a location consistent with the Swift-BAT event, using the standard search protocol with a S/N of 13. The GBM targeted search event was found with the highest significance with a "normal" spectral template (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3).
The GBM light curve consists of multiple overlapping pulses. The time-averaged spectrum from T0-26 s to T0+16 s is best fit by a power law function with an exponential high-energy cutoff (T0 is 2021-09-05 00:12:41 UT). The power law index is -1.19 +/- 0.13 and the cutoff energy, parameterized as Epeak, is 204 +/- 45 keV.
The event fluence (10-1000 keV) in this time interval for the best fitting model is (6.08 +/- 0.59)E-6 erg/cm^2. Using the redshift z=6.318 reported by Tanvir et al. (GCN 30771), we derive an isotropic equivalent energy in the 1-10,000 keV range of (4.25 +/- 0.41)E+53 erg.
This analysis is preliminary.
[1] Goldstein et al. 2019 arXiv:1903.12597 "
GCN Circular #30780
D. Frederiks, S. Golenetskii, A.Lysenko, D. Svinkin, A. Ridnaya, A. Tsvetkova, M. Ulanov, and T. Cline, report:
The long GRB GRB 210905A (Swift-BAT detection: Sonbas et al., GCN 30765; Fermi GBM Sub-Threshold Detection: Veres & Roberts, GCN 30779), T0 (BAT) = 00:12:41, was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in reveals two major emission episodes, separated by ~750 s. The first episode, from ~T0-25.5s to ~t0+13 s, corresponds to the BAT and GBM detections; and the second episode, from ~T0-750 s to ~t0+870 s, corresponds to a bright flare visible in the XRT light curve (https://www.swift.ac.uk/xrt_curves/01071993/ ).
The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB210905A/
Modeling the KW 3-channel spectrum of the first episode by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.45 (-0.24, + 0.38) and Ep = 203 (-58,+111) keV. The spectrum of the second episode can be described by a CPL with alpha = -0.88 (-0.30, + 0.76) and Ep = 167 (-61,+88) keV.
In the 10 keV -10 MeV band, standard for the KW analysis, the total burst fluence is (1.7 � 0.7)x10^-5 erg/cm^2, and the 2.944 s peak energy flux is (3.6 � 0.7)x10^-7 erg/cm^2.
Assuming the redshift z=6.318 (Tanvir et al., GCN 30771) 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 isotropic energy release E_iso to ~1.1x10^54 erg, the isotropic luminosity L_iso to ~1.7x10^53 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z to ~1300 keV. With these values, GRB 210905A lies within 68% prediction bands for for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2021, ApJ, 908, 83), see http://www.ioffe.ru/LEA/GRBs/GRB210905A/GRB210905A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
GCN Circular #30781
A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg), and A. Rau (MPE Garching) report:
We observed the field of GRB 210905A (Swift trigger #1071993; Sonbas et al., GCN 30765) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m MPG telescope at La Silla Observatory (Chile).
Observations started at 23:35 UT on September 5, about 23.2 hr after the GRB trigger. They were performed at an average seeing of 1.7 arcsec and at an average airmass of 1.2.
Based on combined images with 22 min total exposure in g'r'i'z' and 25 min in JHK, at a mid-time of 23:55 UT on 2021-09-05 for the afterglow (Strausbaugh & Cucchiara GCN 30769 and 30770; Tanvir et al., GCN 30771; D'Avanzo et al., GCN 30772; Dobie et al., GCN 30773) we derive the following preliminary AB magnitudes and 3-sigma upper limits:
```
g' > 24.3,
r' > 24.3,
i' > 23.8,
z' = 21.6 +/- 0.2,
J  = 20.2 +/- 0.2,
H  = 20.1 +/- 0.2,
K  > 18.2.
```
Given magnitudes are calibrated against the SkyMapper catalog (Wolf et al., 2018, PASA 35, e010) in g'r'i'z' and 2MASS field stars in JHK (Skrutskie et al., 2006, AJ 131, 1163).
We thank Maren Hempel and Regis Lachaume for excellent support and for performing the observations.
GCN Circular #30782
V. Prasad (IUCAA), P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed detection of a long GRB 210905A, which was also detected by Swift-BAT (Sonbas et al., GCN 30765) and a sub-threshold detection in Fermi-GBM (Veres & Roberts, GCN 30779).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-09-05 00:12:40.5 UT. The measured peak count rate associated with the burst is 87 (+37.9, -7) cts/s above the background in the combined data of two quadrants (out of four), with a total of 1092 (+250, -294) cts. The local mean background count rate was 286.0 (+2, -2) cts/s. Using cumulative rates, we measure a T90 of 24 (+11, -7) s.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb [1]. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
```
Links:
------
[1] http://astrosat.iucaa.in/czti/?q=grb
```
GCN Circular #30783
T. Laskar (University of Bath), K. D. Alexander (Northwestern), R. Margutti (Berkeley), E. Berger (Harvard), W. Fong (Northwestern), R. Chornock (Berkeley), C. G. Mundell (University of Bath), and P. Schady (University of Bath) report on behalf of a larger collaboration:
"We observed GRB 210905A (Sonbas et al. GCN 30765) with the Atacama Large Millimeter/Submillimeter Array (ALMA) at 97.5 GHz beginning on 2021 September 05 23:41 UT (0.98 days after the burst).
Preliminary analysis reveals a mm source with flux density of ~ 0.1 mJy at position:
```
RA (J2000) = 20:36:11.5685 (+/- 0.0002)
Dec (J2000) = -44:26:24.840 (+/- 0.002)
```
consistent with the X-ray position (Beardmore et al., GCN 30768) and optical position (Strausbaugh & Cucchiara, GCN 30769).
We thank the JAO staff, AoD, P2G, and the entire ALMA team for their help with these observations."
GCN Circular #30784
T. Laskar (University of Bath), S. Bhandari (CSIRO), R. Margutti (UC Berkeley), K. D. Alexander (Northwestern), E. Berger (Harvard), R. Chornock (UC Berkeley), D. Coppejans (Northwestern), M. Drout (U. Toronto), H. van Eerten (University of Bath), W. Fong (Northwestern), C. Guidorzi (U. Ferrara), C. G. Mundell (University of Bath), P. Schady (University of Bath), and G. Schroeder (Northwestern) report:
"We observed GRB 210905A (Sonbas et al., GCN 30765) with the Australia Telescope Compact Array (ATCA) at multiple frequencies beginning on 2021 Sep 08 14:20 UT. We detect a radio counterpart at 5.5 and 9.0 GHz at a position consistent with the X-ray position (Beardmore et al., GCN 30768), optical position (Strausbaugh & Cucchiara, GCN 30769), and mm-band position (Laskar et al., GCN 30783) with a flux density of ~ 0.1 mJy at 9.0 GHz at a mid-time of 3.65 days after the burst.
We thank the CSIRO staff for approving and scheduling these observations.
The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site."
GCN Circular #30785
M. H. Siegel (PSU) and E. Sonbas (Adiyaman Univ.) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210905A 157 s after the BAT trigger (Sonbas et al., GCN Circ. 30765). No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 30768) 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

u_FC               157          407          246         >20.1
v                 4193         4393          197         >19.3
b                 3782         3982          197         >21.4
w1                4603         4803          197         >20.1
m2                4398         4597          197         >19.5
w2                3988         4188          197         >19.4
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.034 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #31127
T. Laskar (Radboud University), R. Margutti (UC Berkeley), K. D. Alexander (Northwestern), E. Berger (Harvard), and R. Chornock (UC Berkeley) report:
"We observed GRB 210905A (Sonbas et al., GCN 30765) with Chandra/ACIS, starting on 2021 November 24 at 13:08:25 UT (80.7 days after the GRB trigger), for a total exposure of 20 ks. We detect a point source at the position of the Swift/XRT afterglow with a 0.5-8 keV (observed) count rate of ~ 3.1e-4 counts/s. Using spectral parameters from fitting the Swift/XRT PC-mode spectrum at a redshift of z=6.318 (Tanvir et al., GCN 30771), we find a preliminary unabsorbed flux of ~ 5.4e-15 erg/(s cm^2) in the 0.3-10 keV band (observer frame).
This measurement confirms a potential break in the Swift/XRT observations at ~ 30 days after the trigger. The post-break decline rate is consistent with -2. Interpreting this break as a jet break, assuming EKiso ~ Egamma,iso, and using the isotropic-equivalent gamma-ray energy from Konus-Wind (Frederiks et al., GCN 30780), the inferred opening angle is ~ 9 deg * (E/1.1e54 erg) / (n/ (1particle/cm^3))] ^(-3/8) for a uniform density environment, leading to a beaming-corrected energy of ~ 1.3e52 erg. Further analysis is underway.
We thank Harvey Tananbaum and Pat Slane for approving our DDT request and the entire CXC staff for arranging and executing the observations."

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