Gamma-ray Burst 210826A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:02:18 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     651654110
GRB_RA:           83.750d {+05h 35m 00s} (J2000),
                  83.584d {+05h 34m 20s} (current),
                  84.137d {+05h 36m 33s} (1950)
GRB_DEC:         -74.900d {-74d 54' 00"} (J2000),
                 -74.887d {-74d 53' 11"} (current),
                 -74.929d {-74d 55' 45"} (1950)
GRB_ERROR:       5.87 [deg radius, statistical plus systematic]
GRB_INTEN:       334 [cnts/sec]
DATA_SIGNIF:     27.80 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         130.00 [deg]
GRB_THETA:        45.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.80
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   2%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 1,1,0, 0,0,
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 09"}
SUN_DIST:         95.27 [deg]   Sun_angle= 4.8 [hr] (West of Sun)
MOON_POSTN:       18.97d {+01h 15m 53s}   +4.10d {+04d 05' 58"}
MOON_DIST:        87.56 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      286.23,-31.07 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      280.96,-81.42 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 129.75,-5.38 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:02:09 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     651654110
GRB_RA:           84.400d {+05h 37m 36s} (J2000),
                  84.238d {+05h 36m 57s} (current),
                  84.776d {+05h 39m 06s} (1950)
GRB_DEC:         -74.733d {-74d 43' 59"} (J2000),
                 -74.721d {-74d 43' 16"} (current),
                 -74.760d {-74d 45' 33"} (1950)
GRB_ERROR:       12.87 [deg radius, statistical plus systematic]
GRB_INTEN:       131 [cnts/sec]
DATA_SIGNIF:     7.90 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         130.00 [deg]
GRB_THETA:        45.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.97
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      98%  GRB
2nd_MOST_LIKELY:   1%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 1,1,0, 0,0,
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 09"}
SUN_DIST:         95.05 [deg]   Sun_angle= 4.7 [hr] (West of Sun)
MOON_POSTN:       18.97d {+01h 15m 53s}   +4.10d {+04d 05' 56"}
MOON_DIST:        87.65 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      286.00,-30.94 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      280.16,-81.63 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 129.75,-5.38 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:02:26 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     651654110
GRB_RA:           57.900d {+03h 51m 36s} (J2000),
                  57.776d {+03h 51m 06s} (current),
                  58.197d {+03h 52m 47s} (1950)
GRB_DEC:         -75.780d {-75d 46' 47"} (J2000),
                 -75.716d {-75d 42' 56"} (current),
                 -75.927d {-75d 55' 37"} (1950)
GRB_ERROR:       4.17 [deg radius, statistical only]
DATA_SIGNIF:     21.70 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         136.00 [deg]
GRB_THETA:        50.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 09"}
SUN_DIST:        101.81 [deg]   Sun_angle= 6.5 [hr] (West of Sun)
MOON_POSTN:       18.97d {+01h 15m 54s}   +4.10d {+04d 05' 60"}
MOON_DIST:        82.96 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      290.42,-36.62 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      303.84,-76.44 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_651654110.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:03:00 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     651654110
GRB_RA:           68.660d {+04h 34m 38s} (J2000),
                  68.428d {+04h 33m 43s} (current),
                  69.207d {+04h 36m 50s} (1950)
GRB_DEC:         -77.610d {-77d 36' 35"} (J2000),
                 -77.566d {-77d 33' 56"} (current),
                 -77.710d {-77d 42' 35"} (1950)
GRB_ERROR:       3.53 [deg radius, statistical only]
DATA_SIGNIF:     16.30 [sigma]
DATA_INTERVAL:   7.168 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         136.00 [deg]
GRB_THETA:        47.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 08"}
SUN_DIST:         99.37 [deg]   Sun_angle= 5.8 [hr] (West of Sun)
MOON_POSTN:       18.98d {+01h 15m 55s}   +4.10d {+04d 06' 07"}
MOON_DIST:        86.00 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      290.64,-33.55 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      290.84,-77.32 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_651654110.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9362).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:03:17 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      2
TRIGGER_NUM:     651654110
GRB_RA:           64.630d {+04h 18m 31s} (J2000),
                  64.434d {+04h 17m 44s} (current),
                  65.092d {+04h 20m 22s} (1950)
GRB_DEC:         -77.070d {-77d 04' 11"} (J2000),
                 -77.018d {-77d 01' 04"} (current),
                 -77.188d {-77d 11' 17"} (1950)
GRB_ERROR:       1.79 [deg radius, statistical only]
DATA_SIGNIF:     33.40 [sigma]
DATA_INTERVAL:   11.264 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         136.00 [deg]
GRB_THETA:        48.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 08"}
SUN_DIST:        100.21 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:       18.98d {+01h 15m 55s}   +4.10d {+04d 06' 11"}
MOON_DIST:        84.98 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      290.60,-34.59 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      295.37,-77.07 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_651654110.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9362).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:05:01 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      3
TRIGGER_NUM:     651654110
GRB_RA:           66.150d {+04h 24m 36s} (J2000),
                  65.898d {+04h 23m 36s} (current),
                  66.745d {+04h 26m 59s} (1950)
GRB_DEC:         -78.270d {-78d 16' 11"} (J2000),
                 -78.221d {-78d 13' 15"} (current),
                 -78.381d {-78d 22' 52"} (1950)
GRB_ERROR:       1.68 [deg radius, statistical only]
DATA_SIGNIF:     43.90 [sigma]
DATA_INTERVAL:   14.336 [sec]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         137.00 [deg]
GRB_THETA:        47.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       155.21d {+10h 20m 50s}  +10.30d {+10d 18' 06"}
SUN_DIST:         99.94 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:       18.99d {+01h 15m 58s}   +4.11d {+04d 06' 35"}
MOON_DIST:        86.05 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      291.64,-33.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      290.58,-76.48 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_651654110.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9362).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 07:11:06 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     651654110
GRB_RA:           64.630d {+04h 18m 31s} (J2000),
                  64.434d {+04h 17m 44s} (current),
                  65.092d {+04h 20m 22s} (1950)
GRB_DEC:         -77.070d {-77d 04' 11"} (J2000),
                 -77.018d {-77d 01' 04"} (current),
                 -77.188d {-77d 11' 17"} (1950)
GRB_ERROR:       2.12 [deg radius, statistical only]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.16 SOD {07:01:45.16} UT
GRB_PHI:         136.00 [deg]
GRB_THETA:        48.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:       155.21d {+10h 20m 51s}  +10.30d {+10d 18' 01"}
SUN_DIST:        100.21 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:       19.04d {+01h 16m 10s}   +4.13d {+04d 07' 56"}
MOON_DIST:        85.00 [deg]
MOON_ILLUM:      85 [%]
GAL_COORDS:      290.60,-34.59 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      295.37,-77.07 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_locplot_all_bn210826293.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice was generated completely by automated pipeline processing.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9362).

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Thu 26 Aug 21 07:02:49 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    9362,   Sub_Num: 0
GRB_INTEN:      9.29 [sigma]
GRB_TIME:       25305.39 SOD {07:01:45.39} UT
GRB_DATE:       19452 TJD;   238 DOY;   21/08/26
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.  
COMMENTS:       Time_Scale=2.0000 and Time_Error=1.0000.  
COMMENTS:          
COMMENTS:       NOTE: This SPIACS event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=651654110).  
COMMENTS:
COMMENTS:       The SPIACS lightcurve can be found at:  
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2021-08/2021-08-26T07-01-45.1951-08463-56208-0.lc

GCN Circular #30716
The Fermi GBM team reports the detection of a likely LONG GRB
At 07:01:45 UT on 26 Aug 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210826A (trigger 651654110.161386 / 210826293).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 64.6, Dec = -77.1 (J2000 degrees, equivalent to J2000 04h 18m, -77d 05'), with a statistical uncertainty of 2.1 degrees.
The angle from the Fermi LAT boresight is 48.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_skymap_all_bn210826293.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_healpix_all_bn210826293.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210826293/quicklook/glg_lc_medres34_bn210826293.gif
GCN Circular #30717
B. Biltzinger, F. Kunzweiler, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 651654110 at 07:01:45 on 26 Aug. 2021 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60).
The best-fit position (1 sigma statistical errors) is:
```
RA(2000.0) = 84.3+/-5.4 deg
Decl.(2000.0) = -75.6+/-0.7 deg
```
We estimate an additional systematic error of 2 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB210826293/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB210826293/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB210826293/json

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 26 Aug 21 14:57:13 UT
NOTICE_TYPE:     Fermi-LAT Offline Position
TRIGGER_NUM:     651654110
GRB_RA:           45.300d {+03h 01m 12s} (J2000),
                  45.319d {+03h 01m 17s} (current),
                  45.261d {+03h 01m 03s} (1950)
GRB_DEC:         -71.700d {-71d 42' 00"} (J2000),
                 -71.615d {-71d 36' 54"} (current),
                 -71.896d {-71d 53' 44"} (1950)
GRB_ERROR:       12.00 [arcmin radius, 90% containment, statistical only]
GRB_DATE:        19452 TJD;   238 DOY;   21/08/26
GRB_TIME:        25305.15 SOD {07:01:45.15} UT
TRIGGER_ID:      0x20000000
MISC:            0x40000000
SUN_POSTN:       155.51d {+10h 22m 02s}  +10.19d {+10d 11' 14"}
SUN_DIST:        105.96 [deg]   Sun_angle= 7.3 [hr] (West of Sun)
MOON_POSTN:       22.68d {+01h 30m 44s}   +5.85d {+05d 51' 15"}
MOON_DIST:        78.88 [deg]
MOON_ILLUM:      83 [%]
GAL_COORDS:      289.84,-41.97 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      321.95,-73.71 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi LAT Offline position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        It is the result of human-in-the-loop processing.  
COMMENTS:        This is a human generated position of a LAT ground detection.  
COMMENTS:        This source corresponds to GBM trigger.

GCN Circular #30719
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the Fermi/LAT GRB 210826A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00101
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #30720
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) started inspect of the Fermi GRB 210826A ( Fermi GBM team, GCN 30716) errorbox 36801 sec after notice time and 36879 sec after trigger time at 2021-08-26 17:16:24 UT, with upper limit up to 17.8 mag. Observations started at twilight. The observations began at zenith distance = 71 deg. The sun altitude is -13.0 deg.
The galactic latitude b = -35 deg., longitude l = 291 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1700544
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   36909 | 2021-08-26 17:16:24 |         MASTER-SAAO | (05h 11m 37.00s , -76d 38m 26.5s) |   C |    60 | 17.8 |
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #30721
M. Ohno (Eotvos U./Hiroshima U.), M. Axelsson (KTH & Stockholm Univ.), F. Longo (University and INFN, Trieste), N. Omodei (Stanford Univ.) and F Dirirsa (LAPP, Annecy) report on behalf of the Fermi-LAT Collaboration:
On August 26th, 2021, Fermi-LAT detected high-energy emission from GRB 210826A, which was also detected by Fermi GBM (trigger 651654110.161386 / 210826293; GCN 30716).
The best LAT on-ground location is found to be
RA, Dec 45.3, -71.7 (degrees, J2000)
with an error radius of 0.2 deg (90% containment, statistical error only). This was 55 deg from the LAT boresight at the time of the GBM trigger:
T0 = 07:01:45 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the trigger that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-4000 s after the trigger is 9.3 (-/+ 3.8) e-07 ph/cm2/s.
The estimated photon index above 100 MeV is -1.9 (-/+ 0.3).
The highest-energy photon is a 7.7 GeV event which is observed ~2.6 ks after the trigger.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Feraol Fana Dirirsa (dirirsa@lapp.in2p3.fr).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

GCN Circular #30725
A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 210826A (Ohno et al. GCN Circ. 30721), for a total exposure time of 4.9 ks. The data were collected between T0+36.5 ks and T0+49.7 ks, and are entirely in Photon Counting (PC) mode.
Eight uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. We notice that one of the sources (Source 8) is consistent with a catalogued galaxy at redshift z = 0.05. Details of these sources are given below:
Source 1:

  RA (J2000.0):  45.3361  =  03:01:20.66
  Dec (J2000.0): -71.7072  =  -71:42:25.8
  Error: 8.7 arcsec (radius, 90% conf.)
  Count-rate: (1.46 [+0.80, -0.61])e-3 ct s^-1	 
  Distance: 48 arcsec from Fermi/LAT position.

Source 2:

  RA (J2000.0):  45.0955  =  03:00:22.93
  Dec (J2000.0): -71.6531  =  -71:39:11.1
  Error: 5.0 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: (3.06 [+1.16, -0.94])e-3 ct s^-1	 
  Distance: 286 arcsec from Fermi/LAT position.
  Flux: (8.2 [+3.1, -2.5])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:

  RA (J2000.0):  45.1820  =  03:00:43.67
  Dec (J2000.0): -71.5711  =  -71:34:15.8
  Error: 9.7 arcsec (radius, 90% conf.)
  Count-rate: (1.36 [+0.80, -0.59])e-3 ct s^-1	 
  Distance: 483 arcsec from Fermi/LAT position.
  Flux: (8.2 [+4.8, -3.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

This source is 10" away from the AGN candidate WISEA J030045.23-713422.8 (Assef et al., 2018, ApJS, 234, 23)
Source 5:

  RA (J2000.0):  45.4777  =  03:01:54.65
  Dec (J2000.0): -71.6539  =  -71:39:13.9
  Error: 8.4 arcsec (radius, 90% conf.)
  Count-rate: (3.7 [+1.3, -1.0])e-3 ct s^-1   
  Distance: 260 arcsec from Fermi/LAT position.
  Flux: (5.8 [+2.0, -1.6])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 6:

  RA (J2000.0):  45.1850  =  03:00:44.41
  Dec (J2000.0): -71.7836  =  -71:47:00.9
  Error: 10.0 arcsec (radius, 90% conf.)
  Count-rate: (1.60 [+0.86, -0.65])e-3 ct s^-1	 
  Distance: 327 arcsec from Fermi/LAT position.
  Flux: (4.2 [+2.2, -1.7])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 7:

  RA (J2000.0):  45.3683  =  03:01:28.39
  Dec (J2000.0): -71.6617  =  -71:39:42.1
  Error: 10.3 arcsec (radius, 90% conf.)
  Count-rate: (1.54 [+0.84, -0.63])e-3 ct s^-1	 
  Distance: 158 arcsec from Fermi/LAT position.
This source is 6" away from  the AGN candidate WISEA
J030129.33-713938.6 (Assef et al., 2018, ApJS, 234, 23)

Source 8:

  RA (J2000.0):  44.7903  =  02:59:9.68
  Dec (J2000.0): -71.6112  =  -71:36:40.2
  Error: 9.3 arcsec (radius, 90% conf.)
  Count-rate: (1.11 [+0.78, -0.56])e-3 ct s^-1	 
  Distance: 660 arcsec from Fermi/LAT position.
This source is 9" away from the catalogued galaxy 2MASX
J02591150-7136430 at redshift z = 0.05

Source 9:

  RA (J2000.0):  45.6834  =  03:02:44.02
  Dec (J2000.0): -71.6574  =  -71:39:26.7
  Error: 8.8 arcsec (radius, 90% conf.)
  Count-rate: (2.16 [+1.02, -0.79])e-3 ct s^-1	 
  Distance: 460 arcsec from Fermi/LAT position.
  Flux: (8.1 [+3.8, -3.0])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00101.
This circular is an official product of the Swift-XRT team.

GCN Circular #30729
A. A. Breeveld (UCL-MSSL) and T. Sbarrato (INAF-IASFPA) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210826A 36747 s after the LAT trigger (Ohno et al., GCN Circ. 30721). No new optical source consistent with the any of the 8 candidate XRT positions (D'Ai et al., GCN Circ. 30725) 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 initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

v                36747        49716         4869         >20.9
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.032 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #30737
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, 2020, arxiv:2011.07067) showed detection of a long GRB 210826A, which was also detected by Fermi-GBM (trigger no. 210826293, GCN 30716) and Fermi-LAT (Ohno et al., GCN 30721).
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 2021-08-26 07:01:53.50 UT. The measured peak count rate associated with the burst is 183 (+45, -24) cts/s above the background in the combined data of four quadrants, with a total of 2161 (+327, -549) cts. The local mean background count rate was 560 (+4, -2) cts/s. Using cumulative rates, we measure a T90 of 24 (+17, -10) s.
It was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-08-26 07:01:47.03 UT. The measured peak count rate is 200 (+95, -5) cts/s above the background in the combined Veto data of four quadrants, with a total of 1953 (+648, -720) cts. The local mean background count rate was 1907 (+6, -6) cts/s. We measure a T90 of 14 (+8, -5) s from the cumulative Veto light curve.
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 #30799
P. D'Avanzo, M. G. Bernardini, A. Melandri, T. Sbarrato (INAF-OAB), P. A. Evans (U. Leicester) report on behalf of the Swift team:
Swift-XRT has performed further follow-up observations of GRB 210826A (Ohno et al. GCN Circ. 30721), collecting a total of 14.6 ks of Photon Counting (PC) mode data between T0+36.5 ks ks and T0+1.26e6 s.
Of the 8 X-ray uncatalogued sources detected in the first observing epoch (D'Ai et al., GCN Circ. 30725), Source 1 and Source 5 are still detected with a consistent count-rate. The other sources are not detected down to a typical 3sigma upper limit of ~ 3e-3 ct/s. Therefore, we found no clear evidence for an X-ray afterglow candidate of GRB 210826A.
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00101.
This circular is an official product of the Swift-XRT team.

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Jochen Greiner, last update: 10-Sep-2021 [Disclaimer]