//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30716 SUBJECT: GRB 210826A: Fermi GBM Final Real-time Localization DATE: 21/08/26 07:12:03 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30717 SUBJECT: GRB 210826A: BALROG localization (Fermi Trigger 651654110 / GRB 210826293) DATE: 21/08/26 07:41:33 GMT FROM: Jochen Greiner at MPE,Garching 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30719 SUBJECT: GRB 210826A: Tiled Swift observations DATE: 21/08/26 17:11:02 GMT FROM: Phil Evans at U of Leicester 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30720 SUBJECT: Fermi GRB 210826A: Global MASTER-Net observations report DATE: 21/08/26 17:30:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30721 SUBJECT: GRB 210826A: Fermi-LAT detection DATE: 21/08/26 19:15:46 GMT FROM: Masanori Ohno at Hiroshima U 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30725 SUBJECT: GRB 210826A: Swift-XRT observations DATE: 21/08/27 10:16:23 GMT FROM: Paolo D'Avanzo at INAF - OAB 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30729 SUBJECT: GRB 210826A: Swift/UVOT Upper Limits DATE: 21/08/27 15:38:05 GMT FROM: Alice Breeveld at MSSL-UCL 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). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30737 SUBJECT: GRB 210826A: AstroSat CZTI detection DATE: 21/08/28 14:30:28 GMT FROM: Gaurav Waratkar at IIT,Bombay 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30799 SUBJECT: GRB 210826A: further Swift-XRT observations DATE: 21/09/10 15:32:21 GMT FROM: Paolo D'Avanzo at INAF-OAB 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.