//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29390 SUBJECT: GRB 210204A: Fermi GBM Final Real-time Localization DATE: 21/02/04 06:39:48 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 06:29:25 UT on 4 Feb 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210204A (trigger 634112970.655966 / 210204270). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 109.1, Dec = 9.7 (J2000 degrees, equivalent to J2000 07h 16m, 9d 41'), with a statistical uncertainty of 4.0 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210204270/quicklook/glg_skymap_all_bn210204270.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/bn210204270/quicklook/glg_healpix_all_bn210204270.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210204270/quicklook/glg_lc_medres34_bn210204270.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29391 SUBJECT: GRB 210204A: BALROG localization (Fermi Trigger 634112970 / GRB 210204270) DATE: 21/02/04 06:59:58 GMT FROM: Jochen Greiner at MPE,Garching F. Kunzweiler, B. Biltzinger, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 634112970 at 06:29:25 on 04 Feb. 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) = 118.6+/-3.1 deg Decl.(2000.0) = 12.0+/-3.1 deg We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB210204270/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB210204270/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB210204270/json //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29392 SUBJECT: GRB 210204A: GECAM detection DATE: 21/02/04 07:51:58 GMT FROM: Shaolin Xiong at IHEP C. Y. Li, S. L. Xiong, S. Xiao, C. Cai, Y. Huang, Y. Zhao, J. C. Liu, J. J. He, Q. B. Yi, B. X. Zhang, Y. Q. Zhang, S. Y. Zhao, C. Zheng, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, B. Li, C. Li, J. H. Li, Q. X. Li, X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu, X. J. Liu, Y. Q. Liu, F. J. Lu, Q. Luo, X. Ma, G. Ou, W. X. Peng, R. Qiao, D. L. Shi, J. Y. Shi, L. M. Song, X. Y. Song, G. X. Sun, X. L. Sun, Y. L. Tuo, C. W. Wang, J. Z. Wang, P. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, W. C. Xue, S. Yang, M. Yao, C. Y. Zhang,D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Z. Zhang, X. Y. Zhao, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team: During the commissioning phase, GECAM-B in-flight triggered (Trig# 66119400) a long burst, GRB 210204A, at 2021-02-04T06:30:00.600 UTC (T0), which was also reported by Fermi/GBM (GCN 29390) and CALET/CGBM (Trig# 1296455384). GECAM alert data was promptly downlinked to the ground through the short message service of BeiDou Navigation Satellite System (BDS). The time latency of the first BeiDou message relative to the trigger time is about 1 minute. According to the BDS alert data, this burst mainly consists of multiple pulses, while the later bright pulse is evident in the alert data although it falls in the last wide time bin. The burst spectrum extends above about 400 keV. An automatic on-ground localization was calculated using the light curves and spectrum in the alert data. Although the in-flight calibration of energy response and localization has not been finalized yet, GECAM-B localized this burst to the following position (J2000): Ra: 121.7 deg  Dec: 1.5 deg Err: 7.5 deg (1-sigma, statistical only) The current systematic error of location is estimated to be several degrees which could be minimized by the ongoing calibration. The GECAM-B location is consistent with the Fermi/GBM position (GCN 29390, 29391) within error. The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_66119400.png The GECAM preliminary on-ground location could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_skymap_bdm_66119400_V01.png As the detailed science data are downloaded, all analyses would be improved. Please note that all GECAM results here are preliminary. The final analysis will be published in journal papers or GECAM online catalog. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time), which was funded by the Chinese Academy of Sciences (CAS). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29393 SUBJECT: GRB 210204: Fermi GBM observation DATE: 21/02/04 16:16:59 GMT FROM: Elisabetta Bissaldi at INFN,Bari E. Bissaldi (Politecnico and INFN Bari) reports on behalf of the Fermi GBM Team: "At 06:29:25.66 UT on 4 February 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210204A (trigger 634112970 / 210204270). The Fermi GBM Final Real-time Localization was reported in GCN 29390. The angle from the Fermi LAT boresight at the GBM trigger time is 57 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 210 s (50-300 keV). The time-averaged spectrum encompassing the first two emission episodes from T0-8 s to T0+45 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.51 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 162 +/- 33 keV. The event fluence (10-1000 keV) in this time interval is (5.76 +/- 0.04)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+201.5 s in the 10-1000 keV band is 29.3 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak = 140 +/- 50 keV, alpha = -1.5 +/- 0.1, and beta = -2.3 +/- 0.5. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29395 SUBJECT: Fermi GRB 210204A: Global MASTER-Net observations report DATE: 21/02/05 01:45:09 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 210204A ( Fermi GBM team, GCN 29390) errorbox 60315 sec after notice time and 60380 sec after trigger time at 2021-02-04 23:15:45 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 53 deg. The sun altitude is -41.7 deg. The galactic latitude b = 10 deg., longitude l = 207 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1539740 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 60410 | 2021-02-04 23:15:45 | MASTER-SAAO | (07h 36m 18.07s , +12d 00m 15.6s) | C | 60 | 19.5 | 60650 | 2021-02-04 23:19:45 | MASTER-SAAO | (07h 33m 16.34s , +10d 00m 28.3s) | C | 60 | 19.4 | 61528 | 2021-02-04 23:34:23 | MASTER-SAAO | (07h 36m 15.36s , +12d 02m 18.2s) | C | 60 | 19.3 | 62007 | 2021-02-04 23:42:22 | MASTER-SAAO | (07h 33m 06.36s , +10d 00m 56.4s) | C | 60 | 19.4 | 62087 | 2021-02-04 23:43:42 | MASTER-SAAO | (07h 37m 16.25s , +10d 01m 05.7s) | C | 60 | 19.4 | 62845 | 2021-02-04 23:56:20 | MASTER-SAAO | (07h 36m 14.47s , +12d 01m 44.5s) | C | 60 | 19.4 | 63325 | 2021-02-05 00:04:21 | MASTER-SAAO | (07h 33m 07.78s , +10d 02m 43.9s) | C | 60 | 19.4 | 63503 | 2021-02-05 00:07:18 | MASTER-SAAO | (07h 37m 07.26s , +10d 03m 31.2s) | C | 60 | 19.4 | 64498 | 2021-02-05 00:23:53 | MASTER-SAAO | (07h 37m 02.39s , +10d 02m 11.3s) | C | 60 | 19.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29408 SUBJECT: IPN triangulation of GRB 210204A DATE: 21/02/05 23:27:45 GMT FROM: Dmitry Svinkin at Ioffe Institute K. Hurley, on behalf of the IPN, I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team, D. Svinkin, S. Golenetskii, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, and C. Wilson-Hodge on behalf of the Fermi GBM team, A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 210204A (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 29390; Bissaldi, GCN Circ. 29393; BALROG localization: Kunzweileret al., GCN Circ. 29391; GECAM detection: Li, GCN Circ. 29392) has been detected by Fermi (GBM trigger 634112970), INTEGRAL (SPI-ACS), Konus-Wind, Mars-Odyssey (HEND), and Swift (BAT), so far, at about 23365 s UT (06:29:25). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 118.116 (07h 52m 28s) +15.249 (+15d 14' 57") Corners: 120.374 (08h 01m 30s) +23.758 (+23d 45' 30") 115.277 (07h 41m 07s) +4.395 ( +4d 23' 43") 114.946 (07h 39m 47s) +4.455 ( +4d 27' 16") 120.017 (08h 00m 04s) +23.825 (+23d 49' 30") --------------------------------------------- The error box area is 6.7 sq. deg, and its maximum dimension is 20.0 deg (the minimum one is 20 arcmin). The Sun distance was 155 deg. This box may be improved. The IPN localization is consistent with, but reduces the area of, the Fermi RoboBA and BALROG localizations (GCN Circ. 29390 and 29391). The optical transient ZTF21aagwbjr/AT2021buv (Kool et al., GCN Circ. 29405) is inside the box, lending support to the association of the transient and the burst. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/IPN/ The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29410 SUBJECT: GRB 210204A: AstroSat CZTI Detection DATE: 21/02/06 10:46:42 GMT FROM: Gaurav Waratkar at IIT,Bombay G. Waratkar (IITB), V. Shenoy (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), P. Sawant (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 bright long GRB 210204A, which was also detected by Fermi-GBM (GCN #29390, #29393) and GECAM-B (GCN #29392). The source was clearly detected in the 20-200 keV energy range. The light curve showed two isolated emission peaks with the stronger peak at 2021-02-04 06:32:45 UT in all four quadrants. The measured peak count rate associated with the burst is 789 (+58, -61) cts/s above the background in the combined data of four quadrants, with a total of 18141 (+1631, -1364) cts. The initial fainter peak contributed to about 6% of the reported total counts. The local mean background count rate was 480 (+2, -3) cts/s. Using cumulative rates, we measure a T90 of 200 (+7, -10) s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed two isolated peaks of emission with the stronger peak at 2021-02-04 06:32:45 UT. The initial fainter peak contributed less than 5% of total counts and hence was excluded from the following analysis. The measured peak count rate is 754 (+76, -80) cts/s above the background in the combined Veto data of four quadrants, with a total of 15971 (+827, -996) cts. The local mean background count rate was 1575 (+2, -3) cts/s. We measure a T90 of 57 (+7, -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. 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29411 SUBJECT: VLT/X-shooter redshift of 1.466 for ZTF21aagwbjr/AT2021buv, strengthening its association with GRB 210204A DATE: 21/02/06 11:15:41 GMT FROM: Maryam Arabsalmani at University of Melbourne L. Izzo (DARK/NBI), J. P. U. Fynbo (DAWN/NBI), D. A. Kann (HETH/IAA-CSIC), S. D. Vergani (GEPI, Observatoire de Paris), D. B. Malesani (DTU Space), M. Arabsalmani (ICRAR/UWA), A. Rossi (INAF-OAS), G. Pugliese (API, Univ. Amsterdam), D. Xu (NAOC), report on behalf of the Stargate consortium: We observed the fast optical transient ZTF21aagwbjr/AT2021buv (Kool et al., GCN 29405), likely associated with the Fermi, GECAM, and IPN GRB 210204A (The Fermi GBM team, GCN 29390; F. Kunzweiler et al., GCN 29391; Li et al., GCN 29392; Hurley et al., GCN 29408) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Spectroscopic observations started at 01:38 UT on 06 February 2021, i.e. ~1.8 days after the burst detection and they consisted of 4 x 600 s exposures. In the resulting spectrum, we find a series of strong absorption lines that we identify as Mg II, Si IV, C IV, and Ca II at a common redshift of 1.466. At this redshift, we also detect emission lines of [O II], [O III] and H-alpha Balmer line. We therefore conclude that z = 1.466 is the redshift of ZTF21aagwbjr/AT2021buv. The measured redshift implies a high intrinsic brightness (absolute magnitude ~ 28 at an epoch of 45 min after the GRB; Kool et al., GCN 29405), which is typical of long GRB afterglows. This, coupled with the observed absorption lines set, typical of long GRB environments, further strengthens the association between ZTF21aagwbjr/AT2021buv and GRB 210204A. Further analysis is undergoing. We acknowledge support from the ESO observing staff at Paranal, in particular Zahed Wahhaj. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29412 SUBJECT: GRB 210204A: Swift ToO observations DATE: 21/02/06 11:56:02 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Fermi/GBM GRB 210204A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00014055 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. 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: 29413 SUBJECT: GRB 210204A / ZTF21aagwbjr: Swift-XRT observations DATE: 21/02/06 16:22:25 GMT FROM: Phil Evans at U of Leicester J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of ZTF21aagwbjr (Kool et al., 29405), which may be related to the Fermi/GBM / GECAM / IPN detected burst GRB 210204A (GCN Circ., 29390, GCN Circ. 29392, GCN Circ. 29408), collecting 2.9 ks of Photon Counting (PC) mode data between T0+160.9 ks and T0+173.2 ks. An uncatalogued X-ray source is detected consistent with being within 1 arcsec of the ZTF position and is believed to be the afterglow, or at least, the X-ray counterpart of the ZTF21aagwbjr. Using 2886 s of PC mode data and 6 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 117.08071, +11.40951 which is equivalent to: RA (J2000): 07h 48m 19.37s Dec(J2000): +11d 24' 34.2" with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position is 0.7 arcsec from the ZTF position. The light curve is consistent with a constant source of mean count rate 9.1e-02 ct/sec. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.73 (+0.31, -0.29). The best-fitting absorption column is 1.7 (+1.3, -1.1) x 10^21 cm^-2, in excess of the Galactic value of 3.5 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 4.0 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.7 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 3.5 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 1.73 (+0.31, -0.29) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00014055. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00014055. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29414 SUBJECT: GRB 210204A: Optical Observations from HCT DATE: 21/02/07 04:46:24 GMT FROM: Anirban Dutta at Indian Inst. of Astrophysics Teja, R.S.; Dutta, Anirban (IIA, Bengaluru); Kumar, Harsh (IIT, Bombay); Sujith, D.S.; Sahu, D.K.; Anupama, G.C.; Barway, Sudhansu (IIA, Bengaluru); Bhalerao, Varun (IIT, Bombay) We observed the field of GRB 210204A / ZTF21aagwbjr (Fermi-GBM, GCN #29390; Li et al., GCN #29392; Izzo et al., GCN #29411) with the Himalayan Faint Object Spectrograph and Camera (HFOSC) mounted on the 2-m Himalayan Chandra Telescope (IAO, Hanle, India). Multiple frames (each 300 sec) of the GRB field in Bessell R and I bands were obtained with an average airmass of 1.21 under good seeing conditions. Preliminary PSF photometry on the stacked images was performed and calibrated against USNO-B1 catalogue. We clearly detected an OT in the stacked images in both the bands. The estimated magnitudes of the OT (not corrected for the Galactic extinction) are as under - ------------------------------------------------------------------------------------- Date | UT (mean) | Filter | Exp. time x No. of frames | Magnitude (err) ------------------------------------------------------------------------------------- 2021-02-06 15:11:11 R 300 sec x 4 20.07 (0.13) 2021-02-06 15:40:29 I 300 sec X 4 19.79 (0.15) ------------------------------------------------------------------------------------- The observations were carried out under the ToO program HCT-2021-C1-P2. We thank the staff at IAO and CREST for helping us with the observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29415 SUBJECT: Konus-Wind detection of GRB 210204A / ZTF21aagwbjr DATE: 21/02/07 14:27:40 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 210204A (Fermi GBM detection: Bissaldi, GCN 29393; GECAM detection: Li et al, GCN 29392; IPN triangulation: Hurley et al., GCN 24908; AstroSat CZTI Detection: Waratkar et al., GCN 29410), associated with the fast optical transient ZTF21aagwbjr/AT2021buv (Kool et al., GCN 29405), triggered Konus-Wind (KW) at T0=23570.576 s UT (06:32:50.576). The burst light shows a bright, multi-peaked pulse, which starts at ~T0-30 s and has a duration of ~80 s. A weaker precursor is clearly visible in the KW waiting mode data around ~T0-165 s. The emission in the main pulse is seen up to ~3 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/ As observed by Konus-Wind, the burst had a fluence of (5.7 ± 0.9)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+2.304, of (5.0 ± 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+49.408 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.04 (-0.12,+0.18), the high energy photon index beta = -2.43 (-0.18,+0.31), the peak energy Ep = 137 (-25,+22) keV, chi2 = 79/97 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.28 (-0.54,+0.64), the high energy photon index beta = -2.12 (-0.24,+0.11), the peak energy Ep = 123 (-24,+49) keV, chi2 = 109/97 dof. Assuming the redshift z=1.466 (Izzo et al., GCN 29411) 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 ~2.3x10^53 erg, the isotropic luminosity L_iso to ~7.1x10^52 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z to ~340 keV. With these values, GRB 210204A is within 68% prediction bands for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., ApJ, in press), see http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/GRB210204A_rest_frame.pdf All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29417 SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): Mondy and AbAO optical observations DATE: 21/02/07 16:34:13 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO), N. Pankov (HSE) report on behalf of GRB IKI FuN: We observed the ZTF21aagwbjr/AT2021buv transient (Kool et al., GCN 29405) at the redshift of 1.466 (Izzo et al., GCN 29411) which is most probably is an afterglow (Kennea et al., GCN 29413; Teja et al., GCN 29414) of GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415). Images in R-filter were taken in AZT-33IK telescope of Sayan observatory (Mondy) and AS-32 telescope of Abastumani observatory (AbAO). Preliminary photometry of the optical transient in a combined image is following Date UT start t-T0 Filter Exp. OT Err. UL(3s) Telescope (mid, days) (s) 2021-02-06 12:33:10 2.26579 R 38*60 19.94 0.09 21.7 AZT-33IK 2021-02-06 16:50:17 2.44748 R 47*60 20.1 0.4 20.1 AS-32 The photometry is based on the nearby USNO-B1.0 stars. USNO-B1.0_id R2 1014-0149033 15.43 1014-0149115 17.00 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29424 SUBJECT: Konus-Wind detection of GRB 210204A (correction to GCN 29415) DATE: 21/02/08 11:35:19 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, on behalf of the Konus-Wind team: The KW spectral data and energetics of GRB 210204A reported in Frederiks et al., GCN 29415 contain errors due to an incorrect detector response matrix used in the calculations. The correct spectra and energetics are provided below, we are sorry for the inconvenience. The burst time-integrated spectrum (measured from T0 to T0+49.408 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.45 (-0.08,+0.09), the high energy photon index beta = -2.63 (-0.41,+0.20), the peak energy Ep = 136 (-16,+21) keV, chi2 = 76/97 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.12 (-0.18,+0.34), the high energy photon index beta = -2.45 (-0.46,+0.26), the peak energy Ep = 175 (-42,+34) keV, chi2 = 104/96 dof. As observed by Konus-Wind, the burst had a fluence of (7.0 ± 0.9)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+2.304, of (5.2 ± 0.9)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). Assuming the redshift z=1.466 (Izzo et al., GCN 29411) 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 ~3.9x10^53 erg, the isotropic luminosity L_iso to ~7.1x10^52 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z to ~333 keV. With these values, GRB 210204A is within 68% prediction bands for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., ApJ, in press), see http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/GRB210204A_rest_frame.pdf All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29432 SUBJECT: GRB 210204A: redshift revision of ZTF21aagwbjr/AT2021buv (correction to GCN 29411) DATE: 21/02/08 18:20:17 GMT FROM: Daniele B Malesani at DTU Space D. Xu (NAOC), L. Izzo (DARK/NBI), J. P. U. Fynbo (DAWN/NBI), D. A. Kann (HETH/IAA-CSIC), S. D. Vergani (GEPI, Observatoire de Paris), D. B. Malesani (DTU Space), M. Arabsalmani (ICRAR/UWA), A. Rossi (INAF-OAS), G. Pugliese (API, Univ. Amsterdam), J.-B. Vielfaure (APC), report on behalf of the Stargate consortium: Off-line reanalysis of our data of GRB 210204A (ZTF21aagwbjr/AT2021buv; Kool et al., GCN 29405) made us realise that we had used an incorrect data set for our previous GCN circular (Izzo et al., GCN 29411). We report here the correct analysis and results, and urge users to disregard GCN 29411. We regret for any confusion created by this mishap. Our data of GRB 210204A were acquired with the X-shooter spectrograph installed on the ESO VLT UT3 (Melipal) telescope. Four spectra by 600 s each were secured, starting on 2021 Feb 6.08 UT (1.79 days after the trigger) and covering the wavelength range 3000-21000 AA. Continuum is clearly detected across the entire trace. A number of absorption features are detected; we identify, among others, Al II, Zn II, Fe II, Mg II, Mg I, Ca II H and K at a common redshift z = 0.876. In particular, fine-structure lines from Fe II* are also visible, which confirms the association of this absorption system with the GRB. Emission lines due to [O II], [O III], H beta and H alpha are also detected at z = 0.876. We thus conclude that ZTF21aagwbjr/AT2021buv is at redshift z = 0.876. Three intervening Mg II absorbers are also detected, at redshift 0.71, 0.66, and 0.57. The revision of the redshift value does not affect our previous conclusion that ZTF21aagwbjr/AT2021buv is the likely afterglow of GRB 210204A (Fermi GBM Team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410): at z = 0.876, the transient reached an absolute magnitude of ~ -26.7 (Kool et al., GCN 29405), within the range of long GRB afterglows. The set of absorption features (including those due to fine-structure transitons) is also typical of GRB environments. We recompute the isotropic-equivalent gamma-ray energy using the fluence reported by Konus-Wind (Frederiks, GCN 29424) and the correct redshift value, which turns to be ~8.7*10^52 erg. We acknowledge the observing staff at Paranal, in particular Zahed Wahhaj. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29433 SUBJECT: GRB 210204A: LBT observations and jet break DATE: 21/02/08 19:23:12 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS Bologna), A. Melandri (INAF-OAB) report on behalf of the CIBO collaboration: We observed the field of GRB210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415) simultaneously in the g'r'i' and z' bands with the LBC imager mounted on LBT (Mt Graham, AZ, USA). We obtained 20min of imaging for each band at the midtime 08:20 UT on 2021-02-07, 3.08 days after the burst trigger. We clearly detect the afterglow (Kool et al., GCN 29405) and we preliminary measure the following AB magnitudes: g = 21.1 +- 0.1 r = 20.7 +- 0.1 i = 20.4 +- 0.1 z = 20.2 +- 0.1 calibrated against SDSS field stars. Modelling the observations available (Kool et al., GCN29405 ; Belkin et al., GCN29417; Teja et al., GCN 29414) with a broken power-law, we find that the light curve first decays with index alpha_1=0.60+-0.05, then breaks at t_b=2.2+-0.2 days, and afterwards it is described by a decay index alpha_2~1.7+-0.5. The last one is constrained only by the LBT detection, but is ~0.4 magnitude fainter than the brightness predicted extrapolating the pre-break decay. We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly B. Rothberg, F. Cusano and D. Paris, in obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29438 SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued Mondy optical observations DATE: 21/02/09 12:40:35 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (HSE) report on behalf of GRB IKI FuN: We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which is an afterglow (Kennea et al., GCN 29413; Teja et al., GCN 29414) of GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415). Images in R-filter were taken in AZT-33IK telescope of Sayan observatory (Mondy) on Feb.7 and Feb.8. Preliminary photometry of the optical transient in combined images in two epochs is following Date UT start t-T0 Filter Exp. OT Err. UL(3s) Telescope (mid, days) (s) 2021-02-07 13:43:58 3.32260 R 60*60 20.61 0.04 22.8 AZT-33IK 2021-02-08 15:22:01 4.39035 R 59*60 20.92 0.05 22.7 AZT-33IK The photometry does not contradict a possible jet-break suggested by Rossi et al (GCN 29433). The photometry is based on the nearby USNO-B1.0 stars USNO-B1.0_id R2 1014-0149033 15.43 1014-0149115 17.00 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29490 SUBJECT: GRB 210204A: observations with the 3.6m Devasthal Optical Telescope and possible jet break DATE: 21/02/12 12:06:31 GMT FROM: Rahul Gupta at ARIES, India R. Gupta, S. B. Pandey, A. Kumar, Dimple, A. Ghosh, A. Aryan, K. Misra (ARIES), D. Bhattacharya (IUCAA), V. Bhalerao (IITB), A. Pozanenko (IKI), and D. Buckley (SAAO) as a part of larger BRICS collaboration: GRB 210204A was triggered by the Fermi-GBM at 06:29:25 UT on 4 Feb 2021 (GCNs 29390, and 29393) and the prompt emission was also detected by other space-based facilities like GECAM (29392), AstroSat (GCN 29410), and Konus-Wind (GCNC 29415) up to MeV energies. So, we searched for extended GeV emission for a temporal window of 50 ks since GBM trigger-based on available LAT data, however, we do not find detection of any GeV photons with a probability greater than 50 % to be associated with the source. The optical counterpart associated with this burst was independently discovered by Kool et al., 2021 using the ZTF telescope (GCN 29405) and later follow-up observations were continued by several ground-based facilities (GCNs 29411, 29414, 29417, 29432, 29433, and 29438). Xu et al. 2021 report a redshift value of 0.876 for this burst using VLT/X-shooter observations (GCN 29411). We performed late time follow-up observations of the optical counterpart using the 4Kx4K CCD Imager (Pandey et al. 2017, arXiv:1711.05422v1) mounted at the axial port of the 3.6m Devasthal Optical Telescope of ARIES Nainital starting ~ 58 hours after the burst. Multiple frames were taken in various broad-band filters including B, V, R, and I bands. A fading afterglow candidate was clearly seen in individual frames decayed around ~ 0.6 mags in R Band during our observing run. We report the preliminary brightness of the afterglow to be R= 20.19 +/- 0.03 mag ~ 58 hours after the GBM trigger. The magnitude value reported is calibrated against UNSO B1 nearby stars. Our R-band light curve along with early data published by Kool et al., 2021 (GCN 29405) is well-described with a broken power-law model. We found that the temporal decay index before break time (~ 36 hours post burst) is 0.55 +/- 0.03 steepen to 1.43 +/- 0.09 at later epochs. Considering this break as a jet break (as reported in GCN 29433), we calculated the optical spectral index (using BVRI data at ~ 58 hours) \beta_O to be 1.08 +/- 0.10. Considering the closure relations after the jet break (both for ISM and WIND like a medium, without energy injection), the optical emission could be better described with spectral regime \nu > \nu_c for WIND medium demanding electron energy index value $p$ equal to 2.16 +/- 0.20 for the available data-set so far. This circular maybe cited. 3.6m Devasthal Optical Telescope (DOT) is a recently commissioned facility in the Northern Himalayan region of India (long:79 41 04E, lat:29 21 40N, alt:2540m) owned and operated by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital ( https://www.aries.res.in). Authors of this GCN circular thankfully acknowledge consistent support from the staff members to run and maintain the 3.6m DOT. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29499 SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued CrAO and AbAO optical observations DATE: 21/02/12 23:18:51 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO), R. Ya. Inasaridze (AbAO), N. Pankov (HSE) report on behalf of GRB IKI FuN: We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which is an afterglow (Kennea et al., GCN 29413; Teja et al., GCN 29414; Belkin et al., GCNs 29417, 29438; Rossi et al., GCN 29433; Gupta et al., GCN 29490) of GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415). Images in R-filter were taken with AS-32 telescope of Abastumani observatory (AbAO) and ZTSh 2.6m telescope of CrAO observatory on 2021-02-09 and 2021-02-11. Preliminary photometry of the afterglow in combined images is following Date UT start t-T0 Filter Exp. OT Err. UL(3s) Telescope (mid, days) (s) 2021-02-09 18:41:28 5.52572 R 25*120 21.09 0.08 22.6 ZTSh 2021-02-09 19:28:42 5.55610 R 43*60 21.4 0.2 22.5 AS-32 2021-02-11 18:18:20 7.50966 R 50*60 21.8 0.2 22.5 AS-32 2021-02-11 21:32:47 7.64817 R 30*120 21.6 0.3 21.8 ZTSh The photometry is based on the nearby USNO-B1.0 stars USNO-B1.0_id R2 1014-0149033 15.43 1014-0149115 17.00 A light curve can be found in http://grb.rssi.ru/GRB210204A/GRB210204A_lc.png Our photometry confirms suggested jet-break (Rossi et al. GCN 29433; Gupta et al., GCN 29490). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29520 SUBJECT: GRB 210204A (ZTF21aagwbjr/AT2021buv): continued Assy and Mondy optical observations DATE: 21/02/17 22:55:05 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), V. Kim (FAI, Pulkovo Observatory), E. Klunko (ISTP), N. Pankov (HSE), M. Krugov (FAI) report on behalf of GRB IKI FuN: We continued observation of the ZTF21aagwbjr/AT2021buv transient (Kool et al., GCN 29405) at the redshift of 0.876 (Xu et al., GCN 29432) which is an afterglow (Kennea et al., GCN 29413; Teja et al., GCN 29414; Belkin et al., GCNs 29417, 29438, 29499; Rossi et al., GCN 29433; Gupta et al., GCN 29490) of GRB 210204A (Fermi GBM team, GCN 29390; Li et al., GCN 29392; Hurley et al., GCN 29408; Waratkar et al., GCN 29410; Frederiks et al., GCN 29415). Images in R-filter were obtained at AZT-33IK telescope of Sayan observatory (Mondy) on Feb.12, 16 and in r'-filter at AZT-22 telescope of Assy-Turgen observatory on Feb.15, 16. Preliminary photometry of the optical transient in combined images is following Date UT start t-T0 Filter Exp. OT Err. UL(3s) Telescope (mid, days) (s) 2021-02-12 16:11:09 8.41787 R 20*120 21.66 0.09 22.9 AZT-33IK 2021-02-15 15:40:01 11.40667 r' 70*60 21.86 0.15 23.6 AZT-20 2021-02-16 14:39:53 12.36212 R 31*120 21.8 0.4 21.8 AZT-33IK 2021-02-16 16:57:06 12.44700 r' 32*60 22.18 0.14 23.3 AZT-20 The photometry is based on the nearby USNO-B1.0 stars USNO-B1.0_id R2 1014-0149033 15.43 1014-0149115 17.00 and the same stars from SDSS-DR12 SDSS-DR12 RA DEC g dg r dr 117.03151400 +11.42180300 17.036 0.005 15.624 0.005 117.07973400 +11.41971200 17.909 0.006 17.191 0.006 The updated light curve can be found in http://grb.rssi.ru/GRB210204A/GRB210204A_lc.png //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29541 SUBJECT: uGMRT radio detection of GRB 210204A DATE: 21/02/22 11:21:18 GMT FROM: Poonam Chandra at TIFR Poonam Chandra (NCRA-TIFR), Varun Bhalerao (IIT-B), Kuntal Misra (ARIES) and G. C. Anupama (IIA) report on behalf of a larger collaboration: We carried out radio observations of GRB 210204A (GCN#29390) with the upgraded Giant Metrewave Radio Telescope (uGMRT) in uGMRT band 5 (1000-1450 MHz). The observations were taken on 2021 Feb 20 and the preliminary flux at at a position RA, Dec(J2000) 07:48:19.345, 11:24:33.91 is ~140 uJy. The uncertainty in the measurements is ~20 uJy. Further observations are planned. We thank GMRT staff for making these observations possible.