//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29903 SUBJECT: GRB 210427A: Fermi GBM Final Real-time Localization DATE: 21/04/27 05:07:38 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 04:57:12 UT on 27 Apr 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210427A (trigger 641192237.991858 / 210427206). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 177.3, Dec = -53.4 (J2000 degrees, equivalent to J2000 11h 49m, -53d 23'), with a statistical uncertainty of 1.1 degrees. The angle from the Fermi LAT boresight is 146.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_skymap_all_bn210427206.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/bn210427206/quicklook/glg_healpix_all_bn210427206.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29904 SUBJECT: Fermi GRB 210427A: Global MASTER-Net observations report DATE: 21/04/27 05:45:22 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 210427A ( Fermi GBM team, GCN 29903) errorbox 83 sec after trigger time at 2021-04-27 04:58:36 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 41 deg. The sun altitude is -71.8 deg. The galactic latitude b = 8 deg., longitude l = 294 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1602343 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 93 | 2021-04-27 04:58:36 | MASTER-OAFA | (11h 30m 41.80s , -52d 41m 19.0s) | C | 20 | 16.8 | 149 | 2021-04-27 04:59:26 | MASTER-OAFA | (11h 35m 39.45s , -51d 53m 30.7s) | C | 30 | 17.0 | 203 | 2021-04-27 05:00:15 | MASTER-OAFA | (11h 35m 46.94s , -51d 53m 27.2s) | C | 40 | 17.1 | 267 | 2021-04-27 05:01:15 | MASTER-OAFA | (11h 35m 42.92s , -51d 51m 45.2s) | C | 50 | 17.2 | 342 | 2021-04-27 05:02:25 | MASTER-OAFA | (11h 35m 42.91s , -51d 53m 27.9s) | C | 60 | 17.3 | 432 | 2021-04-27 05:03:45 | MASTER-OAFA | (11h 35m 45.38s , -51d 51m 52.5s) | C | 80 | 17.4 | 542 | 2021-04-27 05:05:24 | MASTER-OAFA | (11h 35m 40.74s , -51d 52m 31.1s) | C | 100 | 17.5 | 671 | 2021-04-27 05:07:24 | MASTER-OAFA | (11h 47m 58.15s , -52d 31m 41.5s) | C | 120 | 17.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29905 SUBJECT: GRB 210427A: BALROG localization (Fermi Trigger / GRB 210427206) DATE: 21/04/27 07:48:15 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 at 04:57:12 on 27 April 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) = 172.6+/-2.5 deg Decl.(2000.0) = -54.4+/-1.7 deg We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB210427206/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB210427206/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB210427206/json //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29906 SUBJECT: GRB 210427A: GECAM detection DATE: 21/04/27 10:03:19 GMT FROM: Shenglun Xie at IHEP S. L. Xie,Y. Huang, S. L. Xiong, S. Xiao, C. Cai, Y. Zhao, J. C. Liu, C. Y. Li, Y. Q. Zhang, W. C. Xue, C. Zheng, Z. W. Guo, X. Y. Zhao, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He, 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, S. Yang, M. Yao, Q. B. Yi, B. X. Zhang, C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Z. Zhang, S. Y. Zhao, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team: During the commissioning phase, GECAM-B was triggered by a long GRB 210427A at 2021-04-27T04:57:13.100 UTC (denoted as T0), which was also observed by Fermi/GBM (GCN #29903). 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 with a duration of about 20s. An automatic on-ground localization was calculated using the light curves and spectrum. 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: 175.26 deg dec: -59.87 deg err: 5.75 deg (statistical only) The current systematic error of location is estimated to be several degrees which could be minimized by the ongoing calibration. The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_73198633.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: 29997 SUBJECT: IPN triangulation of GRB 210427A DATE: 21/05/11 22:57:01 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, 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 210427A (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 29903; BALROG localization: Biltzinger et al., GCN Circ. 29905; GECAM detection: Xie et al., GCN Circ. 29906) was detected by Fermi (GBM trigger 641192237), Konus-Wind, Swift (BAT), outside the coded FoV, Mars-Odyssey (HEND), and GECAM-B at about 17832 s UT (04:57:12). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 177.792 (11h 51m 10s) -52.866 (-52d 51' 57") Corners: 176.862 (11h 47m 27s) -54.591 (-54d 35' 28") 176.750 (11h 47m 00s) -54.533 (-54d 31' 59") 178.678 (11h 54m 43s) -51.138 (-51d 08' 18") 178.782 (11h 55m 08s) -51.196 (-51d 11' 46") --------------------------------------------- The error box area is 1036 sq. arcmin, and its maximum dimension is 3.6 deg (the minimum one is 4.8 arcmin). The Sun distance was 93 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. 29903 and 29905). It was inside the Transiting Exoplanet Survey Satellite (TESS) field of view. We thank Robert Wilson for pointing out the TESS/IPN coincidence. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB210427_T17835/IPN/ The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.