//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29849 SUBJECT: GRB 210421A: Swift detection of a burst DATE: 21/04/21 00:39:04 GMT FROM: David Palmer at LANL M. J. Moss (GWU), S. D. Barthelmy (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:27:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210421A (trigger=1044426). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 104.908, +4.934, which is RA(J2000) = 06h 59m 38s Dec(J2000) = +04d 56' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~2 sec after the trigger. The XRT began observing the field at 00:28:58.1 UT, 87.8 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 104.87569, 4.92168 which is equivalent to: RA(J2000) = 06h 59m 30.17s Dec(J2000) = +04d 55' 18.0" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 124 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density. The initial flux in the 0.1 s image was 1.51e-08 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 96 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29850 SUBJECT: Swift GRB 210421A: Global MASTER-Net observations report DATE: 21/04/21 00:42:22 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) was pointed to the Swift GRB 210421A ( M. J. Moss et al., GCN 29849) errorbox 13 sec after notice time and 47 sec after trigger time at 2021-04-21 00:28:17 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 54 deg. The sun altitude is -30.5 deg. The galactic latitude b = 5 deg., longitude l = 210 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1597889 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 52 | MASTER-OAFA | C | 10 | 16.4 | 82 | MASTER-OAFA | C | 10 | 16.4 | 116 | MASTER-OAFA | C | 20 | 16.8 | 160 | MASTER-OAFA | C | 30 | 17.0 | 215 | MASTER-OAFA | C | 40 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29857 SUBJECT: GRB 210421A: DDOTI Upper Limit DATE: 21/04/21 04:56:00 GMT FROM: Alan M Watson at UNAM Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report: We observed the field of the Swift/BAT GRB 210421A (Moss et al., GCN Circ. 29849) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-21 03:05 to 04:33 UTC (from 2.6 to 4.1 hours after the trigger) and obtained 4320 seconds of exposure in the w filter. We observed a region covering aproximately 7 degrees in RA and 10 degrees in declination (about 70 square degrees), including the XRT position. We calibrated our images against the APASS catalog. We do not detect any source in the XRT region to a 3-sigma limiting AB magnitude of w = 21.1. We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29865 SUBJECT: GRB 210421A: Enhanced Swift-XRT position DATE: 21/04/21 15:22:26 GMT FROM: Phil Evans at U of Leicester P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1675 s of XRT Photon Counting mode data and 1 UVOT images for GRB 210421A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 104.87443, +4.92232 which is equivalent to: RA (J2000): 06h 59m 29.86s Dec (J2000): +04d 55' 20.4" with an uncertainty of 2.4 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29870 SUBJECT: GRB 210421B: Fermi GBM Final Localization DATE: 21/04/21 20:03:10 GMT FROM: Joe Mangan at UCD The Fermi GBM team reports the detection of a likely short GRB At 10:54:44.812 UT on 21 Apr 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210421B (trigger 640695289 / 210421455). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 272.1, Dec = 57.2(J2000 degrees, equivalent to J2000 18h 08m, 57d 09'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 20.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_skymap_all_bn210421455.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/bn210421455/quicklook/glg_healpix_all_bn210421455.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_lc_medres34_bn210421455.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29871 SUBJECT: GRB 210421C: Fermi GBM Final Real-time Localization DATE: 21/04/21 20:23:17 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely SHORT GRB At 20:12:53 UT on 21 Apr 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210421C (trigger 640728778.025922 / 210421842). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 192.2, Dec = -61.9 (J2000 degrees, equivalent to J2000 12h 48m, -61d 53'), with a statistical uncertainty of 14.3 degrees. The angle from the Fermi LAT boresight is 125.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421842/quicklook/glg_skymap_all_bn210421842.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/bn210421842/quicklook/glg_healpix_all_bn210421842.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421842/quicklook/glg_lc_medres34_bn210421842.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29873 SUBJECT: Fermi GRB 210421C: Global MASTER-Net observations report DATE: 21/04/21 21:30:14 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 210421C ( Fermi GBM team, GCN 29871) errorbox 3606 sec after notice time and 3636 sec after trigger time at 2021-04-21 21:13:29 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 24 deg. The sun altitude is -62.3 deg. The galactic latitude b = 1 deg., longitude l = 303 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1598370 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 3666 | 2021-04-21 21:13:29 | MASTER-SAAO | (12h 44m 20.32s , -55d 59m 18.1s) | C | 60 | 18.5 | 3839 | 2021-04-21 21:16:21 | MASTER-SAAO | (13h 00m 06.56s , -55d 58m 20.2s) | C | 60 | 17.6 | 3918 | 2021-04-21 21:17:41 | MASTER-SAAO | (12h 35m 41.98s , -53d 57m 24.5s) | C | 60 | 18.4 | 4248 | 2021-04-21 21:23:10 | MASTER-SAAO | (12h 47m 33.26s , -53d 57m 52.4s) | C | 60 | 18.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29874 SUBJECT: GRB 210421B: Correction of GRB Type to "Likely Long GRB" DATE: 21/04/21 21:45:35 GMT FROM: Joe Mangan at UCD Correction to GCN Circ. 29870 for GRB 210421B, GRB type originally reported as "likely short GRB", corrected to "likely long GRB". //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29875 SUBJECT: GRB 210421A: Swift-XRT refined Analysis DATE: 21/04/21 22:39:46 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester) and M.J. Moss report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 210421A (Moss et al. GCN Circ. 29849), from 91 s to 68.9 ks after the BAT trigger. The data comprise 130 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 29865). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=2.6 (+0.8, -0.9). At T+109 s the decay steepens to an alpha of 4.96 (+0.17, -0.15) before breaking again at T+397 s to a final decay with index alpha=0.59 (+0.22, -0.14). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.74 (+/-0.08). The best-fitting absorption column is 5.3 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 4.6 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.17 (+0.19, -0.14) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (6.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.6 (+0.8, -0.0) x 10^21 cm^-2 Galactic foreground: 4.6 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.17 (+0.19, -0.14) If the light curve continues to decay with a power-law decay index of 0.59, the count rate at T+24 hours will be 0.011 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x 10^-13 (7.4 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01044426. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29877 SUBJECT: GRB 210421B: Swift/BAT-GUANO detection and arcminute localization DATE: 21/04/21 22:47:22 GMT FROM: Aaron Tohuvavohu at U Toronto James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU) report: Swift/BAT did not trigger on GRB 210421B (T0: 2021-04-21 10:54:44 UTC, Fermi/GBM GCN 29870, 29874; INTEGRAL/SPI-ACS trigger 9154). The INTEGRAL/SPI-ACS notice, distributed in near real-time triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 90 seconds of BAT event-mode data from [-45,+45] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The burst is strongly detected in BAT with a duration of ~15 seconds, confirming the long classification correction of Fermi/GBM (GCN 29874). The burst occurred during a Swift slew. The position of the burst was found with SNR of 9.7 using a novel slew image mosaicing procedure (DeLaunay et al. 2021, in prep.), and so the positional uncertainty is not yet well characterized. The BAT position is RA, Dec = 270.817, 56.828 deg which is RA(J2000) = 18h 03m 16.08s Dec(J2000) = 56d 49’ 40.8” with an estimated uncertainty of at least 5 arcmin. This position is consistent with the Fermi GBM localization (GCN 29870). XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29878 SUBJECT: GRB 210421B: Swift ToO observations DATE: 21/04/22 01:26:20 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 Swift/BAT GRB 210421B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021429 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 Swift/BAT 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: 29882 SUBJECT: GRB 210421A: MITSuME Akeno optical upper limits DATE: 21/04/22 14:52:20 GMT FROM: Naohiro Ito at Tokyo Tech N. Ito, K. L. Murata, R. Hosokawa, M. Niwano, H. Takamatsu, Y. Yatsu, and N.Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 210421A (M. J. Moss et al. GCN Circular #29849, V. Lipunov et al. GCN Circular #29850, Alan M. Watson et al. GCN Circular #29857, P.A. Evans et al. GCN Circular #29865, P.A. Evans et al. GCN Circular #29875) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation with a series of 60 sec exposures started at 2021-04-21 09:51:58 UT (9.4 hours after the Swift BAT trigger) We stacked the images with good conditions. We did not detect any sources within the enhanced XRT error region (P.A. Evans et al. GCN Circular #29865) in all three bands. We obtained the 5-sigma limits of the stacked images as follows. T0+[hour] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 9.8 11:25 7020 g'>18.8, Rc>18.8, Ic>18.4 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29885 SUBJECT: GRB 210421A: Swift/UVOT Upper Limits DATE: 21/04/22 18:53:07 GMT FROM: Samantha Oates at MSSL S. R. Oates (U.Birmingham) and M. J. Moss (GWU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210421A 96 s after the BAT trigger (Moss et al., GCN Circ. 29849). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 29865). is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 96 246 147 >20.4 white 96 1912 191 >20.6 v 1608 1800 39 >17.9 b 1534 1899 58 >19.2 u_FC 308 484 173 >19.5 u 308 1874 211 >19.6 uvw1 1658 1850 39 >18.1 uvm2 1633 1825 39 >17.9 uvw2 1584 1776 39 >18.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.318 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29888 SUBJECT: GRB 210421B: AstroSat CZTI detection DATE: 21/04/23 06:09:12 GMT FROM: Dipankar Bhattacharya at IUCAA P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (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 210421B, which was also detected by Fermi-GBM (GCN #29870) and Swift-BAT (GCN #29877). 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 2021-04-21 10:54:43.5 UT. The measured peak count rate associated with the burst is 165 (+42, -33) cts/s above the background in the combined data of four quadrants, with a total of 905 (+230, -297) cts. The local mean background count rate was 504 (+4, -3) cts/s. Using cumulative rates, we measure a T90 of 16 (+3, -10) s. It was also clearly 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 2021-04-21 10:54:43.6 UT. The measured peak count rate is 320 (+72, -54) cts/s above the background in the combined Veto data of four quadrants, with a total of 1481 (+436, -479) cts. The local mean background count rate was 1629 (+5, -6) cts/s. We measure a T90 of 17 (+4, -11) 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: 29889 SUBJECT: GRB 210421A: GECAM detection DATE: 21/04/23 06:37:40 GMT FROM: QiBin Yi at IHEP, HXMT S. L. Xie, X. Y. Song, Q. B. Yi, X. Y. Zhao, Y. Huang, S. L. Xiong, S. Xiao, C. Cai, Y. Zhao, J. C. Liu, Y. Q. Zhang, W. C. Xue, C. Zheng, Z. W. Guo, C. W. Wang, D. Y. Guo, P. Wang, X. B. Li, W. X. Peng, R. Qiao, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He, B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. 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, D. L. Shi, J. Y. Shi, L. M. Song, G. X. Sun, X. L. Sun, Y. L. Tuo, J. Z. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, S. Yang, M. Yao, 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 triggered a long burst, GRB 210421A, at 2021-04-21T00:27:32.000 UTC (denoted as T0), which was also detected by Swift/BAT(GCN #29849). According to the GECAM-B light curves in about 8 keV - 115 keV, this burst mainly consists of multiple pulses with duration of about 20 s. Although in-flight calibration has not been finalized yet, GECAM-B localized this burst to the following position (J2000): Ra: 103.56 deg Dec: 2.26 deg Err: 3.46 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. GECAM location is consistent with the Swift/BAT(GCN #29849) position within the error. The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/multiLCvsE_2021-04-21T003A273A32.950_.pdf 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: 29891 SUBJECT: GRB 210421B: AstroSat CZTI detection DATE: 21/04/23 12:44:05 GMT FROM: Varun Bhalerao at Indian Inst of Tech P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IITB), 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 210421B, which was also detected by Fermi-GBM (GCN #29870) and Swift (BAT - GCN #29877). 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 2021-04-21 10:54:43.5 UT. The measured peak count rate associated with the burst is 165 (+42, -33) cts/s above the background in the combined data of four quadrants, with a total of 905 (+230, -297) cts. The local mean background count rate was 504 (+4, -3) cts/s. Using cumulative rates, we measure a T90 of 16 (+3 -10) s. It was also clearly 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 2021-04-21 10:54:43.647 UT. The measured peak count rate is 320 (+72, -54) cts/s above the background in the combined Veto data of four quadrants, with a total of 1481 (+436, -479) cts. The local mean background count rate was 1629 (+5, -6) cts/s. We measure a T90 of 17 (+4, -11) 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. Thanks, Pallavi //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29892 SUBJECT: GRB 210421B: Swift-XRT observations DATE: 21/04/23 15:32:05 GMT FROM: Phil Evans at U of Leicester M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), K.L. Page (U. Leicester), 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 the Swift/BAT-detected burst GRB 210421B (James DeLaunay et al. GCN Circ. 29877), collecting 2.0 ks of Photon Counting (PC) mode data between T0+45.1 ks and T0+85.2 ks. No X-ray sources have been detected. The 3-sigma upper limit in the field ranges from ~0.004 to ~0.008 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.6e-13 to 3.4e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). 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/ToO_GRBs/00021429. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29893 SUBJECT: GRB 210421A: Swift-BAT refined analysis DATE: 21/04/23 16:41:44 GMT FROM: Sibasish Laha at GSFC T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210421A (trigger #1044426) (Moss et al., GCN Circ. 29849). The BAT ground-calculated position is RA, Dec = 104.882, 4.928 deg which is RA(J2000) = 06h 59m 31.7s Dec(J2000) = +04d 55' 41.2" with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 44%. The BAT light curve showed a complex structure with a duration of about ~60 sec. T90 (15-350 keV) is 79.52 +- 26.78 sec (estimated error including systematics). The time-averaged spectrum from T-21.74 to T+73.22 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.10 +- 0.72, and Epeak of 35.2 +- 8.5 keV (chi squared 61.93 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+2.47 sec in the 15-150 keV band is 2.0 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.10 +- 0.13 (chi squared 69.44 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/BATbursts/1044426/bascript/top.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30225 SUBJECT: GRB 210421B: Fermi GBM detection DATE: 21/06/12 17:55:20 GMT FROM: Joe Mangan at UCD J. Mangan (UCD), R. Dunwoody (UCD), C. Meegan (UAH) report on behalf of the Fermi GBM Team: At 10:54:44.812 UT on 21 Apr 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210421B (trigger 640695289 / 210421455) which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2021, GCN 29877) The Fermi GBM Final Real-time Localization (GCN 29870) is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 20.1 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 11 s (50-300 keV). The time-averaged spectrum from T0-1.536 s to T0+9.728 is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.98 +/- 0.11 and the cutoff energy, parameterized as Epeak, is 1253.00 +/- 500.00 keV The event fluence (10-1000 keV) in this time interval is (3.655 +/- 0.225)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.384 s in the 10-1000 keV band is 2.74 +/- 0.26 ph/s/cm^2. 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/