GRB250321A

This page lists all entries on GRB250321A in GRBweb

Summary Fermi GBM Swift GCN 39793 GCN 39794 GCN 39795 GCN 39798 GCN 39799 GCN 39801 GCN 39802 GCN 39814 GCN 39816 GCN 39820 GCN 39821 GCN 39837

Summary table
Variable Value Source
GRB_name_Fermi GRB250321030
T0 0:42:38 UTC GCN_circulars,Swift Det
ra 295.0984° Swift
decl 21.0404° Swift
pos_error 3.37e-04° Swift
T90 6.4 s Fermi_GBM
T90_error 2.56 s Fermi_GBM
T90_start 0:42:38.505 UTC Fermi_GBM
fluence 1.19e-06 erg/cm² Fermi_GBM
fluence_error 3.95e-08 erg/cm² Fermi_GBM
T100 6.905 s
GBM_located False
mjd 60755.02960648148 GCN_circulars,Swift Det
Fermi GBM table
GRB_name_Fermi GRB250321030
trigger_name bn250321030
ra 295.0771°
decl 21.0411°
pos_error 3.92e+00°
datum 2025-03-21
t_trigger 0:42:39.017 UTC
T90 6.4 s
T90_error 2.56 s
T90_start 0:42:38.505 UTC
fluence 1.19e-06 erg/cm²
fluence_error 3.95e-08 erg/cm²
flux_1024 4.74e+00 erg/cm²/s
flux_1024_error 2.76e-01 erg/cm²/s
flux_1024_time -1.28e-01 erg/cm²/s
flux_64 7.49e+00 erg/cm²/s
flux_64_error 1.29e+00 erg/cm²/s
Swift table
GRB_name GRB250321A
t_trigger 0:42:38 UTC
ra 295.0984°
decl 21.0404°
pos_error 3.37e-04°
T90 6.21 s
fluence 6.70e-07 erg/cm²
GCN 39793 table
GRB_name GRB250321A
GCN_number 39793
Detection_method Fermi GBM final loc
t_trigger 0:42:39 UTC
ra 299.0000°
decl 17.1000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39793 SUBJECT: GRB 250321A: Fermi GBM Final Real-time Localization DATE: 25/03/21 00:53:07 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 00:42:39 UT on 21 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564.016716 / 250321030). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 299.0, Dec = 17.1 (J2000 degrees, equivalent to J2000 19h 56m, 17d 06'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 44.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_skymap_all_bn250321030.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_healpix_all_bn250321030.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/quicklook/glg_lc_medres34_bn250321030.gif
GCN 39794 table
GRB_name GRB250321A
GCN_number 39794
Detection_method Swift Det
t_trigger 0:42:38 UTC
ra 295.0770°
decl 21.0410°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39794 SUBJECT: GRB 250321A: Swift detection of a burst DATE: 25/03/21 01:04:22 GMT FROM: David Palmer at LANL R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:42:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250321A (trigger=1297508). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 295.077, +21.041 which is RA(J2000) = 19h 40m 19s Dec(J2000) = +21d 02' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Only the first 8 seconds of the BAT light curve after the trigger is available due to a telemetry gap. This data shows a complex structure with a duration of at least 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 00:44:43.60 UT, 125.6 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart. Due to a telemetry gap, UVOT data are not available at this time. Although XRT did not report an X-ray counterpart in the limited immediately transmitted data, the significance of the BAT image (>10 sigma), the shape of the BAT light curve, and the simultaneous detection by Fermi/GBM (trigger 764210564) give us confidence that this is an astrophysical Gamma Ray Burst. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 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/)
GCN 39795 table
GRB_name GRB250321A
GCN_number 39795
Detection_method Fermi GBM Det
t_trigger 0:42:39.020 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 39795 SUBJECT: GRB 250321A: Fermi GBM Observation DATE: 25/03/21 06:04:23 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 00:42:39.02 UT on 21 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564/250321030), which was also detected by Swift BAT (Gupta et al. 2025, GCN 39794). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 39 degrees. The GBM light curve shows one main pulse with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+7.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.20 and the cutoff energy, parameterized as Epeak, is 101 +/- 12 keV. The event fluence (10-1000 keV) in this time interval is (1.04 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.13 s in the 10-1000 keV band is 4.7 +/- 0.3 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/"
GCN 39798 table
GRB_name GRB250321A
GCN_number 39798
Detection_method Swift-XRT Other
ra 295.0987°
decl 21.0415°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39798 SUBJECT: GRB 250321A: Swift-XRT localisation DATE: 25/03/21 07:13:12 GMT FROM: K.L. Page at U Leicester K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team: Using 1.7 ks of XRT Photon Counting mode data starting 134 s after the BAT trigger on GRB 250321A (GCN Circ. 39794), an X-ray source was identified at a position of RA, Dec = 295.09873, 21.04146, which is equivalent to RA (J2000): 19h 40m 23.7s Dec (J2000): 21d 02′ 29.3″ with an uncertainty of 4.2 arcsec. This circular is an official product of the Swift-XRT team.
GCN 39799 table
GRB_name GRB250321A
GCN_number 39799
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39799 SUBJECT: GRB 250321A: GOTO optical upper limits DATE: 25/03/21 07:42:24 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK A. Kumar, S. Belkin, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration: The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) observed the field of GRB 250321A, detected by Fermi/GBM (Fermi GBM Team, GCN 39793) and Swift/BAT (Gupta et al., GCN 39794). The position of the Swift/XRT counterpart (Page, GCN 39798) was covered by GOTO-North at 05:25:29 UT on 2025-03-21 (4.7 hours post-trigger). The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. No optical counterpart is detected in the Swift/XRT localisation region (Page, GCN 39798) down to a 3-sigma L-band limit of 19.6 mag (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN 39801 table
GRB_name GRB250321A
GCN_number 39801
Detection_method Fermi GBM Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39801 SUBJECT: Fermi GRB 250321A: Global MASTER-Net observations report DATE: 25/03/21 08:31:06 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 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 250321A ( Fermi GBM team, GCN 39793) errorbox 25226 sec after notice time and 25261 sec after trigger time at 2025-03-21 07:43:40 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 82 deg. The sun altitude is -37.1 deg. The galactic latitude b = -6 deg., longitude l = 56 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818762 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 25341 | 2025-03-21 07:43:40 | MASTER-OAFA | (19h 30m 40.40s , +20d 25m 41.2s) | C | 160 | 16.0 | 25537 | 2025-03-21 07:46:56 | MASTER-OAFA | (19h 30m 47.85s , +20d 25m 03.0s) | C | 160 | 16.4 | 25733 | 2025-03-21 07:50:11 | MASTER-OAFA | (19h 30m 42.54s , +20d 24m 22.3s) | C | 160 | 16.7 | 26355 | 2025-03-21 08:00:33 | MASTER-OAFA | (19h 30m 43.53s , +20d 26m 11.7s) | C | 160 | 16.4 | 27421 | 2025-03-21 08:19:20 | MASTER-OAFA | (19h 30m 53.70s , +20d 27m 42.1s) | C | 40 | 17.0 | 27431 | 2025-03-21 08:19:20 | MASTER-OAFA | (19h 40m 32.05s , +20d 50m 27.7s) | C | 60 | 16.6 | 27559 | 2025-03-21 08:20:37 | MASTER-OAFA | (19h 30m 47.78s , +20d 27m 00.4s) | C | 160 | 16.8 | 27569 | 2025-03-21 08:20:38 | MASTER-OAFA | (19h 41m 30.19s , +20d 47m 56.2s) | C | 180 | 16.7 | 27694 | 2025-03-21 08:23:53 | MASTER-OAFA | (19h 30m 54.58s , +20d 27m 29.9s) | C | 40 | 17.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.
GCN 39802 table
GRB_name GRB250321A
GCN_number 39802
Detection_method Swift Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39802 SUBJECT: Swift GRB 250321A: Global MASTER-Net observations report DATE: 25/03/21 08:32:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 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 250321A ( R. Gupta et al., GCN 39794) errorbox 27374 sec after notice time and 27401 sec after trigger time at 2025-03-21 08:19:20 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 78 deg. The sun altitude is -30.1 deg. The galactic latitude b = -1 deg., longitude l = 57 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818736 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 27432 | MASTER-OAFA | C | 60 | 16.6 | 27569 | MASTER-OAFA | C | 180 | 16.7 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.
GCN 39814 table
GRB_name GRB250321A
GCN_number 39814
Detection_method Swift-UVOT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39814 SUBJECT: GRB 250321A: Swift/UVOT Upper Limits DATE: 25/03/21 13:55:16 GMT FROM: Sam Shilling at Lancaster University S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250321A 128 s after the BAT trigger (Gupta et al., GCN Circ. 39794). No optical afterglow consistent with the XRT position (Page et al., GCN Circ. 39798) 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 128 278 147 >19.9 white 128 4071 344 >20.6 v 4282 4482 197 >18.9 b 3667 5142 236 >20.0 u 340 5097 232 >19.4 w1 4693 4892 197 >19.3 m2 4487 4687 197 >19.2 w2 4077 4277 197 >19.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 4.368 in the direction of the burst (Schlegel et al. 1998).
GCN 39816 table
GRB_name GRB250321A
GCN_number 39816
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39816 SUBJECT: EP 250321A: Optical counterpart detection by LCO. DATE: 25/03/21 15:19:10 GMT FROM: ankur ghosh at CAPP, University of Johannesburg Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250321A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 39800) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on March 21, 2025, starting 5.46 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Fu et al. GCN 39804, Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812, Lee et al., GCN 39815) in our r, V band image. |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------- 2025-03-21 11:38:04.13 5.468 1 x 900 r r = 21.40 +/- 0.07 2025-03-21 11:38:20.54 5.472 1 x 900 V V = 21.76 +/- 0.09 The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
GCN 39820 table
GRB_name GRB250321A
GCN_number 39820
Detection_method Swift-XRT Other
ra 295.0984°
decl 21.0404°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39820 SUBJECT: GRB 250321A: Swift-XRT refined Analysis DATE: 25/03/21 18:23:30 GMT FROM: Phil Evans at U of Leicester E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for the Swift-BAT-detected burst GRB 250321A, from 108 s to 39.4 ks after the Swift-BAT trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. Using 1662 s of PC mode data and 3 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 = 295.09844, +21.04038 which is equivalent to: RA (J2000): 19h 40m 23.62s Dec(J2000): +21d 02' 25.4" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is 72 arcsec from the Swift-BAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.13 (+0.11, -0.10). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+1.3, -1.0). The best-fitting absorption column is 3.7 (+3.4, -2.2) x 10^22 cm^-2, in excess of the Galactic value of 1.1 x 10^22 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 7.3 x 10^-11 (2.4 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.7 (+3.4, -2.2) x 10^22 cm^-2 Galactic foreground: 1.1 x 10^22 cm^-2 Excess significance: 2.0 sigma Photon index: 2.2 (+1.3, -1.0) If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 6.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x 10^-14 (1.6 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/01297508. This circular is an official product of the Swift-XRT team.
GCN 39821 table
GRB_name GRB250321A
GCN_number 39821
Detection_method Swift-BAT Det
ra 295.1000°
decl 21.0550°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39821 SUBJECT: GRB 250321A: Swift-BAT refined analysis DATE: 25/03/21 18:34:55 GMT FROM: Rahul Gupta at NASA GSFC R. Gupta (GSFC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (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 250321A (trigger #1297508) (Gupta, et al., GCN Circ. 39794). The BAT ground-calculated position is RA, Dec = 295.100, 21.055 deg which is RA(J2000) = 19h 40m 23.9s Dec(J2000) = +21d 03' 16.4" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 24%. The mask-weighted BAT light curve shows a sharp peak at the trigger time, followed by a rapid decline. T90 (15-350 keV) is 6.21 +- 1.36 sec (estimated error including systematics). The time-averaged spectrum from T-0.14 to T+7.35 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.61 +- 0.19. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is 3.2 +- 0.5 ph/cm2/sec. 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/batgrbcat/BAT_refined_circular/1297508
GCN 39837 table
GRB_name GRB250321A
GCN_number 39837
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39837 SUBJECT: GRB 250321a: Liverpool Telescope optical follow-up DATE: 25/03/22 18:25:33 GMT FROM: A. Bochenek at Liverpool John Moores University A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250321a (Hu et al., GCN 39800) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters, starting at 2025-03-22 00:24:35 UT, approximately 18.24 hours after the trigger. We report a detection in the stacked images in the i band at the position of the optical counterpart (Fu et al., GCN 39804) of the magnitude i = 22.08 ± 0.16. In the r-band stacked images, we report a non-detection with the 3-sigma limiting magnitude of r > 22.19 mag. Our results are in agreement with previous observations (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831; Zheng et al., GCN 39832; Pankov et al., GCN 39836). MJD (mid) T_mid - T_0 Filter Mag. (AB) 60756.02120 18.34 h r > 22.19 60756.02976 18.55 h i 22.08 ± 0.16 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.