GRB250504A

This page lists all entries on GRB250504A in GRBweb

Summary Fermi GBM IPN Swift GCN 40342 GCN 40343 GCN 40344 GCN 40345 GCN 40346 GCN 40347 GCN 40350 GCN 40351 GCN 40353 GCN 40354 GCN 40357 GCN 40372

Summary table
Variable Value Source
GRB_name_Fermi GRB250504976
T0 23:25:54 UTC GCN_circulars,Fermi GBM final loc
ra 269.6181° Swift
decl -40.3668° Swift
pos_error 5.18e-04° Swift
T90 48.897 s Fermi_GBM
T90_error 1.056 s Fermi_GBM
T90_start 23:25:55.039 UTC Fermi_GBM
fluence 7.02e-06 erg/cm² Fermi_GBM
fluence_error 4.24e-08 erg/cm² Fermi_GBM
T100 49.936 s
GBM_located False
mjd 60799.976319444446 GCN_circulars,Fermi GBM final loc
Fermi GBM table
GRB_name_Fermi GRB250504976
trigger_name bn250504976
ra 269.6171°
decl -40.3661°
pos_error 3.14e+00°
datum 2025-05-04
t_trigger 23:25:54.783 UTC
T90 48.897 s
T90_error 1.056 s
T90_start 23:25:55.039 UTC
fluence 7.02e-06 erg/cm²
fluence_error 4.24e-08 erg/cm²
flux_1024 3.58e+00 erg/cm²/s
flux_1024_error 2.67e-01 erg/cm²/s
flux_1024_time 1.05e+01 erg/cm²/s
flux_64 6.84e+00 erg/cm²/s
flux_64_error 1.11e+00 erg/cm²/s
IPN table
GRB_name GRB250504A
ra 269.6125°
decl -40.3500°
pos_error 5.00e-02°
Swift table
GRB_name GRB250504A
t_trigger 23:25:57 UTC
ra 269.6181°
decl -40.3668°
pos_error 5.18e-04°
GCN 40342 table
GRB_name GRB250504A
GCN_number 40342
Detection_method Fermi GBM final loc
t_trigger 23:25:54 UTC
ra 265.4000°
decl -40.9000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40342 SUBJECT: GRB 250504A: Fermi GBM Final Real-time Localization DATE: 25/05/04 23:36:31 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 23:25:54 UT on 4 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959.78286 / 250504976). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 265.4, Dec = -40.9 (J2000 degrees, equivalent to J2000 17h 41m, -40d 53'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 113.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_skymap_all_bn250504976.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/bn250504976/quicklook/glg_healpix_all_bn250504976.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250504976/quicklook/glg_lc_medres34_bn250504976.gif
GCN 40343 table
GRB_name GRB250504A
GCN_number 40343
Detection_method Swift Det
t_trigger 23:25:57 UTC
ra 269.6120°
decl -40.3490°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40343 SUBJECT: GRB 250504A: Swift detection of a burst DATE: 25/05/04 23:44:16 GMT FROM: David Palmer at LANL M. J. Moss (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 23:25:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250504A (trigger=1310284). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.612, -40.349 which is RA(J2000) = 17h 58m 27s Dec(J2000) = -40d 20' 57" 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 60 sec. The peak count rate was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 23:27:15.3 UT, 77.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 269.61691, -40.36642 which is equivalent to: RA(J2000) = 17h 58m 28.06s Dec(J2000) = -40d 21' 59.1" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 64 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.12 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 250 seconds with the U filter starting 137 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. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 0.00% of the XRT error circle. No correction has been made for the expected extinction corresponding to E(B-V) of 0.191. 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/)
GCN 40344 table
GRB_name GRB250504A
GCN_number 40344
Detection_method Fermi GBM Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40344 SUBJECT: Fermi GRB 250504A: Global MASTER-Net observations report DATE: 25/05/05 00:01:03 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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-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 250504A ( Fermi GBM team, GCN 40342) errorbox 1 sec after notice time and 43 sec after trigger time at 2025-05-04 23:26:38 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 29 deg. The sun altitude is -70.3 deg. The galactic latitude b = -6 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2860892 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 49 | 2025-05-04 23:26:38 | MASTER-SAAO | (17h 56m 41.66s , -40d 35m 44.3s) | C | 10 | 16.7 | 77 | 2025-05-04 23:27:07 | MASTER-SAAO | (17h 56m 41.67s , -40d 35m 44.8s) | C | 10 | 16.7 | 111 | 2025-05-04 23:27:36 | MASTER-SAAO | (17h 56m 41.71s , -40d 35m 45.1s) | C | 20 | 17.0 | 151 | 2025-05-04 23:28:15 | MASTER-SAAO | (17h 56m 41.72s , -40d 35m 45.3s) | C | 20 | 17.0 | 249 | 2025-05-04 23:29:43 | MASTER-SAAO | (17h 56m 41.65s , -40d 35m 44.1s) | C | 40 | 17.2 | 313 | 2025-05-04 23:30:42 | MASTER-SAAO | (17h 56m 41.63s , -40d 35m 43.6s) | C | 50 | 17.2 | 387 | 2025-05-04 23:31:51 | MASTER-SAAO | (17h 56m 41.55s , -40d 35m 43.1s) | C | 60 | 17.3 | 466 | 2025-05-04 23:33:10 | MASTER-SAAO | (17h 56m 41.50s , -40d 35m 42.3s) | C | 60 | 17.3 | 545 | 2025-05-04 23:34:29 | MASTER-SAAO | (17h 56m 41.40s , -40d 35m 41.4s) | C | 60 | 17.3 | 624 | 2025-05-04 23:35:48 | MASTER-SAAO | (17h 56m 41.29s , -40d 35m 40.5s) | C | 60 | 17.3 | 703 | 2025-05-04 23:37:08 | MASTER-SAAO | (17h 56m 41.19s , -40d 35m 39.7s) | C | 60 | 17.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.
GCN 40345 table
GRB_name GRB250504A
GCN_number 40345
Detection_method Swift-XRT Det
ra 269.6181°
decl -40.3668°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40345 SUBJECT: GRB 250504A: Enhanced Swift-XRT position DATE: 25/05/05 07:32:59 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 940 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250504A, 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 = 269.61806, -40.36676 which is equivalent to: RA (J2000): 17h 58m 28.34s Dec (J2000): -40d 22' 00.3" with an uncertainty of 4.0 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.
GCN 40346 table
GRB_name GRB250504A
GCN_number 40346
Detection_method Fermi GBM Det
t_trigger 23:25:54.780 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 40346 SUBJECT: GRB 250504A: Fermi GBM Observation DATE: 25/05/05 08:00:47 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:25:54.78 UT on 04 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250504A (trigger 768093959/250504976), which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 40343). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 111 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 49 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+59.393 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 621 +/- 130 keV. The event fluence (10-1000 keV) in this time interval is (1.20 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 3.6 +/- 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 40347 table
GRB_name GRB250504A
GCN_number 40347
Detection_method Optical
ra 269.6182°
decl -40.3665°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40347 SUBJECT: GRB 2050504A: MeerLICHT optical afterglow detection DATE: 25/05/05 08:04:54 GMT FROM: Simon de Wet at DTU Space S. de Wet (DTU Space), P.M. Vreeswijk (Radboud) and P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT consortium: The 0.6 m wide-field MeerLICHT optical telescope located in Sutherland, South Africa, obtained a repeating series of 60 s exposures in the q,u,g,r,i,z bands of GRB 250504A following the Swift detection (Moss et al., GCN 40343). Observations started at 23:29:27 UT on 2025 May 5 (210 seconds post-trigger) and continued for a further 3 hours, following the filter sequence quqgqrqiqz. We find a new transient candidate in our first q-band exposure at the following coordinates: RA (J2000) = 17:58:28.38 (269.61827d) Dec (J2000) = -40:21:59.58 (-40.36655d) calibrated against Gaia DR2. The astrometric uncertainty is ~0.3" in each coordinate. This position is outside the initial XRT error circle reported by Moss et al. (GCN 40343) but within the updated XRT error circle reported by Osborne et al. (GCN 40345). We regard this object as the optical afterglow to GRB250504A. We report the following AB magnitudes and non detections from our first exposures: q = 19.32 +/- 0.05 at 23:29:59 UT u > 19.34 (3sigma) at 23:31:20 UT g = 19.69 +/- 0.10 at 23:34:04 UT r = 19.52 +/- 0.11 at 23:36:48 UT i = 19.32 +/- 0.13 at 23:39:31 UT z = 18.85 +/- 0.20 at 23:42:14 UT MeerLICHT is built and run by a consortium consisting of Radboud University, University of Cape Town, the South African Astronomical Observatory, the University of Oxford, the University of Manchester and the University of Amsterdam.
GCN 40350 table
GRB_name GRB250504A
GCN_number 40350
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40350 SUBJECT: GRB 250504A: REM optical/NIR observations DATE: 25/05/05 10:35:35 GMT FROM: Riccardo Brivio at INAF-OAB R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250504A detected by Fermi/GBM (Fermi GBM team, GCN 40342) and Swift/BAT (Moss et al., GCN 40343) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 05 at 01:09:20 UT (i.e. 1.7 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any counterpart at the position of the optical afterglow (de Wet et al., GCN. 40347) down to the following 3sigma limits: r > 19.3 (AB; calibrated against the SkyMapper catalogue), at a mid-time of 2.2 hours after the trigger; H > 15.7 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 2.1 hours after the trigger.
GCN 40351 table
GRB_name GRB250504A
GCN_number 40351
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40351 SUBJECT: GRB 250504A: SVOM/VT upper limit DATE: 25/05/05 14:53:47 GMT FROM: SVOM_group L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, D.H. Zhao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT Instrument Center: SVOM/VT conducted ToO follow-up observations of GRB 250504A detected by Fermi (Fermi/GBM team, GCN 40342; Bala et al., GCN 40346) and Swift (Moss et al., GCN 40343). The observation started on 2025-05-05T01:11:01 UT, 2025 May 05, ~1.75 hr after the burst. Our preliminary analysis shows no detection of an optical counterpart in VT_B-band stacked images (3975 s total effective exposure) at both the de Wet et al. (GCN 40347) position and the enhanced XRT position (4.0 arcsec error radius; Osborne et al. GCN 40345), with a 3 sigma upper limit of VT_B > 22.0 mag (AB) at 2.74 hr post-burst. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
GCN 40353 table
GRB_name GRB250504A
GCN_number 40353
Detection_method Swift-BAT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 40353 SUBJECT: GRB 250504A: VLT/X-shooter upper limits DATE: 25/05/05 19:26:55 GMT FROM: Andrea Saccardi at CEA/Irfu A. Saccardi (CEA/Irfu), M. Garnichey (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (Leicester), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration: We observed the field of GRB 250504A detected by Fermi/GBM (Fermi GBM team, GCN 40342; Bala et al., GCN 40346) and Swift/BAT (Moss et al., GCN 40343) using the ESO VLT UT3 (Melipal) with the X-shooter acquisition camera. A short sequence of imaging was secured in the r (3x30 s), g (3x60 s), and z (3x40 s) bands. No afterglow is detected consistent with the optical position reported by de Wet et al. (GCN 40347) with the following 5 sigma upper limit calibrated against nearby SkyMapper stars: r > 23.4 (AB) on 2025 May 05 at 03:21:58 UT (3.93 hr after the burst). We acknowledge excellent support from the ESO observing staff in Paranal, in particular Abigail Frost, Florian Rodler, Marco Berton, and Rodrigo Palominos.
GCN 40354 table
GRB_name GRB250504A
GCN_number 40354
Detection_method Swift-XRT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40354 SUBJECT: GRB 250504A: Swift-XRT refined Analysis DATE: 25/05/05 21:00:16 GMT FROM: Phil Evans at U of Leicester J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M. A. Williams (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.9 ks of XRT data for GRB 250504A, from 81 s to 56.7 ks after the BAT trigger. The data comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.26 (+0.05, -0.04). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.60 (+0.24, -0.22). The best-fitting absorption column is 2.9 (+1.4, -0.7) x 10^21 cm^-2, consistent with the Galactic value of 2.1 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.8 x 10^-11 (6.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+1.4, -0.7) x 10^21 cm^-2 Galactic foreground: 2.1 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.60 (+0.24, -0.22) If the light curve continues to decay with a power-law decay index of 1.26, the count rate at T+24 hours will be 1.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x 10^-14 (1.0 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/01310284. This circular is an official product of the Swift-XRT team.
GCN 40357 table
GRB_name GRB250504A
GCN_number 40357
Detection_method Swift-BAT Det
ra 269.6050°
decl -40.3450°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40357 SUBJECT: GRB 250504A: Swift-BAT refined analysis DATE: 25/05/06 02:54:01 GMT FROM: Mike Moss at NASA GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), 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 250504A (trigger #1310284) (Moss, et al., GCN Circ. 40343). The BAT ground-calculated position is RA, Dec = 269.605, -40.345 deg which is RA(J2000) = 17h 58m 25.3s Dec(J2000) = -40d 20' 41.8" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 98%. The mask-weighted light curve shows a complex light curve with several pulses. T90 (15-350 keV) is 52.39 +- 2.31 sec (estimated error including systematics). The time-averaged spectrum from T-2.96 to T+55.10 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.27 +- 0.08. The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+7.70 sec in the 15-150 keV band is 1.6 +- 0.2 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/1310284
GCN 40372 table
GRB_name GRB250504A
GCN_number 40372
Detection_method Swift-BAT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 40372 SUBJECT: GRB 250504A: EIRSAT-1 GMOD Detection DATE: 25/05/06 21:03:59 GMT FROM: Padraig McDermott at University College Dublin P. McDermott, D. Murphy, C. McKenna, C. de Barra, A. Ulyanov, G. Finneran, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the long gamma-ray burst GRB 250504A by the Gamma-ray Module (GMOD) instrument, which was also detected by Fermi GBM (GCN [40342](https://gcn.nasa.gov/circulars/40342) and [40346](https://gcn.nasa.gov/circulars/40346)) and Swift-BAT (GCN [40343](https://gcn.nasa.gov/circulars/40343)). The GMOD detection was made starting at 2025-05-04 23:25:56.5 UTC. The GMOD light curve for GRB 250405A, with 1.2s binning, shows multiple peaks consistent with the detections by Fermi GBM and Swift-BAT. The spacecraft location at time of detection was 9.886º S, 164.567° E and an altitude of 386 km. The light curve for this event as measured by GMOD can be found here: https://grb.eirsat1.ie/250504A/250504A_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023.