GRB250506A

This page lists all entries on GRB250506A in GRBweb

Summary Fermi GBM GCN 40355 GCN 40358 GCN 40359 GCN 40361 GCN 40362 GCN 40363 GCN 40364 GCN 40366 GCN 40371 GCN 40373 GCN 40378 GCN 40382 GCN 40387 GCN 40392 GCN 40394 GCN 40396 GCN 40405 GCN 40440 GCN 40453

Summary table
Variable Value Source
GRB_name_Fermi GRB250506100
T0 2:23:22 UTC GCN_circulars,Fermi GBM final loc
ra 219.2827° GCN_circulars,Swift-XRT Other
decl 28.8784° GCN_circulars,Swift-XRT Other
T90 48.129 s Fermi_GBM
T90_error 1.305 s Fermi_GBM
T90_start 2:23:23.372 UTC Fermi_GBM
fluence 1.80e-05 erg/cm² Fermi_GBM
fluence_error 5.12e-08 erg/cm² Fermi_GBM
T100 49.501 s
GBM_located False
mjd 60801.09956018518 GCN_circulars,Fermi GBM final loc
Fermi GBM table
GRB_name_Fermi GRB250506100
trigger_name bn250506100
ra 219.6100°
decl 29.2800°
pos_error 2.75e+00°
datum 2025-05-06
t_trigger 2:23:22.604 UTC
T90 48.129 s
T90_error 1.305 s
T90_start 2:23:23.372 UTC
fluence 1.80e-05 erg/cm²
fluence_error 5.12e-08 erg/cm²
flux_1024 2.74e+01 erg/cm²/s
flux_1024_error 5.36e-01 erg/cm²/s
flux_1024_time 3.38e+01 erg/cm²/s
flux_64 3.38e+01 erg/cm²/s
flux_64_error 2.33e+00 erg/cm²/s
GCN 40355 table
GRB_name GRB250506A
GCN_number 40355
Detection_method Fermi GBM final loc
t_trigger 2:23:22 UTC
ra 219.9000°
decl 26.9000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40355 SUBJECT: GRB 250506A: Fermi GBM Final Real-time Localization DATE: 25/05/06 02:33:50 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely LONG GRB At 02:23:22 UT on 6 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250506A (trigger 768191007.604196 / 250506100). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.9, Dec = 26.9 (J2000 degrees, equivalent to J2000 14h 39m, 26d 53'), with a statistical uncertainty of 2.1 degrees. The angle from the Fermi LAT boresight is 107.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250506100/quicklook/glg_skymap_all_bn250506100.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/bn250506100/quicklook/glg_healpix_all_bn250506100.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250506100/quicklook/glg_lc_medres34_bn250506100.gif
GCN 40358 table
GRB_name GRB250506A
GCN_number 40358
Detection_method Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40358 SUBJECT: GRB 250506A: SVOM detection of a burst DATE: 25/05/06 03:20:58 GMT FROM: SVOM_group Chenwei Wang (IHEP), Lin LAN, Wenjin XIE, Donghua ZHAO (NAOC), Li ZHANG (IHEP), Pierre MAGGI (ObAS) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered and located GRB 250506A (SVOM burst-id sb25050601) at 2025-05-06T02:23:24.501UTC. The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 12.51 in the [8-120] keV energy band over a time window of 2.50 seconds starting at 2025-05-06T02:23:22.001 The localization of the best alert is R.A., Dec. 219.61, 29.28 degrees: R.A. (J2000) = 14h38m27.02s Dec. (J2000) = 29d16m38.09s with a 90% confidence level (C.L.) radius of 6.47 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM with 3 GRDs but only the first pulse is detected, since the other part is in occultation. The lightcurve of GRM could be found in the link below: https://www.bursthub.cn//admin/static/svgrb250506A.png SVOM slewed to the burst. It was occulted by the Earth at the time of the alert, thus neither MXT nor VT data are available for the early time. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is Chenw ei Wang: cwwang@ihep.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN 40359 table
GRB_name GRB250506A
GCN_number 40359
Detection_method Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40359 SUBJECT: GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart DATE: 25/05/06 04:50:55 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS Antonio de Ugarte Postigo (LAM), William H. Lee (UNAM), Sarah Antier (OCA), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM); Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Chenw ei Wang (IHEP) report: We imaged the field of GRB 250506A (Wang et al. GCN 40358) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We started observations at 2025-05-06 03:29:48 (1.106 hours after the trigger). An initial stack with 16 minutes of exposure in the i filter was obtained with a mean epoch 1.266 hrs after the burst. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction. No credible counterpart is detected down to an AB 5-sigma limit of i > 22.2 mag. Further observations are ongoing. We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
GCN 40361 table
GRB_name GRB250506A
GCN_number 40361
Detection_method Swift Other
ra 219.6418°
decl 29.2174°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40361 SUBJECT: GRB 250506A: Swift XRT observations and possible counterpart detection DATE: 25/05/06 10:03:08 GMT FROM: P.A. Evans at U. Leicester A.P. Beadmore, K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team, Swift-XRT has observed the location of the SVOM and Fermi-detected GRB 250506A (GCN Circs. 40355, 40358), gathering 1.7 ks of data between 1.5 ks and 13.7ks after the Fermi trigger. The observations are centred on the SVOM/ECLAIRs position. We find a single, uncatalogued X-ray source with an enhanced XRT position of RA, Dec = 219.64184, 29.21742 which is equivalent to: RA (J2000) = 14h 38m 34.04s Dec (J2000) = +29° 13′ 02.7 with an uncertainty of 4.6 arcsec (radius, 90% confidence). This source shows evidence for fading at the 2.2-sigma level. As noted by Liu et al. (GCN Circ. 50360), this is spatially consistent with an optical source which Gaia classifies as a "quasar with 100.00% probability” (Gaia DR3 1281175103580872064). The source also appears in the ALLWISEAGN catalogue (Secrest et al., 2015, ApJS, 221, 12). The XRT observations show a mean count-rate of 2.9 (+/- 0.007) ct sec and the spectrum can be modelled with an absorbed power-law with photon index 1.8 (+0.8, -0.5). The intrinsic absorption is <1.8e21 cm^-2, in addition to the Galactic column of 1.44e20 cm^-2. Using these paramters the mean 0.3-10 keV flux is 8.2 (+1.8, -1.7)e-13 erg cm^-2 s^-1. No other X-ray sources are detected, to an upper limit of ~6e-3 ct/sec which corresponds to 2.6e-13 erg cm^-2 s^-1 (0.3-10 keV) assuming a standard power-law spectrum (photon index 1.7, absorption column 3e20 cm^-2). Given the lack of other sources and how early the XRT observations started, combined with the apparent fading of the XRT afterglow, we consider it likely that this source is the counterpart to the Fermi and SVOM triggers; however, follow up observations are encouraged to determine the nature of this event. Automated analysis of the observations is available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00014/. This circular is an official product of the Swift-XRT team.
GCN 40362 table
GRB_name GRB250506A
GCN_number 40362
Detection_method Fermi GBM Det
t_trigger 2:23:22.600 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 40362 SUBJECT: GRB 250506A: Fermi GBM Observation DATE: 25/05/06 13:07:40 GMT FROM: Rushikesh Sonawane at IISER, TVM R. Sonawane (IISER, TVM), S. Bala (USRA), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:23:22.60 UT on 06 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250506A (trigger 768191007/250506100). which was also detected by SVOM/ECLAIRs (Wang et al. 2025, GCN 40358). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 116 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 48 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+61.441 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 280 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (2.36 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+34 s in the 10-1000 keV band is 27.4 +/- 0.5 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 40363 table
GRB_name GRB250506A
GCN_number 40363
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40363 SUBJECT: GRB 250506A: REM optical/NIR upper limits DATE: 25/05/06 14:25:25 GMT FROM: Matteo Ferro at INAF-OAB M. Ferro, R. Brivio, P. D'Avanzo, M. G. Bernardini, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi GBM (Fermi GBM team, GCN 40355; Sonawane et al., GCN 40362) 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 06 at 02:43:22 UT (i.e. 20 minutes after the burst), and lasted for about 3 hours. From preliminary inspection, we do not detect any possible counterpart inside the SVOM error circle, in agreement with other follow-up observations (de Ugarte Postigo et al., GCN 40359; Liu et al., GCN 40360; Beardmore et al., GCN 40361), down to the following 3sigma limits: r > 19.8 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 54 minutes after the trigger; H > 16.4 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 31 minutes after the trigger.
GCN 40364 table
GRB_name GRB250506A
GCN_number 40364
Detection_method Swift Other
ra 219.2667°
decl 28.8594°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40364 SUBJECT: GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow DATE: 25/05/06 14:47:41 GMT FROM: SVOM_group P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) on behalf of the SVOM/MXT Team report: M. Brunet, S. Guillot (IRAP), S. Schanne (CEA) on behalf of the SVOM/ECLAIRs Team report: Using the full X band dataset a corrected ECLAIRs position could be derived for GRB 250506A/sb25050601 (Wang et al., GCN 40358). The improved ECLAIRs position is RA=219.373, Dec=28.909 with a 90% c.l. of 6.4 arc min. The burst appeared very close to the Earth limb and only part of the burst signal was considered by the onboard processing, explaining the localization error. SVOM MXT observed the ECLAIRs error region starting at T0 = 2025-05-06T03:09:28.279 (46 min after trigger time Tb). MXT observed it during 5 orbits for a 10.9 ks effective exposure. Using the full X band dataset, we find an uncatalogued source. The source is fading with time and not detected after the fourth orbit (t+T0 > 23 ks). The best position is obtained from first orbit data (t+T0 < 2.5ks), at RA=219.267, Dec=28.8593 corresponding to: RA (J2000) = 14h37m04. Dec (J2000) = +28d51m34. with a statistical 90% C.L. radius of 32.5” to which a 35” systematic uncertainty is to be added in quadrature. The afterglow spectrum is modelled by an absorbed power law fading with time. The absorption column is NH = 3+/-1 x 1e21 /cm2 (90% C.L. uncertainties) and a photon index of 2.3 (+0.7/-0.6) in first orbit softening to 3.3 (+2.5/-1.2) in the second orbit. The average observed flux in the 0.3-8 keV band is 6.8 (+3.4/-2.2) x1e-11 erg/cm2/s during the first orbit and 1.4 (<2.7) x1e-11 erg/cm2/s during the second one. The ECLAIRs and MXT position are consistent, confirming that the MXT source is the afterglow of the GRB 250506A. This position corrects and supersedes the one reported by Wang et al. (GCN 40358). The active QSO detected by TRT (Liu et al., GCN 40360) and Swift XRT (Beardmore et al., GCN 40361) is thus unrelated to GRB 250506A. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. ECLAIRs was developed jointly by CNES, IRAP, APC and CEA. The Burst Advocate (BA) on shift for this burst is Chenwei Wang: cwwang@ihep.ac.cn Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN 40366 table
GRB_name GRB250506A
GCN_number 40366
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40366 SUBJECT: GRB 250506A: Xinglong 2.16m optical upper limit DATE: 25/05/06 16:04:35 GMT FROM: Liping Xin at NAOC, SVOM L. P. Xin, J. Zhen, J. Wang, H. L. Li, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, P. P. Zhang, Y. J. Xiao, L. Lan, W. J. Xie, J. S. Deng, J. Y. Wei (NAOC) report on behalf of SVOM follow-up team: We observed the field of GRB 250506A (Wang et al., GCN 40358; Maggi et al., GCN 40364; Fermi team GCN 4035). using the 2.16-m telescope located at Xinglong observatory, China, equipped with the BFOSC camera. The weather is not good. We obtained 2*200s and 7x300s frames in R-band, starting at 14:00:19 UT on 2025-05-06,about 11.65 hrs after the trigger. No any uncatalogued sources were detected within the error box of EP/FXT(Zhang et al., GCN 40365) or SVOM/Eclairs or SVOM/MXT (Maggi et al., GCN 40364) in our stacked image, down to a 3 sigma limiting magnitude of R~21.0 mag, calibrated with the nearby PanSTARRS field.
GCN 40371 table
GRB_name GRB250506A
GCN_number 40371
Detection_method Swift Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40371 SUBJECT: GRB 250506A: Swift ToO observations DATE: 25/05/06 19:55:53 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 SVOM/ECLAIRs-detected event GRB 250506A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021828 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 SVOM/ECLAIRs 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.
GCN 40373 table
GRB_name GRB250506A
GCN_number 40373
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40373 SUBJECT: GRB 250506A: Mephisto optical upper limits DATE: 25/05/07 02:43:57 GMT FROM: Brajesh Kumar at SWIFAR, YNU Dezi Liu, Ziwei Li, Tao Wang, Shuang Lin, Xiangru Qian, Guowang Du, Xingzhu Zou, Yu Pan, Xinlei Chen, Xufeng Zhu, Helong Guo, Yuan Fang, Jinghua Zhang, Chenxu Liu, Edoardo Lagioia, Brajesh Kumar, Jianhui Lian, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: We conducted simultaneous multi-band photometric observations of the GRB 250506A (SVOM burst-id sb25050601) detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and by Fermi (Fermi GBM team, GCN 40362) with the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. Simultaneous u, g, and i band observations were initiated at 14:08:39 UTC on 2025-05-06 (~12.5 hours after the trigger). We obtained four exposures of 300 seconds each in ugi bands. No optical counterpart was detected at the refined position reported by the SVOM team (Maggi et al., GCN 40364). The preliminary 3-sigma upper limits are below: | UT Start | T-T0 (hr) | Band | Exp | LimMag (AB) | |-------------------|-----------|------|--------|-------------| | 2025/5/6 14:08:40 | 12.53 | u | 4x300s | > 21.82 | | 2025/5/6 14:08:40 | 12.53 | g | 4x300s | > 22.42 | | 2025/5/6 14:08:39 | 12.53 | i | 4x300s | > 21.84 | These limits are consistent with previously reported non-detections (Xin et al., GCN 40366; Ferro et al., GCN 40363; Liu et al., GCN 40360; Postigo et al., GCN 40359). ---------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ----------------------------------------------------------
GCN 40378 table
GRB_name GRB250506A
GCN_number 40378
Detection_method Swift-XRT Other
ra 219.2827°
decl 28.8784°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40378 SUBJECT: GRB 250506A: Swift-XRT observations DATE: 25/05/07 09:35:26 GMT FROM: Phil Evans at U of Leicester D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/MXT-detected burst GRB 250506A at the revised position given in GCN Circ. 40364, collecting 2.9 ks of Photon Counting (PC) mode data between T0+63.2 ks and T0+70.1 ks. One uncatalogued X-ray source has been detected, it is below the RASS limit and shows no definitive signs of fading. Therefore, at the present time we cannot confirm this as the afterglow. Details of this source are given below: Source 1: RA (J2000): 219.28269 = 14:37:7.85 Dec (J2000): +28.87835 = +28:52:42.1 Error: 2.6 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.0586 +/- 0.0052 ct s^-1 Distance: 84 arcsec from SVOM/MXT position. Flux: (2.16 +/- 0.19)e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) 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/00021828. This circular is an official product of the Swift-XRT team.
GCN 40382 table
GRB_name GRB250506A
GCN_number 40382
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40382 SUBJECT: GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/05/07 14:39:13 GMT FROM: J.-G. Ducoin at CPPM Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Chenwei WANG (IHEP) and Lin LAN (NAOC): We imaged the field of the SVOM GRB 250506A (Wang et al., GCN Circ. 40358) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-07T03:44:16 to 05:14:17 UTC (from 1.12 to 1.22 days after the trigger) and obtained 64 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the improved MXT position (Maggi et al., GCN Circ. 40364) and at the XRT position (Burrows et al., GCN Circ. 40378) down to the following 5-sigma limit (AB): i > 22.4 This upper limit is consistent with the one reported by Xin et al. (GCN Circ. 40366), Ferro et al. (GCN Circ. 40363), Liu et al. (GCN Circ. 40360), Postigo et al. (GCN Circ. 40359), and Liu et al. (GCN Circ. 40373). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN 40387 table
GRB_name GRB250506A
GCN_number 40387
Detection_method Swift-UVOT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 40387 SUBJECT: GRB 250506A: Swift/UVOT Upper Limits DATE: 25/05/07 20:04:42 GMT FROM: Samantha Oates at University of Birmingham S. R. Oates (Lancaster U.) and N. Klinger (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250506A 63 ks after the of the SVOM and Fermi-detected GRB 250506A (GCN Circs. 40355, 40358). No optical afterglow consistent with the SVOM MXT (Maggi et al., GCN Circ. 40364) and the XRT position (Burrows et al. GCN Circ. 40378) is detected in the initial UVOT exposures. Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 64170 70154 1176 >22.1 v 64937 65102 163 >19.3 u 63403 69711 1530 >21.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).
GCN 40392 table
GRB_name GRB250506A
GCN_number 40392
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40392 SUBJECT: GRB 250506A: SVOM/VT optical upper limit DATE: 25/05/08 07:22:50 GMT FROM: SVOM_group L. Lan(NAOC), C. W. Wang(IHEP), R. C. Chen(NJU), W. J. Tan(IHEP), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA) report on behalf of the SVOM mission team. After the trigger by SVOM/ECLAIRs and Fermi/GBM at 2025-05-06T02:23:22 UTC (SVOM burst-id sb25050601, Fermi burst-id bn250506100), VT performed ToO observations on the burst in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started at 13.69 hours after the SVOM trigger. No uncataloged sources are detected in single or stacked images within the errorbox of Eclairs or MXT (Maggi et al., GCN 40364), compared to the Legacy survey. The 3 sigma upper limits are derived below: Mid_time | Band | Exposure Time (second) | Upper limit (AB) 15.64 hour | VT_B | 100*63 | 23.7 15.64 hour | VT_R | 100*73 | 23.6 This results are consistent with the report (de Ugarte Postigo et al. GCN 40359). 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 40394 table
GRB_name GRB250506A
GCN_number 40394
Detection_method Swift-XRT Other
ra 219.2827°
decl 28.8784°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40394 SUBJECT: GRB 250506A: Swift-XRT afterglow detection DATE: 25/05/08 08:42:38 GMT FROM: Phil Evans at U of Leicester D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the SVOM/MXT-detected burst GRB 250506A. The observations now extend from T0+63.4 ks to T0+138.3 ks and have a total exposure time of 6.3 ks. The source previously reported, "Source 1", is fading with 2.8 sigma significance and thus is believed to be the GRB afterglow. Using 2772 s of PC mode data and 2 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 = 219.28269, +28.87835 which is equivalent to: RA (J2000): 14h 37m 07.85s Dec(J2000): +28d 52' 42.0" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is 84 arcsec from the SVOM/MXT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.7 (+0.5, -0.4). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.74 (+0.34, -0.21). The best-fitting absorption column is 2.1 (+7.8, -0.4) x 10^20 cm^-2, consistent with the Galactic value of 1.6 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 3.8 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+7.8, -0.4) x 10^20 cm^-2 Galactic foreground: 1.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.74 (+0.34, -0.21) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021828. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021828. This circular is an official product of the Swift-XRT team.
GCN 40396 table
GRB_name GRB250506A
GCN_number 40396
Detection_method Swift-XRT Other
ra 219.2827°
decl 28.8784°
Circular_text TITLE: GCN CIRCULAR NUMBER: 40396 SUBJECT: GRB 250506A: GECAM detection DATE: 25/05/08 14:13:56 GMT FROM: Chenwei Wang at IHEP Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 250506A at 2025-05-06T02:23:22.850 UTC (denoted as T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #40355) and SVOM (Wang et al., GCN #40358). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 34.6 +0.8/-1.9 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250506A.png With the localization of RA, Dec = 219.28269, +28.87835, as determined by Swift/XRT (D.N. Burrows et al., GCN #40394), the time-averaged spectrum from T0-10s to T0+60 s is best fitted by a powerlaw with an alpha of -2.02 +/- 0.11. The event fluence (10-1000 keV) in this time interval is (2.60 +/- 0.14)E-05 erg/cm^2. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN 40405 table
GRB_name GRB250506A
GCN_number 40405
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 40405 SUBJECT: GRB 250506A: NOT optical upper limits DATE: 25/05/09 09:37:58 GMT FROM: Gregory Corcoran at University College Dublin Z. P. Zhu (NAOC), B. Schneider (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), T. T. Hansen, W. M. Ali, P. H. Chan, N. Hölinger, E. Lamprou, R. Lesley, H. Lundberg, J. Pajak, L. Peschieras, and N. Valsamidis (all Stockholm University), report on behalf of a larger collaboration. We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi/GBM (Sonawane et al., GCN 40362), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT) centered at the X-ray source detected by EP/FXT (Zhang et al. GCN 40365). We obtained exposures in the SDSS r (3x600 s) and z (4x300 s) bands starting at 23:44:29 UT on 2025-05-06 (21.35 hr after the SVOM/ECLAIRs trigger). No new optical source is detected at a position consistent with the Swift/XRT error region (the best currently available for this event; Burrows et al., GCN 40378) in the stacked images of either band down to the 5-sigma limiting AB magnitudes of r > 23.6 and z > 22.5, calibrated against nearby Pan-STARRS stars.
GCN 40440 table
GRB_name GRB250506A
GCN_number 40440
Detection_method Fermi GBM Det
t_trigger 2:23:56.500 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 40440 SUBJECT: GRB 250506A: GRBAlpha detection DATE: 25/05/12 14:45:14 GMT FROM: Andras Pal at Konkoly Observatory A. Pal (Konkoly Observatory), M. Dafcikova, J. Ripa, N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250506A (Fermi/GBM detection: GCN 40355; SVOM/GRM and ECLAIRs detection: GCN 40358; GECAM-B detection: GCN 40396) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-05-06 02:23:56.5 UTC. The T90 duration measured by GRBAlpha is 41 s and the overall significance during T90 reaches 22 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250506A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
GCN 40453 table
GRB_name GRB250506A
GCN_number 40453
Detection_method Konus-Wind Det
t_trigger 2:23:25.817 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 40453 SUBJECT: Konus-Wind detection of GRB 250506A DATE: 25/05/13 10:36:33 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 250506A (Fermi-GBM detection: The Fermi GBM team, GCN 40355; SVOM detection: Wang et al., GCN 40358; GECAM-B detection: Wang et al., GCN 40396; GRBAlpha detection: Pal et al., GCN 40440;) triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817). The burst light curve shows a multi-peaked structure which starts at ~T0-2.1 s and has a total duration of ~56 s. The emission is seen up to ~7 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605 As observed by Konus-Wind, the burst had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+33.728 s, of 8.39(-0.74,+0.75)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+57.600 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.06(-0.04,+0.08), the high energy photon index beta = -3.51(-6.49,+0.91), the peak energy Ep = 284(-28,+28) keV (chi2 = 123/97 dof). The spectrum near the maximum count rate (measured from T0+33.024 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.02(-0.07,+0.08) and Ep = 278(-21,+25) keV (chi2 = 111/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 111/97 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.