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[vsnet-grb-info 38392] GRB 250506A: REM optical/NIR upper limits
by GCN Circulars 06 May '25

06 May '25

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 <matteo.ferro(a)inaf.it> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38391] GRB 250506A: Fermi GBM Observation
by GCN Circulars 06 May '25

06 May '25

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 <rushikesh23(a)iisertvm.ac.in> 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/40362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38390] GRB 250506A: Swift XRT observations and possible counterpart detection
by GCN Circulars 06 May '25

06 May '25

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 <pae9(a)leicester.ac.uk> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38389] GRB 250506A: TRT optical observations
by GCN Circulars 06 May '25

06 May '25

TITLE: GCN CIRCULAR NUMBER: 40360 SUBJECT: GRB 250506A: TRT optical observations DATE: 25/05/06 09:28:48 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and probably by Fermi/GBM as well (Fermi GBM team, GCN 40355), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Within the Swift/XRT error circle (https://www.swift.ac.uk/SVOM/SVOM_FIELD00014/), a brightening, catalogued, and seemingly round source is detected at coordinates R.A. (J2000) = 14:38:34.03 Dec. (J2000) = +29:13:02.10 which has r = 18.41+/- 0.01 in the TRT image (calibrated with PanSTARRS) at a median time of 4.48 hrs after the SVOM trigger, while it has has r = 19.00 +/- 0.01 mag in PanSTARRS. This source is also covered by SDSS, Legacy Survey, and GAIA. In GAIA, it is classified as a QSO. The source has a photometric redshift of z ~ 0.46+/-0.10 from SDSS and z ~ 0.49+/-0.26 from Legacy Survey. No new source is detected within the Swift/XRT error circle, down to a limiting magnitude of r ~ 21.8 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/40360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38388] GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
by GCN Circulars 06 May '25

06 May '25

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 <adeugartepostigo(a)gmail.com> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38387] GRB 250506A: SVOM detection of a burst
by GCN Circulars 06 May '25

06 May '25

TITLE: GCN CIRCULAR NUMBER: 40358 SUBJECT: GRB 250506A: SVOM detection of a burst DATE: 25/05/06 03:20:58 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> 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(a)ihep.ac.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38386] GRB 250504A: Swift-BAT refined analysis
by GCN Circulars 06 May '25

06 May '25

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 <mikejmoss3(a)gmail.com> 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/40357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38385] GRB 250430A: Swift-BAT refined analysis
by GCN Circulars 06 May '25

06 May '25

TITLE: GCN CIRCULAR NUMBER: 40356 SUBJECT: GRB 250430A: Swift-BAT refined analysis DATE: 25/05/06 02:50:20 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> M. J. Moss (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (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-61 to T+242 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250430A (trigger #1308754) (Parsotan, et al., GCN Circ. 40292). The BAT ground-calculated position is RA, Dec = 233.395, -18.101 deg which is RA(J2000) = 15h 33m 34.7s Dec(J2000) = -18d 06' 03.2" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 72%. The mask-weighted light curve displays a double peaked structure. The T90 (15-350 keV) is 9.17 +- 1.70 sec (estimated error including systematics). The time-averaged spectrum from T+0.10 to T+11.86 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.66 +- 0.11. The fluence in the 15-150 keV band is 8.9 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+0.31 sec in the 15-150 keV band is 2.3 +- 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/1308754 View this GCN Circular online at https://gcn.nasa.gov/circulars/40356. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38384] GRB 250506A: Fermi GBM Final Real-time Localization
by GCN Circulars 06 May '25

06 May '25

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 <do_not_reply(a)GIOC.nsstc.nasa.gov> 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/… 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/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250506100/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40355. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38383] GRB 250504A: Swift-XRT refined Analysis
by GCN Circulars 05 May '25

05 May '25

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 <pae9(a)star.le.ac.uk> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40354. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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