October 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 40574] Fermi-LAT Gamma-ray Observations of IceCube-251025A
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42489 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-251025A DATE: 25/10/27 17:51:55 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC251025A neutrino event (GCN 42436) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 25-10-25 at 13:47:53.26 UTC (T0) with J2000 position RA = 145.63 (+0.88, -0.88) deg, Decl. = 15.06 (+0.65, -0.62) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC251025A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC251025A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC251025A best-fit position, the >100 MeV flux upper limit (95% confidence) is <2.8e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <2.8e-09 (<4.6e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/42489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40573] GRB 251023B: Swift-UVOT Upper Limits
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42488 SUBJECT: GRB 251023B: Swift-UVOT Upper Limits DATE: 25/10/27 17:38:43 GMT FROM: noelklin(a)umbc.edu Swift-UVOT has performed follow-up observations of the EP-detected burst GRB 251023B (Wu et al. GCN 42415), collecting 1.7 ks of observations between T0+6.6 ks and T0+26.9 ks. No source was detected in the UVOT data at the position of the optical afterglow (Mandarakas et al., 42404; He at al., GCN 42418; Adami et al., 42421; Méndez et al. 42424). 3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag U 6573 26943 1737 >21.92 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.416 in the direction of the burst (Schlegel et al. 1998). We note that in the first snapshot (1531.80 s worth of data), the optical afterglow's position landed on a UVOT detector patch of small scale sensitivity inhomogeneity. In the U-band this can cause a source's flux to appear 5-16% lower than it actually is. The above limits are not corrected for this. See https://swift.gsfc.nasa.gov/analysis/uvot_digest/sss_check.html for more information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40572] Konus-Wind detection of GRB 251022A
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42487 SUBJECT: Konus-Wind detection of GRB 251022A DATE: 25/10/27 17:16:14 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 251022A (Fermi-GBM detection: The Fermi GBM team, GCN 42380; Mukherjee & Meegan, GCN 42410; Fermi-LAT detection: Di Lalla et al., GCN 42384; SVOM/GRM observation: Ren et al., GCN 42484) triggered Konus-Wind (KW) at T0=81287.312 s UT (22:34:47.312). The burst consists of multiple emission pulses in the interval from T0-35 s to T0+90; the total duration of the burst is ~125 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251022_T81287/ As observed by Konus-Wind, the burst had a fluence of (4.14 ± 0.71)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 23.168 s, of (1.09 ± 0.36)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+90.368 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.37 (-0.08,+0.07), the high energy photon index beta = -2.06 (-0.22,+0.13), the peak energy Ep = 178 (-38,+80) keV, chi2 = 96/97 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.71 (-0.42,+0.80), the high energy photon index beta = -2.13 (-0.84,+0.24), the peak energy Ep = 161 (-56,+84) keV, chi2 = 91/97 dof. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/42487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40571] GRB 251027A: Swift-XRT observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42486 SUBJECT: GRB 251027A: Swift-XRT observations DATE: 25/10/27 16:36:26 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 251027A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+4.5 ks and T0+12 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 2 uncatalogued X-ray sources * 0 known X-ray sources Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J062052.1+114644): ================================== RA (J2000.0): 95.2175 = 06 20 52.20 Dec (J2000.0): +11.7792 = +11 46 45.1 Error: 7.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 5.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.4 [+2.7, -2.0])e-3 ct s^-1 Mean flux: (1.90 [+0.95, -0.72])e-10 erg cm^-2 s^-1 Peak rate: (5.4 [+2.7, -2.0])e-3 ct s^-1 Peak flux: (1.90 [+0.95, -0.72])e-10 erg cm^-2 s^-1 ECF: 3.52e-08 erg cm^-2 ct^-1 assuming NH=1.86e+24 cm^-2, gamma=-3.00 determined from a spectral fit. XMM UL: 2.1e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 2.2-sigma above this 3-sigma upper limit. There is no evidence for fading. A SIMBAD object `NVSS J062052+114645' is 0.1" away. There are 4 2MASS objects within the source's 3-sigma error radius. Source 3 (SWIFT J062105.2+112959): ================================== RA (J2000.0): 95.2720 = 06 21 05.28 Dec (J2000.0): +11.4998 = +11 29 59.3 Error: 8.8 (arcsec, radius, 90% confidence). Detect flag: POOR Distance: 12.3 arcmin from the SVOM/ECLAIRs position. Mean rate: (5.7 [+3.5, -2.5])e-3 ct s^-1 Mean flux: (2.4 [+1.5, -1.1])e-13 erg cm^-2 s^-1 Peak rate: (5.7 [+3.5, -2.5])e-3 ct s^-1 Peak flux: (2.4 [+1.5, -1.1])e-13 erg cm^-2 s^-1 XMM UL: 3.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There are 5 2MASS objects within the source's 3-sigma error radius. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. 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/SVOM/SVOM_FIELD00046. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40570] EP251027.145: COLIBRÍ optical upper limits
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42485 SUBJECT: EP251027.145: COLIBRÍ optical upper limits DATE: 25/10/27 15:48:00 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> William H. Lee (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU),Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ramandeep Gill (UNAM), Noémie Globus (UNAM), Ocelotl López (UNAM), Diego López-Cámara (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP251027.145 (ID=01709247525) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-27 07:47 to 09:09 UTC (from 4.3 to 5.7 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any uncatalogued source at the EP/WXT position down to the following 5-sigma limit: r > 23.6 z > 22.3 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40569] GRB 251022A: SVOM/GRM observation
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42484 SUBJECT: GRB 251022A: SVOM/GRM observation DATE: 25/10/27 15:46:15 GMT FROM: renyz16607(a)163.com GRB 251022A: SVOM/GRM observation SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251022A at 2025-10-22T22:34:19.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42380), Swift/BAT (James DeLaunay et al., GCN#42409) and Fermi/LAT ( N. Di Lalla et al., GCN #42384), With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 106 +6/-2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251022A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 74.5, Dec = -22.7, GCN #42380), is located at about 102 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-20 to T0+101 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.49 +0.12/-0.11 and the cutoff energy, parameterized as Epeak, is 330 +162/-80 keV. The event fluence (10-1000 keV) in this time interval is (4.07 +0.27/-0.27)E-05 erg/cm^2. The localization of GRB 251022A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251022A_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40568] GRB 251026B: Swift ToO observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42483 SUBJECT: GRB 251026B: Swift ToO observations DATE: 25/10/27 15:40:49 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Fermi/GBM-detected event GRB 251026B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021872 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 Fermi/GBM 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40567] GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42482 SUBJECT: GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient DATE: 25/10/27 15:36:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), J. H. Wu (GZHU), H. Q. Cheng and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251026a. The ground analysis of the WXT data shows that the event started at T0=2025-10-26T08:26:33 (UTC). The WXT position of the source is R.A. = 72.663 deg, DEC = 51.775 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). This transient is temporally and spatially coincident with GRB 251026A (GCN 42454). The analysis of the WXT data shows that the event lasted for about 500 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.00 (-0.37/+0.38). The derived average unabsorbed 0.5-4 keV flux is 1.35 (-0.6/+0.7) x 10^-9 erg/s/cm^2. The peak flux is around 2.1 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.07 (-0.53/+0.55). We note that the late release of this transient is mostly due to the delay in the data transmission. Follow-up observations with EP-FXT has been scheduled and more information will be reported when the telemetry data arrives. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/42482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40566] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40565] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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