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[vsnet-grb-info 40215] GRB 251007A: Swift detection of a burst with an optical counterpart
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42146 SUBJECT: GRB 251007A: Swift detection of a burst with an optical counterpart DATE: 25/10/07 19:53:26 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL), A. Melandri (INAF-OAR), M. J. Moss (GSFC), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 19:36:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251007A (trigger=1402466). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 128.173, +21.823 which is RA(J2000) = 08h 32m 42s Dec(J2000) = +21d 49' 24" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with an initial sequence of peaks followed by a larger complex peak with a total duration of about 100 sec. The peak count rate was ~12000 counts/sec (15-350 keV), at ~56 sec after the trigger. The XRT began observing the field at 19:38:07.4 UT, 69.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 128.1775, 21.8138 which is equivalent to: RA(J2000) = 08h 32m 42.60s Dec(J2000) = +21d 48' 49.7" with an uncertainty of 5.4 arcseconds (radius, 90% containment). This location is 36 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 78 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 08:32:42.40 = 128.17665 DEC(J2000) = +21:48:46.1 = 21.81280 with a 90%-confidence error radius of about 0.63 arc sec. This position is 4.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.38 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.039. Burst Advocate for this burst is E. Ambrosi (elena.ambrosi AT inaf.it). 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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42146. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40214] GRB 250702B/EP250702a: JWST/NIRCam Observations
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42145 SUBJECT: GRB 250702B/EP250702a: JWST/NIRCam Observations DATE: 25/10/07 18:49:45 GMT FROM: Huei Sears at Rutgers University <huei.sears(a)rutgers.edu> H. Sears (Rutgers University), P. K. Blanchard (Harvard), R. Chornock (UC Berkeley), Nayana AJ (UC Berkeley), T. Ahumada (Caltech), K. D. Alexander (Arizona), I. Andreoni, A. Anumarlapudi, J. Carney (UNC), J. Freeburn (UNC), O. Graur (Portsmouth), X. J. Hall (CMU), E. Hammerstein (UC Berkeley), S. W. Jha (Rutgers), M. Kasliwal (Caltech), T. Laskar (Utah), R. Margutti (UC Berkeley), B. O’Connor (CMU), D. Pasham (MIT), I. Sfaradi (UC Berkeley), and Y. Yao (UC Berkeley) report: We obtained imaging of the field of GRB 250702B/EP250702a (GCNs 40883, 40886, 40890, 40906) with JWST/NIRCam under DD program 9447 (PI: H. Sears) starting at 2025-Oct-05 02:05:52 UT (~ 95 days post Fermi Gamma-ray trigger). The images were taken in the F150W, F200W, F277W, F356W, and F444W filters with exposure times of 10,049; 5024; 5024; 5024; and 5024 s, respectively. The host galaxy of the transient has a complex morphology in the short-wavelength filters, F150W and F200W. The prominent separation between two brighter nuclear regions seen in the Hubble Space Telescope (HST) F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784) is also visible at these shorter wavelengths. In the long wavelength filters, however, the galaxy has a smooth profile, including near the nucleus. This morphology supports the interpretation that the host is a single system with a prominent dust lane in a disk viewed nearly edge-on. Visual inspection reveals emission near the position of the transient in F150W and F200W that is not apparent in the longer wavelength filters. This excess emission is coincident with the excess flux noted in the HST F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784). The associated color and morphology suggests emission from an underlying star-forming region rather than solely from the transient. We use GALFIT to subtract two Sérsic components for the long-wavelength + F200W filters and one component for the F150W filter. To place limits on any transient flux, we additionally include one point source component in all filters fixed at the location of the HAWK-I H+K source as reported in A. Levan et al. 2025, ApJL, 990, L28; R.A. (J2000) = 18h 58m 45.s 57, decl. (J2000) = –07d 52 26.2. While the excess flux noticed in the F150W and F200W imaging is ~0.15’’ offset from the HAWK-I position, we believe this is likely to be due to imprecise absolute astrometry. For completeness, we report photometry for the transient at both locations. At the HAWK-I location, we report preliminary host-galaxy subtracted, 3-sigma upper-limits of m_F444W > 25.5 AB, m_F356W > 25.7 AB, m_F277W > 26.2 AB, m_F200W > 27.8 AB, and m_F150W > 28.6 AB (faint with high uncertainty). If, instead, we force the location of the transient to be at the excess flux noted in F150W and F200W, we report preliminary detections of m_F200W = 27.97 +/- 0.32 AB and m_F150W = 29.01 +/- 0.43 AB and find similar limits in the long-wavelength filters. Of note, these magnitudes are not corrected for Galactic nor host extinction. Further analysis is ongoing. We thank STScI staff members Alison Vick, Ben Sunnquist, and the entire JWST team for the successful implementation of this DD program. View this GCN Circular online at https://gcn.nasa.gov/circulars/42145. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40213] GRB 251006A: Swift/BAT-GUANO subthreshold detection of a short burst
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42144 SUBJECT: GRB 251006A: Swift/BAT-GUANO subthreshold detection of a short burst DATE: 25/10/07 17:49:15 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251006A onboard (T0: 2025-10-06T13:27:35.03 UTC, Fermi/GBM trig 781450060, Glowbug GCN 42130) The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 7.1 in a 0.256 s analysis time bin, starting at T0 - 0.064 s. This corresponds to a FAR ~ 9e-4 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 16,319 deg2 and the 50% credible area is 6,346 deg2. The integrated probability inside the coded field of view is 5%. The NITRATES skymap is very large but is consistent with the Fermi localization reported in the final position notice (GCN 42124). A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=781450091/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/781450091/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/781450091/0_n_JOI… Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=781450091 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/42144. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40212] GRB 251005B: Glowbug gamma-ray detection
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42143 SUBJECT: GRB 251005B: Glowbug gamma-ray detection DATE: 25/10/07 15:50:03 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251005B, which was also detected by Fermi/GBM (GCN 42112). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-05 14:27:57.168 with a duration of 6.1 s and a total significance of about 14.1 sigma. The Glowbug onset is ~38 s after the Fermi/GBM trigger time (14:27:19) and corresponds to the second, brighter peak seen in the Fermi/GBM light curve. A search of the Glowbug data for the initial fainter peak at the Fermi/GBM T0 was inconclusive. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42143. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40211] EP251003a: LCO and VST fading optical counterpart
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42142 SUBJECT: EP251003a: LCO and VST fading optical counterpart DATE: 25/10/07 14:34:45 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (U. Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), F. E. Bauer (SSI and UTA), and J. A. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP251003a (Liu et al., GCN 42107) with the Sinistro instrument mounted on the 1-m telescopes at Cerro Tololo Inter-American Observatory, available via the LCO network. Six 200 s exposures were obtained in the SDSS i filter starting at 2025-10-05 UT 07:16:29 (~35.1 hr post trigger). Within the WXT and FXT error circles (Liu et al., GCN 42107), we identify a new source. Calibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude i = 21.6 +/- 0.2 (AB), not corrected for Galactic extinction. No corresponding object is visible in the Legacy Survey down to an AB magnitude of i > 24.2. We obtained an additional observation with the VLT Survey Telescope (VST). Six exposures of 300 s each were obtained in the SDSS i filter as well ten 200 s exposures in the SDSS z filter, starting at 2025-10-06 UT 06:47:12 (~58.6 hr post trigger). The counterpart identified in the LCO image is again detected, and we measure a magnitude of i = 22.87 +/- 0.07 and z = 23.23 +/- 0.14 (AB). Given the significant fading, the consistency with the X-ray localization, and the lack of a bright archival counterpart, we consider this source as the likely counterpart of EP251003a. The most accurate coordinates of the counterpart as measured from the VST image are: RA(J2000): 03:47:40.99 DEC(J2000): -10:55:55.0 We estimate an uncertainty of 0.2" in both RA and Dec. View this GCN Circular online at https://gcn.nasa.gov/circulars/42142. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40210] GRB 251006B/EP251006a: SVOM/VT optical candidate
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42141 SUBJECT: GRB 251006B/EP251006a: SVOM/VT optical candidate DATE: 25/10/07 14:11:15 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, 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), J. Palmerio (CEA), Z. Q. Wang, K. Liu (GXU) report on behalf of the SVOM/VT team. SVOM/VT conducted ToO follow-up observations of GRB 251006B / EP251006a (Fermi GBM Team, GCN 42131; Yin et al. GCN 42137; Wang et al., GCN 42139). The observation started on 2025-10-07T09:37:56 UT (i.e. 13.56 hour after Fermi trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. Within the error box of EP-FXT source 2 (Yin et al., GCN 42140), an uncatalogued source was detected, compared to the Legacy survey. The position is at R.A., Dec. = 40.518487, -6.034955 degrees, equivalent to: R.A. (J2000) = 02:42:04.43 Dec. (J2000) = -06:02:05.8 with an uncertainty of 0.5 arcsec. The magnitudes of the candidate are given below: Mid_time Band Exposure Time Magnitude (AB) 13.5672 hour VT_B 41*70 sec 22.37+/-0.11 mag 13.5672 hour VT_R 39*70 sec 22.12+/-0.12 mag Our photometry is in AB magnitude and not corrected for Galactic extinction. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42141. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40209] GRB 251006B/EP251006a: EP-FXT follow-up observation
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42140 SUBJECT: GRB 251006B/EP251006a: EP-FXT follow-up observation DATE: 25/10/07 13:03:20 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139) at 2025-10-07T06:50:56 (UTC), about 11 hours after the WXT detection, with an exposure time of 2.7 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138). Two uncatalogued sources were detected within the WXT error circle. Preliminary analyses on these sources are automatically conducted, and the details are listed as follows. Source 1: EPF_J024205.3-055701 RA (J2000): 40.5219 Dec (J2000): -5.9501 Flux: 3.25 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 9.45 x 10^-14 erg/s/cm^2 (1 sigma) Source 2: EPF_J024204.7-060206 RA (J2000): 40.5194 Dec (J2000): -6.0350 Flux: 3.52 x 10^-12 erg/s/cm^2 (observed, 0.5-10 keV) Flux_err: 4.30 x 10^-13 erg/s/cm^2 (1 sigma) 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/42140. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40208] GRB 251006B: SVOM/GRM observation
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42139 SUBJECT: GRB 251006B: SVOM/GRM observation DATE: 25/10/07 11:08:42 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP), Olivier GODET (IRAP), Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251006B (SVOM trigger reference: sb25100602) at 2025-10-06T20:05:08.000 (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42131). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two pulses with a T90 of 6.2 +0.2/-0.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251006B.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 40.5, Dec = -4.0, GCN #42131), is located at about 40.5 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view. But ECLAIRs was not collecting data at the time of this burst. With this localization, the time-averaged spectrum from T0-5 to T0+5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.76 +0.03/-0.03 and the cutoff energy, parameterized as Epeak, is 433 +27/-24 keV. The event fluence (10-1000 keV) in this time interval is (2.02 +0.05/-0.05)E-05 erg/cm^2. The localization of GRB 251006B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251006B_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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42139. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40207] GRB 251006B: COLIBRÍ optical upper limit
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42138 SUBJECT: GRB 251006B: COLIBRÍ optical upper limit DATE: 25/10/07 09:36:59 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Jean-Grégoire Ducoin (CPPM), Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), 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 Fermi GRB 251006B (Fermi GBM Team, GCN Circ. 42131, Preis et al., GCN Circ 42132, Yin et al., GCN Circ. 42137) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-07T06:00:50 to 06:19:48 UTC (from 9.93 to 10.25 hours after the trigger) and obtained 13 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 new source at the EP-WXT source position (Yin et al., GCN Circ. 42137) down to the following 5-sigma limit: r > 21.0 z > 20.6 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/42138. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40206] GRB 251006B/EP251006a: EP-WXT detection
by GCN Circulars 07 Oct '25

07 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42137 SUBJECT: GRB 251006B/EP251006a: EP-WXT detection DATE: 25/10/07 03:30:56 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP251006a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0 = 2025-10-06T20:05:04 (UTC). The position of the source is R.A. = 40.505 deg, DEC = -5.989 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 251006B (GCN 42131, GCN 42132). The analysis of the WXT data shows that the event lasted for about 100 seconds with a two-pulse main emission within T0 - T0 + 10 s followed by a much weaker tail. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.28 (-0.60/+0.64). The derived average unabsorbed 0.5-4 keV flux is 1.61 (-0.72/+0.50) x 10^-10 erg/s/cm^2. The peak flux is around 9.09 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 2.98 x 10^20 cm^-2 and a photon index of 1.09 (-0.76/+0.84). 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/42137. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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