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[vsnet-grb-info 38306] EP250428b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40277 SUBJECT: EP250428b: Einstein Probe detection of a fast X-ray transient DATE: 25/04/29 17:30:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) 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 EP250428b (GCN Notice … [View More]

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[vsnet-grb-info 38305] Fermi-LAT Gamma-ray Observations of IceCube-250426A
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40276 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250426A DATE: 25/04/29 11:02:04 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), 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 IC250426A neutrino event (GCN 40254) with all-sky survey … [View More]

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[vsnet-grb-info 38304] EP250427a / GRB 250427A: OHP/T193 photometric observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40275 SUBJECT: EP250427a / GRB 250427A: OHP/T193 photometric observations DATE: 25/04/29 08:49:00 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> P. Amram (LAM/AMU), C. Adami (LAM/Pytheas/AMU), S. Vergani (CNRS, Obs. de Paris, LUX), S. Basa (Pytheas/OHP/LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of the MISTRAL-GRB collaboration: We observed EP250427a / GRB 250427A (Wang et al. GCN 40257, Ravasio et al. GCN 40262) … [View More]

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[vsnet-grb-info 38303] EP250427a: EP-FXT follow-up observations
by GCN Circulars 29 Apr '25

29 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40274 SUBJECT: EP250427a: EP-FXT follow-up observations DATE: 25/04/29 07:11:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), D. Y. Li (NAO, CAS), Y. Q. Zhao (USTC, PRIC), J. H. Wu (GZHU), Y. Liu (NAO, CAS) behalf of the Einstein Probe (EP) team: After the EP-WXT detection of the fast X-ray transient EP250427a (Wang et al., GCN 40257), two follow-up observations have been conducted by EP-FXT. The first follow-up observation … [View More]was performed at 2025-04-27T08:38:17 (UTC), about 5.6 hours after the trigger, with an exposure time of 4.1 ks. On-ground analysis of the EP-FXT data identified an uncatalogued X-ray source within the EP-WXT error circle, at the coordinates (J2000): R.A., Dec. = 277.2728, 7.5625 deg, with an uncertainty of about 10 arcsec (radius, 90% confidence level, including both statistical and systematic errors). The 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the column density nH fixed at the Galactic value of 3.01e21 cm^-2, and a photon index of 1.89(+0.18, -0.18). The unabsorbed 0.5-10 keV flux is 4.2 (+0.6, -0.5) e-12 erg/s/cm^2. This is consistent with the Swift-XRT refined analysis (D'Elia et al. GCN 40268). The FXT localization is consistant with the positions of the optical conterparts. The detection of the optical and IR counterpart has been reported in several GCNs (Lipunov et al. GCN 40258; Perez-Garcia et al. GCN 40259; Liu et al. GCN 40260; Becerra et al. GCN 40261; Brivio et al. GCN 40264; Saccardi et al. GCN 40266; Pérez-Fournon et al. GCN 40267; Xi et al. GCN 40269; Swain et al. GCN 40270; Magnani et al. GCN 40271; de Wet et al. GCN 40272), and the event was also detected as the sub-threshold GRB 250427A by Fermi/GBM (Ravasio et al. GCN 40262). And the redshift of EP240527a was measured to be 1.519 (Chornock et al. GCN 40265) or 1.520 (Saccardi et al. GCN40266). The second follow-up observation was performed at 2025-04-28T14:13:49 (UTC), about 35.1 hours after the trigger, with an exposure time of 5.9 ks. The 0.5-10 keV spectrum can also be fitted with an absorbed power-law model, with nH fixed at the Galactic value of 3.01e21cm^-2, and a photon index fixed of 1.66 (+0.44, -0.41). The unabsorbed 0.5-10 keV flux is 5.0 (+2.1, -1.3) e-13 erg/s/cm^2. All uncertainties quoted above are at the 90% confidence level. 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/40274. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L… [View Less]

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[vsnet-grb-info 38302] EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40273 SUBJECT: EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart DATE: 25/04/28 17:06:44 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of EP250427a (Wang et al., GCN 40257; Lipunov et al., GCN 40258; Perez-Garcia et al., … [View More]

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[vsnet-grb-info 38301] EP250427a: Lesedi optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40272 SUBJECT: EP250427a: Lesedi optical counterpart detection DATE: 25/04/28 13:43:45 GMT FROM: Simon de Wet at University of Cape Town <simdewet(a)gmail.com> S. de Wet (DTU space), N. Erasmus (SAAO), W.X. Li (NAOC), N.C. Sun (UCAS,NAOC) report: The SAAO 1-m Lesedi telescope located at Sutherland, South Africa, obtained 2x60 s exposures with the Mookodi low-resolution spectrograph and imager in each of the g,r and i bands of EP250427a (Wang et al.,… [View More]

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[vsnet-grb-info 38300] EP250427A: COLIBRÍ Continuing Optical Observations
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40271 SUBJECT: EP250427A: COLIBRÍ Continuing Optical Observations DATE: 25/04/28 12:30:11 GMT FROM: Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), … [View More]

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[vsnet-grb-info 38299] GRB250427A/EP250427a GIT optical afterglow detection:
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40270 SUBJECT: GRB250427A/EP250427a GIT optical afterglow detection: DATE: 25/04/28 12:10:05 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Swain (IITB), A. Salgundi (IITB), Y. Wagh (IITB), A.P. Saikia (IITB), D. Eappachen (IIA), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of of EP 250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (… [View More]

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[vsnet-grb-info 38298] EP250427a: LT optical counterpart detection
by GCN Circulars 28 Apr '25

28 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40269 SUBJECT: EP250427a: LT optical counterpart detection DATE: 25/04/28 07:34:08 GMT FROM: qiang xi <xiqiang051(a)gmail.com> Qiang Xi (UCAS), I. Pérez-Fournon, F. Poidevin, D.S. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun, Z.X. Niu (UCAS and NAOC), W.X. Li, Y.N. Wang (NAOC): We observed the field of the Einstein Probe WXT event EP250427a (Wang et al., GCN circ. 40257), using the 2.0-meter Liverpool Telescope (LT) located at the … [View More]

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[vsnet-grb-info 38297] GRB 250427A: Swift-XRT refined Analysis
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40268 SUBJECT: GRB 250427A: Swift-XRT refined Analysis DATE: 25/04/27 17:49:43 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> V. D'Elia (ASI-SSDC), E. Ambrosi (INAF/IASFPA), K.L. Page (U Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have … [View More]analysed 1.7 ks of XRT data for the Einstein Probe/WXT-detected burst GRB 250427A, from 22.9 ks to 28.9 ks after the Einstein Probe/WXT trigger. The data are entirely in Photon Counting (PC) mode. We found an uncatalogued X-ray source within the estimated 3-sigma EP-WXT error region. We find an XRT position: RA, Dec = 277.27280, +7.5632 which is equivalent to: RA (J2000): 18h 29m 05.47s Dec (J2000): +07° 33′ 47.6″ with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position is 6.9 arcsec from the EP-WXT position, and consistent with the X-ray counterpart found in EP/FXT data (Wang et al. GCN 40257) and with the optical counterpart reported by Perez-Garcia et al. (GCN 40259), Becerra et al. (GCN 40261), Ghosh et al. (GCN 40263), Brivio et al. (GCN 40264). The light curve is consistent with a constant source with a hint of fading in the last segment. However, given the corresponding optical counterpart and the measured redshift, we believe this to be the X-ray afterglow. Further observations are planned. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.78 (+0.39, -0.28). The best-fitting absorption column is consistent with the Galactic value of 2.9 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 4.3 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-1.3) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.78 (+0.39, -0.28) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019750. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40268. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L… [View Less]

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