vsnet-grb-info May 2025

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[vsnet-grb-info 38330] GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40301 SUBJECT: GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767 DATE: 25/05/01 10:00:04 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> M. Garnichey (LUX-Paris Obs.), A. Saccardi (CEA/Irfu), B. Schneider (LAM), G. Corcoran (UCD), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration: We observed the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000 - 21000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 2025 May 01 at 04:00:11 UT (10.87 hr after the Swift/BAT trigger). In a 3x30-s image, taken in the r band at a mid time of 10.34 hr after the trigger, the optical counterpart is detected at RA, Dec 233.3872, -18.1184 which is equivalent to: RA (J2000) = 15:33:32.93 Dec (J2000) = -18:07:06.3 These coordinates are in good agreement with those reported by Odeh et al. (GCN 40295). We measure a preliminary AB magnitude r = 21.97 +/- 0.06, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we observe a continuum over the entire covered wavelength range, fainter in the UVB and VIS arms than in the NIR. A few absorption features are detected, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2374, 2383, 2587, 2600), all at the common redshift z = 0.767. No emission lines are observed across the whole covered spectrum. We note the presence of a catalogued object in the Legacy Survey DR10 at a position consistent with the optical afterglow. The magnitudes of the galaxy are g = 24.59 +/- 0.25, r = 23.22 +/- 0.10, i = 21.96 +/- 0.05, and z = 21.35 +/- 0.04, and its centroid is 0.5" away from the optical afterglow position. Our spectroscopic redshift measurement is consistent with the photometric redshift value provided of 0.89 +/- 0.11. This object is the likely host galaxy of GRB 250430A, though we notice that its red colors and lack of emission lines are not typical of a long (collapsar) GRB host. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Palominos, and Camila de Sa Freitas. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495). View this GCN Circular online at https://gcn.nasa.gov/circulars/40301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38329] SVOM/sb25043004: EP-FXT observations
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40300 SUBJECT: SVOM/sb25043004: EP-FXT observations DATE: 25/05/01 08:55:01 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Q. Jiang, H.Y. Liu, R.D. Liang, H.W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation on SVOM/sb25043004 at 2025-04-30T17:26:25 (UTC), about 7 hours after the SVOM/ECLAIRs trigger (Liang et al. GCN # 40287). Two previously known X-ray sources and an uncatalogued X-ray source are detected within the ECLAIRs error circle. Preliminary analysis on these source are automatically conducted, and details are listed as follows. Source 1: EPF_J180814.9-384246 (1eRASS J180815.0-384254) RA (J2000): 272.0610 Dec (J2000): -38.7126 Flux: 1.77 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 3.7 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180815.0-384254, which has a flux of 8.34 (+4.22/-3.17, 1 sigma) x 10^-14 erg/cm^2/s (0.2-2.3 keV). Source 2: EPF_J180840.1-384205 (1eRASS J180840.7-384211) RA (J2000): 272.1683 Dec (J2000): -38.7025 Flux: 4.88 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 5.9 x 10^-14 erg/cm^2/s (1 sigma) Note: The source is spatially consistent with 1eRASS J180840.7-384211, which has a flux of 1.41 (+0.52/-0.41, 1sigma) x 10^-13 erg/cm^2/s (0.2-2.3 keV). Source 3: EPF_J180801.1-384501 (uncataloged) RA (J2000): 272.0057 Dec (J2000): -38.7511 Flux: 2.44 x 10^-13 erg/cm^2/s (observed, 0.5-10 keV) Flux_error: 4.6 x 10^-14 erg/cm^2/s (1 sigma) Note: The upper limit given by eROSITA DR1 is 1.71 x 10^-13 erg/cm^2/s (0.2-2.3 keV). The position uncertainties of the above sources are about 10 arcsec in radius (90% C.L. statistical and systematic). 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/40300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38328] EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40299 SUBJECT: EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission DATE: 25/05/01 08:11:44 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Wang (THU), H. L. Peng (NJNU), Y. Q. Zhao (USTC, PRIC), W. Yuan (NAO, CAS), 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 EP250430a. The WXT detection was not triggered onboard due to the closeness of the source position to the bright X-ray source Sco X-1, but was made in the onground analysis of the telemetry data later. No automated follow-up X-ray observation was performed. The WXT position of the source is R.A. = 233.399 deg, DEC = -18.130 deg (J2000) with an uncertainty of 2.9 arcmin in radius (90% C.L. statistical and systematic), which is offset by 1.0 arcmin from the Swift/XRT position of the likely long GRB 250430A (Lipunov et al., GCN 40291; Parsotan et al., GCN 40292; Kawabata et al., GCN 40294; Odeh et al., GCN 40295). The X-ray rise time precedes the GRB trigger time by approximately 23 seconds, and the X-ray duration is longer than that of the GRB by about 30 seconds. The X-ray emission peaked at 2025-04-30T17:31:05.5 (UTC). The consistency of EP250430a and GRB 250430A in position and time suggests EP250430a to be the X-ray counterpart of GRB 250430A. Note that the source parameters given above are only approximate and detailed analysis is onging. The averaged WXT spectrum in 0.5-4 keV can be fitted by an absorbed power law model with a photon index of 2.37 (+0.61, -0.54) and a column density of 3.80 (+1.50, -1.31) x 10^21 cm^-2. The average unabsorbed 0.5-4 keV flux is about 1.63 (+0.69, -0.36) x 10^-10 erg/cm^2/s. These parameters derived are at the 1-sigma confidence level. Further observations with the Follow-up X-ray Telescope (FXT) on board EP may be considered at a later stage. Contact transient advocate (TA) for EP250430a is C. Y. Wang (wang-cy22(a)mails.tsinghua.edu.cn) and please contact the TA for information regarding the EP observation of this source. 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/40299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38327] GRB 250424A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 01 May '25

01 May '25

TITLE: GCN CIRCULAR NUMBER: 40298 SUBJECT: GRB 250424A: CALET Gamma-Ray Burst Monitor detection DATE: 25/05/01 03:19:12 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> GRB 250424A: CALET Gamma-Ray Burst Monitor detection S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 250424A (Swift detection: Cenko et al., GCN Circ. 40224; Swift-BAT refined analysis: Markwardt et al., GCN Circ. 40255; AstroSat CZTI detection: Harsha et al., GCN Circ. 40231; Konus-Wind detection: Ridnaia et al., GCN Circ. 40243; EIRSAT-1 GMOD Detection: McKenna et al., GCN Circ. 40249; SVOM/GRM observation: Jin-Peng et al., GCN Circ. 40252) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 06:52:04.323 UTC on 24 April 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1429512582/index.html). The burst signal was seen by all CGBM detectors. The burst light curve shows a single pulse that starts at T+2.5 sec, peaks at T+8.4 sec, and ends at T+27.5 sec. The T90 and T50 durations measured by the SGM data are 13.5 +/- 0.8 sec and 4.6 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1429512582/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/40298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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