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

[vsnet-grb-info 38296] EP250427a / GRB 250427A: LCO optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40267 SUBJECT: EP250427a / GRB 250427A: LCO optical counterpart detection DATE: 25/04/27 16:30:09 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) Following the detection of the fast X-ray transient EP250427a (Wang et al., GCN circ. 40257), detected also by Fermi-GBM, GRB 250427A (Ravasio et al., GCN circ. 40262), we observed the field with one of the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas) in the SDSS r filter. The observation started at 2025-04-27 10:10:47 UTC, about 6.53 hours after the EP-WXT trigger. An uncatalogued source is clearly detected at the optical counterpart position first reported by Perez-Garcia et al. (GCN circ. 40259) and with other optical and near-infrared detections reported by Liu et al. (GCN circ. 40260), Becerra et al. (GCN circ. 40261), Brivio et al. (GCN circ. 40264), Chornock et al. (redshift of z = 1.519, GCN circ. 40265), and Saccardi et al. (redshift of z = 1.520, GCN circ. 40266). We measure the following magnitude, calibrated against Pan-STARRS DR2 stars, that is not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-04-27 10:10:47 18.55 0.10 r 180 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40267. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38295] EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40266 SUBJECT: EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520 DATE: 25/04/27 15:39:47 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. Saccardi (CEA/Irfu), V. Abril-Melgarejo (LUX-Paris Obs.), Z. P. Zhu (NAOC), V. D’Elia (ASI/SSDC), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Schneider (LAM), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), S. D. Vergani (LUX-Paris Obs.), K. Wiersema (Hertfordshire), D. Xu (NAOC), report on behalf of the Stargate collaboration: We observed the optical counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261; Brivio et al., GCN 40264) of EP250427a / GRB 250427A (Wang et al., GCN 40257; Ravasio et al., GCN 40262) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21,000 AA, and consist of 2 exposures of 600 s each. The observation mid time was 2025 Apr 27.394 UT (5.80 hr after the GRB). In a 30-s image taken in the r band at a mid time of 5.61 hr after the trigger, we measure a magnitude r = 18.40 +- 0.02 AB, calibrated against nearby stars from the Pan-STARRS catalog. In a preliminary reduction of the spectra, we clearly observe a bright continuum over the entire covered wavelength range, detected at high S/N. The sightline is rich with intervening absorption systems, in particular C IV absorbers (1548,1550 doublet) are detected at z = 1.146, 1.222, 1.231, 1.405, 1.407, 1.518, and 1.520. The highest-redshift system is only securely detected in C IV and Si IV (at both z = 1.518 and 1.520). There is a possible indication of Lyman alpha absorption at the very blue end of the spectrum, with very low column density (much less than a DLA). The system at z = 1.405/1.407 is on the other hand the strongest and has detection in many species at both high and low ionization, including Si II, C II, Si IV, C IV, Fe II, Al II, Al III, Mg II and Mg I, as well as a rich velocity structure. No emission lines are visible at any of the above mentioned redshifts. Our data are therefore in good agreement with the results and the redshift value z = 1.520 already reported by Chornock et al. (GCN 40265) using the Keck telescope. We acknowledge expert and efficient support from the observing staff at Paranal, in particular Boris Haeussler, Francesca Lucertini, Rodrigo Romero, and Elisa Garro. View this GCN Circular online at https://gcn.nasa.gov/circulars/40266. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38294] EP250427A/GRB250427A: Keck/LRIS redshift
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40265 SUBJECT: EP250427A/GRB250427A: Keck/LRIS redshift DATE: 25/04/27 14:11:22 GMT FROM: Ryan Chornock at UC Berkeley <chornock(a)berkeley.edu> R.Chornock, E. Hammerstein, X. Guo (UC Berkeley) report: We observed the optical afterglow (GCNs 40258, 40259, 40260, 40261, 40263, 40264) of EP250427a (GCN 40257)/GRB 250427a (GCN 40262) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 12:36UT on 2025 Apr 27. Observations covered the range 3140-10300 Angstroms. A continuum is well detected across the full spectral range with many absorption lines present. We identify a strong doublet at observed wavelengths of 3900.3,3906.7 Angs as CIV at z=1.519 from the highest redshift system detected. There are also many lines (C II, C IV, Fe II, Mg I, Mg II) from a stronger low-redshift system at z=1.406. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/40265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38293] EP250427a: REM optical/NIR afterglow detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40264 SUBJECT: EP250427a: REM optical/NIR afterglow detection DATE: 25/04/27 13:23:16 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP250427a detected by EP/WXT (Wang et al., GCN 40257), also seen by Fermi/GBM (Ravasio et al., GCN 40262) 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 April 27 at 07:20:13 UT (i.e. 3.7 h after the burst). From preliminary photometry, we detect the optical/NIR counterpart (Perez-Garcia et al., GCN 40259; Liu et al., GCN 40260; Becerra et al., GCN 40261) with the following magnitudes: r = 18.1 +/- 0.3 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 3.7 h after the trigger, H = 15.3 +/- 0.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 3.7 h after the trigger, View this GCN Circular online at https://gcn.nasa.gov/circulars/40264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38292] GRB 250424A: LCO optical observation
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40263 SUBJECT: GRB 250424A: LCO optical observation DATE: 25/04/27 13:05:34 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration. We observed the field of the GRB 250424A triggered by Swift (Cenko et al., GCN 40224), AstroSat CZTI (Harsha et al., GCN 40231), Konus-Wind (Ridnaia et al., GCN 40243) and EIRSAT-1 GMOD (McKenna et al., GCN 40249)in B, V, r filters of the 1-meter Sinistro at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on , starting from 2025-04-24, 17.8 hours after the GRB trigger. Observation for later epochs are still going on. We clearly detect the optical transient (OT) reported by GCNs (Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; and D. Turpin et al., GCN 40240, Dutton et al., GCN Circ. 40241, Siegel et al., GCN 40244) in our B, V, r band images. ------------------------------------------------------------------------------------------------------ |Date| Start JD |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-04-25 2460790.52730 17.78 1 x 900 V V = 21.31+/- 0.08 2025-04-25 2460790.78105 23.87 1 x 900 B B = 22.07+/- 0.08 2025-04-25 2460790.79155 24.12 1 x 900 r r = 21.04 +/- 0.05 ------------------------------------------------------------------------------------------------------ The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38291] GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40262 SUBJECT: GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection DATE: 25/04/27 12:34:44 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), Adam Goldstein (USRA) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP250427a detected by EP-WXT (Wang et al., GCN 40257). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-04-27T03:38:45 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at T0+53 s on a 32 s timescale, with a false alarm rate of 5.9e-05 Hz (although there is evidence for signal at ~T0-10s). The localisation is consistent with the EP one, with a spatial association probability of 98.5%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38290] EP250427A: COLIBRÍ Optical Detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40261 SUBJECT: EP250427A: COLIBRÍ Optical Detection DATE: 25/04/27 10:34:16 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA/IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of EP250427A (Wang et al., GCN Circ. 40257) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico on the night of 2025-04-27 UTC. We observed from 2025-04-27 08:54 to 09:27 UTC (T+5.3 to T+5.8 hours after the trigger) and obtained 3-minute exposures in the g, r, and i filters (for each one). Our observations were performed under regular weather conditions. The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. Within the EP/FXT (Wang et al., GCN Circ. 40257) error region, we detect an uncatalogued source at R.A. = 277.2746 deg, DEC = 7.5639 deg (J2000), with an uncertainty of 0.4 arcsec, with magnitudes of: g= 18.91 +/- 0.04 r= 18.42 +/- 0.04 i= 17.88 +/- 0.04 This source is consistent with the candidate reported by BOOTES-7 (Perez-Garcia et al., GCN Circ. 40259) and TRT (Liu et al., GCN Circ. 40260). Further observations and analysis 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/40261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38289] EP250427a: TRT optical counterpart detection
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40260 SUBJECT: EP250427a: TRT optical counterpart detection DATE: 25/04/27 10:13:08 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> X. Liu, Z.P. Zhu, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250427a (Wang et al., GCN 40257), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 07:24:25.019 UTC on 2025-04-27, i.e., ~3.67 hr after the EP/WXT trigger and 6x200 s frames in the Sloan r-band were obtained. An uncatalogued and varying optical source is detected within the EP/FXT error circle (Wang et al., GCN 40257) at coordinates R.A. (J2000) = 18:29:05.73 Dec. (J2000) = +7:33:46.27 with an uncertainty of ~ 0.5 arcsec. Preliminary photometry shows that the source has r ~ 17.9 mag at 3.96 hr post-trigger, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. We think that this source is the optical counterpart of the event. View this GCN Circular online at https://gcn.nasa.gov/circulars/40260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38288] EP 250427a: BOOTES-7 optical afterglow candidate
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40259 SUBJECT: EP 250427a: BOOTES-7 optical afterglow candidate DATE: 25/04/27 10:11:14 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, A. J. Castro-Tirado, E. Fernandez-Garcia, S.-Y. Wu, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), C. Perez del Pulgar (Univ. de Malaga), G. Garcia-Segura (Inst. de Astronomia, UNAM), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), Y.-D. Hu (GuangXi Univ.), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of EP 250427a by EP (Wang et al., GCNC 40257), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) automatically responded to this fast X-ray transient starting on Apr 27, 07:21:09 UT (i.e., ~4 hours after detection). In the first 60 s exposure image, an uncatalogued source is detected at the EP-FXT position, at coordinates (J2000): RA = 18:29:05.7, Dec = +07:33:46.5, with a preliminary magnitude of 18.1 +/- 0.08 mag (clear filter) using GaiaDR3 Gmag as a reference, which we propose to be the optical afterglow to EP 250427a. Spectroscopic observations are encouraged. We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38287] EP250427a: Global MASTER-Net observations report
by GCN Circulars 27 Apr '25

27 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40258 SUBJECT: EP250427a: Global MASTER-Net observations report DATE: 25/04/27 10:09:47 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250427a ( EP Team et al., GCN 40257) errorbox 254 sec after notice time and 21870 sec after trigger time at 2025-04-27 09:43:15 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 41 deg. The sun altitude is -17.5 deg. The galactic latitude b = 8 deg., longitude l = 37 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2854486 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21901 | 2025-04-27 09:43:15 | MASTER-OAFA | (18h 28m 05.12s , +07d 20m 04.3s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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