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

[vsnet-grb-info 37880] GRB 250322A: further NOT optical observations
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39863 SUBJECT: GRB 250322A: further NOT optical observations DATE: 25/03/24 16:33:39 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. M. Kadela (NOT and NBI) report on behalf of a larger collaboration: We secured a second observation of the field of GRB 250322A (Gupta et al., GCN 39835; Tembhurnikar et al., GCN 39849) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Our observation consisted of 7x360 s in the r-band, with mean time 2025 Mar 23.88 UT (29.7 hr after the GRB). Unfortunately, the delivered seeing is worse than in our first epoch (Martin-Carrillo et al., GCN 39842), taken 4.65 hr after the GRB (1.5 vs 1.0"). The galaxy noted by Martin-Carrillo et al. (GCN 39842), Becerra et al. (GCN 39844, 39845), Kilpatrick & Fong (GCN 39846), and Fong et al. (GCN 39852) is detected in our second epoch. Image subtraction was carried out using Hotpants. No residuals are detected in the difference image, corresponding to a limiting magnitude of r > 23.2 (AB). For the galaxy, we measure (in our first epoch) r = 22.04 +/- 0.12 (AB), calibrated against nearby Pan-STARRS point-like objects. Considering a 2.5”-radius XRT error circle (Goad et al., GCN 39841; Perri et al., 39855), we estimate a chance association probability of 2%, which provides moderate evidence for a physical association with the GRB. View this GCN Circular online at https://gcn.nasa.gov/circulars/39863. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37879] EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39862 SUBJECT: EP-WXT trigger 01709133021: Optical upper limit through Kinder observations DATE: 25/03/24 14:56:49 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> C.-H. Lai, Y.-H. Lee, A. Aryan, T.-W. Chen, Y. J. Yang (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), W.-J. Hou, H.-Y. Hsiao, C.-C. Ngeow, Y.-C. Pan, A. Sankar. K, M.-H. Lee, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the Einstein Probe (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics) discovered X-ray transient with WXT trigger ID 01709133021 using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first LOT epoch of observations in the r band started at 11:29 UT on the 24th of March 2025 (MJD = 60758.4017), ~1.84 hr post the EP-WXT trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames, we do not detect any potential uncataloged optical afterglow counterpart candidate within EP-WXT localization circle with a radius of ~3 arcminutes. Moreover, we used the Kinder pipeline (Yang et al. 2021, A&A, 646, 22) to subtract the stacked images using the templates from Pan-STARRS1 (Chambers et al. 2016 arXiv:1612.05560). We also utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, 62) to perform template subtraction using the "sfft" (Hu, 2022, ApJ, 936, 157) and "hotpants" (Becker A., 2015, ascl.soft. ascl:1504.004) algorithms. We found no evidence of any prominent optical counterpart candidate in the difference images as well. We further employed AutoPhOT to perform PSF photometry on the combined frames. The details of the observation and 3-sigma upper limits (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | tmid-t0 (hr)| Exposure (s) | Magnitude | Average Seeing | Median Airmass LOT | r | 60758.4017 | 1.84 | 2.65 | 300 * 12 | >22.77 | 1".15 | 1.56 The non-detection of any optical afterglow counterpart candidate is consistent with the previous report by Ducoin et al. (GCN 39860). The presented upper limit was calibrated using the field stars from the SDSS catalog and was not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.05 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). We are grateful to the EP team for providing useful communications through GCN Notices. View this GCN Circular online at https://gcn.nasa.gov/circulars/39862. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37878] GRB 250322A: Swift/UVOT Upper Limits
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39861 SUBJECT: GRB 250322A: Swift/UVOT Upper Limits DATE: 25/03/24 12:52:39 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250322A 77 s after the BAT trigger (Gupta et al., GCN Circ. 39835). No optical afterglow consistent with the enhanced XRT position (Goad et al., GCN Circ. 39841) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 77 226 147 >20.5 u_FC 291 541 246 >19.8 white 77 1711 411 >20.9 v 620 1760 136 >18.9 b 546 1686 117 >19.7 u 291 1661 343 >20.0 w1 669 1807 134 >19.2 m2 644 1785 136 >19.0 w2 596 1736 136 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.153 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/39861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37877] EP250324A: COLIBRÍ/DDRAGO Optical Observations
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39860 SUBJECT: EP250324A: COLIBRÍ/DDRAGO Optical Observations DATE: 25/03/24 11:57:56 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Margarita Pereyra (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (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) and Ny Avo Rakotondrainibe (LAM) report: We observed the field of EP250324A (ID=01709133021) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-24 10:12 to 10:27 UTC (0.6 to 0.8 hours after the trigger). The data were coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. Within the EP/WXT localization, we do not detect any uncatalogued sources to a 5-sigma limiting magnitude of : i > 22.20 Further analysis of the additional images is 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/39860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37876] GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39859 SUBJECT: GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy DATE: 25/03/24 11:41:00 GMT FROM: Yu-Han Yang at University of Rome Tor Vergata <yyang(a)roma2.infn.it> Yu-Han Yang (U Rome), Eleonora Troja (U Rome), Rosa Becerra (U Rome), Massine El Kabir (U Rome) report on behalf of the ERC BHianca team: We observed the bright galaxy within the localization of GRB 250322A (Gupta et al., GCN 39835, Goad et al. GCN 39841, Martin-Carillo et al. GCN 39842) with the X-Shooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+32.2 hours and obtained a total of 2x600s spectra at an average airmass of about 1.2 and seeing of 0.6”. We detect a bright continuum in the VIS and NIR arms and identify multiple emission lines, including H_alpha, H_beta, NII, OII, SII, at a common redshift of 0.4215±0.0005, consistent with measurement by Fong et al. (GCN 39852). We estimated that the chance coincidence between the bright galaxy and the XRT localization is <2% (Bloom et al. 2002), supporting it as a likely host galaxy of the GRB. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37875] FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
by GCN Circulars 24 Mar '25

24 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39858 SUBJECT: FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060 DATE: 25/03/24 05:14:31 GMT FROM: Margarita Pereyra Talamantes at IA-UNAM Ensenada <mpereyra(a)astro.unam.mx> Margarita Pereyra (UNAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the Einstein Probe source EP J120944.2+585060 (Sun et al., GCN Circ. 39834) possibly associated with FRB 250316A (ID=439373176) detected by CHIME/FRB (Mason et al., ATel #[17081](https://www.astronomerstelegram.org/?read=17081) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed the field centred in the position of EP J120944.2+585060 from 2025-03-23 08:23:56 to 12:32:11 UTC (6.99 to 7.17 days after the discovery of FRB 250316A) and obtained 2.82 hrs of exposure in the i filter. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction. Consistent with previous reports (Becerra et al. ATel #[17082](https://www.astronomerstelegram.org/?read=17082), Niuno et al. ATel #[17084](https://www.astronomerstelegram.org/?read=17084), Hashimoto et al. ATel #[17095](https://www.astronomerstelegram.org/?read=17095), Aryan et al. Circ. GCN 39839, Yang et al. ATel #[17101](https://www.astronomerstelegram.org/?read=17101), Becerra et al. GCN 39843 and Becerra et al. GCN 39853), we do not detect any uncatalogued source to an estimated 5-sigma upper limit of i > 23.6 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/39858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37874] GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39857 SUBJECT: GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst DATE: 25/03/23 17:06:49 GMT FROM: Brian Grefenstette at Caltech/NuSTAR <bwgref(a)srl.caltech.edu> B. Grefenstette (Caltech) reports on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the Long GRB 250322B in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe detectors. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-03-22 20:08:06.000 with a resolution ~5-seconds. This is consistent with the detection by AstroSat CZT (Waratkar et al., GCN circ. 39848). The NuSTAR CsI shield data are recorded at 1 Hz. The GRB appears to be a complex, broad burst with peak count rates near 4,000 cps over a baseline of ~1,000 cps. The burst lasts for over 100-s above background. We see clear evidence for correlated >100 keV X-rays in both CdZnTe focal planes for at least one of the multiple peaks in the burst. Offline analysis of the CsI lightcurve shows complex features, including at least four quasi-periodic “dips” in the emission with intervals of roughly 20-s between the dips. A more detailed analysis of these features will follow. Discovery report and a preliminary lightcurve for this GRB showing the dips can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250322B/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/39857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37873] GRB 250321B: Swift-XRT observations
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39856 SUBJECT: GRB 250321B: Swift-XRT observations DATE: 25/03/23 16:57:22 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 250321B, collecting 2.7 ks of Photon Counting (PC) mode data between T0+81.0 ks and T0+92.8 ks. No X-ray sources have been detected. The 3-sigma upper limit in the field ranges from ~0.005 to ~0.006 ct s^-1, corresponding to a 0.3-10 keV observed flux of 2.1e-13 to 2.4e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). 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/ToO_GRBs/00021824. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37872] GRB 250322A: Swift-XRT refined Analysis
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39855 SUBJECT: GRB 250322A: Swift-XRT refined Analysis DATE: 25/03/23 16:54:19 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Perri (SSDC & INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), M. A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 3.7 ks of XRT data for GRB 250322A, from 58 s to 22.2 ks after the BAT trigger. The data comprise 7 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=2.28 (+0.18, -0.17). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.09 (+0.49, -0.26). The best-fitting absorption column is consistent with the Galactic value of 2.7 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 3.6 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.7 (+/-2.3) x 10^21 cm^-2 Galactic foreground: 2.7 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.09 (+0.49, -0.26) If the light curve continues to decay with a power-law decay index of 2.28, the count rate at T+24 hours will be 2.2 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.9 x 10^-18 (1.2 x 10^-17) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01297832. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37871] EP250321a: TNOT Observation of Optical Counterpart
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39854 SUBJECT: EP250321a: TNOT Observation of Optical Counterpart DATE: 25/03/23 16:31:37 GMT FROM: Xiaofeng Wang at Tsinghua University <wang_xf(a)mail.tsinghua.edu.cn> Haichang Zhu (THU), A. Iskandar(XAO), Xiaofeng Wang (THU), and Letian Wang (XAO) report the detection of the optical counterpart that is associated with the X-ray transient EP250321a (Hu et al., GCN 39800; Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831). We obtained the r-band images (~12.44 hours after the burst) with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy observatory, starting on 2025-03-21 (UT)18:36:10. From the stacked images with a total exposure time of 100sx15, we did not detect the optical afterglow down to a limiting magnitude of about 22.2 mag (MJD=60755.775). The above photometric result is calibrated using the field stars from the Pan-STARRS catalog and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37870] FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39853 SUBJECT: FRB 250316A: DDOTI Continued Optical Observations (Third Epoch) DATE: 25/03/23 15:37:35 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Margarita Pereyra (UNAM), Simone Dichiara (Penn State University), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM) report: We observed the field of FRB 250316A (ID=439373176) detected by CHIME/FRB (Mason, ATel #17081) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-03-23 UTC. DDOTI observed the field centred in the position of EP J120944.2+585060 RA = 182.4341 deg, Dec = 58.8499 deg (J2000) from 03:00 UTC to 12:18 UTC (from T+6.8 days to T+7.2 days after the discovery of FRB 250316A) with a total exposure of 240 minutes. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no evident uncatalogued sources within the observed field to a 3-sigma limiting AB magnitude of w > 22.4 This non-detection is consistent with those reported by Becerra et al. 2025 ATel 17082, Niuno et al. 2025, ATel 17084, Hashimoto ATel 17095, Aryan et al. 2025, Circ. GCN 39839, Yang et al. 2025, ATel 17101, and Becerra et al. GCN 39843. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37869] GRB 250322A: Gemini-North redshift of candidate host galaxy
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39852 SUBJECT: GRB 250322A: Gemini-North redshift of candidate host galaxy DATE: 25/03/23 13:40:27 GMT FROM: Wen-fai Fong at Northwestern University <wfong(a)northwestern.edu> W. Fong (Northwestern), A. J. Levan (Radboud), J.C. Rastinejad (Northwestern), N. R. Tanvir (Leicester), C. D. Kilpatrick (Northwestern) report on behalf of a larger collaboration: We observed the putative host galaxy within the XRT localization (Goad et al., GCN 39841) of the short-duration GRB 250322A (Gupta et al., GCN 39835; Tembhurnikar et al., GCN 39849) using the Gemini Multi-Object Spectrograph (GMOS-N) mounted on Gemini-North telescope in Hawaii. We obtained 4x900-sec exposures using the R400 grating, spanning approximately 5000A to 9500A, starting at 2025-03-23 05:33:34 UT (approx 13.5 hr post-burst), under Program GN-2025A-Q-114 (PI: Fong). The continuum is well-detected along with several prominent emission lines. In particular, we identify emission lines of H-alpha, NII, OIII (5007), H-beta and H-gamma, corresponding to a common redshift of z=0.42. We thank Jennifer Andrews, Adam Smith, and Hyewon Suh for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37868] EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39851 SUBJECT: EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm DATE: 25/03/23 09:41:34 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> L. Izzo (INAF-OACN and DARK/NBI), A. Martin-Carrillo (UCD), D. B. Malesani (Radboud and DAWN/NBI), A. J. Levan (Radboud and Warwick), P. G.Jonker (Radboud Univ.), L. Cotter (UCD), J. van Dalen (Radboud Univ.), G. Corcoran (UCD), K. Wiersema (Herts), F. E. Bauer (PUC), report on behalf of a larger collaboration: We observed the optical counterpart (Liu et al., GCN 39583; Page et al., GCN 39584; Saccardi et al., GCN 39585; Shilling et al., GCN 39587; Gupta et al., GCN 39593; Ghosh et al., GCN 39594) of the fast X-ray transient EP250304a (Chen et al., GCN 39580) using the ESO VLT UT4 (Yepun) equipped with the MUSE spectrograph on 2025-03-22 at 02:45:04 UT (about 18.05 days after trigger, 15 days in the rest frame). A series of 4x470 s exposures were taken for this observation. From a preliminary reduction, the continuum is well detected over the wavelength range of 5000 to 9000 AA. Broad features, typical of broad-lined supernovae expanding at relativistic speeds, can be clearly identified, with SNID finding a good match with SN1998bw at 14 days after the explosion. Further observations are planned. We acknowledge the excellent support from the ESO staff in Paranal, in particular Thallis Pessi and Francisco Caceres. View this GCN Circular online at https://gcn.nasa.gov/circulars/39851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37867] SVOM/sb25032302: SVOM detection of a long X-ray transient
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39850 SUBJECT: SVOM/sb25032302: SVOM detection of a long X-ray transient DATE: 25/03/23 09:18:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Ziming Wang (BNU), Yifang Liang (PMO), An Li (BNU), Wenjin Xie, Donghua Zhao (NAOC), Stephane Schanne, Nicolas Dagoneau (CEA) Report on behalf of the SVOM mission team. SVOM/ECLAIRs triggered and located a soft X-ray transient source (SVOM burst-id sb25032302) starting at 2025-03-23T04:08:21 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert with the signal-to-noise-ratio (SNR) of 7.90 in the 5-8 keV energy band over a time window of 1310.72 seconds starting at Tb. The localization of the best alert is R.A., Dec 194.8370, 28.0383 degrees: RA (J2000) = 12h59m20.87s Dec (J2000) = 28d02m17.90s with a 90% C.L. radius of 9.95 arcmin (including systematic error of 2 arcmin added in quadrature). We notice that this error-box overlaps with the Coma cluster containing several X-ray sources which could produce such a transient. This trigger did not reach the slew threshold, hence no automatic slew was performed. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The Burst Advocate (BA) on shift for this burst is Ziming Wang (202421101144(a)mail.bnu.edu.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/39850. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37866] GRB 250322A: AstroSat CZTI detection of a short burst
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39849 SUBJECT: GRB 250322A: AstroSat CZTI detection of a short burst DATE: 25/03/23 08:02:08 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar(IUCAA), J. Joshi (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short-duration GRB 250322A which was also detected by Swift/BAT (Gupta et.al., GCN Circ. 39835). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-22 16:06:12.85 UTC. The measured peak count rate, as measured with 10 ms binning, associated with the burst is 1322 (+851, -197) counts/s above the background in the combined data of all quadrants, with a total of 113 (+37, -25) counts. The local mean background count rate was 426 (+24, -61) counts/s. Using cumulative rates, we measure a T90 of 0.18 (+0.04, -0.03) s. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/39849. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37865] GRB 250322B: AstroSat CZTI detection of a bright long burst
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39848 SUBJECT: GRB 250322B: AstroSat CZTI detection of a bright long burst DATE: 25/03/23 06:45:11 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), J. Joshi (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250322B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-22 20:08:27.0 UTC. The measured peak count rate associated with the burst is 183 (+9, -10) counts/s above the background in the combined data of two quadrants (out of four), with a total of 9235 (+367, -313) counts. The local mean background count rate was 148 (+1, -1) counts/s. Using cumulative rates, we measure a T90 of 73 (+2, -2) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-03-22 20:08:19.9 UTC. The lightcurve shows a small precursor peak around 50 s before the main burst, which itself consists of multiple peaks. This initial feature is absent from the CZT data due to data quality issues. Due to the low intensity of the precursor, it does not impact T90 duration measurements in the Veto detector. The measured peak count rate associated with the burst is 3634 (+111, -117) counts/s above the background in the combined data of all quadrants, with a total of 150040 (+1345, -1413) counts. The local mean background count rate was 1238 (+3, -3) counts/s. We measure a T90 of 75 (+1, -1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/39848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37864] GRB250322A: STEP/T80S optical limits
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39847 SUBJECT: GRB250322A: STEP/T80S optical limits DATE: 25/03/23 04:56:42 GMT FROM: André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos(a)gmail.com> A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration: We conducted optical follow up with the T80S 0.8-m robotic telescope (Santos et al., 2024, MNRAS, 529, 59) of the short gamma-ray burst GRB250322A discovered by the Swift-BAT and XRT instruments (GCN [39835](https://gcn.nasa.gov/circulars/39835), [39841](https://gcn.nasa.gov/circulars/39841)). The T80S observations started on Mar 23 00:08:38 UT (~8 hours after the trigger). We obtained images totaling 1800s (6x300s) in g-band with the T80S camera centered at the position of the latest XRT position (GCN [39841](https://gcn.nasa.gov/circulars/39841)) at R.A.=07:07:02.52 and Decl.=+07:11:35.3 (J2000). After subtracting a Pan-STARRS template image from the T80S frames using photpipe (Rest et al., 2005), we do not detect any transient source in our difference image within the XRT error circle and derive a 3-sigma limiting magnitude of g > 22.48 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/39847. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37863] GRB 250322A: Gemini-South optical observations
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39846 SUBJECT: GRB 250322A: Gemini-South optical observations DATE: 25/03/23 03:06:38 GMT FROM: Charles Kilpatrick at Northwestern U <ckilpatrick(a)northwestern.edu> C. D. Kilpatrick and W. Fong (Northwestern) report on behalf of a larger collaboration: We observed the location of the short-duration GRB 250322A (Gupta et al., GCN 39835) with the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South under Program GS-2025A-Q-112 (PI: Fong). We obtained 10x120-sec imaging each in the r- and i-bands starting at 2025-03-23 00:06:31 UT (8.0 hrs post-burst), at a median airmass of 1.3 and seeing of 0.6-0.9’’. Within or proximate to the enhanced XRT localization (Goad et al., GCN 39841), we do not detect any additional sources relative to Pan-STARRS1, to 3-sigma limits of r > 24.2 AB mag and i > 24.4 AB mag (calibrated to Pan-STARRS), consistent with the non-detections reported (Martin-Carrillo et al., GCN 39842; Becerra et al. GCN 39845). Regarding the galaxy within the XRT position, first pointed out by Martin-Carrillo et al. (GCN 39842), we measure magnitudes of r = 21.7 +/- 0.1 AB mag and i = 21.1 +/- 0.1 AB mag. We note that these are ~0.3-0.6 mag brighter than the catalogued Pan-STARRS values (Flewelling et al., 2020, ApJS, 251, 7). We caution that these differences are not significant enough to claim presence of an afterglow and could instead be due to a combination of filter differences or aperture differences for the catalog values. Further observations are planned to monitor the variability of the source. We thank Jennifer Andrews, Veronica Firpo, Daniel May, and Aleksandar Cipota for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37862] GRB 250322A: VLT optical observations
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39845 SUBJECT: GRB 250322A: VLT optical observations DATE: 25/03/23 02:42:36 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa Becerra (U Rome), Yu-Han Yang (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250322A (Gupta et al., GCN 39835, Goad et al. GCN 39841) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began at T+8.1 hours after the trigger and were carried out in the R filter with a total exposure of 1200 seconds, at an average seeing of 0.5" and airmass about 1.2. We do not detect any new source at the enhanced Swift-XRT position (Goad et al. GCN 39841) down to the following 5-sigma limit R>25.8 AB mag (Vega) calibrated with nearby Pan-STARRS stars and without Galactic extinction correction. In our images, we detect the host galaxy candidate reported by Martin-Carrillo et al. (GCN 39842) with no significant variation in brightness. We thank the staff at the VLT for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39845. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37861] GRB 250322A: VLT near-infrared observations
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39844 SUBJECT: GRB 250322A: VLT near-infrared observations DATE: 25/03/23 02:40:38 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa Becerra (U Rome), Yu-Han Yang (U Rome), Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250322A (Gupta et al., GCN 39835) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+7.4 hr with a total exposure of 360 sec in the J filter, and were carried out at an average airmass of about 1.2 and seeing of 0.56’’. We do not detect any new source at the enhanced Swift-XRT position (Goad et al. GCN 39841) down to the following 5-sigma limit J>23.0 mag (Vega) calibrated using nearby stars in the 2MASS Catalogue. We detect the host galaxy candidate reported by Martin-Carrillo et al. 2025 (GCN 39842) in our image. We estimate a preliminary magnitude of J=18.9±0.2 mag (Vega). Further observations are planned to investigate potential variations in the brightness. We thank the staff at the VLT, especially Thomas Rivinius, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39844. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37860] FRB 250316A: DDOTI Continued Optical Observations
by GCN Circulars 23 Mar '25

23 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39843 SUBJECT: FRB 250316A: DDOTI Continued Optical Observations DATE: 25/03/23 02:08:14 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Eleonora Troja (U Roma), Margarita Pereyra (UNAM), Simone Dichiara (Penn State University), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM) report: We observed the field of FRB 250316A (ID=439373176) detected by CHIME/FRB (Mason, ATel #17081) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-03-22 UTC. DDOTI observed the field centred in the position of EP J120944.2+585060 RA = 182.4341 deg, Dec = 58.8499 deg (J2000) from 12:05 UTC to 12:29 UTC with a total exposure of 24 minutes down to a 3-sigma limiting AB magnitude of w = 21.3 consistent with previous reports by Becerra et al. 2025 ATel 17082, Niuno et al. 2025, ATel 17084, Hashimoto ATel 17095, Aryan et al. 2025, Circ. GCN 39839 and Yang et al. 2025, ATel 17101. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no evident uncatalogued sources within the observed field to our 3-sigma limit. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37859] GRB 250322A: NOT optical upper limits
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39842 SUBJECT: GRB 250322A: NOT optical upper limits DATE: 25/03/22 23:10:07 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo (UCD), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), L. Izzo (INAF/OACn and DARK/NBI), D. Xu (NAOC), A. A. Djupvik (NOT), and A. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the field of the GRB 250322A (Gupta et al., GCN 39835) using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 5 exposures of 300 s each in the SDSS-r and SDSS-z band, starting at 20:45:22 UT on 2025-03-22 (4.65 hr after the trigger). Preliminary analysis shows that no new source is detected within the Swift/XRT enhanced error box (Goad et al., GCN 39841), down to the 5-sigma AB limiting magnitudes r > 24.3 and z > 22.6, calibrated with nearby Pan-STARRS stars and without Galactic extinction correction. We note that the XRT location includes an extended object (J2000 coordinates RA = 07:07:02.60, Dec = +07:11:33.8) also visible in the Pan-STARRS images, which is a host galaxy candidate for the GRB. Photometry of this source reveals a magnitude consistent with that reported in the Pan-STARRS catalogue, indicating no bright additional component on top of it. View this GCN Circular online at https://gcn.nasa.gov/circulars/39842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37858] GRB 250322A: Enhanced Swift-XRT position
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39841 SUBJECT: GRB 250322A: Enhanced Swift-XRT position DATE: 25/03/22 21:33:49 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1707 s of XRT Photon Counting mode data and 1 UVOT images for GRB 250322A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 106.76048, +7.19313 which is equivalent to: RA (J2000): 07h 07m 2.52s Dec (J2000): +07d 11' 35.3" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37857] GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39840 SUBJECT: GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations DATE: 25/03/22 19:49:21 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> Jean-Grégoire Ducoin (CPPM), Ny Avo Rakotondrainibe (LAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), and Stéphane Schanne (CEA) report: We imaged the field of the SVOM/ECLAIRs GRB 250321B (Schanne et al., GCN Circ. 39818) with the DDRAGO imager on the SVOM/COLIBRÍ (formerly SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-22 08:07 to 10:20 UTC (28.52 to 30.74 hours after the trigger) and obtained 100 minutes of exposure in the i band. The data were coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. Within the ECLAIRs localization of the source (Schanne et al., GCN Circ. 39818) we do not detect any uncatalogued sources to a 10-sigma limiting magnitude of : i > 22.68 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/39840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37856] FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39839 SUBJECT: FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060 DATE: 25/03/22 18:49:41 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Aryan, T.-W. Chen (both NCU), S. Yang (HNAS), C.-C. Ngeow, Y. J. Yang, Y.-H. Lee, A. Sankar. K, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), T. Hashimoto, V.V. Vignesh, M. Mohanraj, T.-C. Yang (all NCHU), T. Goto (NTHU), C.-H. Niu (CCNU), S. C.-C. Ho (ANU), E. Kilerci-Eser (Sabanci U.), Y.-H. Zhu (NAOC), D. Li (Tsinghua U.), Y. Niino (U. Tokyo), S. Yamasaki (NCHU), Y.-A. Chen (NTHU), J.-S. Zhang (CAS), P. Wang (CAS), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), M.-H. Lee, Y.-C. Pan, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast radio burst 20250316A (Ng et al., ATel#17081; Leung et al., ATel#17086) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). A candidate associate X-ray source was detected by the EP mission (Sun et al., GCN 39834). The first LOT epoch of observations in the r band started at 11:30 UT on the 22nd of March 2025 (MJD = 60756.479), ~6.12 days after the CHIME detection (3.84 days after the EP X-ray source), while the first SLT epoch of observations in the z band started at 12:57 UT on the 22nd of March 2025 (MJD = 60756.540), ~7.18 days after the CHIME detection (3.90 days after the EP X-ray source). We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames, we do not detect any potential uncataloged optical afterglow counterpart candidate within the updated localization provided by Leung et al. (ATel#17086). Moreover, we used the Kinder pipeline (Yang et al. 2021, A&A, 646, A22) to subtract the stacked images using the templates from Pan-STARRS1 (Chambers et al. 2016 arXiv:1612.05560). We also utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction utilizing the "sfft" (Hu, 2022, ApJ, 936, 157) and "hotpants" (Becker A., 2015, ascl.soft. ascl:1504.004) algorithms. We found no evidence of any prominent optical afterglow counterpart candidate in the difference images as well. We further employed AutoPhOT to perform PSF photometry on the combined frames. The details of the observation and 3-sigma upper limits (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t_CHIME (d) | t-t_EP (d) | Exposure (s) | Magnitude | Average Seeing | MedianAirmass LOT | r | 60756.479 | 6.12 | 3.84 | 300 * 12 | >22.31 | 1".4 | 1.59 LOT | g | 60756.501 | 6.14 | 3.86 | 300 * 6 | >22.32 | 1".3 | 1.66 LOT | i | 60756.529 | 6.17 | 3.89 | 300 * 12 | >22.40 | 1".2 | 1.40 SLT | z | 60756.540 | 7.18 | 3.90 | 300 * 31 | >20.51 | 1".4 | 1.30 The non-detection of optical afterglow counterpart candidate is consistent with previous reports by Becerra et al. (ATel#17082), Niino et al. (ATel#17083), and our previous observations reported in Hashimoto et al. (Atel#17095). t_CHIME is the discovery time of CHIME FRB 20250316A, and t_EP is detection time of the corresponding EP X-ray source EP J120944.2+585060. The presented upper limits were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_g = 0.07 mag, A_r = 0.05, A_i = 0.03 mag, and A_z = 0.02 mag, respectively, in the direction of the burst (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37855] GRB 250322A: MASTER optical observation
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39838 SUBJECT: GRB 250322A: MASTER optical observation DATE: 25/03/22 18:47:54 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, G.Antipov,D.Vlasenko,K.Zhirkov, P.Balanutsa, N.Tyurina, Ya.Kechin, A.Chasovnikov, V.Topolev, V.Senik, K.Labzina (Lomonosov MSU), D.Buckley (SAAO), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A.Sosnovskij (Crao RAS), O.Gress, N.Budnev, O.Ershova (ISU), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South African Astronomical Observatory was pointed to the SWIFT (GCN 39835, Gupta et al.) GRB250322A (trigger No 1297832,07h 06m 56.00s , +07d 11m 56.0s, R=0.05) errorbox 4876 sec after notice time (5017 sec after trigger time) at 2025-03-22 17:29:49 UT,with upper limit up to 18.5 mag. Observations started at twilight. The observations began at zenith distance = 39 deg. The sun altitude is -9.8 deg. The galactic latitude b = 7 deg., longitude l = 209 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2820337 We obtain the following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment 5032 | MASTER-SAAO | C | 30 | 16.7 | 5077 | MASTER-SAAO | C | 120 | 17.4 | Coadd 5082 | MASTER-SAAO | C | 30 | 16.8 | 5146 | MASTER-SAAO | C | 60 | 16.9 | 5226 | MASTER-SAAO | C | 60 | 17.0 | 5320 | MASTER-SAAO | C | 90 | 17.0 | 5415 | MASTER-SAAO | C | 60 | 17.4 | 5494 | MASTER-SAAO | C | 60 | 17.4 | 5559 | MASTER-SAAO | C | 30 | 17.4 | 5604 | MASTER-SAAO | C | 120 | 18.2 | Coadd 5608 | MASTER-SAAO | C | 30 | 17.5 | 5672 | MASTER-SAAO | C | 60 | 17.6 | 5752 | MASTER-SAAO | C | 60 | 17.7 | 5812 | MASTER-SAAO | C | 180 | 18.3 | Coadd 5831 | MASTER-SAAO | C | 60 | 17.8 | 5910 | MASTER-SAAO | C | 60 | 17.8 | 6020 | MASTER-SAAO | C | 120 | 17.6 | 6129 | MASTER-SAAO | C | 60 | 17.8 | 6209 | MASTER-SAAO | C | 60 | 17.9 | 6289 | MASTER-SAAO | C | 60 | 17.9 | 6398 | MASTER-SAAO | C | 120 | 17.8 | 6537 | MASTER-SAAO | C | 120 | 17.8 | 6677 | MASTER-SAAO | C | 120 | 17.9 | 6816 | MASTER-SAAO | C | 120 | 17.9 | 6961 | MASTER-SAAO | C | 120 | 17.7 | 7036 | MASTER-SAAO | C | 270 | 18.1 | Coadd 7100 | MASTER-SAAO | C | 120 | 17.6 | 7194 | MASTER-SAAO | C | 30 | 17.8 | 7243 | MASTER-SAAO | C | 30 | 17.9 | 7273 | MASTER-SAAO | C | 90 | 18.5 | Coadd 7292 | MASTER-SAAO | C | 30 | 17.8 | 7342 | MASTER-SAAO | C | 30 | 17.8 | 7391 | MASTER-SAAO | C | 30 | 17.9 | 7421 | MASTER-SAAO | C | 90 | 18.4 | Coadd 7440 | MASTER-SAAO | C | 30 | 17.8 | 7490 | MASTER-SAAO | C | 30 | 17.8 | 7539 | MASTER-SAAO | C | 30 | 17.8 | 7569 | MASTER-SAAO | C | 90 | 18.5 | Coadd 7588 | MASTER-SAAO | C | 30 | 17.8 | 7637 | MASTER-SAAO | C | 30 | 17.9 | 7687 | MASTER-SAAO | C | 30 | 17.7 | 7736 | MASTER-SAAO | C | 30 | 17.8 | 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/39838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37854] GRB 250321a: Liverpool Telescope optical follow-up
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39837 SUBJECT: GRB 250321a: Liverpool Telescope optical follow-up DATE: 25/03/22 18:25:33 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250321a (Hu et al., GCN 39800) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters, starting at 2025-03-22 00:24:35 UT, approximately 18.24 hours after the trigger. We report a detection in the stacked images in the i band at the position of the optical counterpart (Fu et al., GCN 39804) of the magnitude i = 22.08 ± 0.16. In the r-band stacked images, we report a non-detection with the 3-sigma limiting magnitude of r > 22.19 mag. Our results are in agreement with previous observations (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831; Zheng et al., GCN 39832; Pankov et al., GCN 39836). MJD (mid) T_mid - T_0 Filter Mag. (AB) 60756.02120 18.34 h r > 22.19 60756.02976 18.55 h i 22.08 ± 0.16 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39837. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37853] EP250321a: Mondy AZT-33IK Optical Observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39836 SUBJECT: EP250321a: Mondy AZT-33IK Optical Observations DATE: 25/03/22 17:46:10 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of EP250321a (Hu et. al, GCN 39800; Page et. al, GCN 39811, Hu et. al, GCN 39833) at the redshift of z = 4.368 (Zhu et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-21 16:42:58, i.e. about 0.46 days since trigger. The optical afterglow (Fu et. al, GCN 39804; Perez-Garcia et. al, GCN 39805; Brivio et. al, GCN 39807; Zhu et. al, GCN 39809; Becerra et. al, GCN 39810; Pérez-Fournon et. al, GCN 39812; Lee et. al, GCN 39815; Han et. al, GCN 39817; Jin et. al, GCN 39822; Zhu et. al, GCN 39827; Gill et. al, GCN 39831; Zheng et. al, GCN ) is detected in the stacked image. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-21 16:42:58 0.46042 30*120 R 22.41 0.28 22.8 The photometry is based on nearby stars of SDSS-DR12 and has not been corrected for the Galactic extinction. SDSS-DR12 RA Dec R(Lupton transformations, 2005) 179.2552 +17.3825 18.123 +/- 0.049 179.2436 +17.3713 18.846 +/- 0.012 View this GCN Circular online at https://gcn.nasa.gov/circulars/39836. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37852] GRB 250322A: Swift detection of a short burst
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39835 SUBJECT: GRB 250322A: Swift detection of a short burst DATE: 25/03/22 16:26:08 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Gupta (NASA GSFC), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), J. A. Kennea (PSU), H. A. Krimm (NSF), M. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:06:12 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250322A (trigger=1297832). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 106.734, +7.199 which is RA(J2000) = 07h 06m 56s Dec(J2000) = +07d 11' 56" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 1 sec. The peak count rate was ~10,000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 16:07:25.4 UT, 73 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 106.76025, 7.19285 which is equivalent to: RA(J2000) = 07h 07m 02.46s Dec(J2000) = +07d 11' 34.2" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.70 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of 150 seconds with the White filter starting 76 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.154. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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/39835. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37851] FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39834 SUBJECT: FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe DATE: 25/03/22 15:11:56 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Sun, H. Q. Cheng, D. Y. Li, H. Y. Liu, C. C. Jin, Z. X. Ling, W. D. Zhang, Y. Liu (NAO, CAS), B. Zhang (UNLV), D. F. Hu, Y. Li, J. J. Geng, X. F. Wu (PMO, CAS), J. W. Hu, H. W. Pan, C. Zhang, L. Chen, S. Q. Jiang, Y. J. Song, T. Zhao (NAO, CAS), Y. Chen, C. K. Li, J. Guan, S. M. Jia, H. S. Zhao, J. Zhang, M. Y. Ge, W. W. Cui, H. Feng, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, D. W. Han, S. N. Zhang, X. F. Zhao, Q. C. Zhao, Z. H. Yang, Q. C. Shui (IHEP, CAS), Q. C. Liu (THU), L. Piro (INAF), V. Burwitz, P. Friedrich, N. Meidinger, K. Nandra, A. Rau (MPE), J.-U. Ness, A. Santovincenzo (ESA), Nanda Rea (ICE-CSIC), P. O'Brien (Univ. of Leicester), B. Cordier (CEA), W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team: We observed the field of the bright fast radio burst FRB 20250316A (Ng, ATel #17081) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. A total of four observations were conducted. In the first observation, which began at 2025-03-17T16:57:29 with an exposure time of 2.9 ks, no X-ray sources were detected within 3 arcmin of the CHIME position. In the second observation, starting at 2025-03-18T15:23:50 with also 2.9 ks exposure, FXT detected a weak, uncatalogued X-ray source, designated as EP J120944.2+585060. The position of this source is consistent with the refined localization provided by CHIME (Leung, ATel #17086). The unabsorbed X-ray flux is 3.4 x 10^-14 erg/cm2/s in the 0.5 - 10 keV band. In the third observation starting at 2025-03-21T05:50:01 with an exposure of 5.8 ks, the X-ray source was clearly detected at a flux consistent with the previous level. The refined source position is RA = 182.4341 deg, Dec = 58.8499 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). This position remains consistent with the CHIME localization, suggestive of EP J120944.2+585060 being likely associated with the source of FRB 20250316A. Preliminary analysis of the forth observation, taken 11 hours after the third one, shows a marginal trend of decrease of the source flux, though the the telemetry data received is not complete yet. Further analysis is ongoing. A Chandra DDT observation has been requested. If EP J120944.2+585060 is indeed associated with FRB 20250316A and located near the candidate host galaxy NGC 4141, which has a redshift of 0.0067 (Connor, ATel #17091), the inferred X-ray luminosity is approximately 3 x 10^39 erg/s in the 0.5 - 10 keV band during the EP observations. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. View this GCN Circular online at https://gcn.nasa.gov/circulars/39834. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37850] EP250321a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39833 SUBJECT: EP250321a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/03/22 09:11:25 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. F. Hu (PMO, CAS), H. Q. Cheng (NAO, CAS), Z. H. Yang, Q. C. ZHAO (IHEP, CAS), L. Chen, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250321a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 39800), and followed up by several telescopes (Lipunov et al., GCN 39803, Fu et al., GCN 39804, Perez-Garcia et al., GCN 39805, Brivio et al., GCN 39807, Zhu et al., GCN 39809, Becerra et al., GCN 39810, Page et al., GCN 39811, Pérez-Fournon et al., GCN 39812, Lee et al., GCN 39815, Ghosh et al., GCN 39816, Han et al., GCN 39817, Jin et al., GCN 39822, Zhu et al., GCN 39827, Gill et al., GCN 39831, Zheng et al., GCN 39832), with an optical counterpart detected at a redshift of 4.368 (Zhu et al., GCN 39809). Refined analysis of the WXT data shows that the event started at T0=2025-03-21T06:06:44.850 (UTC) and lasted for about 600s, with the tail of the fading light curve undetected due to the interruption of the observation. The peak flux approximately reached 4.2 x 10^(-9) erg/s/cm2 in the 0.5-4 keV band. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 4 x 10^20 cm^-2 and a photon index of 0.66 (-/+0.17). The derived average unabsorbed 0.5-4 keV flux is 1.73(-0.19/+0.21) x 10^(-9) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source about 16 ks after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 179.2623, DEC = 17.3621 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is spatially consistent with the WXT transient. The FXT position was found to be consistent with the source detected by Swift-XRT (Page et al., GCN 39811) and optical/infrared counterparts as well. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 4 x 10^20 cm^-2 and a photon index of 1.98 (-/+0.06). The derived average unabsorbed 0.5-10 keV flux is 9.23 (-0.54/+0.58) x 10^(-12) erg/s/cm^2 with an exposure time of about 2990 seconds. 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/39833. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37849] EP250321a: KAIT optical observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39832 SUBJECT: EP250321a: KAIT optical observations DATE: 25/03/22 05:56:29 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, automatically responded to EP250321a detected by Einstein Probe (Hu et al., GCN 39800) starting at 07:05:35 UT, about 0.93 hours after the trigger and lasted for ~4 hours. A set of 60s exposure images were obtained in the clear (roughly R) filters. We detect the optical afterglow (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831) with a mag of 18.7 +/- 0.2 (Vega) at 0.93 hours, it decayed to ~20.7 +/- 0.3 mag at ~5.4ks. The OT started getting brighter slowly and reach a peak of ~19.5 +/- 0.2 mag around 9.5ks, then decayed after that. View this GCN Circular online at https://gcn.nasa.gov/circulars/39832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37848] EP250321A: COLIBRÍ Continuing Optical Observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39831 SUBJECT: EP250321A: COLIBRÍ Continuing Optical Observations DATE: 25/03/22 05:50:58 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Ramandeep Gill (UNAM), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), 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), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM) and Antonio de Ugarte Postigo (LAM), and report: We continued our observations of the field of EP250321A (Hu et al., GCN Circ. 39800) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-22 03:55 to 05:25 UTC (21.75 to 23.26 hours after the trigger). The data were coadded with the custom software and analysed with STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. We detect the optical counterpart (Fu et al. 2025, GCN Circ. 39804; Perez-Garcia et al. 2025, GCN Circ. 39805; Brivio et al. 2025, GCN Circ. 39807; Zhu et al. 2025, GCN Circ. 39809; Becerra et al. 2025, GCN Circ. 39810; Pérez-Fournon et al. 2025, GCN Circ. 39812; Lee et al. 2025, GCN Circ. 39815; Han et al. 2025, GCN Circ. 39817; Sharma et al. 2025, GCN Circ. 39822) with a magnitude of: i = 22.5 +/- 0.1 Compared to the latest reported measurement in i (Lee et al, GCN Circ. 39815), this corresponds to a decay with a power-law index of approximately -1.3. Further observations are planned. 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/39831. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37847] GRB 250225B: GECAM-A detection
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39830 SUBJECT: GRB 250225B: GECAM-A detection DATE: 25/03/22 05:45:38 GMT FROM: zhengchao_astro(a)foxmail.com Jia-Cong Liu, Shao-Lin Xiong, Peng Zhang, Yan-Qiu Zhang, Chen-Wei Wang (IHEP) report on behalf of the GECAM team: GECAM-A detected a long burst, GRB 250225B, at 2025-02-25T19:39:13 UTC (denoted as T0), which was also observed by Swift/BAT (H. A. Krimm et al. 2025, GCN 39473), SVOM/GRM (Yan-Qiu Zhang et al. 2025, GCN 39493), Fermi/GBM (M. Godwin et al. 2025, GCN 39502), and Konus-Wind (A. Tsvetkova et al. 2025, GCN 39498). According to the GECAM-A light curves in about 50-200 keV, this burst mainly consists of multiple pulses with a T90 of about 63.2 ± 2.5 s. The GECAM light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250225B.png We note that these results are preliminary. Refined analysis will be reported. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/39830. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37846] GRB 250312A: GECAM-A detection
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39829 SUBJECT: GRB 250312A: GECAM-A detection DATE: 25/03/22 05:44:25 GMT FROM: zhengchao_astro(a)foxmail.com Jia-Cong Liu, Shao-Lin Xiong, Peng Zhang, Yan-Qiu Zhang, Chen-Wei Wang (IHEP) report on behalf of the GECAM team: GECAM-A detected a long burst, GRB 250312A, at 2025-03-12T13:24:17 UTC (denoted as T0), which was also observed by Swift/BAT (A. Melandri et al. 2025, GCN 39686). According to the GECAM-A light curves in about 50-200 keV, this burst mainly consists of a pulse with a T90 of about 5.0 ± 0.2 s. The GECAM light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250312A.png We note that these results are preliminary. Refined analysis will be reported. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/39829. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37845] GRB 250321B: Swift ToO observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39828 SUBJECT: GRB 250321B: Swift ToO observations DATE: 25/03/22 03:45:08 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 SVOM/ECLAIRs GRB 250321B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021824 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 SVOM/ECLAIRs 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/39828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37844] EP250321a: WFST optical observations
by GCN Circulars 22 Mar '25

22 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39827 SUBJECT: EP250321a: WFST optical observations DATE: 25/03/22 02:51:05 GMT FROM: Jin-Jun Geng at PMO <jjgeng(a)pmo.ac.cn> Jia-Zheng Zhu, Jin-Jun Geng, Ze-Lin Xu, Ning Jiang, Yan-Long Hua, Yi-Fang Liang, Ding-Fang Hu, Ji-An Jiang, Xue-Feng Wu, and Tian-Rui Sun report on behalf of the WFST team: Following the detection of EP250321a by Einstein Probe (Hu et al., GCN 39800), we use the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at Lenghu Astronomical Observation Base (Qinghai province, China) to search and follow up its afterglow. We observed the target position with 3x120s exposure in r-band starting from 2025-03-21T14:17:14. We clearly detect the optical transient (OT) reported by GCNs (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822) in our image. Our preliminary results are as follows: |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------- 2025-03-21 14:17:14 8.12 3 x 120 r 22.57 +/- 0.12 We thank the WFST staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39827. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37843] GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39826 SUBJECT: GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis DATE: 25/03/21 21:58:08 GMT FROM: Brian Grefenstette at Caltech/NuSTAR <bwgref(a)srl.caltech.edu> B. Grefenstette (Caltech) reports on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the Long GRB 250320B in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe detectors. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-03-20 23:16:29.000 on the second of two bright, broad bursts (with a resolution ~5-seconds). This is consistent with the detections by the Fermi LAT (Airasca et al, GCN circ. 39819), Fermi GBM (Neights et al., GCN circ. 39823), AstroSat CZT (Waratkar et al., GCN circ. 39808) and SVOM/GRM (Zhang et al., GCN circ. 39813). The NuSTAR CsI shield data are recorded at 1 Hz. The GRB appears to be composed of two, broad bursts, each strongly detected above background with peak count rates near 3,000 cps over a baseline of ~1,000 cps. We see clear evidence for correlated >100 keV X-rays in both CdZnTe focal planes for both bursts at the time of the GRB. Using the localization from Fermi LAT at RA = 244.66, Dec = -30.37 implies an offset from the NuSTAR boresight of only 60.49 (e.g., through the side of the instrument) and the offset from the geocenter of 143.51-deg. Discovery report and preliminary reports for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250320B/ Additional analysis will follow. Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/39826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37842] GRB 250321C: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39825 SUBJECT: GRB 250321C: Fermi GBM Final Real-time Localization DATE: 25/03/21 21:57:57 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 21:47:36 UT on 21 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321C (trigger 764286461.175894 / 250321908). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 89.3, Dec = -28.5 (J2000 degrees, equivalent to J2000 05h 57m, -28d 30'), with a statistical uncertainty of 5.0 degrees. The angle from the Fermi LAT boresight is 53.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321908/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321908/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321908/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39825. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37841] GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39824 SUBJECT: GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results DATE: 25/03/21 21:49:59 GMT FROM: Brian Grefenstette at Caltech/NuSTAR <bwgref(a)srl.caltech.edu> B. Grefenstette (Caltech) reports on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the Long GRB 250320A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-03-20 06:06:19.000 (with a resolution ~5-seconds). This is consistent with the detections by the Fermi GBM (Fermi GBM Team, GCN circ. 39789). The NuSTAR CsI shield data are recorded at 1 Hz. The GRB appears to be composed of a single, broad burst with a duration of over a minute. The peak count rate is roughly 1,500 cps over a baseline rate is ~1,000 cps during this time period. We do not see a clear evidence in the signal above 100 keV in the CdZnTe detectors. Using the localization from Fermi GBM at RA = 263.0, Dec = 47.3 implies an offset from the NuSTAR boresight of only 17.52 (e.g., through the front of the instrument) and the offset from the geocenter of 103-deg. Discovery report and preliminary reports for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250320A/ Additional analysis will follow. Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/39824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37840] GRB 250320B: Fermi GBM Observation
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39823 SUBJECT: GRB 250320B: Fermi GBM Observation DATE: 25/03/21 21:09:51 GMT FROM: eliza.neights(a)gmail.com E. Neights (GWU, NASA/GSFC), R. Hamburg (UAH), C. Meegan (UAH) and O.J. Roberts (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:15:22.02 UT on 20 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250320B (trigger 764205327/250320969). which was also detected by AstroSat CZTI (Joshi et al. 2025, GCN 39808), SVOM/GRM (Zhang et al. 2025, GCN 39813), and Fermi LAT (Holzmann Airasca et al. 2025, GCN 39819). The Fermi GBM on-ground location is consistent with the LAT position. The angle from the Fermi LAT boresight is 40 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 86 s (50-300 keV). The time-averaged spectrum from T0-2.0 to T0+107.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.16 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 570 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (9.02 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+75 s in the 10-1000 keV band is 21.6 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak = 547 +/- 22 keV, alpha = -1.16 +/- 0.01 and beta = -2.7 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/39823. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37839] EP250321a: Xinglong 216 decaying optical observations
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39822 SUBJECT: EP250321a: Xinglong 216 decaying optical observations DATE: 25/03/21 19:24:45 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Jinlei-Zhang (NAOC), Pengliang-Du (NAOC), Feng-Xiao(NAOC),Zhou-Fan (NAOC), Hong-Wu (NAOC) We performed optical observations of the field of a fast X-Ray transient EP250321a【( Zhu】 et. al, GCN 【39550】; ) in the Free filter using 2.16-m telescope located at Xinglong, Hebei, China. In the band a 600 s exposures were taken , with a median observation time of 2025-03-02T20:32:28, approximately 5 hours after the EP FXT trigger (2025-03-21T17:04:56). We measure a preliminary magnitude of 20.697 +/- 0.267, mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. We summarize our observation results as follows: 1 | 2025-03-02T20:32:28 | 600 s | Free |20.697 +/- 0.267| 2.16-m telescope View this GCN Circular online at https://gcn.nasa.gov/circulars/39822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37838] GRB 250321A: Swift-BAT refined analysis
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39821 SUBJECT: GRB 250321A: Swift-BAT refined analysis DATE: 25/03/21 18:34:55 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> R. Gupta (GSFC), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250321A (trigger #1297508) (Gupta, et al., GCN Circ. 39794). The BAT ground-calculated position is RA, Dec = 295.100, 21.055 deg which is RA(J2000) = 19h 40m 23.9s Dec(J2000) = +21d 03' 16.4" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 24%. The mask-weighted BAT light curve shows a sharp peak at the trigger time, followed by a rapid decline. T90 (15-350 keV) is 6.21 +- 1.36 sec (estimated error including systematics). The time-averaged spectrum from T-0.14 to T+7.35 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.61 +- 0.19. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is 3.2 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1297508 View this GCN Circular online at https://gcn.nasa.gov/circulars/39821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37837] GRB 250321A: Swift-XRT refined Analysis
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39820 SUBJECT: GRB 250321A: Swift-XRT refined Analysis DATE: 25/03/21 18:23:30 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for the Swift-BAT-detected burst GRB 250321A, from 108 s to 39.4 ks after the Swift-BAT trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. Using 1662 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 295.09844, +21.04038 which is equivalent to: RA (J2000): 19h 40m 23.62s Dec(J2000): +21d 02' 25.4" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This position is 72 arcsec from the Swift-BAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.13 (+0.11, -0.10). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+1.3, -1.0). The best-fitting absorption column is 3.7 (+3.4, -2.2) x 10^22 cm^-2, in excess of the Galactic value of 1.1 x 10^22 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 7.3 x 10^-11 (2.4 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.7 (+3.4, -2.2) x 10^22 cm^-2 Galactic foreground: 1.1 x 10^22 cm^-2 Excess significance: 2.0 sigma Photon index: 2.2 (+1.3, -1.0) If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 6.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x 10^-14 (1.6 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01297508. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39820. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37836] GRB 250320B: Fermi-LAT detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39819 SUBJECT: GRB 250320B: Fermi-LAT detection DATE: 25/03/21 18:05:59 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari), S. Lopez (CNRS / IN2P3), P. Monti-Guarnieri (University and INFN, Trieste), N. Di Lalla (Stanford Univ.), F. Longo (University and INFN, Trieste) and R. Gupta (NASA GSFC) report on behalf of the Fermi-LAT Collaboration: On March 20, 2025, Fermi-LAT detected high-energy emission from GRB 250320B, which was also detected by Fermi-GBM (trigger 764205327 / 250320969, GCN 39792), AstroSat CZTI (GCN 39808) and SVOM/GRM (GCN 39813). The best LAT on-ground location is found to be: RA, Dec = 244.66, -30.37 (J2000) with an error radius of 0.3 deg (90 % containment, statistical error only). This was 40 deg from the LAT boresight at the time of the GBM trigger (T0 = 23:15:22.02 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1400 s after the GBM trigger is (3.6 ± 1.1) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.35 ± 0.31. The highest-energy photon is a 1.9 GeV event which is observed ~ 245 seconds after the GBM trigger. A Swift ToO has been requested for this burst. The Fermi-LAT point of contact for this burst is Aldana Holzmann Airasca (aldana.holzmannairasca(a)ba.infn.it). 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/39819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37835] GRB 250321B: SVOM detection of a sub-threshold transient event
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39818 SUBJECT: GRB 250321B: SVOM detection of a sub-threshold transient event DATE: 25/03/21 16:40:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> S. Schanne (CEA), M. Brunet (IRAP), D. Turpin (CEA), T. Maiolino, F. Piron (LUPM), O. Godet, J-L. Atteia (IRAP) report on behalf of the SVOM mission team The SVOM/ECLAIRs telescope detected a transient source appearing below the onboard trigger thresholds, labelled GRB 250321B starting at 2025-03-21T03:36:28 UTC (Tb). The information of this sub-threshold source was received on the ground with low-latency by the SVOM VHF Alert Network. After arrival of the X-band data the source detection is confirmed. The burst was detected below the thresholds applied onboard by both the Count-Rate Trigger (CRT) and Image Trigger (IMT). It has been reported in the log messages of the onboard trigger downloaded via X-band. The best detection is found by IMT with a signal-to-noise ratio of 6.45 in the 8-120 keV energy band over a time window of 20.48 s starting at Tb. After reprocessing the photon by photon data in the onboard trigger replay with lower thresholds, as well as the on-ground offline trigger, a point-like source is confirmed in the reconstructed sky images. The localization of the source is RA, Dec = 169.687, 39.560 (J2000). The uncertainty on this position is about 12 arcminutes at 90% C.L. We notice the presence of several quasars in this error box, among which the closest is SDSS J111850.26+393258.6 located at 1.2 arcmin. We encourage follow-up observation of this source candidate. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The point of contact for this event is Stéphane Schanne (s.schanne AT cea.fr) by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/39818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37834] EP250321a: SVOM/VT optical observation
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39817 SUBJECT: EP250321a: SVOM/VT optical observation DATE: 25/03/21 15:58:18 GMT FROM: Xuhui Han at NAOC/SVOM <hxh(a)nao.cas.cn> X. H. Han, Z. H. Yao, L. P. Xin, Y. L. Qiu, H. L. Li, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the X-ray transient EP250321a (Hu et al., GCN 39800) at the location of WXT position in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The optical counterpart of EP250321a (Trigger ID: 01709133009, Fu et al., GCN 39804; Perez-Garcia et al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815) was clearly detected in VT_R and VT_B images. The brightness in AB magnitude was estimated to be: Mid time UTC | Band | Exposure Time (second) | Magnitude | Magnitude error 2025-03-21T10:29:29 | VT_B | 2940 | 21.85 | 0.09 2025-03-21T10:29:29 | VT_R | 2940 | 19.39 | 0.03 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/39817. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37833] EP 250321A: Optical counterpart detection by LCO.
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39816 SUBJECT: EP 250321A: Optical counterpart detection by LCO. DATE: 25/03/21 15:19:10 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250321A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 39800) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . 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 March 21, 2025, starting 5.46 hours after the GRB trigger. We clearly detect the optical transient (OT) reported by GCNs (Fu et al. GCN 39804, Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812, Lee et al., GCN 39815) in our r, V band image. |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------- 2025-03-21 11:38:04.13 5.468 1 x 900 r r = 21.40 +/- 0.07 2025-03-21 11:38:20.54 5.472 1 x 900 V V = 21.76 +/- 0.09 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/39816. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37832] EP250321a: Kinder optical follow-up observations
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39815 SUBJECT: EP250321a: Kinder optical follow-up observations DATE: 25/03/21 14:45:24 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> Y.-H. Lee, A. Aryan, T.-W. Chen, Y. J. Yang, W.-J. Hou, H.-Y. Hsiao (all NCU), A. K. H. Kong (NTHU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), M.-H. Lee, Y.-C. Pan, C.-C. Ngeow, A. Sankar. K, C.-H. Lai, C.-S. Lin, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, L. L. Fan, Z. N. Wang, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250321a (Hu et al., GCN 39800) using the 1m LOT (in g and r band) and 40cm SLT (in i and z band) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2024, arXiv:2406.09270). The first LOT epoch of observations in the r band started at 11:57 UT on the 21st of March 2025 (MJD 60755.498), ~5.78 hrs after the EP trigger, while the first SLT epoch of observations in the i band started at 12:23 UT on the 21st of March 2025 (MJD 60755.516), ~6.21 hrs after the EP trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked images, we clearly detected the optical counterpart candidate proposed by Fu et al. (GCN 39804) and confirmed by several other observations (e.g., Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812). We employed the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry on individual frames. The details of the observation and measured photometry from the first frame (in the AB system) were as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | Seeing | Airmass LOT | r | 60755.498 | 5.78 | 300 * 6 | 21.86 +/- 0.07 | 1".1 | 1.63 SLT | i | 60755.516 | 6.21 | 300 * 12 | 20.75 +/- 0.10 | 1".4 | 1.36 LOT | g | 60755.520 | 6.31 | 300 * 6 | >22.04 | 1".5 | 1.41 The presented magnitudes were calibrated using the field stars from the Pan-STARRS1 catalog and were not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_r = 0.12 mag, A_i = 0.09 mag, and A_g = 0.17 mag, respectively, in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/39815. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37831] GRB 250321A: Swift/UVOT Upper Limits
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39814 SUBJECT: GRB 250321A: Swift/UVOT Upper Limits DATE: 25/03/21 13:55:16 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250321A 128 s after the BAT trigger (Gupta et al., GCN Circ. 39794). No optical afterglow consistent with the XRT position (Page et al., GCN Circ. 39798) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 128 278 147 >19.9 white 128 4071 344 >20.6 v 4282 4482 197 >18.9 b 3667 5142 236 >20.0 u 340 5097 232 >19.4 w1 4693 4892 197 >19.3 m2 4487 4687 197 >19.2 w2 4077 4277 197 >19.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 4.368 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/39814. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37830] GRB 250320B: SVOM/GRM observation of a long burst
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39813 SUBJECT: GRB 250320B: SVOM/GRM observation of a long burst DATE: 25/03/21 13:20:50 GMT FROM: wenlongzhang2018(a)163.com SVOM/GRM team: Wen-Long Zhang, Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250320B (SVOM trigger reference: sb25032001) at 2025-03-20T23:15:23.000 (T0), which was also observed by Fermi/GBM (Fermi GBM team, GCN #39792) and AstroSat CZTI (J. Joshi et al., GCN 39808). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-peaks with a T90 of 86.5 +0.5/-1.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250320B.png In addition, the position of this burst, as determined by Fermi/GBM (Fermi GBM Team, GCN #39792), is located at about 53.9 degrees (with a few degrees of statistical and systematic errors) from the SVOM optical axis. This burst was detected by the Count-Rate Trigger onboard ECLAIRs, as an increase in counts over background, but it was not localized by the coded-mask imaging process, which confirms that the burst occurred outside the ECLAIRs field of view. 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: Wen-Long Zhang (IHEP) (zhangwl(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/39813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37829] EP250321a: LCO optical counterpart detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39812 SUBJECT: EP250321a: LCO optical counterpart detection DATE: 25/03/21 12:58:42 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, I. Correa-Plasencia, A.E. Hernández-Díaz (ULL), D. Aguado, A. López-Oramas, D. Nespral (IAC and ULL), N.C. Sun (UCAS), W. Li, Y. Wang, and Z. Niu (NAOC) We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of EP250321a detected by EP/WXT (Hu et al., GCN circ. 39800), and Swift-XRT (Page et al., GCN circ. 39811). We observed the field of EP250321a with one of the two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas). We obtained a 200-sec exposure in the SDSS i' filter starting at 2025-03-21 09:38:42 UT, about 3.48 hr after the EP trigger. An uncatalogued source is detected at the position of the optical and near-IR counterpart reported by Fu et al. (GCN circ. 39804), Perez-Garcia et al. (GCN circ. 39805), Brivio et al. (GCN circ. 39807), Zhu et al. (GCN circ. 39809), and Becerra et al. (GCN circ. 39810). Zhu et al. (GCN circ. 39809) have reported a redshift of z = 4.368. We measure the following magnitude, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | mag | error | filter | ---------------------------------------------- 2025-03-21 09:38:42 19.3 0.15 i' 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/39812. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37828] EP250321a: Swift-XRT detection of an X-ray source
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39811 SUBJECT: EP250321a: Swift-XRT detection of an X-ray source DATE: 25/03/21 11:18:07 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, P.A. Evans (U.Leicester) and M.H. Siegel (PSU) report on behalf of the Swift-XRT Team: On 2025 March 21 at 07:26 UT, Swift started observing EP250321a, 4.6 ks after the Einstein Probe trigger (GCN Circ. 39800). A previously-uncatalogued X-ray source was identified, at a position of RA, Dec = 179.26259, +17.3628, which is equivalent to RA (J2000): 11h 57m 03.02s Dec (J2000): +17d 21' 46.1" with an uncertainty of 2.6 arcsec (radius, 90% confidence). This is consistent with the position of the optical and NIR source reported (GCN Circs. 39804, 39805, 39807, 39809, 39810). The first snapshot of data, spanning 4.6-6.2 ks after the trigger, shows some X-ray flaring, with a mean X-ray flux of 3.7 (+0.4, -0.4) x 10^-11 erg cm-2 s-1 (observed, 0.3-10 keV). View this GCN Circular online at https://gcn.nasa.gov/circulars/39811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37827] EP250321A: COLIBRÍ Optical Observations
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39810 SUBJECT: EP250321A: COLIBRÍ Optical Observations DATE: 25/03/21 10:50:05 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Ny Avo Rakotondrainibe (LAM), Ramandeep Gill (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), William H. Lee (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM) and Antonio de Ugarte Postigo (LAM), and report: We imaged the field of EP250321A (Hu et al., GCN Circ. 39800) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We started observing at 2025-03-21 07:42 UTC (1.54 hours after the trigger). The data were coadded with the COLIBRÍ pipeline and analysed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction. At a mid-time T+1.9 h after the trigger, we detect the optical counterpart (Fu et al. 2025, GCN Circ. 39804; Perez-Garcia et al. 2025, GCN Circ. 9805; Brivio et al. 2025, GCN Circ. 39807; Zhu et al. 2025, GCN Circ. 39809) with AB magnitudes of: r = 20.69 +/- 0.05 i = 19.12 +/- 0.04 Further analysis of the additional images is ongoing. Further observations are planned. 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/39810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37826] EP250321a: VLT/X-shooter redshift z = 4.368
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39809 SUBJECT: EP250321a: VLT/X-shooter redshift z = 4.368 DATE: 25/03/21 09:49:05 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> Z. P. Zhu (NAOC), B. Schneider (LAM), A. Saccardi (CEA/Irfu), D. Xu (NAOC), V. D’Elia (SSDC & INAF-OAR), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI & Radboud), P. T. O’Brien (Leicester), J. T. Palmerio (CEA/Irfu), S. D. Vergani (CNRS, Obs. Paris/LUX), report on behalf of the Stargate collaboration: We observed the optical and NIR counterpart (Fu et al., GCN 39804; Perez-Garcia et al., GCN 39805; Brivio et al., GCN 39807) of the Einstein Probe transient EP250321a (Hu et al., GCN 39800) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations were conducted in rapid response mode (RRM) using the X-shooter spectrograph, and were requested as soon as we became aware of the optical counterpart. In a 10-s r-band exposure taken with the acquisition camera (102.8 min after the EP trigger), the counterpart is well detected with a magnitude r = 20.2 +/- 0.1 (AB, calibrated against a single Pan-STARRS object). Comparing with the report by Fu et al. (GCN 39804), our measurement indicates fading and confirms this object as the optical afterglow of EP250321a. Our spectra, covering the wavelength range 3000-21000 AA, consist of 2 exposures of 600 s each. The observation mid time was 2025 Mar 21.336 UT (1.91 hr after the EP trigger). In a preliminary reduction of the spectra, we clearly detect a continuum down to ~4930 AA, and a broad trough at ~6525 AA. These two features are consistent with Lyman limit and Lyman alpha, respectively. From the detection of a plethora of narrow absorption features, including S II, Si II, Si II*, O I, OI*, C II, C II*, Ni II, Si IV, C IV, Fe II, Fe II*, Al II, Al III, Mg II, Mg I, we infer a redshift of z = 4.368. The detection of fine-structure lines robustly confirms the physical association between this absorption system and the high-energy transient. We thus conclude that EP250321a was at z = 4.368. We wish a happy March equinox to the whole GCN community. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Enrico Congiu, Israel Blanchard, Julien Drevon, and Miguel Lopez. View this GCN Circular online at https://gcn.nasa.gov/circulars/39809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37825] GRB 250320B: AstroSat CZTI detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39808 SUBJECT: GRB 250320B: AstroSat CZTI detection DATE: 25/03/21 09:26:45 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> J. Joshi (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250320B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 39792). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-03-20 23:15:29.50 UTC. The measured peak count rate associated with the burst is 350 (+38, -29) counts/s above the background in the combined data of three quadrants (out of four), with a total of 5456 (+403, -388) counts. The local mean background count rate was 207 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 85 (+3, -4) s. In the preliminary analysis, we find 997 Compton events associated with this event. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-03-20 23:15:28.37 UTC. The measured peak count rate associated with the burst is 2028 (+97, -71) counts/s above the background in the combined data of all quadrants, with a total of 27352 (+899, -1147) counts. The local mean background count rate was 1278 (+4, -4) counts/s. We measure a T90 of 81 (+3, -1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/39808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37824] EP250321a: REM optical/NIR afterglow detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39807 SUBJECT: EP250321a: REM optical/NIR afterglow detection DATE: 25/03/21 09:16:29 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 EP250321a (Hu et al., GCN 39800) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2025 March 21 at 07:05:26 UT (i.e. ~0.92 hr after the EP trigger), and lasting for about 2 hours. From preliminary photometry we detect the counterpart in the optical and NIR images at the position of the optical afterglow (Fu et al., GCN 39804; Perez-Garcia et al., GCN 39805) with the following magnitudes: r = 19.9 +/- 0.2 (AB; calibrated against the Pan-STARRS catalogue) at a mid-time of t - t0 = 1.78 hr after the trigger; H = 15.3 +/- 0.2 (Vega; calibrated against the 2MASS catalogue) at a mid-time t - t0 = 1.06 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/39807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37823] Fermi GRB 250320B: Global MASTER-Net observations report
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39806 SUBJECT: Fermi GRB 250320B: Global MASTER-Net observations report DATE: 25/03/21 09:16:08 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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) started inspect of the Fermi GRB 250320B ( Fermi GBM team, GCN 39792) errorbox 33041 sec after notice time and 33077 sec after trigger time at 2025-03-21 08:26:39 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 12 deg. The sun altitude is -28.6 deg. The galactic latitude b = 16 deg., longitude l = 357 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818681 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 33098 | 2025-03-21 08:26:39 | MASTER-OAFA | (16h 26m 20.48s , -22d 13m 22.4s) | C | 40 | 17.1 | 33138 | 2025-03-21 08:26:39 | MASTER-OAFA | (16h 26m 20.49s , -22d 13m 22.3s) | C | 120 | 17.8 | Coadd 33108 | 2025-03-21 08:26:40 | MASTER-OAFA | (16h 36m 11.47s , -21d 49m 19.6s) | C | 60 | 18.3 | 33173 | 2025-03-21 08:27:55 | MASTER-OAFA | (16h 26m 22.64s , -22d 11m 46.3s) | C | 40 | 17.2 | 33184 | 2025-03-21 08:27:55 | MASTER-OAFA | (16h 36m 13.62s , -21d 47m 42.5s) | C | 60 | 18.3 | 33249 | 2025-03-21 08:29:10 | MASTER-OAFA | (16h 26m 17.85s , -22d 12m 32.3s) | C | 40 | 17.2 | 33259 | 2025-03-21 08:29:10 | MASTER-OAFA | (16h 36m 08.92s , -21d 48m 27.6s) | C | 60 | 18.4 | 33354 | 2025-03-21 08:30:25 | MASTER-OAFA | (16h 26m 16.38s , -22d 11m 33.0s) | C | 100 | 17.5 | 33484 | 2025-03-21 08:30:25 | MASTER-OAFA | (16h 26m 16.37s , -22d 11m 32.9s) | C | 360 | 18.2 | Coadd 33364 | 2025-03-21 08:30:26 | MASTER-OAFA | (16h 36m 07.07s , -21d 47m 24.6s) | C | 120 | 15.3 | 33490 | 2025-03-21 08:32:41 | MASTER-OAFA | (16h 26m 23.41s , -22d 12m 34.3s) | C | 100 | 17.5 | 33530 | 2025-03-21 08:32:41 | MASTER-OAFA | (16h 26m 23.41s , -22d 12m 34.3s) | C | 180 | 17.9 | Coadd 33625 | 2025-03-21 08:34:57 | MASTER-OAFA | (16h 26m 17.86s , -22d 13m 34.9s) | C | 100 | 17.5 | 33791 | 2025-03-21 08:37:12 | MASTER-OAFA | (16h 26m 22.80s , -22d 13m 29.4s) | C | 160 | 17.7 | 33928 | 2025-03-21 08:40:29 | MASTER-OAFA | (16h 26m 20.00s , -22d 12m 03.3s) | C | 40 | 17.1 | 33938 | 2025-03-21 08:40:29 | MASTER-OAFA | (16h 36m 11.27s , -21d 47m 56.2s) | C | 60 | 18.3 | 34002 | 2025-03-21 08:41:44 | MASTER-OAFA | (16h 26m 19.86s , -22d 13m 31.8s) | C | 40 | 17.2 | 34013 | 2025-03-21 08:41:44 | MASTER-OAFA | (16h 36m 11.25s , -21d 49m 24.6s) | C | 60 | 18.3 | 34077 | 2025-03-21 08:42:58 | MASTER-OAFA | (16h 26m 22.13s , -22d 11m 55.1s) | C | 40 | 17.1 | 34087 | 2025-03-21 08:42:59 | MASTER-OAFA | (16h 36m 13.43s , -21d 47m 47.9s) | C | 60 | 18.3 | 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/39806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37822] EP250321a: BOOTES-5/JGT optical afterglow detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39805 SUBJECT: EP250321a: BOOTES-5/JGT optical afterglow detection DATE: 25/03/21 08:52:33 GMT FROM: ipg(a)iaa.es I. Perez-Garcia, E. J. Fernandez-Garcia, G. Garcia-Segura, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar, A. Castellon (Univ. de Malaga), Y.-D. Hu (INAF-OAB, Brera), S. Jeong (ADD, Daejeon) and D. Hiriart and W. H. Lee (UNAM), on behalf of a larger collaboration, report: Following the detection of EP250321a by Einstein Probe (Hu et al. GCNC 39800), the BOOTES-5/JG robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically responded to this X-ray transient starting on 2025-03-21 07:27:36 UT (23 min after notification). Series of images in clear filter were gathered and we detect and uncatalogud source at RA, Dec = 11:57:03.0, +17:21:46.2 (179.26263, 17.36283) within the WXT region, for which we measure a magnitude of 19.6 +- 0.1, consistent with Fu et al. (GCNC 39800). Further analysis of the additional images is ongoing. We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37821] EP250321a: TRT optical counterpart detection
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39804 SUBJECT: EP250321a: TRT optical counterpart detection DATE: 25/03/21 08:39:06 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Y. Fu (HUST), W.X. Li, J. An, S.Q. Jiang (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, Z.P. Zhu, Z. Fan, N.C. Sun, D. Xu, Y.N. Wang (NAOC) report on behalf of a large collaboration: We observed the field of EP250321a detected by EP/WXT (Hu et al., GCN 39800) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Sierra Remote Observatories in California. We obtained several 300 s frames in the R and I filters. An uncatalogued and decaying optical source is detected within the error circle at coordinates R.A. (J2000) = 11:57:03.02 Dec. (J2000) = +17:21:45.94 with an uncertainty of ~0.5 arcsec. The source has R ~ 19.7 mag at 1.24 hr and I ~ 18.8 mag at 1.72 hr after the EP trigger, calibrated with nearby Pan-STARRS DR2 stars and not corrected for Galactic extinction. We think that the source is very likely the optical counterpart of EP250321a. View this GCN Circular online at https://gcn.nasa.gov/circulars/39804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37820] EP250321a: Global MASTER-Net observations report
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39803 SUBJECT: EP250321a: Global MASTER-Net observations report DATE: 25/03/21 08:36:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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 EP250321a ( EP Team et al., GCN 39800) errorbox 141 sec after notice time and 7118 sec after trigger time at 2025-03-21 08:08:37 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 70 deg. The sun altitude is -32.2 deg. The galactic latitude b = 74 deg., longitude l = 250 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2819086 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 7149 | 2025-03-21 08:08:37 | MASTER-OAFA | (11h 56m 58.33s , +17d 45m 08.7s) | C | 60 | 18.7 | 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/39803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37819] Swift GRB 250321A: Global MASTER-Net observations report
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39802 SUBJECT: Swift GRB 250321A: Global MASTER-Net observations report DATE: 25/03/21 08:32:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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 Swift GRB 250321A ( R. Gupta et al., GCN 39794) errorbox 27374 sec after notice time and 27401 sec after trigger time at 2025-03-21 08:19:20 UT, with upper limit up to 16.7 mag. The observations began at zenith distance = 78 deg. The sun altitude is -30.1 deg. The galactic latitude b = -1 deg., longitude l = 57 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818736 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 27432 | MASTER-OAFA | C | 60 | 16.6 | 27569 | MASTER-OAFA | C | 180 | 16.7 | 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/39802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37818] Fermi GRB 250321A: Global MASTER-Net observations report
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39801 SUBJECT: Fermi GRB 250321A: Global MASTER-Net observations report DATE: 25/03/21 08:31:06 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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) started inspect of the Fermi GRB 250321A ( Fermi GBM team, GCN 39793) errorbox 25226 sec after notice time and 25261 sec after trigger time at 2025-03-21 07:43:40 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 82 deg. The sun altitude is -37.1 deg. The galactic latitude b = -6 deg., longitude l = 56 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2818762 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 25341 | 2025-03-21 07:43:40 | MASTER-OAFA | (19h 30m 40.40s , +20d 25m 41.2s) | C | 160 | 16.0 | 25537 | 2025-03-21 07:46:56 | MASTER-OAFA | (19h 30m 47.85s , +20d 25m 03.0s) | C | 160 | 16.4 | 25733 | 2025-03-21 07:50:11 | MASTER-OAFA | (19h 30m 42.54s , +20d 24m 22.3s) | C | 160 | 16.7 | 26355 | 2025-03-21 08:00:33 | MASTER-OAFA | (19h 30m 43.53s , +20d 26m 11.7s) | C | 160 | 16.4 | 27421 | 2025-03-21 08:19:20 | MASTER-OAFA | (19h 30m 53.70s , +20d 27m 42.1s) | C | 40 | 17.0 | 27431 | 2025-03-21 08:19:20 | MASTER-OAFA | (19h 40m 32.05s , +20d 50m 27.7s) | C | 60 | 16.6 | 27559 | 2025-03-21 08:20:37 | MASTER-OAFA | (19h 30m 47.78s , +20d 27m 00.4s) | C | 160 | 16.8 | 27569 | 2025-03-21 08:20:38 | MASTER-OAFA | (19h 41m 30.19s , +20d 47m 56.2s) | C | 180 | 16.7 | 27694 | 2025-03-21 08:23:53 | MASTER-OAFA | (19h 30m 54.58s , +20d 27m 29.9s) | C | 40 | 17.1 | 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/39801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37817] EP250321a: Einstein Probe detection of an X-ray transient
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39800 SUBJECT: EP250321a: Einstein Probe detection of an X-ray transient DATE: 25/03/21 08:04:38 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. F. Hu (PMO, CAS), H. Q. Cheng (NAO, CAS), Z. H. Yang, Q. C. ZHAO (IHEP, CAS), L. Chen, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250321a. The transient triggered EP-WXT (ID: 01709133009) at 2025-03-21 06:09:59 (UTC). The WXT position of the source is R.A. = 179.262 deg, DEC = 17.386 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received. 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/39800. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37816] GRB 250321A: GOTO optical upper limits
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39799 SUBJECT: GRB 250321A: GOTO optical upper limits DATE: 25/03/21 07:42:24 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, S. Belkin, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. O'Neill, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration: The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) observed the field of GRB 250321A, detected by Fermi/GBM (Fermi GBM Team, GCN 39793) and Swift/BAT (Gupta et al., GCN 39794). The position of the Swift/XRT counterpart (Page, GCN 39798) was covered by GOTO-North at 05:25:29 UT on 2025-03-21 (4.7 hours post-trigger). The observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. No optical counterpart is detected in the Swift/XRT localisation region (Page, GCN 39798) down to a 3-sigma L-band limit of 19.6 mag (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/39799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37815] GRB 250321A: Swift-XRT localisation
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39798 SUBJECT: GRB 250321A: Swift-XRT localisation DATE: 25/03/21 07:13:12 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team: Using 1.7 ks of XRT Photon Counting mode data starting 134 s after the BAT trigger on GRB 250321A (GCN Circ. 39794), an X-ray source was identified at a position of RA, Dec = 295.09873, 21.04146, which is equivalent to RA (J2000): 19h 40m 23.7s Dec (J2000): 21d 02′ 29.3″ with an uncertainty of 4.2 arcsec. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/39798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37814] GRB 250314A: Keck/NIRC2 J-band upper limit
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39797 SUBJECT: GRB 250314A: Keck/NIRC2 J-band upper limit DATE: 25/03/21 06:55:25 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng, Alexei V. Filippenko (UC Berkeley), Chris Fassnacht, Prayaag Katta (UC Davis), D. B. Malesani (DAWN/NBI) and Jing Wang (NAOC), report on behalf of the KAIT GRB team: We observed the field of the SVOM GRB 250314A (Wang et al., GCN 39719) with the NIRC2 camera on the Keck II 10 m telescope. The observations were performed in the J band (without AO) starting on 2025 March 16 at 12:54:21 UTC (i.e., 2.0 days after the burst), and consisted of 2x120 s exposures. At the reported NIR afterglow position (Malesani et al., GCN 39727; Malesani et al., GCN 39732), we do not detect any counterpart with an upper limit of J > 19.4 mag (Vega). View this GCN Circular online at https://gcn.nasa.gov/circulars/39797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37813] EP250226a/GRB 250226A: KAIT optical observations
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39796 SUBJECT: EP250226a/GRB 250226A: KAIT optical observations DATE: 25/03/21 06:54:07 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of EP250226a/GRB 250226A (Fermi GBM team, GCN 39479; Jiang et al., GCN 39482; Jiang et al., GCN 39513; Zhang et al., GCN 39492; Thakur et al., GCN 39518; Pathak et al., GCN 39530; Svinkin et al., GCN 39542; Ronchini et al., GCN 39672) on Feb 26 at 09:27:20 (~2.88 hours after GBM trigger) and lasted for 4 hours. A set of 160x60s images were obtained in the clear (roughly R) filters. We detect the optical afterglow (An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani et. al, GCN 39488; Li et. al, GCN 39489; Aryan et. al, GCN 39509; Zou et al., GCN 39511; Li et. al, GCN 39514; Jiang et al., GCN 39515; Poidevin et al., GCN 39524; Tanasan et al., GCN 39554) in our single images. We measure the OT brightness to be 19.6 +/- 0.1 mag (Vega) at 2.88 hours after GBM trigger. We observed the OT again on the following night with 60x60s exposures and detected the OT in the coadd image with 22.2 +/- 0.2 mag (Vega) at a mid time of 1.17 days. This gives a decay index of -1.04 between the two nights. View this GCN Circular online at https://gcn.nasa.gov/circulars/39796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37812] GRB 250321A: Fermi GBM Observation
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39795 SUBJECT: GRB 250321A: Fermi GBM Observation DATE: 25/03/21 06:04:23 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 00:42:39.02 UT on 21 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564/250321030), which was also detected by Swift BAT (Gupta et al. 2025, GCN 39794). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 39 degrees. The GBM light curve shows one main pulse with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+7.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.20 and the cutoff energy, parameterized as Epeak, is 101 +/- 12 keV. The event fluence (10-1000 keV) in this time interval is (1.04 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.13 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/39795. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37811] GRB 250321A: Swift detection of a burst
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39794 SUBJECT: GRB 250321A: Swift detection of a burst DATE: 25/03/21 01:04:22 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:42:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250321A (trigger=1297508). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 295.077, +21.041 which is RA(J2000) = 19h 40m 19s Dec(J2000) = +21d 02' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Only the first 8 seconds of the BAT light curve after the trigger is available due to a telemetry gap. This data shows a complex structure with a duration of at least 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 00:44:43.60 UT, 125.6 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart. Due to a telemetry gap, UVOT data are not available at this time. Although XRT did not report an X-ray counterpart in the limited immediately transmitted data, the significance of the BAT image (>10 sigma), the shape of the BAT light curve, and the simultaneous detection by Fermi/GBM (trigger 764210564) give us confidence that this is an astrophysical Gamma Ray Burst. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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/39794. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37810] GRB 250321A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Mar '25

21 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39793 SUBJECT: GRB 250321A: Fermi GBM Final Real-time Localization DATE: 25/03/21 00:53:07 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 00:42:39 UT on 21 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250321A (trigger 764210564.016716 / 250321030). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 299.0, Dec = 17.1 (J2000 degrees, equivalent to J2000 19h 56m, 17d 06'), with a statistical uncertainty of 6.3 degrees. The angle from the Fermi LAT boresight is 44.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250321030/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39793. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37809] GRB 250320B: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39792 SUBJECT: GRB 250320B: Fermi GBM Final Real-time Localization DATE: 25/03/20 23:25:50 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 23:15:22 UT on 20 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250320B (trigger 764205327.02257 / 250320969). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 249.2, Dec = -21.8 (J2000 degrees, equivalent to J2000 16h 36m, -21d 48'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 31.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320969/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320969/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320969/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37808] GRB250309B: Proof-of-concept for Joint ZTF+EP Experiment
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39791 SUBJECT: GRB250309B: Proof-of-concept for Joint ZTF+EP Experiment DATE: 25/03/20 20:29:02 GMT FROM: Tomas Ahumada Mena at Caltech <tahumada(a)caltech.edu> T. Ahumada (Caltech), E. C. Bellm (UW), L. Yan, T. du Laz, M. M. Kasliwal (Caltech), Q. Y. Wu, S. Q. Jiang (NAOC, CAS), J. H. Wu (GZHU), Y. Liu, C. Jin, W. Yuan (NAOC, CAS) report on behalf of the Zwicky Transient Facility Partnership and Einstein Probe Team Starting Feb 27, 2025, the Zwicky Transient Facility (ZTF) partnership is collaborating with the Einstein Probe (EP) team to map multiple EP pointings concurrently every night with ZTF. By cross-matching ZTF alerts with EP alerts, we report our first proof-of-concept cross-match. On March 9, 2025, Fermi-GBM detected GRB 250309B at 07:38:30 UTC (Preis and Greiner, GCN 39629; Fermi GBM team, GCN 39635; McDermott et al., GCN 39642). As part of the regular schedule, EP was set to cover the region, with ZTF scheduled to shadow EP. Both EP and ZTF subsequently observed the afterglow, ZTF25aaitvjt/AT2025dws. The Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission began observations from 2025-03-09T10:38:05(UTC) (~T0+3h) with an exposure time of 4.8 ks. The WXT position of the source is R.A. = 210.800 deg, DEC = -8.500 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic), which is consistent with the optical counterpart AT2025dws (Stein et al., GCN 39639) and the X-ray counterpart (Page and Evans, GCN 39649). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 3.0 x 10^20 cm^-2 and a photon index of 1.8 (-1.2/+1.6). The derived average unabsorbed 0.5-4 keV flux is 9.2 (-5.3/+10.8) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. In this particular example, we clarify that ZTF was double-triggered to observe this field - once by the joint ZTF+EP experiment and once by the IceCube neutrino experiment. Both experiments recovered AT2025dws. We observed a fading rate of 2.5 mag / hour in the r-band. This source was promptly reported by ZTF in Stein et al. GCN 39639. 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). Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. View this GCN Circular online at https://gcn.nasa.gov/circulars/39791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37807] GRB 250317B: Mondy AZT-33IK Optical Observations
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39772 SUBJECT: GRB 250317B: Mondy AZT-33IK Optical Observations DATE: 25/03/18 15:19:56 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) at the redshift of z=3.44 (Thoene et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-17 15:41:49, i.e. about 0.58 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Thoene et. al, GCN 39769; Zhu et. al, GCN 39770) is clearly visible in the stacked image. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-17 15:41:49 0.58173 28*120 R 20.88 0.13 22.8 Ref. stars from SDSS-DR12 RA Dec R R_err 211.6590 +40.0703 16.451 0.029 211.5997 +40.0619 18.859 0.055 The photometry is based on nearby stars (see the list above) from the SDSS-DR12 catalog (R magnitudes were obtained using Lupton 2005 transformations) and has not been corrected for the Galactic extinction. Using a simple power law fit to the observed data in the r and R filters, we estimate the light curve decay index to be about -1.5. View this GCN Circular online at https://gcn.nasa.gov/circulars/39772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37806] GRB 250317B: Mondy AZT-33IK Continued Optical Observations
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39790 SUBJECT: GRB 250317B: Mondy AZT-33IK Continued Optical Observations DATE: 25/03/20 13:21:09 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) at the redshift of z=3.44 (Thoene et. al, GCN 39769) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on 2025-03-18 at 18:45:47 (UT), i.e. about 1.72 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Thoene et. al, GCN 39769; Zhu et. al, GCN 39770; Pankov et. al, GCN 39772; Moretti & Pavoni, GCN 39774; Schneider et. al, GCN 39777; Atteia et. al, GCN 39784) is not detected. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-18 18:45:47 1.72130 45*120 R n/d n/d 22.9 2025-03-19 18:02:14 2.70077 59*120 R n/d n/d 23.3 Ref. stars from SDSS-DR12 RA Dec R R_err 211.6590 +40.0703 16.451 0.029 211.5997 +40.0619 18.859 0.055 The photometry is based on nearby stars (see the list above) from the SDSS-DR12 catalog (R magnitudes were obtained using Lupton 2005 transformations) and has not been corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37805] GRB 250320A: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39789 SUBJECT: GRB 250320A: Fermi GBM Final Real-time Localization DATE: 25/03/20 06:16:17 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 06:05:44 UT on 20 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250320A (trigger 764143549.57948 / 250320254). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 263.0, Dec = 47.3 (J2000 degrees, equivalent to J2000 17h 32m, 47d 17'), with a statistical uncertainty of 1.2 degrees. The angle from the Fermi LAT boresight is 105.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320254/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320254/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320254/… View this GCN Circular online at https://gcn.nasa.gov/circulars/39789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37804] Fermi GRB 250319B: Global MASTER-Net observations report
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39788 SUBJECT: Fermi GRB 250319B: Global MASTER-Net observations report DATE: 25/03/20 05:30:23 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250319B ( Fermi GBM team, GCN 39783) errorbox 44851 sec after notice time and 82295 sec after trigger time at 2025-03-20 03:59:04 UT, with upper limit up to 16.7 mag. Observations started at twilight. The observations began at zenith distance = 40 deg. The sun altitude is -9.9 deg. The galactic latitude b = -15 deg., longitude l = 319 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2817489 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 82326 | 2025-03-20 03:59:04 | MASTER-SAAO | (16h 07m 31.63s , -71d 07m 28.6s) | C | 60 | 16.7 | 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/39788. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37803] FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
by GCN Circulars 20 Mar '25

20 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39787 SUBJECT: FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations DATE: 25/03/20 02:49:24 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Yan-Qiu Zhang, Wang-Chen Xue, Shao-Lin Xiong, Yue Wang (IHEP) and Ce Cai (HEBNU) report on behalf of the Insight-HXMT team: At the event time 2025-03-16T08:33:50.842 UTC (T0) of FRB 20250316A (Ng et al., ATel 17081; Leung et al., ATel 17086), Insight-HXMT/HE was observing normally and monitored the full location error region of FRB 20250316A. The routine blind search of Insight-HXMT/HE data found no burst candidate around the time of FRB 20250316A. Thus, we implemented a targeted search [1] from T0 - 100 s to T0 + 5 s, and identified no candidate above 3 sigma. Considering three typical spectral models (i.e. soft, normal and hard Band functions), three timescales and the FRB localization (RA = 182.476 deg, Dec = +58.8494 deg (J2000)), the 3 sigma upper limits of the gamma-ray transient energy flux (10 keV-1 MeV, in units of 10^-7 erg/s/cm^2) are reported below: Timescale (s) Soft Normal Hard 0.1 7.17 7.48 3.27 1 2.26 2.36 1.03 10 0.72 0.75 0.33 With the distance of 40.8 Mpc from NGC 4141, the probable host galaxy of this FRB, we further calculate the following upper limits of the gamma-ray transient intrinsic isotropic luminosity (1 keV-10 MeV, in units of 10^47 erg/s): Timescale (s) Soft Normal Hard 0.1 1.43 1.49 0.65 1 0.45 0.47 0.21 10 0.14 0.15 0.07 We note that the above results are preliminary. Refined results will be reported. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/. [1] C. Cai et al. MNRAS, 508, 3910–3920 (2021) https://doi.org/10.1093/mnras/stab2760 View this GCN Circular online at https://gcn.nasa.gov/circulars/39787. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37802] GRB 250313A: GRBAlpha detection
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39786 SUBJECT: GRB 250313A: GRBAlpha detection DATE: 25/03/19 21:08:05 GMT FROM: Michaela Ďuríšková at Masaryk University <505876(a)mail.muni.cz> M. Duriskova, M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, L. Szakszonova, M. Kolar,J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250313A (FERMI/GBM: GCN Circular 39703, FERMI/LAT: GCN Circular 39711, AstroSat/CZTI: GCN Circular 39714, SVOM/GRM: GCN Circular 39716, Konus-Wind: GCN Circular 39721, CALET/CGBM: GCN Circular 39725) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-03-13 14:34:41.7 UTC. The T90 duration measured by GRBAlpha is 13 s and the overall significance during T90 reaches 52.3 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250313A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/39786. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37801] LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39785 SUBJECT: LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn DATE: 25/03/19 17:15:20 GMT FROM: Hsin-Yu Chen at The University of Texas at Austin <hsinyu(a)austin.utexas.edu> Hsin-Yu Chen (UT Austin), Greg Zeimann (UT McDonald Observatory), J. Craig Wheeler (UT Austin), and Jozsef Vinko (Konkoly Observatory) report on behalf of the LIGHETR Collaboration: We conducted targeted follow-up observations of AT 2025azn (Hosseinzadeh et al., GCN 39191), a potential electromagnetic counterpart to the LIGO/Virgo/KAGRA gravitational-wave event S250206dm (LVK Collaboration, GCN 39175), using the Low Resolution Spectrograph (LRS2) on the Hobby-Eberly Telescope (HET) [1]. The observations were carried out 9 to 14 days after the gravitational-wave event and consisted of two 1800s exposures with LRS2-R (covering 650–842 nm and 818–1050 nm) and two 1800s exposures with LRS2-B (covering 370–470 nm and 460–700 nm) [2]. Our preliminary analysis did not reveal any emission beyond that of the host galaxy. Further analysis is ongoing. [1] Bustamante Rosell et al, ApJ (2023) [2] Chonis et al, Proceedings of the SPIE (2014) View this GCN Circular online at https://gcn.nasa.gov/circulars/39785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37800] GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39784 SUBJECT: GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations DATE: 25/03/19 17:09:35 GMT FROM: Jean-Luc Atteia at IRAP <jean-luc.atteia(a)irap.omp.eu> Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM) report: We imaged the field of the SVOM/ECLAIRs GRB 250317B (Zhao et al. GCN Circ. 39752, Zhao et al. GCN Circ. 39753) with the DDRAGO imager on the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-19 06:32 to 11:00 UTC and obtained 200 minutes of exposure in the r filter at a mean observing time To+54.5h. The data were coadded with custom software and analyzed with STDpipe (Karpov 2024) with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. We detect the optical afterglow (Watson et al. GCN Circ. 39754, Pérez-Fournon et al. GCN Circ. 39757, Ghosh et al. GCN Circ. 39759, Ferro et al. GCN Circ. 39764, Schneider et al. GCN Circ. 39767, Schneider et al. GCN Circ. 39767, Thoene et al. GCN Circ. 39769, Zhu et al. GCN Circ. 39770, Zhu et al. GCN Circ. 39770, Pankov et al. GCN Circ. 39772, Moretti et al. GCN Circ. 39774, Schneider et al. GCN Circ. 39777) with a magnitude of r = 23.95 +/- 0.25 This confirms the break of the optical light-curve pointed by Schneider et al. in GCN Circ. 39777. We acknowledge excellent support from the staff of the Observatorio Astronómico Nacional. View this GCN Circular online at https://gcn.nasa.gov/circulars/39784. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37799] GRB 250319B: Fermi GBM Final Localization
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39783 SUBJECT: GRB 250319B: Fermi GBM Final Localization DATE: 25/03/19 15:50:43 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely SHORT GRB "At 05:07:28.91 UT on 19 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250319B (trigger 764053653/250319214). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 246.18, Dec = -70.90 (J2000 degrees, equivalent to J2000 16h 25m, 70d 54'), with a statistical uncertainty of 3.18 degrees. The angle from the Fermi LAT boresight is 29 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319214/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319214/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319214/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/39783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37798] GRB 250319A: Fermi GBM Final Localization
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39782 SUBJECT: GRB 250319A: Fermi GBM Final Localization DATE: 25/03/19 15:14:51 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely LONG GRB "At 04:52:59.46 UT on 19 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250319A (trigger 764052784/250319203). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 335.24, Dec = -62.32 (J2000 degrees, equivalent to J2000 22h 21m, -62d 19'), with a statistical uncertainty of 6.84 degrees. The angle from the Fermi LAT boresight is 25 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319203/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319203/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250319203/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/39782. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37797] GRB250317D: EIRSAT-1 GMOD Detection
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39781 SUBJECT: GRB250317D: EIRSAT-1 GMOD Detection DATE: 25/03/19 14:00:39 GMT FROM: Caimin McKenna at University College Dublin <caimin.mckenna(a)ucdconnect.ie> C. McKenna, D. Murphy, C. de Barra, A. Ulyanov, P. McDermott, G. Finneran, M. Doyle, R. Dunwoody, J. Mangan, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team: EIRSAT-1 reports the detection of the long gamma-ray burst GRB250317D by the Gamma-ray Module (GMOD) instrument, which also triggered Fermi GBM (Fermi Trigger 763933627 / bn250317824, retrieved from Fermi GBM burst catalog [von Kienlin, A. et al. 2020, Gruber, D. et al. 2014, von Kienlin, A. et al. 2014, and Bhat, P. et al. 2016]) The GMOD detection was made starting at 2025-03-17 19:47:53.5 UTC. The GMOD light-curve for GRB250317D with 1.2s binning shows a bright pulse starting at 19:47:53.5 UTC, also visible on the Fermi light-curve, followed by a less significant second pulse of one bin width. The pulses seen earlier than this time in the Fermi light-curve cannot be distinguished against the background in the GMOD light-curve. The spacecraft location at the time of detection was 17.359 N, 35.838 E, at an altitude of 414.30 km. The GMOD light curve for this event can be found here: https://grb.eirsat1.ie/250317D/250317D_LC_onboard_preliminary.png EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023. View this GCN Circular online at https://gcn.nasa.gov/circulars/39781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37796] LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39780 SUBJECT: LIGO/Virgo/KAGRA S250319bu: Updated Sky localization DATE: 25/03/19 13:55:10 GMT FROM: Aditya Vijaykumar <aditya.vijaykumar(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250319bu (GCN Circular 39776). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250319bu For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 989 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4713 +/- 1546 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/39780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37795] GRB 250314A: ATCA radio upper limits
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39779 SUBJECT: GRB 250314A: ATCA radio upper limits DATE: 25/03/19 13:49:11 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Tao An, Yuanqi Liu, Kexuan Chong (SHAO), Jinjun Geng, Xuefeng Wu (PMO), report on behalf of a large collaboration: We have conducted radio observations of the high-redshift gamma-ray burst GRB 250314A (GCN 39719, 39729; redshift z ~ 7.3, GCN 39732, 39743) using the Australia Telescope Compact Array (ATCA). Our observations were performed on 2025 March 15, from UT 13:00 to 19:00, simultaneously at central frequencies of 5.5 GHz and 9 GHz. The achieved 1-sigma image rms noise levels are approximately 13 microJy/beam at 5.5 GHz and 9 microJy/beam at 9 GHz. At the position of the potential optical counterpart reported in GCN 39727, we find no significant radio emission above a 3-sigma threshold at either frequency. We thank Jamie Stevens for his rapid response in scheduling these observations. We thank the CSIRO Space and Astronomy staff for supporting these observations. The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. View this GCN Circular online at https://gcn.nasa.gov/circulars/39779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37794] EP250302a: VLA observations
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39778 SUBJECT: EP250302a: VLA observations DATE: 25/03/19 11:45:41 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Ailing Wang (IHEP), Tao An (SHAO), Cuiyuan Dai and Xiangyu Wang (NJU), report on behalf of a larger collaboration: We report radio observations of EP250302a (GCN 39556) conducted with the Karl G. Jansky Very Large Array (VLA) on 2025 March 15, UT02:17-03:38 (approximately T0+13 days after the initial trigger). Observations were carried out across three frequency bands (Ku/X/C bands). The preliminary results show 4-4.5 sigma detection at the position reported by X-ray and optical observations (e.g., GCN 39550, 39557). The image noise ranges from 6.4 to 10 microJy/beam. The source exhibits a relatively flat spectrum between 4 and 18 GHz. Follow-up VLA observations are planned to verify the detection and trace the flux density evolution. View this GCN Circular online at https://gcn.nasa.gov/circulars/39778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37793] GRB 250317B: OHP/T193 continued follow-up
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39777 SUBJECT: GRB 250317B: OHP/T193 continued follow-up DATE: 25/03/19 08:16:18 GMT FROM: Emeric Le Floc'h at CEA-Saclay <emeric.lefloch(a)cea.fr> B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Ugarte Postigo (LAM), M. Dennefeld (IAP/CNRS/Sorbonne U.) and D. Turpin (CEA/Irfu) report on behalf of the MISTRAL-GRB collaboration: We performed additional observations of the optical counterpart of GRB 250317B (Zhao et al., GCN 39753; Watson et al., GCN 39754; Palmerio et al., GCN 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759, Ferro et al., GCN 39764, Schneider et al., GCN 39767; Thöne et al., GCN 39769; Zhu et al., GCN 39770; Pankov et al., GCN 39772; Moretti et al., GCN 39774) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 1 exposure of 600s and 5 exposures of 720s in the r-band starting at 19:22 UT on 2025-03-18 (1.84 days after the trigger). In the final stacked image, the afterglow is marginally detected, at a level much fainter than the phase of rebrightening reported earlier by Thöne et al. (GCN 39769) and Zhu et al. (GCN 39770). The preliminary magnitude derived for the source is : r = 23.5 +/- 0.4 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen et Andres Carmona for the MISTRAL observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37792] LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39776 SUBJECT: LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate DATE: 25/03/19 07:43:35 GMT FROM: sreedevi_p230198ph(a)nitc.ac.in The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250319bu during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-03-19 06:25:36.479 UTC (GPS time: 1426400754.479). The candidate was found by the GstLAL [1], MBTA [2], and SPIIR [3] analysis pipelines. S250319bu is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.7e-10 Hz, or about one in 67 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250319bu The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<1%), or BNS (<1%). The LIGO Hanford detector lost its working point about two seconds after the merger time. That has been carefully investigated by the LVK rapid response team and should have no impact on the significance of the signal nor on its classification or skymap. Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. Three sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [5], distributed via GCN notice about 23 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN notice about 28 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], distributed via GCN notice about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 2057 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4372 +/- 1308 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [2] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [3] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/39776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37791] GRB 250317C: SVOM/GRM observation of a long burst
by GCN Circulars 19 Mar '25

19 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39775 SUBJECT: GRB 250317C: SVOM/GRM observation of a long burst DATE: 25/03/19 02:11:00 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Tais Maiolino, Frédéric Piron (LUPM), Stéphane Schanne (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250317C (SVOM trigger reference: sb25031702) at 2025-03-17T17:31:28.000 (T0). This burst was also detected by GECAM-B and AstroSat CZTI (Wang et al., GCN 39768; S. Salunke et al., GCN 39771). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of single main pulse with a T90 of 23.4 +3.7/-2.0 s in the 15-5000 keV band. In addition, ECLAlRs was taking data and did not trigger, since the position of this burst, as determined by GECAM-B (GCN 39768, RA: 320.42 deg, DEC: -16.07 deg, Error: 8.59 deg), is located at about 108.3 degrees from the SVOM optical axis, and outside the ECLAIRs field of view. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250317C.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/39775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37790] GRB 250317B: Leavitt Observatory optical upper limit
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39774 SUBJECT: GRB 250317B: Leavitt Observatory optical upper limit DATE: 25/03/18 20:04:16 GMT FROM: leavittob(a)gmail.com L. Moretti, E. Pavoni (Leavitt Observatory, Italy) Members of: GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani ATA - Associazione Tuscolana di Astronomia In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), report: We observed the field of the GRB 250317B triggered by SVOM/ECLAIRs (Zhao et al., GCN 39752 and GCN 39753) and SVOM/MXT (Zhao et al., GCN 39752 and GCN 39753; and Götz et al., GCN 39756) with our RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Manciano, Italy. The observations started approximately 19 hours after the SVOM/ECLAIRs trigger time, with good weather conditions, stacking a set of unfiltered FITS frames. Images were processed using the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A). In the stacked frame, we did not found any optical uncatalogued object within the SVOM error circle. Mid-Time (UTC) Limit (clear filter) Error 2025-03-17T21:18:03 >20.0 +/- 0.1 Magnitudes were estimated with the BP-band of Gaia DR3 catalogue (*) and are not corrected for galactic dust extinction. The message may be cited. Reference: https://leavittobservatory.altervista.org (*) https://gea.esac.esa.int/archive/documentation/GEDR3/Data_processing/chap_c… View this GCN Circular online at https://gcn.nasa.gov/circulars/39774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37789] GRB 250309B/AT2025dws: further ATCA observations
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39773 SUBJECT: GRB 250309B/AT2025dws: further ATCA observations DATE: 25/03/18 17:15:37 GMT FROM: James Leung at U. Toronto / HUJI <jamesk.leung(a)utoronto.ca> J. K. Leung (U. Toronto/HUJI), G. E. Anderson (Curtin University), A. J. van der Horst (GWU), L. Rhodes (TSI/McGill), Maria Drout (U. Toronto), Andrew Hughes (U. Oxford) report on behalf of a larger collaboration: We report a second epoch of Australia Telescope Compact Array (ATCA) radio observations centred in the direction of the candidate optical counterpart AT2025dws (Stein et al., GCN 29639; Pérez-Fournon et al., GCN 29643; Alexander et al., GCN39645; Stein et al, GCN 39644; Perley et al. GCN 39646; Wang et al., GCN 39648; Ducoin et al., GCN 39650; Shin et al., GCN 39654) to GRB 250309B (Preis and Greiner, GCN 39629; McDermott et al., GCN 39642; Page and Evans, GCN 39649; Kozyrev et al., GCN 29652; and Frederiks et al., GCN 39655). These observations follow an earlier detection of the radio counterpart by the ATCA (An et al., GCN 39699). The observations were taken at a mean epoch of UT12:57 on 2025-03-13T12:57 at central frequencies 5.5, 9, and 16.7 GHz. In our preliminary analysis, we detect a clear radio source at the position of the candidate optical and radio counterparts in both the 5.5 and 9 GHz images (0.24+/-0.04 mJy and 0.30+/-0.03 mJy, respectively) and attain a 5-sigma non-detection limit of <0.45 mJy/beam at 16.7 GHz. We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO. View this GCN Circular online at https://gcn.nasa.gov/circulars/39773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37788] GRB 250317B: Mondy AZT-33IK Optical Observations
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39772 SUBJECT: GRB 250317B: Mondy AZT-33IK Optical Observations DATE: 25/03/18 15:19:56 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 250317B (Zhao et. al, GCN 39753; Götz et. al, GCN 39756; Melandri et. al, GCN 39763) in the R filter with the 1.5-meter AZT-33IK telescope of the Sayan Solar Observatory (Mondy). The observations started on (UT) 2025-03-17 15:41:49, i.e. about 0.58 days since trigger. The optical afterglow (Watson et. al, GCN 39754; Pérez-Fournon et. al, GCN 39757; Ghosh et. al, GCN 39759; Ferro et. al, GCN 39764; Schneider et. al, GCN 39767; Zhu et. al, GCN 39770) is clearly visible in the stacked image. The preliminary photometry is as follows: Date UT start t-T0 Exp. Filter OT Err UL(3sigma) (mid, days) (s) 2025-03-17 15:41:49 0.58173 28*120 R 20.94 0.06 23.3 The photometry is based on nearby stars from the USNO-B1.0 catalog (R2 magnitudes) and has not been corrected for the Galactic extinction. Using a simple power law fit to the observed data in the r and R filters, we estimate the light curve decay index to be about -1.5. View this GCN Circular online at https://gcn.nasa.gov/circulars/39772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37787] GRB 250317C: AstroSat CZTI detection
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39771 SUBJECT: GRB 250317C: AstroSat CZTI detection DATE: 25/03/18 15:13:24 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 250317C which was also detected by GECAM-C (Wang et al., GCN Circ. 39768). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-17 17:31:23.50 UTC. The measured peak count rate associated with the burst is 87 (+34, -21) counts/s above the background in the combined data of three quadrants (out of four), with a total of 356 (+153, -114) counts. The local mean background count rate was 278 (+3, -5) counts/s. Using cumulative rates, we measure a T90 of 8.1 (+1.62, -3.35) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-03-17 17:31:25.21 UTC. The measured peak count rate associated with the burst is 225 (+62, -64) counts/s above the background in the combined data of all quadrants, with a total of 770 (+299, -346) counts. The local mean background count rate was 1266 (+9, -9) counts/s. We measure a T90 of 8.29 (+1.8, -4.7) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/39771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37786] GRB 250317B: NOT optical observations suggest an optical plateau phase
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39770 SUBJECT: GRB 250317B: NOT optical observations suggest an optical plateau phase DATE: 25/03/18 13:35:17 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Z. P. Zhu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), B. Schneider (LAM), A. Martin-Carrillo (UCD), A. Henderson de la Fuente (NOT), report on behalf of a larger collaboration: We observed the field of the GRB 250317B (Zhao et al., GCN 39753) using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 2 exposures of 300 s each in the SDSS-r band starting at 22:43:24 UT on 2025-03-17 (20.56 hr after the trigger). The optical counterpart reported by Watson et al. (GCN 39754), Palmerio et al. (GCN 39755), Pérez-Fournon et al. (GCN 39757), Ghosh et al. (GCN 39759), Ferro et al. (GCN 39764) and Schneider et al. (GCN 39767) is well detected in the stacked image, with a preliminary magnitude of r = 21.7 +/- 0.1 mag (AB). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitude is not corrected for Galactic extinction. We note that the measured magnitude is consistent with those reported by Schneider et al. (GCN 39767), obtained ~1 hr before our observation, and Thoene et al. (GCN 39769), obtained about 0.6 hr after our observation, suggesting a possible optical plateau or rebrightening episode. Further observations are planned and encouraged to monitor the evolution of the optical afterglow. View this GCN Circular online at https://gcn.nasa.gov/circulars/39770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37785] GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39769 SUBJECT: GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44 DATE: 25/03/18 12:43:40 GMT FROM: Christina Thöne at ASU-CAS <christina.thoene(a)gmail.com> C. C. Thoene (AbAO), A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. F. Agui Fernandez (CAHA), N. A. Rakotondrainibe (LAM), A. Martin-Carrillo (UCD), N. R. Tanvir (Univ. Leicester), L. Izzo (INAF/OACn and DARK/NBI), J. P. U. Fynbo (DAWN/NBI), S. Geier (GTC), G. Lombardi (GTC), Antonio García (GTC), Daniel González (GTC), and Antonio Cabrera-Lavers (GTC) report: We obtained spectroscopy of the afterglow of the SVOM-detected GRB 250317B (Zhao et al. GCN 39752, Watson et al. GCN 39754, Götz et al. GCN 39756, Pérez-Fournon et al. GCN 39757, Melandri et al. GCN 39763, Ferro et al. GCN 39764, Schneider et al. GCN 39767). Our observations consisted of 4x1200s exposures with grism R1000B, covering the range between 3600 and 7880 AA with a resolving power of around 600 at a mean epoch 2025-03-18T00:16:22 UT (22.07 hr after the burst). In the acquisition image, obtained 21.328 hr after the burst, the afterglow is detected at a magnitude of r_AB=21.72 +/- 0.05, indicating a slight rebrightening with respect to the OHP observation (Schneider et al. GCN 39767) obtained 1.6 hr earlier. Further monitoring of this behaviour is encouraged. The spectrum shows continuum above 4000 AA, with features consistent with at least two low-column density Lyman systems at redshifts of z=3.442 and 3.447 (or a dynamic separation of 1500 km/s), likely corresponding to the same galaxy or system. There are tentative detections of SiII, SiII*, OI, SiIV, CIV, FeII and AlII a those same redshifts, which we identify as corresponding to the GRB. Additionally, we identify two intervening absorbers, one at z=3.196 with absorptions in several Lyman lines, SII and SiII, and a second one at z=1.029 showing the MgII doublet. View this GCN Circular online at https://gcn.nasa.gov/circulars/39769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37784] GRB 250317C: GECAM-B detection
by GCN Circulars 18 Mar '25

18 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39768 SUBJECT: GRB 250317C: GECAM-B detection DATE: 25/03/18 11:31:10 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Shao-Lin Xiong, Chen-Wei Wang report on behalf of the GECAM team: GECAM-B was triggered both in-flight and on-ground by a long burst, GRB 250317C, at 2025-03-17T17:31:21.700 UTC (T0). According to the event-by-event data, the GECAM-B light curve shows a main pulse with a with a T90 of 23.0 +3.0/-4.0 s in the 40-6000 keV band. The GECAM-B light curve could be found here: https://www.bursthub.cn//admin/static/gecamgrb250317C.png Using the automatic on-ground localization pipeline, GECAM-B localized this burst to the following position (J2000): Ra: 320.42 deg Dec: -16.07 deg Err: 8.59 deg (1-sigma, statistical only) We note that these results are preliminary. Refined analysis will be reported later. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/39768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37783] GRB 250317B: OHP/T193 optical observations
by GCN Circulars 17 Mar '25

17 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39767 SUBJECT: GRB 250317B: OHP/T193 optical observations DATE: 25/03/17 23:30:24 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Ugarte Postigo (LAM), M. Dennefeld (IAP/CNRS/Sorbonne U.) and D. Turpin (CEA/Irfu) report on behalf of a larger collaboration: We observed the field of the GRB 250317B (Zhao et al., GCN 39753) using the T193cm telescope at the Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 9 exposures (8x360 s and 1x300 s) in the r-band starting at 21:56:41 UT on 2025-03-17 (19.74 hours after the trigger). In the stacked image, we clearly detected the optical counterpart reported by Watson et al., GCN 39754; Palmerio et al., GCN 39755; Pérez-Fournon et al., GCN 39757; Ghosh et al., GCN 39759 and Ferro et al., GCN 39764. The preliminary magnitude derived for that source is: r = 21.87 +/- 0.08 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen et Andres Carmona for the MISTRAL observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/39767. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37782] Fermi trigger No 763933627: Global MASTER-Net observations report
by GCN Circulars 17 Mar '25

17 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39766 SUBJECT: Fermi trigger No 763933627: Global MASTER-Net observations report DATE: 25/03/17 23:02:10 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250317.82 (trigger No 763933627,04h 54m 02.40s , -35d 41m 24.0s, R=1.38) errorbox 18 sec after notice time and 9688 sec after trigger time at 2025-03-17 22:28:31 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 79 deg. The sun altitude is -56.6 deg. The galactic latitude b = -38 deg., longitude l = 238 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2814784 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 9718 | 2025-03-17 22:28:31 | MASTER-SAAO | (04h 53m 49.54s , -35d 43m 51.2s) | C | 60 | 17.4 | 9778 | 2025-03-17 22:28:31 | MASTER-SAAO | (04h 53m 49.54s , -35d 43m 51.2s) | C | 180 | 18.0 | Coadd 9798 | 2025-03-17 22:29:50 | MASTER-SAAO | (04h 53m 50.06s , -35d 43m 48.1s) | C | 60 | 17.5 | 9877 | 2025-03-17 22:31:09 | MASTER-SAAO | (04h 53m 50.57s , -35d 43m 45.2s) | C | 60 | 17.4 | 9956 | 2025-03-17 22:32:28 | MASTER-SAAO | (04h 53m 51.09s , -35d 43m 42.4s) | C | 60 | 17.4 | 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/39766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37781] GRB250312A: Swift/UVOT Upper Limits
by GCN Circulars 17 Mar '25

17 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39765 SUBJECT: GRB250312A: Swift/UVOT Upper Limits DATE: 25/03/17 20:21:01 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H.Siegel (PSU) and A. Melandri (INAF-OAR) on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250312A 464s after the BAT trigger (Melandri et al., GCN Circ. 39686). No optical afterglow consistent with the enhanced XRT position (Evans et al., GCN Circ. 39693) is detected in the initial UVOT exposures.Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (fc) 464 1563 165 >20.47 white 743 1563 223 >20.50 b 718 1539 38 >18.84 b 6529 33943 1081 >20.52 u 6324 23538 403 >19.80 uvw1 21814 22713 885 >19.99 uvm2 10515 16904 1012 >19.85 uvw2 6939 28312 1082 >20.24 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.015 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/39765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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