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

[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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