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

[vsnet-grb-info 39656] EP250828a: Optical counterpart detection with Kinder observations
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41591 SUBJECT: EP250828a: Optical counterpart detection with Kinder observations DATE: 25/08/29 10:12:24 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, C.-S. Lin (both NCU), Y. J. Yang (NYUAD), A. K. H. Kong (NTHU), T.-W. Chen (NCU), J. Gillanders (Oxford), S. J. Smartt (Oxford/QUB), Y.-H. Lee, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, 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: Followed by our r-band observations using the 1m LOT (Aryan et al., GCN 41579), we continued to observe the field of the fast X-ray transient EP250828a (Liu et al., GCN 41574) in i-band using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first SLT epoch of observations in i-band started at 14:17 UTC on the 28th of August 2025 (MJD 60915.595), 6.74 hr after 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. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the Pan-STARRS1 (Chambers et al., 2016 arXiv:1612.05560) image using the 'sfft' (Hu et al., 2022, ApJ, 936,157) algorithm. In the stacked as well as in the difference image, we weakly detected the optical counterpart candidate proposed by Taguchi et al., (GCN 41582). The candidate counterpart was also confirmed by Yao et al. (GCN 41583) and Fu et al. (GCN 41584). In our i-band difference image, the optical counterpart was detected with an SNR of 2.5. The details of the observations and the measured photometry (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | i | 60915.595 | 6.74 | 300 * 24 | 22.46 +/- 0.27 | 1".48 | 1.01 The presented magnitude is calibrated using the field stars from the Pan-STARRS1 catalog and is not corrected for the expected Galactic foreground extinction of A_i = 0.21 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/41591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39655] EP250828a: Liverpool Telescope upper limits
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41590 SUBJECT: EP250828a: Liverpool Telescope upper limits DATE: 25/08/29 09:28:38 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 EP250828a (Liu et al., GCN 41574) 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 2025-08-29 22:33:53 UT, approximately 15 hours after the trigger. We do not detect the reported optical counterpart (Taguchi et al., GCN 41582; Yao et al., GCN 41583) or any new objects within the EP/FXT error region of the transient (Liu et al., GCN 41574). The 3-sigma limiting magnitudes on the stacked images are r > 23.7 mag and i > 23.6 mag. This is consistent with the detection of an optical counterpart candidate by NOT at r ~ 24.4 at 15.2 hours post trigger (Fu et al., GCN 41584). View this GCN Circular online at https://gcn.nasa.gov/circulars/41590. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39654] Swift GRB 250828B: Global MASTER-Net observations report
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41589 SUBJECT: Swift GRB 250828B: Global MASTER-Net observations report DATE: 25/08/29 08:58:29 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250828B ( P. A. Evans et al., GCN 41581) errorbox 36970 sec after notice time and 36991 sec after trigger time at 2025-08-29 08:50:09 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 76 deg. The sun altitude is -27.3 deg. The galactic latitude b = 11 deg., longitude l = 239 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2978941 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 37021 | MASTER-OAFA | C | 60 | 17.9 | 37101 | MASTER-OAFA | C | 60 | 18.0 | 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/41589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39653] EP250828a: Global MASTER-Net observations report
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41588 SUBJECT: EP250828a: Global MASTER-Net observations report DATE: 25/08/29 08:54:21 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250828a ( EP Team et al., GCN 41574) errorbox 75567 sec after notice time and 1 days 1111 sec after trigger time at 2025-08-29 07:51:04 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 76 deg. The sun altitude is -39.8 deg. The galactic latitude b = -26 deg., longitude l = 76 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2978651 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 87541 | 2025-08-29 07:51:04 | MASTER-OAFA | (21h 51m 57.17s , +20d 28m 10.2s) | C | 60 | 18.8 | 87618 | 2025-08-29 07:52:21 | MASTER-OAFA | (21h 52m 02.14s , +20d 27m 10.6s) | C | 60 | 18.6 | 87694 | 2025-08-29 07:53:37 | MASTER-OAFA | (21h 51m 56.69s , +20d 26m 10.1s) | C | 60 | 18.6 | 87771 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 01.95s , +20d 26m 11.4s) | C | 60 | 18.6 | 87831 | 2025-08-29 07:54:54 | MASTER-OAFA | (21h 52m 02.01s , +20d 26m 11.0s) | C | 180 | 18.5 | Coadd 87844 | 2025-08-29 07:56:07 | MASTER-OAFA | (21h 50m 57.78s , +20d 27m 39.7s) | C | 60 | 18.5 | 87918 | 2025-08-29 07:57:20 | MASTER-OAFA | (21h 50m 57.71s , +20d 27m 39.6s) | C | 60 | 18.5 | 87991 | 2025-08-29 07:58:34 | MASTER-OAFA | (21h 50m 57.62s , +20d 27m 39.5s) | C | 60 | 18.5 | 88064 | 2025-08-29 07:59:46 | MASTER-OAFA | (21h 50m 57.50s , +20d 27m 39.7s) | C | 60 | 18.4 | 88137 | 2025-08-29 08:00:59 | MASTER-OAFA | (21h 50m 57.38s , +20d 27m 40.1s) | C | 60 | 18.3 | 88723 | 2025-08-29 08:10:46 | MASTER-OAFA | (21h 52m 01.43s , +20d 26m 02.4s) | C | 60 | 17.4 | 88801 | 2025-08-29 08:12:04 | MASTER-OAFA | (21h 51m 59.20s , +20d 27m 52.2s) | C | 60 | 17.3 | 88879 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.14s , +20d 26m 02.3s) | C | 60 | 17.3 | 88939 | 2025-08-29 08:13:22 | MASTER-OAFA | (21h 51m 59.16s , +20d 26m 02.1s) | C | 180 | 17.4 | Coadd 88954 | 2025-08-29 08:14:36 | MASTER-OAFA | (21h 52m 02.29s , +20d 27m 53.3s) | C | 60 | 17.0 | 89030 | 2025-08-29 08:15:53 | MASTER-OAFA | (21h 51m 56.83s , +20d 26m 54.8s) | C | 60 | 16.6 | 89107 | 2025-08-29 08:17:09 | MASTER-OAFA | (21h 51m 55.72s , +20d 27m 52.7s) | C | 60 | 16.0 | 89182 | 2025-08-29 08:18:25 | MASTER-OAFA | (21h 52m 01.38s , +20d 26m 50.8s) | C | 60 | 15.7 | 89256 | 2025-08-29 08:19:38 | MASTER-OAFA | (21h 51m 55.58s , +20d 25m 48.1s) | C | 60 | 15.1 | 89331 | 2025-08-29 08:20:53 | MASTER-OAFA | (21h 52m 01.76s , +20d 26m 13.7s) | C | 60 | 13.9 | 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/41588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39652] EP-WXT trigger 01709200800 : KAIT optical observations
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41587 SUBJECT: EP-WXT trigger 01709200800 : KAIT optical observations DATE: 25/08/29 06:20:25 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 EP-WXT trigger 01709200800 (Ni et al., GCN 41561) starting at 11:39, Aug 27 UT, about 17 minutes after the trigger. A set of clear (roughly R) filter images were obtained and lasted for ~70 minutes. We performed the photometry on the suggested flare star LSPM J0220+3320 and saw some variation in the magnitude, which faded from 11.92 +/- 0.03 mag to 11.99 +/- 0.03 mag during our observation. The field was observed again on the following night at ~21.98 hours and lasted for ~2 hours. We saw similar variation in magnitude but in rising phase, suggesting it is a variable star. View this GCN Circular online at https://gcn.nasa.gov/circulars/41587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39651] EP250828a: KAIT optical upper limit
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41586 SUBJECT: EP250828a: KAIT optical upper limit DATE: 25/08/29 06:16:36 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 EP250828a (Liu et al., GCN 41574) starting at 09:30, Aug 28 UT, about 1.97 hours after the burst. A set of clear (roughly R) filter images were obtained. In our coadd image, we did not detect the reported afterglow (Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN 41584) down to a limiting mag of 20.5 mag (Vega) at a mid-time of 2.67 hours after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/41586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39650] EP250827a: Swift/UVOT Detection
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41585 SUBJECT: EP250827a: Swift/UVOT Detection DATE: 25/08/29 04:18:21 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of EP250827a 3.2 ks after the EP trigger (Hua et al., GCN Circ. 41553). An uncatalogued source consistent with the XRT position (Evans et al., GCN Circ. 41563) and the optical transient (Levan et al., GCN Circ. 41554; Li et al., GCN Circ. 41555; Lipunov et al., GCN Circ. 41558; Gritsevich et al., GCN Circ. 41559; An et al., GCN Circ. 41560; Ghosh et al., GCN Circ. 41564; O'Neill et al., GCN Circ. 41567) is detected in the UVOT exposures. The preliminary UVOT position is: RA (J2000) = 00:13:52.24 = 3.46767 (deg.) Dec (J2000) = -56:29:52.2 = -56.49784 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 3192 9257 1566 18.29+/-0.04 u 54232 60071 939 19.69+/-0.19 u 121367 127685 754 >20.36 uvw1 53286 59775 1903 19.86+/-0.13 uvw1 120301 127006 2040 >21.21 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.011 in the direction of the burst (Schlegel et al. 1998) View this GCN Circular online at https://gcn.nasa.gov/circulars/41585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39649] EP250828a: NOT optical counterpart confirmation
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41584 SUBJECT: EP250828a: NOT optical counterpart confirmation DATE: 25/08/29 04:00:42 GMT FROM: syfu(a)nao.cas.cn S.Y. Fu (HUST), J. An, L.B. He, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), A. Henderson (NOT) report: We observed the field of EP250828a (Liu et al., GCN 41574) using the Nordic Optical Telescope (NOT) located in La Palma (Canary Islands, Spain). Observations were carried out in the r and z filters. The previously reported counterpart (candidate) within the EP/FXT error circle by Seimei (Taguchi et al., GCN 41582) and SVOM/VT (Yao et al., GCN 41583) is detected in our stacked r-band image and has decayed to r ~ 24.4 (AB) at a median time of 0.634 day post-trigger, calibrated with PanSTARRS-DR2 and not corrected for Galactic extinction. We thus confirm it is the counterpart of EP2508028a. View this GCN Circular online at https://gcn.nasa.gov/circulars/41584. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39648] EP250828a: SVOM/VT optical candidate
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41583 SUBJECT: EP250828a: SVOM/VT optical candidate DATE: 25/08/29 03:36:21 GMT FROM: zhyao(a)bao.ac.cn Z. H. Yao, L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP250828a detected by EP/WXT (Liu et al. GCN 41574). SVOM/VT began observing the field at 2025-08-28T11:45:13.5 UTC, 4.21 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source compared to Legacy survey is found using VT Xband data, within the error box of EP/FXT (Liu et al. GCN 41574) at R.A., Dec 327.89185, 20.54341 degrees: RA (J2000) = 21:51:34.04 Dec (J2000) = 20:32:36.27 with an uncertainty of 0.5 arcsec. The optical candidate is detected in both VT_B and VT_R band, and the magnitudes are: Mid-Time (T - T0) | exposure time | band | mag (AB) | mag err --------------------|-----------------|------|----------|-------- 4.33 hour | 13*70 sec | VT_B | 23.5 | 0.3 4.33 hour | 12*70 sec | VT_R | 22.27 | 0.08 Our photometry was not corrected for Galactic extinction. 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/41583. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39647] EP250828a: Seimei/TriCCS optical counterpart detection
by GCN Circulars 29 Aug '25

29 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41582 SUBJECT: EP250828a: Seimei/TriCCS optical counterpart detection DATE: 25/08/29 02:57:38 GMT FROM: Kenta Taguchi <kentagch(a)kusastro.kyoto-u.ac.jp> Kenta Taguchi (Kyoto U.), Masaomi Tanaka, Seiji Toshikage (Tohoku U.) report on behalf of a larger collaboration: We observed the field of EP250828a detected by the Einstein Probe (Liu et al., GCN 41574, Aryan et al., GCN 41579) using the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei Telescope at the Okayama Observatory of Kyoto University. Our observation started at 13:20:39 UT on 2025-08-28 (MJD = 60915.5560). For each band, we took 37 exposures of 30 seconds (i.e., the total exposure time is 1110 s = 18.5 min). From our preliminary analysis, the 5 sigma limiting magnitudes are 22.3, 22.1, and 22.5 AB mag for g, r, and i-band, respectively. Only in the i-band image, we detected an uncatalogued source of 22.3 +/- 0.2 mag at 21:51:34.02 +20:32:36.3 = 327.8917, 20.5434 (J2000), which is within the FXT error circle (16.5 arcsec from the center). View this GCN Circular online at https://gcn.nasa.gov/circulars/41582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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