May 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 42860] GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44731 SUBJECT: GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations DATE: 26/05/29 02:17:48 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Brendan O'Connor (CMU), Malte Busmann (LMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 260527A/EP260527a (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727) using the GMOS-S instrument mounted on the Gemini-South telescope. Our observations were carried out in the r and i filters for 10x90 s exposure in each band. At the location of the optical counterpart (Aguilar-Ruiz et al., GCN 44719), we detect a source with magnitude i = 23.2 +/- 0.1 AB mag, consistent with recent reports (Busmann et al., GCN 44728; Corcoran et al., GCN 44729; El Kabir et al., GCN 44730). The photometry is calibrated against the PS1 catalog and is not corrected for the minimal Galactic extinction along the line of sight. We thank the Gemini staff, in particular Aleksandar Cikota, for the rapid scheduling and execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44731. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42859] EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
by GCN Circulars 29 May '26

29 May '26

TITLE: GCN CIRCULAR NUMBER: 44730 SUBJECT: EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart DATE: 26/05/29 02:09:56 GMT FROM: Massine El Kabir <m.elkabir(a)campus.unimib.it> M. El Kabir, Y. Yang and E. Troja (U Rome) report on behalf of the ERC BHianca team: We observed the field of EP260527a (Yang et al., GCN 44718), likely associated with the short GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724; Kawakubo et al., GCN 44726), with the FORS2 and HAWK-I on the ESO Very Large Telescope (VLT). Observations started about 41.4 hrs after the GRB trigger and were performed at an airmass of ~1.2 in excellent conditions. The field was imaged using the r, z, J and K filters. Photometric calibration was performed using nearby stars from the Pan-STARRS and 2MASS catalogues. Magnitudes are reported in the AB system and are not corrected for Galactic extinction. At the position of the optical counterpart (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Busmann et al.44728; Corcoran et al. GCN 44729 ), we detect a source with the following preliminary magnitude: z = 23.1 +/- 0.1 J = 23.0 +/- 0.1 Compared to earlier observations (Aguilar-Ruiz et al., GCN 44719), our measurements suggest a rapid fading of the afterglow, consistent with the observed X-ray behavior (Yang et al. GCN, 44725). 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/44730. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42858] EP260527a / GRB 260527A: NOT optical observations
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44729 SUBJECT: EP260527a / GRB 260527A: NOT optical observations DATE: 26/05/28 23:47:22 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> G. Corcoran (UCD), J. An (NAOC), A. van Hoof (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), Dimple (Birmingham), R. A. J. Eyles-Ferris (Leicester), B. P. Gompertz (Birmingham), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), A. M. Kadela (NOT and NBI), report on behalf of a larger collaboration: We observed the optical afterglow (Aguilar-Ruiz et al., GCN 44719; Li et al. GCN 44720; Busman et al., GCN 44728) of EP260527a (Yang et al., GCN 44718), likely associated with GRB 260527A (Svinkin et al., GCN 44722; Yu et al., GCN 44724; Kawakubo et al., GCN 44726), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations were secured in both the i (25x120 s) and z (16x120 s) bands. At mean epochs of 2026 May 28.911 and 28.946 UT (39.59 and 40.44 hr after the Konus/Wind trigger time, respectively), we measure for the counterpart the following magnitudes: i = 23.17 +- 0.15 z = 23.25 +- 0.31 These magnitudes are calibrated against the Pan-STARRS catalog and are not corrected for Galactic extinction. We note the presence of a faint, underlying object cataloged in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey (Aihara et al., doi:10.1093/pasj/psab122) at r = 25.72 +/- 0.17, i = 25.44 +/- 0.18 and z = 25.32 +/- 0.29 (all AB). Due to the lack of sufficient high S/N multiband detections, there is no reliable reported photometric redshift for this object. View this GCN Circular online at https://gcn.nasa.gov/circulars/44729. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42857] GRB 260527A/EP260527a: FTW optical and NIR observations
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44728 SUBJECT: GRB 260527A/EP260527a: FTW optical and NIR observations DATE: 26/05/28 23:03:55 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O'Connor (CMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander Hall (CMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 260527A/EP260527a (Yang et al., GCN 44718; Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726; Mo et al., GCN 44727) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J-band simultaneously for 45 x 180 s starting at 2026-05-28T19:58:32 UT (1.57 days after the trigger). We detect the counterpart at r = (23.1 +/- 0.2) AB mag, calibrated against the PS1 catalog and not corrected for the Galactic extinction of A_V = 0.050 mag (Schlafly & Finkbeiner 2011). We note that there is a potential host galaxy with a DESI DR1 (DESI Collaboration et al., 2026, AJ, 171, 285) redshift of z = 0.3656 located ~13" North-East from the afterglow position. At this redshift, the projected physical offset is ~66 kpc, which is at the high end of the distribution of short GRB offsets but not unprecedented (O'Connor 2022, MNRAS, 515, 4890). We derive a probability of chance coincidence of Pcc~0.09, suggesting a possible association. However, as this is a very large offset, deep imaging may reveal additional candidate host galaxies. We do note that based on the available DESI DR1 spectra, there appears to be an overdensity of z~0.36 galaxies along this line-of-sight, suggesting a possible origin within or intersection with a low redshift galaxy cluster (Dichiara et al., 2026, ApJL, 999, L42). The spectrum can be viewed at: https://www.legacysurvey.org/viewer/desi-spectrum/dr1/targetid3962782420566…. We thank Christoph Ries for obtaining the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44728. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42856] EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44727 SUBJECT: EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE DATE: 26/05/28 22:59:26 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of EP260527a/GRB 260527A (Yang et al., GCN 44718; Svinkin et al., GCN 44722; Yu et al., GCN 44724; Yang et al., GCN 44725; Kawakubo et al., GCN 44726) in the near-infrared J band with the MDM InfraRed Astronomy inGaas Experiment (MIRAGE) camera on the MDM 1.3 m telescope. Observations began at 2026-05-28T05:00:58 (+23 hours after the EP trigger) in the J band, lasting 600 s under cloudy conditions. We do not detect the optical counterpart (Aguilar-Ruiz et al., GCN 44719; Li et al., GCN 44720), with the following 5-sigma upper limit: J > 18.4 mag AB. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44727. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42855] GRB 260527A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44726 SUBJECT: GRB 260527A: CALET Gamma-Ray Burst Monitor detection DATE: 26/05/28 17:22:16 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> Y. Kawakubo, A. Yoshida, T. Sakamoto, S. Sugita (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) detected the short GRB 260527A (Konus-Wind detection: Svinkin et al., GCN #44722; GECAM-B detection: Yu et al., GCN #44724) at 06:16:09.76 UTC on 27 May 2026 (https://cgbm.calet.jp/cgbm_trigger/flight/1463897683/index.html) The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure starting at T+0.16 s, peaking at T+0.28 s, and ending at T+0.38 s. The T90 and T50 durations measured with the SGM data are 0.19 +/- 0.04 s and 0.06 +/- 0.02 s (40-1000 keV), respectively. Einstein Probe/WXT detected a fast X-ray transient, EP 260527a (Yang et al., GCN #44718), about 4 minutes before the CGBM trigger, and Einstein Probe/FXT follow-up observations were also reported by Yang et al. (GCN Circ. 44725). The position of EP 260527a was observable by CGBM at the CGBM trigger time, with an incident angle of approximately 40 degrees. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1463897683/ The CALET data used in this analysis were provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44726. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42854] EP260527a/GRB 260527A: EP-FXT follow-up observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44725 SUBJECT: EP260527a/GRB 260527A: EP-FXT follow-up observation DATE: 26/05/28 15:02:24 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> J. Yang (ZZU), B. T. Wang (YNAO, CAS), D. F. Hu (PMO, CAS), J. P. Feng, B. Zhang (USTC), D. Zhu, K. J. Zhang (YNU) and W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260527a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44718), was also detected by Konus-Wind and GECAM-B as GRB 260527A (Svinkin et al., GCN 44722, Yu et al., GCN 44724), and was followed by several optical telescopes (Aguilar-Ruiz et al., GCN 44719, Li et al., GCN 44720). EP-FXT performed a follow-up observation of EP260527a about 21 hours after the WXT detection, with an exposure time of 3.4 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 193.0548, DEC = 1.4806 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.57 x 10^20 cm^-2 and a photon index of 2.6 (+1.2/-0.7). The derived unabsorbed 0.5-10 keV flux is approximately 7.7 (+3.7/-3.9) x 10^-14 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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/44725. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42853] GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44724 SUBJECT: GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a DATE: 26/05/28 14:41:34 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng, Cheng-Kui Li (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a short burst GRB 260527A at 2026-05-27T06:16:10.050 UTC (denoted as T0), which is also detected by Konus-Wind (D. Svinkin et al., GCN#44722). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multi-pulses with a duration (T90) of 0.40 +0.02/-0.04 s. The on-ground localization of GECAM-B is: Ra: 206.1 deg Dec: 6.7 deg Err: 4.9 deg (1-sigma, statistical only) Considering possible systematic uncertainties, this localization is consistent with the EP/WXT localization of EP260257a (Yang et al., GCN#44718). The time coincidence and localization coincidence between GRB 260527A and EP260527a strongly support the association of these two events. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260527A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (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/44724. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42852] GRB 260526A: GECAM-B observation
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44723 SUBJECT: GRB 260526A: GECAM-B observation DATE: 26/05/28 13:17:55 GMT FROM: guohx(a)ihep.ac.cn Hao-Xuan Guo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260526A, at 2026-05-26T23:04:00.200 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44707). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 42 +/-6 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260526A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (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/44723. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42851] Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
by GCN Circulars 28 May '26

28 May '26

TITLE: GCN CIRCULAR NUMBER: 44722 SUBJECT: Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a DATE: 26/05/28 12:11:41 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin(a)gmail.com> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The short-duration GRB 260527A triggered Konus-Wind at T0=22572.142 s UT (06:16:12.142). The burst light curve shows a multi-peaked structure which starts at ~T0-0.1 s and has a total duration of ~0.2 s. The emission is seen up to ~10 MeV. The burst occurred ~4 min before the Einstein Probe detection of EP260527a (Yang et al., GCN 44718), and also the KW ecliptic latitude response is consistent with the EP260527a position. This suggests a common origin of two events, which will be further investigated. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260527_T22572/ As observed by Konus-Wind, the burst had the total fluence of 1.99(-0.46,+0.57)x10^-6 erg/cm2, and the 16-ms peak flux, measured from T0-0.008 s, of 3.09(-1.06,+1.28)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.064 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.67(-0.36,+0.46), the high energy photon index beta = -2.13(-0.85,+0.36), the peak energy Ep = 541(-204,+367) keV (pgstat = 33/45 dof). A power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.79(-0.42,+0.49) and Ep = 670(-240,+1097) keV fits this spectrum equally well (pgstat = 35/46 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44722. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0