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

[vsnet-grb-info 39479] GRB 250818B: KAIT optical observations
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41417 SUBJECT: GRB 250818B: KAIT optical observations DATE: 25/08/18 21:38:07 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 GRB 250818B (Wang et al., GCN 41405) with a set of 90x60s images in the clear (roughly R) filters, at a mid time of 8.0 hours after the trigger. We clearly detected the optical afterglow (Kumar et al., GCN 41406; Yao et al, GCN 41409) in the coadd image with a brightness of 19.9 +/- 0.2 mag (Vega). View this GCN Circular online at https://gcn.nasa.gov/circulars/41417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39478] GRB 250818A: Swift/UVOT Upper Limits
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41416 SUBJECT: GRB 250818A: Swift/UVOT Upper Limits DATE: 25/08/18 17:50:17 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250818A 162 s after the BAT trigger (Cenko et al., GCN Circ. 41403). No optical afterglow consistent with the XRT position (Osborn et al., GCN Circ. 41403) 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 u (fc) 162 412 246 >20.3 b 418 438 19 >18.6 v 32212 32641 429. >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.602 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39477] LIGO/Virgo/KAGRA S250818t: Updated Sky localization
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41415 SUBJECT: LIGO/Virgo/KAGRA S250818t: Updated Sky localization DATE: 25/08/18 17:16:28 GMT FROM: lucy.thomas(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 S250818t (GCN Circular 41404). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250818t For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 319 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1209 +/- 290 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/41415. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39476] LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41414 SUBJECT: LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility DATE: 25/08/18 17:01:30 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (JSI/UMD), Tomás Ahumada (Caltech) Mansi Kasliwal (Caltech), Theophile du Laz (Caltech), Utkarsh Pathak (IITB), Vishwajeet Swain (IITB), Anirudh Salgundi (UNC), Varun Bhalerao (IITB), Xander J. Hall (CMU) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: We observed the localization region of the LVK trigger S250818k with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-08-18 04:02 UTC, approximately 2.7 hours after merger. We covered 25.2% (168.3 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 22 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019) , and removing candidates with history of variability prior to the merger time. We are left with 58 transient candidates, all lying within the 95.0% localization of the skymap. We perform additional vetting of these candidates, and identify those which appear to be hosted in galaxies at plausible redshifts for S250818k. We highlight one of these candidates, ZTF25abjmnps/AT2025ulz. +--------------------------------------------------------------------------------+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | +--------------------------------------------------------------------------------+ | ZTF25abjmnps | AT2025ulz | 237.9757129 | +30.9023146 | r | 21.29 | 0.13 | +--------------------------------------------------------------------------------+ ZTF25abjmnps is in an elliptical galaxy with a Legacy Survey photometric redshift of z = 0.091 +/- 0.016, is therefore consistent with the estimated distance of S250818k. The lower 95th percentile limit of the photoz is 0.057, and at this distance S250818k would have an absolute g-band peak magnitude of M=-16.1. However, the higher redshifts would be more consistent with a supernova luminosity of M=-17. Forced photometry of this source reveals several detections in our data. The source appears to possibly be fading in g-band, but given the low SNR and short baseline it is difficult to constrain this. There are also several recent non-detections, but all upper limits are shallower than the magnitude of the transient in our images. We therefore cannot confirm whether the source is young, or if it predates the merger. We encourage observations of ZTF25abjmnps, to determine the nature of this source. Analysis of the remaining ZTF candidates is ongoing. 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. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation. View this GCN Circular online at https://gcn.nasa.gov/circulars/41414. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39475] GRB 250818A: Enhanced Swift-XRT position
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41413 SUBJECT: GRB 250818A: Enhanced Swift-XRT position DATE: 25/08/18 16:24:03 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 431 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250818A, 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 = 213.80012, -58.01403 which is equivalent to: RA (J2000): 14h 15m 12.03s Dec (J2000): -58d 00' 50.5" with an uncertainty of 2.4 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/41413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39474] GRB 250813B: SVOM/ECLAIRs refined analysis
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41412 SUBJECT: GRB 250813B: SVOM/ECLAIRs refined analysis DATE: 25/08/18 15:48:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet, H. Yang (IRAP), W.J. Xie (NAOC), B.T. Wang (YNAO, CAS) report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250813B (SVOM burst-id sb25081303). The burst that triggered ECLAIRs onboard (Xie et al. GCN 41352/[41354](https://gcn.nasa.gov/circulars/41354?view=index&query=250813B…) consists of multiple peaks. By considering only the data before the slew of the platform, the T90-value is 26.8 +0.4/-0.5 s in the 4-120 keV energy band. We note that ECLAIRs detected some emission up to at least T0+90s (T0 = 2025-08-13T22:51:12 UTC). The time-averaged spectrum from T0-5.5 s to T0+36 s in the energy range 4-120 keV is best fitted by a cutoff power law. The powerlaw index is -0.936 +0.031/-0.032 and the cutoff energy, parameterized as Epeak, is 104 +12/-10 keV. With this model, the total flux in 4-120 keV is (1.10 +0.01/-0.03)e-5 erg/cm^2/s. With a redshift of z = 1.752 (Schneider et al., GCN 41363), the burst isotropic energy Eiso (from 1 keV to 10 MeV in its rest frame) is (1.34 +0.07/-0.08)e53 erg, which makes this GRB consistent with type II GRBs in the 'Amati' relation diagram (Amati et al. 2002). We note that the ECLAIRs results are consistent within the errors with those provided by both SVOM/GRM (Tan et al., GCN 41383) and Fermi/GBM (Smith et al., GCN 41376). All quoted errors are at the 68% confidence level. We note that the calibration of SVOM/ECLAIRs is ongoing thus these results are preliminary. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this GCN circular is Marius Brunet: (marius.brunet AT irap.omp.eu). View this GCN Circular online at https://gcn.nasa.gov/circulars/41412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39473] GRB 240818A: Fermi GBM Observation
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41411 SUBJECT: GRB 240818A: Fermi GBM Observation DATE: 25/08/18 15:01:48 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> C. de Barra (University College Dublin) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:31:23.00 UT on 18 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818A (trigger 777173487/250818063) which was also detected by Swift BAT (S. B. Cenko et al. 2025, GCN 41403). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 146 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 101 s (50-300 keV). The time-averaged spectrum from T0-9.2 to T0+94.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.14 and the cutoff energy, parameterized as Epeak, is 83 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (1.62 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+78 s in the 10-1000 keV band is 8.8 +/- 0.7 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/41411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39472] GRB 240418A: Fermi GBM Observation
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41411 SUBJECT: GRB 240418A: Fermi GBM Observation DATE: 25/08/18 15:01:48 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> C. de Barra (University College Dublin) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:31:23.00 UT on 18 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818A (trigger 777173487/250818063) which was also detected by Swift BAT (S. B. Cenko et al. 2025, GCN 41403). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 146 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 101 s (50-300 keV). The time-averaged spectrum from T0-9.2 to T0+94.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.83 +/- 0.14 and the cutoff energy, parameterized as Epeak, is 83 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (1.62 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+78 s in the 10-1000 keV band is 8.8 +/- 0.7 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/41411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39471] LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41410 SUBJECT: LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations DATE: 25/08/18 09:38:35 GMT FROM: Satoshi Sugita at Aoyama Gakuin U. <sugita(a)phys.aoyama.ac.jp> M. Nakajima, H. Negoro, K. Takagi (Nihon U.), N. Kawai, T. Mihara, (RIKEN), S. Sugita, M. Serino, Y. Kawakubo, H. Hiramatsu, Y. Kondo (AGU) report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after compact binary merger candidate S250818k at 2025-08-18 01:20:06.030 UTC. At the trigger time of S250818k, the high-voltage of MAXI/GSC was on. The instantaneous field of view of GSC at the GW trigger time covered 1% of the 90% credible region of the bayestar sky map, in which we found no significant new X-ray source. The first one-orbit (92 min) scan observation with GSC after the event covered 78% of the 90% credible region of the bayestar skymap from 01:20:06 to 02:51:15 UTC (T0+0 to T0+5469 sec). No significant new source was found in the region in the one-orbit scan observation. A typical 1-sigma averaged upper limit obtained in one scan observation is 20 mCrab at 2-20 keV. If you require information about X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. View this GCN Circular online at https://gcn.nasa.gov/circulars/41410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39470] GRB 250818B: SVOM/VT optical observation
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41409 SUBJECT: GRB 250818B: SVOM/VT optical observation DATE: 25/08/18 07:13:51 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z. H. Yao, L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. Q. Wang (GXU), Y. F. Liang (PMOC) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst GRB 250818B triggered by SVOM/ECLAIRs (Wang et al., GCN 41405). SVOM/VT start the observations at 2025-08-18T03:32:27.5, 198.5 seconds after the burst, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, the optical counterpart (GOTO25fzq, Kumar et al., GCN 41406) at the position consistent with the locations of Swift/XRT (Ferro et al., GCN 41407), was clearly detected in VT_B. The magnitudes are: T-T0 (s) | exposure time (s) | band | mag (AB) | mag err ------------------|-------------------|------|----------|-------- 198.5 | 50 | VT_B | 17.61 | 0.03 3963.5 | 50 | VT_B | 19.02 | 0.03 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. The SVOM point of contact for this burst is Ziqi Wang (ziqi.wang(a)st.gxu.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/41409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

2025

2024

2023

2022

2021