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

[vsnet-grb-info 39927] EP250916a: EP-FXT follow-up observation
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41861 SUBJECT: EP250916a: EP-FXT follow-up observation DATE: 25/09/18 07:46:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Q. Y. Wu, D. Y. Li, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250916a (GCN 41841) at 2025-09-17 11:34:24 (UTC), about 32 hours after the WXT detection, with an exposure time of 3.1 ks. FXT detected a bright source within the WXT error circle at R.A. = 268.2379 and Dec. = –35.3222 (J2000), with a positional uncertainty of 10 arcseconds (radius, 90% confidence level, including both statistical and systematic errors). The fit with a power-law spectrum yields Nh = 3.1 × 10^21 cm^-2 and a photon index of 1.66 ± 0.02, with a 0.5–10 keV flux of 5.4 × 10^-10 erg/s/cm^2. Additionally, we note that this source keeps brightening in the WXT monitoring, with the flux rising from approximately 3 × 10^-11 erg/s/cm^2 at 2025-09-16 03:33:13 to about 2 × 10^-10 erg/s/cm^2 at 2025-09-17 17:54:10 (UTC). Further follow-up observations are encouraged to identify the nature of this source. 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/41861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39926] GRB 250916A: MAO/AZT-22 optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41860 SUBJECT: GRB 250916A: MAO/AZT-22 optical observations DATE: 25/09/18 05:09:34 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> O. Burkhonov, Y. Rajabov, B.Abidkhanov, S. Eghamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera(Im et al., 2010). We obtained series of 300 sec. images in Bessel R filter on September 17, 18:35:18-19:02:20 UTC. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858, Moskvitin et al. GCN 41859) is clearly detected in the individual and stacked frames with the brightness of R = 19.76 +/- 0.03 (t_mid - T0 = 1.2229 days = 29.4917 hours). All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog. For image template subrtaction we used PanSTARRS DR2 catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39925] GRB 250916A: SAO RAS optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41859 SUBJECT: GRB 250916A: SAO RAS optical observations DATE: 25/09/17 23:24:23 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained series of 300 sec. images in BVRcIc bands on September 17, 20:21:44--21:42:59 UT. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858) is clearly detected in the individual and stacked frames with the brightness of R = 19.60 +/- 0.02 (t_mid - T0 = 1.3059 days = 31.3419 hours). Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39924] GRB 250916A : GIT optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41858 SUBJECT: GRB 250916A : GIT optical observations DATE: 25/09/17 21:43:01 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of Fermi GRB 250916A (Fermi GBM team, GCN 41839) with 0.7m GROWTH-India Telescope (GIT) in r' filter. We started the observation at 2025-09-17 17:34:08 UT, i.e., 28.08 hours after the Fermi GBM trigger. The source is detected at the position reported by GOTO (Belkin et al., GCN 41847) and photometry result follows as: | MJD (mid) | tmid-t0 (hours) | Filter | Exposure (s) | Mag (AB) | | ------------- | ----------- | ------ | ------------ | -------------- | | 60935.73411 | 28.13 | r' | 360 | 19.73 +- 0.06 | The source is fading and photometric result is consistent with Belkin et al., GCN 41847. More broadband observations are under way. The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39923] LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41857 SUBJECT: LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches DATE: 25/09/17 21:05:39 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S250917aq in a time range of 1000 seconds centered on the alert event time (2025-09-17 13:13:34.401 UTC to 2025-09-17 13:30:14.401 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the significance estimate [3]. Three track-like events are found in spatial and temporal coincidence with the gravitational-wave candidate S250917aq calculated from the map circulated in the 4-Update notice. This represents an overall p-value of 0.0096 from the generic transient search and an overall p-value of 0.0197 for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrinos and GW skymap is RA 243.72, Dec -34.23 degrees in the generic transient search. The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube. Additional details and updates will be posted at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch/. Properties of the coincident events are shown below. | dt(s) | RA(deg) | Dec(deg) | Angular uncertainty(deg)| p-value(generic transient)| p-value(Bayesian) | |-------|----------|----------|-------------------------|---------------------------|-----------------------| | -497.79 | 228.08 | -34.97 | 0.43 | 0.0307 | null | | -82.26 | 243.67 | -34.25 | 0.43 | 0.0096 | 0.0809 | | -62.98 | 38.47 | 36.82 | 3.99 | null | 0.0302 | where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from each search. Event p-values are provided when the per-event p-value is less than 0.1 in either search. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu [1] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39922] LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41856 SUBJECT: LIGO/Virgo/KAGRA S250917aq: Updated Sky localization DATE: 25/09/17 19:57:03 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) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250917aq (GCN Circular 41850). 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/S250917aq For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 5216 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 696 +/- 162 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/41856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39921] GRB 250916A: Glowbug gamma-ray detection
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41855 SUBJECT: GRB 250916A: Glowbug gamma-ray detection DATE: 25/09/17 19:22:38 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 250916A, which was also detected by Fermi/GBM (GCN 41839), AstroSat/CZTI (GCN 41843), and CALET (Trig ID. 1442064382). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-16 13:33:04.840 with a duration of 64.5 s and a total significance of about 110 sigma. The light curve comprises two primary peaks at ~T0+22s and ~T0+44s. A search of the Glowbug data for the earlier, fainter emission reported in GCN 41839 by Fermi/GBM (trigger time 13:29:21) was inconclusive. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39920] GRB250917B: WFST optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41854 SUBJECT: GRB250917B: WFST optical observations DATE: 25/09/17 19:16:36 GMT FROM: ylhua(a)pmo.ac.cn Yan-Long Hua, Bin Li, Bin-Yang Liu, Tian-Rui Sun, Jin-Jun Geng, Xue-Feng Wu, Zhi-Ping Jin, Wen Zhao, Ji-An Jiang report on behalf of the WFST team: Following the detection of GRB 250917B by Fermi GBM (Fermi GBM Team, GCN 41846) and Swift-BAT (R. Caputo, GCN 41848), we performed follow-up observations using the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at the Lenghu Astronomical Observation Base in Qinghai Province, China. Observations were performed in the g/r/i band, starting from 2025-09-17 13:15:02（UTC）to 2025-09-17 13:42:39（UTC）, with an exposure of 120s*3 for each band. The r-band stacked image reaches a limiting magnitude of 22.3 (AB). We performed image subtraction using Pan-STARRS1 (PS1) reference images, but did not find any significant optical counterpart. We also examined the Swift-XRT (J.A. Kennea, GCN 41851) sources within the GRB error region: Source 1 is located near the center of a galaxy, making it difficult to justify an optical counterpart. Source 5 and Source 6 show no detectable optical counterparts in our images. These results suggest that no clear optical afterglow was detected at the positions of the X-ray sources within our observation limits. We thank the WFST staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39919] GRB 250916A: Swift ToO observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41853 SUBJECT: GRB 250916A: Swift ToO observations DATE: 25/09/17 19:02:32 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 Fermi/GBM-detected event GRB 250916A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021859 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 Fermi/GBM 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/41853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39918] GRB 250917B: Fermi GBM Observation
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41852 SUBJECT: GRB 250917B: Fermi GBM Observation DATE: 25/09/17 18:53:07 GMT FROM: Rushikesh Digambar Sonawane PHD231014 at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf ofthe Fermi Gamma-ray Burst Monitor Team:"At 06:27:44.33 UT on 17 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)triggered and located GRB 250917B (trigger 779783269/250917269).which was also detected by Swift BAT (R. Caputo et al. 2025, GCN 41848).The Fermi GBM on-ground location is consistent with the Swift BAT position.The angle from the Fermi LAT boresight is 48 degrees.The GBM light curve consists of a single emission episode with a duration (T90)of about 0.2 s (50-300 keV). The time-averaged spectrumfrom T0-0.2 to T0+0.3 s is best fit bya power law function with an exponential high-energy cutoff.The power law index is -1 +/- 0.2 and the cutoff energy,parameterized as Epeak, is 120 +/- 20 keV.The event fluence (10-1000 keV) in this time interval is(3.2 +/- 0.3)E-07 erg/cm^2. The 64-ms peak photon flux measuredstarting from T0+0.0 s in the 10-1000 keV band is 24 +/- 2 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.htmlFor 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/41852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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