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[vsnet-grb-info 40866] EP251118a: Continued Optical Detection with Kinder observations
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42798 SUBJECT: EP251118a: Continued Optical Detection with Kinder observations DATE: 25/11/22 13:04:05 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> A. Aryan, T.-W. Chen, Y.-H. Lee, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), 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 previous detection (Lee et al., GCN 42780 ), we continued to observe the field of the fast X-ray transient EP251118a (Jiang et al., GCN 42749) using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations began at 18:09 UTC on November 21, 2025 (MJD 61000.756), 73.45 hours 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 DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'hotpants' (Becker A., 2015, ascl.soft. ascl:1504.004) algorithm. In the difference image, we onece again clearly detected the optical counterpart candidate proposed by Malesani et al. (GCN 42751) at a spectroscopic redshift of z = 1.216 (An et al., GCN 42756), and confirmed by Belkin et al. (GCN 42758); Yadav et al. (GCN 42760); Busmann et al. (GCN 42763); Francile et al. (GCN 42767); Urquijo-Rodríguez et al. (GCN 42773); Moskvitin et al. (GCN 42785); Gupta et al. (GCN 42787); and Liu et al (GCN 42793) Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured magnitude(in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 61000.756 | 73.45 | 300 * 6 | 22.5 +/- 0.1 | 0".92 | 1.12 The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.09 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission can be found in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/42798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40865] LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient through targeted search
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42797 SUBJECT: LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient through targeted search DATE: 25/11/22 10:00:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP), L. P. Xin, Y. N. Ma (NAOC) Using the event-by-event data downloaded through the X-band ground stations, we report on the identification of a faint SVOM/ECLAIRs transient detected at 2025-11-05T13:00:48.34 UTC (T0), 88.4 s after the compact binary merger candidate S251105aj (The LIGO-Virgo-Kagra Collaboration, GCN 42587). This transient was detected through an offline targeted search for possible counterparts of the GW event S251105aj. The ECLAIRs source was detected with a timescale of 82 s and below 60 keV, with a best signal-to-noise ratio of 6.1 starting at T0. The localization of the source is RA, Dec = 349.998, -29.022 degrees: RA (J2000) = 23h20m00s Dec (J2000) = -29d01m19s with a 90% C.L. radius of 13.9 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is about 2 degrees outside the 99% area contour of the Bilby.multiorder.fits skymap of S251105aj. At the time of the GW trigger, ECLAIRs was covering 88% of the skymap 99% area. The time-averaged spectrum from T0 to T0+82 s in the energy range of 5-60 keV is well fitted by a blackbody (BB) model, with a measured temperature of 7.8 (+1.5/-1.2) keV. With this model, the total 4-120 keV flux is (3.6+/-0.8)e-9 erg/cm^2/s. Assuming a distance of 2071 Mpc (z=0.374) for the source, this corresponds to a luminosity of 1.8e48 erg/s and a BB emission radius of 1.9e6 cm. A broken power-law model is also tested, providing a comparable fit, though with less well-constrained parameters of photon index 1 around -0.5, break energy of 22 (+21/-10) keV, and photon index 2 around 2.9. At this stage, the nature of this transient is unknown. We conducted SVOM/VT and EP/FXT follow-up observations on this field. The results will be published in dedicated circulars. All the quoted errors are at the 68% confidence level. 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 source is: Hui Yang (IRAP) (hui.yang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/42797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40864] LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42796 SUBJECT: LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates DATE: 25/11/22 07:28:12 GMT FROM: Hemanth kumar <hemanth.bommireddy195(a)gmail.com> Hemanth Bommireddy (U de Chile), Regis Cartier (UA), Felipe Olivares (U Hawaii), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) spectroscopy team: We report spectroscopic observations of the transients AT2025adgp, AT2025adhf, and AT2025adhs obtained with the SOAR telescope on 2025-11-14 at 04:10:05 UTC (PI: Bommireddy). For each source, we obtained an exposure of approximately 900s. The spectra were preliminarily reduced and classified using the NGSF spectral classification software (Goldwasser et al. 2022). Based on the reported redshifts (GCN 42675), the top 3 template fits for each event are listed below. | event | SN type/event/instrument (χ²/dof) | | -----------| --------------------------------------------------------------------------- | | AT2025adgp | II/2013fs/KAST (~0.83), Ic-BL/1998bw/DFOSC (~0.82), IIn/2010jl/KAST (~0.82) | AT2025adhf | Ic-BL/1998bw/DFOSC (~1.96), Ic-BL/1998bw/EFOSC2-3.6 (~1.99), Ic-BL/1998bw/DFOSC (~2.06)| | AT2025adhs | SLSN-I/PTF10aagc/LRIS (~1.57), Ia-pec/2000cx/KAST (~1.61), SLSN-I/PTF12dam/DBSP (~1.62)| We thank the SOAR staff for their support during these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40863] GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42795 SUBJECT: GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst DATE: 25/11/22 03:08:50 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> Jimmy DeLaunay (PSU), Samuele Ronchini (GSSI), Aaron Tohuvavohu (Cosmic Frontier), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report: Swift/BAT did not localize GRB 251121A onboard (T0: 2025-11-21T16:30:58.99 UTC, Fermi Trig 785435463, Glowbug GCN 42794) The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 10.7 in a 0.128 s analysis time bin, starting at T0 - 0.032 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 12,627 deg2 and the 50% credible area is 4,629 deg2 The integrated probability inside the coded field of view is 2%. The NITRATES skymap is consistent with the Ferm/GBM localization reported in the final position notice (GCN 42790). The combined Fermi/GBM+NITRATES 90% credible area is 893 deg2 and the 50% credible area is 256 deg2. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=785435495/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/785435495/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/785435495/0_n_JOI… Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=785435495 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/42795. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40862] GRB 251121A: Glowbug gamma-ray detection of a likely short burst
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42794 SUBJECT: GRB 251121A: Glowbug gamma-ray detection of a likely short burst DATE: 25/11/22 02:28:23 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> R. Woolf, C.C. Cheung, 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 251121A, which was also detected by Fermi/GBM (GCN 42790). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-11-21 16:30:57.936 with a duration of 0.06 s and a total significance of about 9.4 sigma. The light curve comprises a single peak. 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 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/42794. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40861] EP251118a: Xinglong-2.16m optical observation
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42793 SUBJECT: EP251118a: Xinglong-2.16m optical observation DATE: 25/11/22 01:34:51 GMT FROM: liuxing(a)nao.cas.cn X. Liu, J.J. Jin, J. Zheng, Z. Fan, D. Xu, L.B. He, J. An, S.Q. Jiang, Z.P. Zhu, J.J. Jia(NAOC), S.Y. Fu(HUST) report on behalf of a large collaboration: We observed the field of EP251118a detected by EP/WXT (Jiang et al., GCN 42749; Shi et al., GCN 42754;) and likely GRB 251118C (Frederiks et al., GCN 42765; Wang et al., GCN 42766; Delaunay et al., GCN 42770; Woolf et al, GCN 42771) using the Xinglong-2.16m telescope equipped with the BFOSC camera. Observations started at 19:28:32 UT on 2025-11-21 (i.e., 74.77 h after the EP trigger), and 15x300 s R-band frames have been obtained. The optical afterglow (Melasani et al., GCN 42751; An et al., GCN 42756; Belkin et al., GCN42758; Yadav et al., GCN 42760; Busmann et al., GCN 42763; Francile et al., GCN 42767; Rodríguez et al., GCN 42773; Li et al., GCN 42776; Lee et al., GCN 42780; Moskvitin et al., GCN 42785; Gupta et al., GCN42787) was cleary detected in our stacked frame with a magnitude of R = 22.1 +/- 0.1 at a mid-time of 75.28hr, calibrated with Pan-STARRS1 DR2 catalog converted using Lupton (2005) equations and not corrected for Galactic extinction. We thank the staff at Xinglong observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42793. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40860] GRB 251115A: Fermi GBM Observation
by GCN Circulars 21 Nov '25

21 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42792 SUBJECT: GRB 251115A: Fermi GBM Observation DATE: 25/11/21 23:37:57 GMT FROM: Angus Jameson <abj0023(a)uah.edu> A. Jameson (UAH), S. Bala (USRA), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 03:20:02.67 UT on 15 November 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251115A (trigger 784869607/251115139), which was also detected by Fermi-LAT (E. Bissaldi et al. 2025, GCN 42696). The Fermi GBM on-ground location is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 80 degrees. The GBM light curve consists of a double-peaked emission with a duration (T90) of about 13 s (50-300 keV). The time-averaged spectrum from T0-4.1 to T0+13.8 s is best fit by a Band function with Epeak = 36 +/- 6 keV, alpha = -0.7 +/- 0.4, and beta = -2.09 +/- 0.07. The event fluence (10-1000 keV) in this time interval is (3.5 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 9.0 +/- 0.3 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/42792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40859] The EP-WXT trigger 01709248635 is likely a flaring star
by GCN Circulars 21 Nov '25

21 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42791 SUBJECT: The EP-WXT trigger 01709248635 is likely a flaring star DATE: 25/11/21 16:45:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (HKU), B.-T. Wang (YNAO), H.-Z. Wu (HUST) and W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709248635 at the time of 2025-11-21T16:11:59, is likely a stellar flare associated with a T Tauri Star HD 285751. The estimated flux of the flare is around 1.0e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.3e32 erg/s. 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/42791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40858] GRB 251121A: Fermi GBM Final Real-time Localization
by GCN Circulars 21 Nov '25

21 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42790 SUBJECT: GRB 251121A: Fermi GBM Final Real-time Localization DATE: 25/11/21 16:41:36 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 16:30:58 UT on 21 Nov 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251121A (trigger 785435463.990588 / 251121688). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 250.6, Dec = -19.8 (J2000 degrees, equivalent to J2000 16h 42m, -19d 48'), with a statistical uncertainty of 19.5 degrees. The angle from the Fermi LAT boresight is 100.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251121688/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251121688/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251121688/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40857] Fermi Gamma-ray Burst Monitor trigger 785388351 / 251121143 is not a GRB
by GCN Circulars 21 Nov '25

21 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42789 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 785388351 / 251121143 is not a GRB DATE: 25/11/21 14:57:14 GMT FROM: Peter Veres at University of Alabama in Huntsville <veresp(a)gmail.com> P. Veres (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 785388351 / 251121143 at 03:25:46.72 UT on 21 November 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/42789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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