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

[vsnet-grb-info 39596] LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41532 SUBJECT: LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova DATE: 25/08/24 20:46:51 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Smaranika Banerjee (Stockholm University), Maria-Teresa Botticella (INAF - Capodimonte Obs.), Seán J. Brennan (MPE), Enrico Cappellaro (Padua Obs.), Ting-Wan Chen (NCU Taiwan), Paolo D'Avanzo (INAF - Brera Obs.), Valerio D’Elia (ASI-SSDC), Massimiliano De Pasquale (Univ. Messina), Rob A. J. Eyles-Ferris (Leicester), Morgan Fraser (UCD), James H. Gillanders (Oxford), Ben Gompertz (Birmingham), Nusrin Habeeb (Leicester), Luca Izzo (INAF/OAC and DARK/NBI), Peter G. Jonker (Radboud), Andrew J. Levan (Radboud and Warwick), Daniele Bjørn Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Matt Nicholl (QUB), Sam Oates (Lancaster U.), Silvia Piranomonte (INAF-OAR), Luigi Piro (INAF-IAPS), Andrea Rossi (INAF - Bologna), Om Sharan Salafia (INAF - Brera Obs.), Nikhil Sarin (Cambridge), Steve Schulze (Northwestern), Avinash Singh (Stockholm University), Stephen J. Smartt (Oxford), Albert Sneppen (DAWN/NBI), Jesper Sollerman (Stockholm), Danny Steeghs (Warwick), Nial R. Tanvir (Leicester), Aishwarya L. Thakur (INAF-IAPS), report for the ENGRAVE collaboration: We report preliminary analysis from follow-up ESO VLT observations obtained by the ENGRAVE collaboration of SN 2025ulz (Stein et al., GCN 41414), which was discovered within the 3D localization region of the GW alert S250818k (LVK Collaboration, GCNs 41437, 41440). Starting on 2025-08-24 00:03:40 UT, we observed the field of SN 2025ulz using the ESO VLT UT4 (Yepun) equipped with the MUSE integral-field spectrograph. A series of 4x700 s exposures were taken for this observation. From a preliminary reduction, extraction of a spectrum at the position of SN 2025ulz reveals a continuum well detected over the full wavelength range of 5000 to 9000 Å. The spectrum shows a prominent broad feature which we interpret as a P-Cygni profile of the H-alpha line, similar to that observed in young type II or IIb supernovae. The peak of the emission and the absorption trough is consistent with the host galaxy redshift of z = 0.0848 (ENGRAVE GCN 41476, Karambelkar et al., GCN 41436) and an expansion velocity of around 12,000 km/s. There is weaker evidence for an H-beta P-Cygni profile. Plausible matches to young type II and IIb SNe are found with SNID-SAGE (Stoppa et al. in prep, a new enhanced, python version of SNID), although the transient object continuum is contaminated by the host and the absorption line strengths are therefore diluted. We suggest that SN 2025ulz is a type II supernova (of unconfirmed subtype at this point) and is therefore unrelated to S250818k. We acknowledge the excellent support from the ESO staff in Paranal, in particular Camila de Sa Freitas, Israel Blanchard and Sam Kim. View this GCN Circular online at https://gcn.nasa.gov/circulars/41532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39595] GRB 250823A: Swift-XRT refined Analysis
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41531 SUBJECT: GRB 250823A: Swift-XRT refined Analysis DATE: 25/08/24 20:31:05 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.8 ks of XRT data for GRB 250823A, from 111 s to 44.7 ks after the trigger. The data comprise 313 s in Windowed Timing (WT) mode (the first 7 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The light curve initially rises, with an index alpha=-1.5 (+0.0, -0.6). At T+120 s it breaks to an alpha of 3.33 (+/-0.09). The light curve breaks again at T+349 s to a decay with alpha=2.31 (+0.23, -0.21), before a final break at T+1667 s s after which the decay index is 0.78 (+0.13, -0.12). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.91 (+/-0.04). The best-fitting absorption column is 1.99 (+0.16, -0.15) x 10^21 cm^-2, in excess of the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.92 (+0.28, -0.26) and a best-fitting absorption column of 1.9 (+1.0, -0.8) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (5.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.9 (+1.0, -0.8) x 10^21 cm^-2 Galactic foreground: 1.1 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.92 (+0.28, -0.26) If the light curve continues to decay with a power-law decay index of 0.78, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x 10^-13 (4.8 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01344586. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39594] EP250821a: MeerKAT radio counterpart
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41530 SUBJECT: EP250821a: MeerKAT radio counterpart DATE: 25/08/24 16:50:44 GMT FROM: Francesco Carotenuto at INAF/OAR <francesco.carotenuto(a)inaf.it> Authors: F. Carotenuto (INAF-OAR), J. Bright (Oxford), P. G. Jonker (Radboud), on behalf of a larger collaboration We observed the field of EP250821a detected by the Einstein Probe (GCN 41459, 41470, 41490) with the MeerKAT radio telescope from 2025-08-23 21:44 UTC to 2025-08-23 22:31 UTC (with a total time on source of 44 minutes) using the S-band receivers at a central frequency of 3.06 GHz. Analysing the SARAO Science Data Processor output continuum image, we detect a source at the position of EP250821a with a flux density of around 40 uJy/beam, with a typical image noise of around 6 uJy/beam. Pending verification on the host galaxy emission, we tentatively ascribe it to EP250821a. Further observations are planned. We thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the "MPIfR S-band receiver system" designed, constructed and maintained by funding of the MPI für Radioastronomie and the Max-Planck-Society. View this GCN Circular online at https://gcn.nasa.gov/circulars/41530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39593] EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41529 SUBJECT: EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars DATE: 25/08/24 16:50:29 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP/WXT alerts 01709200706 and 01709200707. Observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Targeted observations of EP-WXT 01709200706 were taken at 2025-08-24 12:46:36 UT (+3.13h post trigger) and 2025-24-08 14:10:18 UT (+4.53h post trigger). We detect a single new source in difference imaging, consistent with the flaring star UCAC4 277-216984, as identified by Li et al. (GCN 41524). The star is saturated in our unsubtracted frames, meaning we cannot robustly determine the magnitude other than place lower limits of L>11.94 AB mag and L>12.11 AB mag at +3.13h and +4.53h post trigger, respectively. Targeted observations of EP-WXT 01709200707 were taken at 2025-08-24 12:54:10 UT (+0.22h post trigger) and 2025-08-24 14:02:40 UT (+1.36h post trigger). We identify a new source in differencing imaging consistent with UCAC4 268-197742 identified by Li et al. (GCN 41526). The star reaches a peak magnitude in our unsubtracted frames of L=14.31±0.01 and L=15.16±0.01 AB mag at +0.22h and +1.36h post trigger, respectively. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39592] LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41528 SUBJECT: LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch DATE: 25/08/24 16:00:28 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Rome), Eleonora Troja (U Rome) and Simone Dichiara (PSU) report: We requested a second epoch of ToO observations of AT2025ulz/ZTF25abjmnps (Stein et al.; GCN 41414) discovered within the localization of the candidate gravitational wave signal S250818k (LVK Collaboration, GCN 41437, 41440). The observations started on 2025-08-22 at 21:56 UT, approximately 4.9 days after the trigger, with a total exposure of 3.2 ks. At the transient position, we detect no X-ray source down to a 3-sigma upper limit of 0.004 cts/s (0.3-10 keV), consistent with the result reported by Hall et al. (GCN 41453). Using a power-law with nH=2.2E+20 and a photon index=2, we convert the count rate into an unabsorbed flux of 1.5e-13 erg/cm2/s, which corresponds to a luminosity of 3e42 erg/s at z=0.0848 (Karambelkar et al. GCN 41436). In simultaneous UVOT observations performed with the u filter, we identify some faint diffuse emission likely related to the host galaxy and place 3-sigma upper limit u > 21 AB at the transient’s position, in agreement with the faint detection reported by Troja et al. (GCN 41506). We thank the Swift team and the PI for promptly scheduling and making these observations possible. View this GCN Circular online at https://gcn.nasa.gov/circulars/41528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39591] GRB 250824B: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41527 SUBJECT: GRB 250824B: Fermi GBM Final Real-time Localization DATE: 25/08/24 13:48:54 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 13:38:13 UT on 24 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250824B (trigger 777735498.8624 / 250824568). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 248.3, Dec = -35.6 (J2000 degrees, equivalent to J2000 16h 33m, -35d 36'), with a statistical uncertainty of 7.7 degrees. The angle from the Fermi LAT boresight is 27.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824568/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824568/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250824568/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39590] The EP-WXT trigger 01709200707 is likely a flaring star
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41526 SUBJECT: The EP-WXT trigger 01709200707 is likely a flaring star DATE: 25/08/24 13:31:38 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), C. Y. Wang（THU）, X. Y. Zhou (PRIC), W. D. Zhang (NAOC) report on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709200707 at the time of 2025-08-24T12:40:53, is likely a stellar flare associated with UCAC4 268-197742. The estimated flux of the flare is around 6e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.1e31 erg/s. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an X-ray source was detected at R.A. = 328.5143 deg, DEC = -36.5634 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), 10 arcsec from UCAC4 268-197742. 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/41526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39589] GRB 250823A: COLIBRÍ optical observations
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41525 SUBJECT: GRB 250823A: COLIBRÍ optical observations DATE: 25/08/24 12:59:39 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Alan M. Watson (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of GRB 250823A, detected by Swift/BAT (Siegel et al., GCN Circ. 41511) and Fermi/GBM (Fermi GBM team et al., GCN Circ. 41510) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-24 05:54 to 06:33 UTC (from 9.73 to 10.38 hours after the trigger) and obtained 32 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart first reported by Gompertz et al. (GCN Circ. 41512) and subsequently by Fernandez-Garcia et al. (GCN Circ. 41513), Strausbaugh & Cucchiara (GCN Circ. 41514), Malesani et al. (GCN Circ. 41520), Kuin et al. (GCN Circ. 41521), and Mal et al. (GCN Circ. 41523), at a preliminary magnitude of: i = 22.74 +/- 0.21 This measurement is contemporaneous and consistent with the value reported by SVOM/VT (Mal et al., GCN Circ. 41523). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39588] The EP-WXT trigger 01709200706 is likely a flaring star
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41524 SUBJECT: The EP-WXT trigger 01709200706 is likely a flaring star DATE: 25/08/24 12:37:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), C. Y. Wang（THU）, X. Y. Zhou (PRIC), W. D. Zhang (NAOC) report on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709200706 at the time of 2025-08-24T09:38:33, is likely a stellar flare associated with UCAC4 277-216984. The estimated flux of the flare is around 8e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.4e31 erg/s. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an X-ray source was detected at R.A. = 355.8633 deg, DEC = -34.7836 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), 6 arcsec from UCAC4 277-216984. 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/41524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39587] GRB 250823A: SVOM/VT optical observation
by GCN Circulars 24 Aug '25

24 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41523 SUBJECT: GRB 250823A: SVOM/VT optical observation DATE: 25/08/24 12:20:24 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, 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 performed a Target of Opportunity observation of GRB 250823A detected by Swift/BAT (Siegel et al., GCN 41511) and Fermi/GBM (Fermi GBM Team, GCN 41510). SVOM/VT began observing the field at 2025-08-23T20:38:57 UTC, 0.48 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data availible, the optical counterpart (Gompertz & Dimple, GCN 41512; Fernandez-Garcia et al., GCN 41513; Strausbaugh & Cucchiara, GCN 41514; Malesani et al., GCN 41520; Kuin & Siegel, GCN 41521) at the position consistent with the locations of Swift/XRT (Siegel et al., GCN 41511; Evans et al., GCN 41515), was clearly detected in both VT_B and VT_R. It decayed by about 2 mag in 8 hours. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 1.934 | 37*70 | VT_B | 21.80 | 0.08 1.934 | 37*70 | VT_R | 20.92 | 0.06 9.913 | 28*70 | VT_R | 22.8 | 0.3 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/41523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0