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[vsnet-grb-info 38746] sb25061207: SVOM/VT optical counterpart
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40707 SUBJECT: sb25061207: SVOM/VT optical counterpart DATE: 25/06/12 15:40:31 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), L. Zhang (IHEP), Y.-D. Hu (GXU), X.-L. Chen (YNU) report on behalf of the SVOM mission team SVOM performed an automatic slew on the burst (sb25061207) triggered by SVOM/ECLAIRs (Zhang et al., GCN 40697). SVOM/VT began observing the field at 2025-06-12T10:30:44 UTC, 202 seconds after Tb, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. A candidate is found using VT X-band data, compared to Legacy survey, within the error box of SVOM/Eclairs (Zhang et al., GCN 40697) at R.A., Dec 198.09415, +0.07508 degrees: RA (J2000) = 13:12:22.597 Dec (J2000) = +00:04:30.28 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B bands. With the data available, the light curve shows that this source was fading at first time, and then rebrightening to the peak of VT_R ~ 18.0 mag at around 1000 seconds after the trigger time, and then decayed. mid-time | exposure time | band | mag (AB) ------------ |----------------- |------------------- 1.79 hour | 50 sec | VT_B | 21.6+/-0.2 1.79 hour | 50 sec | VT_R | 20.8+/-0.1 Given the VT colour of the candidate, it might be a low redshift transient. We also noticed that there is a faint blue source at the Legacy survey image at the location of the candidate, which might be the host. More followups are encouraged. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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 Burst Advocate (BA) on shift for this alert is Y.-D. Hu : hyd(a)gxu.edu.cn. View this GCN Circular online at https://gcn.nasa.gov/circulars/40707. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38745] GRB 250612C: BALROG localization (Fermi Trigger 771432801 / GRB 250612620)
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40706 SUBJECT: GRB 250612C: BALROG localization (Fermi Trigger 771432801 / GRB 250612620) DATE: 25/06/12 15:19:24 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 771432801 at 14:53:16 on 12 June 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 118.9 deg Decl.(2000.0) = 18.8 deg The 1 sigma statistical error radius is 1.1 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250612620/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250612620/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250612620/json View this GCN Circular online at https://gcn.nasa.gov/circulars/40706. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38744] GRB 250610B: Swift-XRT refined Analysis
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40705 SUBJECT: GRB 250610B: Swift-XRT refined Analysis DATE: 25/06/12 15:11:21 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 5.0 ks of XRT data for GRB 250610B, from 2.9 ks to 105.7 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. Using 2013 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 200.17991, +31.10477 which is equivalent to: RA (J2000): 13h 20m 43.18s Dec(J2000): +31d 06' 17.2" with an uncertainty of 2.8 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.68 (+0.12, -0.10). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 (+0.33, -0.25). The best-fitting absorption column is 3.1 (+7.7, -2.0) x 10^20 cm^-2, consistent with the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+7.7, -2.0) x 10^20 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.86 (+0.33, -0.25) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019863. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40705. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38743] GRB 250612C: Fermi GBM Final Real-time Localization
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40704 SUBJECT: GRB 250612C: Fermi GBM Final Real-time Localization DATE: 25/06/12 15:02:11 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 LONG GRB At 14:53:16 UT on 12 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250612C (trigger 771432801.582428 / 250612620). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 113.2, Dec = 16.2 (J2000 degrees, equivalent to J2000 07h 32m, 16d 11'), with a statistical uncertainty of 1.4 degrees. The angle from the Fermi LAT boresight is 96.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612620/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612620/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612620/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40704. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38742] EP250610a: Upper limit from Fermi-GBM Observations
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40703 SUBJECT: EP250610a: Upper limit from Fermi-GBM Observations DATE: 25/06/12 14:32:39 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial coverage of the transient EP250610a detected by EP-WXT (Zhang et al., GCN 40660, Lian et al. GCN 40669). There was no Fermi-GBM onboard trigger around the EP starting time T0=2025-06-10T04:23:24 UTC. The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transient, both temporally and spatially, is identified, as confirmed also by visual inspection of the data. Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, we derive a flux upper limit of 2.8e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/40703. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38741] GRB 250612B (250612519/771424081): Fermi GBM Final Localization
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40702 SUBJECT: GRB 250612B (250612519/771424081): Fermi GBM Final Localization DATE: 25/06/12 14:23:44 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 12:27:56.19 UT on 12 June 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250612B (trigger 771424081/250612519). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 231.28, Dec = -29.05 (J2000 degrees, equivalent to J2000 15h 25m, -29d 03'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 71.04 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612519/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612519/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250612519/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40702. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38740] GRB 250612A: BALROG localization (Fermi Trigger 771424081 / GRB 250612519)
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40701 SUBJECT: GRB 250612A: BALROG localization (Fermi Trigger 771424081 / GRB 250612519) DATE: 25/06/12 13:17:08 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 771424081 at 12:27:56 on 12 June 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 226.1 deg Decl.(2000.0) = -28.9 deg The 1 sigma statistical error radius is 2.4 deg. We estimate an additional systematic error of 1 deg. This is consistent in time and position with the Einstein Probe detection of the X-ray transient EP 250612a (GCN 40700). Further details are available at: https://grb.mpe.mpg.de/grb/GRB250612519/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250612519/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250612519/json View this GCN Circular online at https://gcn.nasa.gov/circulars/40701. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38739] EP250612a: Einstein Probe detection of an X-ray transient
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40700 SUBJECT: EP250612a: Einstein Probe detection of an X-ray transient DATE: 25/06/12 13:03:13 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. L. Hua (PMO, CAS), T. Zhao, Y. J. Song, J. W. Hu , W. Yuan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250612a. The transient triggered EP-WXT (ID: 01709178580) at 2025-06-12T12:28:05 (UTC). The WXT position of the source is R.A. = 229.654 deg, DEC = -26.757 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 229.6503 deg, DEC = -26.7661 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. The contact TA of EP250612a is Y. L. Hua, please contact him via email ylhua(a)pmo.ac.cn if needed. 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/40700. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38738] GRB 250610B: Liverpool Telescope continued monitoring
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40699 SUBJECT: GRB 250610B: Liverpool Telescope continued monitoring DATE: 25/06/12 12:54:32 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz (U. Birmingham), Dimple (U. Birmingham) and A. Bochenek (LJMU) report on behalf of a larger collaboration: We continued follow-up observations of GRB 250610B (Saccardi et al., GCN 40671) for a second night with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 21:56:59 UT on 2025-06-11, ~29.4 hr after the SVOM/ECLAIRs trigger, and consisted of 8x180 s exposures in the SDSS r and i filters. We detect the optical counterpart (Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678; Bochenek & Perley, GCN 40684; Qiu et al., GCN 40685; Schneider et al., GCN 40689; Breeveld & Williams, GCN 40691) with AB magnitudes of r = 22.38 ± 0.13 (mid-time t0+1.23 days) and i = 22.13 ± 0.08 (mid-time t0+1.25 days). Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40699. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38737] GRB 250610B: MISTRAL/T193 and T120 OHP further observations
by GCN Circulars 12 Jun '25

12 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40698 SUBJECT: GRB 250610B: MISTRAL/T193 and T120 OHP further observations DATE: 25/06/12 11:57:50 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), A. de Ugarte Postigo (LAM), Y. Degot-Longui (Pytheas/OHP), J. Balcaen (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of a larger collaboration: We re-observed the field of the GRB 250610B (Saccardi et al., GCN 40671; Wang et al., GCN 40672; Gompertz et al., GCN 40674; Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678; Evans et al., GCN 40679; Liang et al., GCN 40681; Wang et al., GCN 40682; Wang et al., GCN 40683; Bochenek et al., GCN 40684; Qiu et al., GCN 40685; Brivio et al., GCN 40687; Schneider et al., GCN 40689; Breeveld et al., GCN 40691; Hamburg et al., GCN 40692; Godet al., GCN 40695) using the T120cm and T193cm (MISTRAL instrument) telescopes at Observatoire de Haute-Provence (France). We obtained 60 minutes with MISTRAL and 75 minutes with the T120 CCD camera simultaneously in the r-band, from 2025-06-11 at 20:41 to 22:17 UTC (from 28.13 to 29.73 hr after the trigger). In the stacked and combined image from both instruments, the optical counterpart is detected at a preliminary magnitude of: r = 22.59 +/- 0.21 mag (AB) The photometric calibration was performed using nearby stars from the PanStarrs catalog and the magnitude is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 and the SOPHIE observer T. Llopis View this GCN Circular online at https://gcn.nasa.gov/circulars/40698. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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