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[vsnet-grb-info 38726] GRB 250610B: REM optical/NIR observations
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40687 SUBJECT: GRB 250610B: REM optical/NIR observations DATE: 25/06/11 11:49:21 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB 250610B detected by SVOM/ECLAIRs (Saccardi et al., GCN 40671) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, and H bands, started on 2025 June 10 at 22:45:52 UT (i.e. 6.2 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any possible counterpart at the position of the optical afterglow (Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678; Bochenek et al., GCN 40684; Qiu et al., GCN 40685) down to the following 3sigma limits: r > 19.6 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 6.7 hr after the trigger; H > 15.6 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 6.2 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40687. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38725] EP250610a: Liverpool Telescope optical upper limits
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40686 SUBJECT: EP250610a: Liverpool Telescope optical upper limits DATE: 25/06/11 10:13:31 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report: We observed the field of the X-ray transient EP250610a (Zhang et al., GCN 40660; Lian et al., GCN 40669) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS r’ and SDSS g’ filters starting at 2025-05-11 00:16:50 UT, approximately 19.9 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. In agreement with Schneider et al. (GCN 40661), Brivio et al. (GCN 40665), Yao et al. (GCN 40666) and Lipunov et al. (GCN 40673), we identify no new sources within the positional uncertainty of the X-ray source identified by Evans et al. (GCN 40662) and Lian et al. (GCN 40669). At the position of the X-ray source, we derive 3-sigma upper limits of r’ > 22.1 and g’ > 22.1 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40686. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38724] GRB 250610B: SVOM/VT optical shallow decay
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40685 SUBJECT: GRB 250610B: SVOM/VT optical shallow decay DATE: 25/06/11 09:54:28 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> Y. L. Qiu, H. L. Li, L. P. Xin, 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), A. Saccardi, J. Rodriguez, N. Dagoneau (CEA), C. Van Hove (IJCLab) report on behalf of the SVOM mission team. SVOM/VT made a second ToO observation for GRB250610B (Saccardi et al., GCN 40671; Wang et al., GCN 40682; Wang et al, GCN 40683). The observation was performed in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With more data, the brightness of the counterpart (Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678; Bochenek et al., GCN 40684) was fading by about 0.6+/-0.1 mag in both band within 9 hours. The latest brightness is derived as follows: Mid-time after the burst | exposure time| band | mag (AB) | mag err -------------------------|--------------|------|----------|-------- 9.53 hour | 14*70 sec | VT_B | 21.3 ｜ 0.1 9.50 hour | 12*70 sec | VT_R | 21.1 ｜ 0.1 Our photometry was not corrected for Galactic extinction. We noticed that there is a faint blue source at the position of the counterpart in Legency Survey DR10 with g=23.0 mag and r=22.75 mag. Considering the possible host galaxy's brightness and blue color，the photometry at later phase might be contaminated by the host galaxy's light, particularly in the VT_B band. With the slow decaying behavior of X-ray emission (Evans et al., GCN 40679; Liang et al., GCN 40681) and optical at early phase, it is not an ordinary GRB event. More multiband follow-up and spectrum observations are encouraged. 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/40685. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38723] GRB 250610B: additional Liverpool Telescope optical observations
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40684 SUBJECT: GRB 250610B: additional Liverpool Telescope optical observations DATE: 25/06/11 08:39:42 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of GRB 250610B (Saccardi et al., GCN 40671) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures in the SDSS r’ and i’ filters starting at 2025-06-10 23:34:02 UT, approximately 7.0 hours after the trigger. We report detections in stacked images in both filters at the position of the reported optical counterpart (Schneider et al., GCN 40676). The obtained magnitudes are r = 21.21 ± 0.11 and i = 21.14 ± 0.13, in line with previous optical observations (Schneider et al., GCN 40676; Gompertz et al., GCN 40677; Li et al., GCN 40678). The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. MJD (mid) T_mid-T_0 Filter Mag. (AB) 60836.98618 7.12 h r 21.21 ± 0.11 60836.99384 7.30 h i 21.14 ± 0.13 View this GCN Circular online at https://gcn.nasa.gov/circulars/40684. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38722] GRB 250610B: SVOM/GRM analysis
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40683 SUBJECT: GRB 250610B: SVOM/GRM analysis DATE: 25/06/11 06:39:58 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: A. Saccardi, J. Rodriguez, N. Dagoneau (CEA) Report on behalf of the SVOM team: SVOM/GRM detected the burst GRB 250610B at 2025-06-10T16:32:58 UTC (T0), which is also detected by SVOM/ECLAIRs (A. Saccardi et al., GCN #40671) and Fermi/GBM (Yun Wang et al., GCN #40682) With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250610B. The GRM light curve shows that this burst consists of a single pulse with a T90 of 94 +/-14 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250610B.png With the localization of ECLAIRs (RA=200.1831, DEC=31.1028), the time-averaged spectrum from T0-10 to T0+80 s is best fitted by a Blackbody function. The temperature, parameterized as kT, is 13 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (2.3 +/- 0.2)E-06 erg/cm^2. The time-averaged spectrum can also be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -1.2 +/- 0.5 and the cutoff energy, parameterized as Epeak, is 66 +15/-12 keV. The event fluence (10-1000 keV) in this time interval is (2.2 +/- 0.3)E-06 erg/cm^2. Thus GRB 250610B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250610B_amati.png We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later. 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/40683. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38721] GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40682 SUBJECT: GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst DATE: 25/06/11 03:32:59 GMT FROM: Hao Zhou at Purple Mountain Observatory, CAS <haozhou(a)pmo.ac.cn> Yun Wang, Hao Zhou, Zhi-Ping Jin, Yi-Zhong Fan (PMO,CAS): We report a possible sub-threshold detection of GRB 250610B by the Fermi Gamma-ray Burst Monitor (GBM). The burst was initially detected by SVOM/ECLAIRs (Saccardi et al., GCN 40671) at T0 = 2025-06-10 16:32:58 UTC. The reported position is R.A., Dec. 200.1831, 31.1028 degrees. Based on the poshist file, the GBM NaI detector with the smallest incident angle to the burst direction was nb. We used the GBM Time-Tagged Event (TTE) data to extract the spectrum over the interval from T0–10 s to T0+80 s. The background was estimated from two intervals: T0–200 s to T0–100 s and T0+300 s to T0+400 s. We fitted the spectrum with a cutoff power-law model (dN/dE ~ (E^-alpha)*exp(-E/Ec)), obtaining alpha ~ -0.6 and a peak energy Ep=(2-alpha)*Ec ~ 55 keV. The energy flux in the 1–10000 keV band is estimated to be ~ 5.72e-9 erg/cm^2/s. The spectrum can be fitted with a blackbody model, yielding a temperature of kT ~13 keV and providing a better goodness of fit than a cutoff power-law model. This is a test using RapidGBM (https://github.com/0neyun/RapidGBM), and the results presented here should be considered preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40682. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38720] GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40681 SUBJECT: GRB 250610B: EP-FXT follow-up observation and afterglow counterpart DATE: 25/06/11 02:44:20 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang, Y. L. Hua (PMO, CAS), X. P. Xu, H. W. Pan(NAO, CAS), A. Saccardi, J. Rodriguez, N. Dagoneau (CEA), C. Van Hove (IJCLab) report on behalf of the Einstein Probe and SVOM team We performed a follow-up observation of GRB 250610B (detected through offline search of SVOM/ECLAIRs, Saccardi et al, GCN #40671; followed by Swift/XRT, Evans et al. GCN #40679), with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2025-06-10T17:04:27 (T-TGRB ~ 1.9ks), and the exposure time is about 5.8 ks. Only 1 uncatalogued source was detected both by FXTA and FXTB in the 90% localization error circle provided by SVOM/ECLAIRs (with a radius of 3.22 arcmin centered at RA, DEC = 200.1831 deg, +31.1028 deg), as listed below (the FXT flux is taken from FXTB module). ------------------------------------------------------------------------------------------------- Source name | RA | DEC | Estimated Flux | SNR | Dist from SVOM/ECLAIRs | | deg | deg | (erg/s/cm^2) | | offset (in arcmin) | EPF_J132043.1+310615 | 200.1795 | 31.1043 | 2.8(+/-0.2) x 10^-12 | 5.9 | 0.21 | ------------------------------------------------------------------------------------------------- Note: * EPF_J132043.1+310615 was also detected by Swift/XRT (GCN #40679) in a ~2.0 ks observation, with a mean flux of ~3.9(+/-0.3)e-12 erg/s/cm^2, the position of this source is also associated with the Optical counterpart detected by SVOM/VT (Li et al. GCN #40678). The above observation was made with the EP-FXT instrument. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. View this GCN Circular online at https://gcn.nasa.gov/circulars/40681. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38719] Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
by GCN Circulars 11 Jun '25

11 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40680 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB DATE: 25/06/11 00:48:18 GMT FROM: sumanbala2210(a)gmail.com S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 771286888/250610932 at 22:21:23.29 UT on 10 June 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40680. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38718] GRB 250610B: Swift-XRT counterpart detection
by GCN Circulars 10 Jun '25

10 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40679 SUBJECT: GRB 250610B: Swift-XRT counterpart detection DATE: 25/06/10 23:55:14 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250610B, collecting 2.0 ks of Photon Counting (PC) mode data between T0+2.8 ks and T0+8.9 ks after the trigger. A likely counterpart has been found consistent with the optical detection (GCN Circ. 40676, 40677 and 40678). The details of this source are: Source 1 (SWIFT J132043.2+310614): ================================== RA (J2000.0): 200.1802 = 13h 20m 43.25s Dec (J2000.0): +31.1040 = +31d 06' 14.4" Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.3 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.1084 +/- 0.0084 ct s^-1 Mean flux: (3.91 +/- 0.30)e-12 erg cm^-2 s^-1 Peak rate: 0.134 +/- 0.022 ct s^-1 Peak flux: (4.85 +/- 0.81)e-12 erg cm^-2 s^-1 ECF: 3.61e-11 erg cm^-2 ct^-1, assuming NH=1.44e+20 cm^-2, gamma=1.78; determined from a spectral fit. XMM UL: 2.4e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.0-sigma above this 3-sigma upper limit. There is no evidence for fading. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM. This circular is an officicial product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38717] GRB 250610B: SVOM/VT optical counterpart
by GCN Circulars 10 Jun '25

10 Jun '25

TITLE: GCN CIRCULAR NUMBER: 40678 SUBJECT: GRB 250610B: SVOM/VT optical counterpart DATE: 25/06/10 23:35:24 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), A. Saccardi, J. Rodriguez, N. Dagoneau (CEA), C. Van Hove (IJCLab) report on behalf of the SVOM mission team. SVOM performed a Target of Opportunity observation of GRB 250610B detected by SVOM/Eclairs (Saccardi et al., GCN 40671). SVOM/VT began observing the field at 2025-06-10 17:04:26 UTC, 0.52 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source, compared to legacy survey, is found using VT X-band data, within the error box of Swift/XRT1 at R.A., Dec 200.179739, 31.10496 degrees: RA (J2000) = 13:20:43.1 Dec (J2000) = +31:06:17.9 with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B, and was fading by 0.3 mag in 2 orbits, the magnitudes are: Mid-time after the burst | exposure time (s) | band | mag (AB) | mag err --------------------|-------------------|------|----------|-------- 1.234 hour | 70 | VT_B | 20.7 ｜ 0.1 1.234 hour | 70 | VT_R | 20.3 ｜ 0.1 This position and the brightness is consistent with the reports (Schneider et al., GCN 40676, Gompertz et al., GCN 40677) 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 Andrea Saccardi(a)cea.fr. View this GCN Circular online at https://gcn.nasa.gov/circulars/40678. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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