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[vsnet-grb-info 38192] EP250416a: Swift/XRT counterpart fading
by GCN Circulars 18 Apr '25

18 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40166 SUBJECT: EP250416a: Swift/XRT counterpart fading DATE: 25/04/18 14:31:17 GMT FROM: Tullia Sbarrato at INAF-OAB <tullia.sbarrato(a)inaf.it> T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), D. Malesani (DAWN/NBI and Radboud), K. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team: Swift-XRT has performed further follow-up observations of the EP-WXT transient EP250416a (Zhao et al., GCN 40154), collecting a total of 4.0 ks of Photon Counting (PC) mode data between T0+17.1 ks and T0+79.8 ks. The X-ray source detected in the first 2.0 ks of data reported as “Source 1”, consistent with the optical counterpart (Levan et al., GCN 40160), and presented as the possible transient counterpart (Sbarrato et al., GCN 40163) has faded more than 3 sigma in the latest observation, confirming the trend observed by EP-FXT about 12.3 hours after the trigger (Zhou et al., GCN 40165). The flux derived from the follow-up observation is 1.8 (+/-0.4) x 10^-2 cts/s, that corresponds to 6.5 (+/-1.3) x 10^-13 erg cm^-2 s^-1. The light curve can be modelled with a power-law decay with an index of alpha=1.18 A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+0.5, -0.4). The best-fitting absorption column is 1.6 (+1.7, -1.3) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.65 x 10^-11 (5.01 x 10^-11) erg cm^-2 count^-1. The observed (unabsorbed) flux obtained from all the PC mode data is thus 1.8 x 10^-12 (2.5 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00034/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38191] EP250416a: refined EP-WXT and EP-FXT analysis
by GCN Circulars 18 Apr '25

18 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40165 SUBJECT: EP250416a: refined EP-WXT and EP-FXT analysis DATE: 25/04/18 01:30:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), G.Y. Zhao (SYSU), C. Zhou (HUST), X.L. Chen, K. Chatterjee (YNU) and C.C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We reduced and analyzed the telemetry data of EP250416a, and all uncertainties reported here are at the 90% confident level. EP250416a became detectable by WXT from ~30 seconds before the trigger time (2025-04-16T17:53:59 UTC, Zhao et al. GCN 40154), and the WXT light curve lasts for ~30 seconds (interupted by the autonomous follow-up observation) with a peak occuring at ~20 seconds after the time when EP250416a became detectable. Lipunov et al. (GCN 40156) and Li et al. (GCN 40157) performed follow-up observations for EP250416a but did not find new optical transient down to i ~20 mag. Later, a possible candidate was detected by Gemini-South (Levan et al. GCN 40160). The WXT spectrum is fitted by an absorbed powerlaw model, which counts for absorption of the Milky Way and the host galaxy. As suggested by Levan et al. (GCN 40160), the redshift of the host is set to 0.72. The equivalent hydrogen column density of the host, NH, is constrained to be less than ~1.9x10^22 cm^-2 by the WXT spectrum. The photon index of the WXT spectrum is hard, 0.32 (-0.78, +1.00). The mean and peak unabsorbed fluxes (0.5-4 keV) are (5.66+/-1.77)x10^-9 erg/s/cm^2 and (1.92+/-0.76)x10^-8 erg/s/cm^2. The autonomous EP-FXT follow-up observation starts about 2 minutes after the trigger and lasts for 2 orbits with total on-source time of 3936 seconds. In addition, about 12.3 hours after the trigger, another follow-up observation with the EP-FXT was performed for 2962 seconds. Results of the autonomous and the follow-up observations are summarized: +--------------------------------------------------------------------------------+ T_Start^a [UTC] | T_mid - T0^b [h] | Exp [s] | Flux (0.5-10 keV) [erg/s/cm^2] +--------------------------------------------------------------------------------+ 2025-04-16T17:54:53 | 0.17 | 929 | (2.56+/-0.17) x 10^-11 2025-04-16T18:55:35 | 1.49 | 3007 | (7.86+/-0.48) x 10^-12 2025-04-17T06:08:14 | 12.68 | 2962 | (1.64+/-0.20) x 10^-12 +--------------------------------------------------------------------------------+ All fluxes are unabsorbed values derived from FXT-A & FXT-B data. a. The first and the second rows represent the first and the second orbits of the autonomous observation. b. Here T0 is the time that EP250416a became detectable, about 30 seconds before the trigger time. The inferred 0.5-10 keV flux at the XRT epoch is consistent the value derived from the XRT observation (Sbarrato et al. GCN 40163). The model, which is same as the model applied to WXT data, is applied to fit FXT spectra. For the three epochs listed in the above table, the best fitted photon indices are 1.88+/-0.14, 1.98+/-0.15 and 2.23+/-0.38, and the NH of the host are (5.06+/-1.74)x10^21 cm^-2, (5.33+/-1.77)x10^21 cm^-2 and (6.66+/-4.54)x10^21 cm^-2. The contact TA of EP250416a is Guo-Ying Zhao. Please contact her via email zhaogy28(a)mail2.sysu.edu.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/40165. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38190] Konus-Wind detection of GRB 250403A
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40164 SUBJECT: Konus-Wind detection of GRB 250403A DATE: 25/04/17 17:43:37 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report The long GRB 250403A (Fermi GBM detection: Fermi GBM team, GCN 40025; Veres et al., GCN 40060; SVOM detection: Julacanti et al., GCN 40026; AstroSat CZTI detection: Tembhurnikar et al., GCN 40077) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~12 sigma count-rate increase in the interval from T0-0.4 s to T0+11.5 s where T0 = 15:15:22 UT. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250403A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.14 (-0.23, + 0.23) and Ep = 83(-6,+6) keV. In the 10 keV -10 MeV band, standard for the KW analysis, the burst fluence is (2.55 ± 0.18)x10^-6 erg/cm^2 and the 2.944 s peak energy flux is (2.51 ± 0.22)x10^-7 erg/cm^2/s. Assuming the redshift z=1.847 (de Ugarte Postigo et al., GCN 40162) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.2 ± 0.2)x10^52 erg, the isotropic peak luminosity L_iso to (6.3 ± 0.6)x10^51 erg/s, and the rest-frame peak spectral energy Ep,z to (236 ± 11) keV. With the obtained estimates, GRB 250403A is consistent (inside 68% prediction bands) of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250403A/GRB250403A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38189] EP20250416a: Swift/XRT counterpart detection
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40163 SUBJECT: EP20250416a: Swift/XRT counterpart detection DATE: 25/04/17 15:06:58 GMT FROM: Tullia Sbarrato at INAF-OAB <tullia.sbarrato(a)inaf.it> T. Sbarrato (INAF-OAB), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), C. Salvaggio (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf the Swift-XRT team: Swift-XRT has performed follow-up observations of EP/WXT-detected transient EP 250416a (Zhao et al., GCN 40154). We searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode data, from T0+17.1 ks to T0+23.2 ks after the EP/WXT trigger. An uncatalogued X-ray source is detected within the estimated 3-sigma EP/WXT error region. Using 2000 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 256.41935, +25.7751 which is equivalent to: RA (J2000): 17h 05m 40.64s Dec(J2000): +25d 46’ 30.4" with an uncertainty of 3.1 arcsec (radius, 90% confidence). This position is 1 arcmin from the EP/WXT position, and consistent with the optical candidate reported by Levan et al., (GCN 40160). The source has a mean count rate of 9.9e-02 ct/sec and currently shows no signs of fading. The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/EP/EP_FIELD00034/ This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40163. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38188] GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40162 SUBJECT: GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847 DATE: 25/04/17 14:35:25 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl> A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Izzo (INAF/OAC and DARK/NBI), J. P. U. Fynbo (DAWN/NBO), Y. Julakanti (Univ. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), S. Savaglio (Univ. Calabria), N. R. Tanvir (Univ. Leicester), S. D. Vergani (LUX-Obs. de Paris, CNRS), report on behalf of the Stargate collaboration: We observed the optical and NIR counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041; Pérez-Fournon et al., GCN 40043; Brivio et al., GCN 40044; Xin et al., GCN 40045; Shilling et al., GCN 40048; Zheng et al., GCN 40065; Leonini et al., GCN 40068) of the SVOM/ECLAIRs (Julakanti et al., GCN 40026), Fermi/GBM (Veres et al., GCN 40060), and AstroSat CZTI (Tembhurnikar et al., GCN 40077) GRB 250403A using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. The 300V grism with no order-blocking filter was adopted, covering the wavelength range 3300-9600 AA (with potential second-order contamination redward of 6600 AA). Observations started on 2025 April 4 at 02:15:01 UT (10.99 hr after the burst). Two exposures of 600 s each were obtained. From a 60 s acquisition image obtained on 2025 April 4 at 02:01:37 UT (10.76 hr after the burst), we measure R ~ 21.1 +/- 0.2 mag (AB) calibrated against nearby Pan-STARRS objects. From a preliminary reduction of the spectrum, continuum is detected over the wavelength range 3600-9600 AA. While the spectrum is noisy blueward of 3720 AA, we can set an upper limit to the redshift z < 2.06 due to the lack of Lyman forest. Four clear absorption features are apparent in clean regions of the spectrum, three of which match Si IV 1393, Si IV 1402 and the (blended) C IV doublet 1548,1550 at a common redshift z = 1.847. The fourth line seems marginally split and could be an intervening C IV doublet at z = 1.763, although no other features are seen to confirm this value. The observed absorption system is somewhat peculiar (but not unprecedented), as some typically strong low-ionization features common in long GRB spectra (de Ugarte Postigo et al. 2012, doi:10.1051/0004-6361/201219894) are either non-detected or only marginally detected. This indicates a high-ionization environment, which has been previously linked to systems with low H I column density (e.g. Jakobsson et al. 2006, doi:10.1051/0004-6361:20066405; Thoene et al. 2011, doi:10.1111/j.1365-2966.2011.18408.x; Vielfaure et al. 2020, doi:10.1051/0004-6361/202038316). We thus consider z = 1.847 a viable possibility, and the most likely redshift of GRB 250403A. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Matias Jones, Claudia Paladini, Jesus Corral-Santana, and Cecilia Bustos. View this GCN Circular online at https://gcn.nasa.gov/circulars/40162. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38187] IceCube-250416A: DDOTI Optical Observations
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40161 SUBJECT: IceCube-250416A: DDOTI Optical Observations DATE: 25/04/17 14:21:17 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report: We observe the field of the IceCube-250416A (bronze) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-17 UTC. DDOTI observed from 03:20 UTC to 04:31 UTC (from T+8.8 h to T+10.0 h after the trigger) with a total exposure of 24 min, alternating with other scientific programs. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues and after performed image subtraction against PanSTARRS PS1 DR2, we detect no uncatalogued sources within the observed field to an average 5-sigma limiting AB magnitude of: w > 20.5. This value has not been corrected for Galactic extinction (A_r∼1.7 mag; Schlafly et al. 2011). We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/40161. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38186] EP250416a: Gemini South-GMOS optical counterpart
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40160 SUBJECT: EP250416a: Gemini South-GMOS optical counterpart DATE: 25/04/17 10:42:52 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> Andrew J. Levan (Radboud), Jonathan Quirola-Vásquez (Radboud), Peter G. Jonker (Radboud), Franz E. Bauer (UTA), Antonio Martin-Carrillo (UCD), Daniele B. Malesani (DAWN/ NBI and Radboud), Javi Sánchez-Sierras (Radboud), Agnes van Hoof (Radboud), Jennifer Chacon (PUC), Joyce van Dalen (Radboud), Gregory Corcoran (UCD) report on behalf of a larger collaboration: We observed the field of the Einstein Probe (EP) transient EP250416a (Zhao et al., GCN 40154) using the Gemini South-GMOS in imaging mode located on Cerro Pachón, Chile. Photometric observations started at 2025-04-17 06:51:03 UTC (i.e., ~0.54 days after the EP detection), consisting of 4 exposures of 60 s each, carried out using filter r'. Consistent with the position of the X-ray source detected by XRT (target ID 19721, PI J. Kennea; https://www.swift.ac.uk/EP/) and the EP/FXT localization, we notice a source at coordinates measured from the WCS-calibrated Gemini image: RA = 17:05:40.83 Dec = +25:46:31.5 This source had magnitude r = 22.8 +/- 0.1 (AB), calibrated against the Pan-STARRS objects in the field. An underlying, fainter source is catalogued in the Legacy Survey (DR10; Dey et al. 2019), with a quoted magnitude of r = 23.16 and photometric redshift of 0.72+-0.24 (Zhou et al. 2021). Based on the position and brighter magnitude relative to the previously catalogued object, we conclude that the source is very likely the optical counterpart of EP250416a. We acknowledge excellent support from the Gemini South staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/40160. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38185] EP250225a: SVOM/VT optical brightening
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40159 SUBJECT: EP250225a: SVOM/VT optical brightening DATE: 25/04/17 07:50:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> X. H. Han(NAOC), L. Zhang(IHEP), X. L. Chen(YNU), Y. D. Hu(GXU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the fast X-ray transient EP250225a (Jiang et al., GCN 39475). The observation started on 2025 Feb 26 09:37:03 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. The candidate (Malesani et al., GCN 39516; Malesani et al., GCN 39573) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 21.80 | VT_B | 3000 | 22.31 | 0.13 21.80 | VT_R | 3000 | 21.50 | 0.10 The source was brightening with about 0.4 mag within 3.3 hours in both channels during our observations. This result is consistent with the report of the brightening compared with the archival brightness in the Legacy survey (Malesani et al., GCN 39516). 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/40159. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38184] SVOM/sb25041603 is not a GRB
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40158 SUBJECT: SVOM/sb25041603 is not a GRB DATE: 25/04/17 07:50:32 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: SVOM/ECLAIRs triggered on the X-ray transient labelled sb25041603 (SVOM burst-id sb25041603, Wang et al. GCN 40147). The field was observed by SVOM/MXT starting at T0 = 2025-04-16T08:57:43 (2.5 hour after trigger time Tb). MXT observed during 3 orbits for 3.0 ks effective exposure. Using the full X-band dataset, we find a source located at RA=183.889, Dec=52.6534 RA (J2000) = 12h15m33 Dec (J2000) = +52d39m12.3 with a statistical 90% C.L. radius of 39", to which a 35” systematic uncertainty is to be added in quadrature. That position matches the M4V star [StKM 2-809](https://simbad.cds.unistra.fr/simbad/sim-id?Ident=%40568434&Name=StKM%202-809), and exclude the potential counterparts V* EG UMa and 2MASS J12161363+5242459 mentioned in GCN 40147. The spectrum is modelled by an absorbed thermal component with a Gaussian distribution of emission measure (`Tbabs*gadem` in xspec). The absorption column is NH = 5 (<10) x 1e20 /cm2 (90% C.L. uncertainties) and a broad distribution of temperature with a mean value of 2.7 (+/- 0.8) keV. The observed average flux in the 0.3-5 keV band is 2.2 (+/-0.4) x1e-11 erg/cm2/s. At the parallactic distance of 25 pc of StKM 2-809, this translates to a luminosity of 1.6e30 erg/s, consistent with a flare from a low-mass main sequence star. Over the 3 orbits the source was fading, from 3.1e-11 erg/cm2/s in the first half to 0.3e-11 erg/cm2/s in the second half. We conclude that SVOM/sb25041603 is likely not a GRB but a flare from the M4V star StKM 2-809. The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this trigger is Ziqi Wang (zq.wang(a)st.gxu.edu.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40158. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38183] EP250416a: GSP optical upper limit
by GCN Circulars 17 Apr '25

17 Apr '25

TITLE: GCN CIRCULAR NUMBER: 40157 SUBJECT: EP250416a: GSP optical upper limit DATE: 25/04/17 06:06:13 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> W. X. Li, S. J. Xue (NAOC), M. Andrews, J. Farah, D. A. Howell, M. Newsome, E. Padilla Gonzalez, C. McCully, and G. Terreran (Las Cumbres Observatory), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP250416a by the Einstein Probe (Zhao et al., GCN 40154), we initiated observations of its location starting on 2025 April 17th at 01:43 UT (~8 hours after the EP/WXT trigger) in the i band. These observations were conducted using the 1-meter telescope at the Las Cumbres Observatory node located at Siding Spring Observatory in Australia. No new optical source was detected in the co-added images within the EP/FXT error box down to ~20 mag. These observations were taken as part of the Global Supernova Project. View this GCN Circular online at https://gcn.nasa.gov/circulars/40157. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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