GRB250813B

This page lists all entries on GRB250813B in GRBweb

Summary Fermi GBM GCN 41353 GCN 41354 GCN 41355 GCN 41359 GCN 41363 GCN 41368 GCN 41369 GCN 41370 GCN 41376 GCN 41383 GCN 41388 GCN 41394 GCN 41412 GCN 41449

Summary table
Variable Value Source
GRB_name_Fermi GRB250813952
T0 22:51:11.236 UTC Fermi_GBM
ra 336.7505° GCN_circulars,Swift-XRT Other
decl 12.4613° GCN_circulars,Swift-XRT Other
T90 24.064 s Fermi_GBM
T90_error 0.362 s Fermi_GBM
T90_start 22:51:12.772 UTC Fermi_GBM
fluence 1.40e-05 erg/cm² Fermi_GBM
fluence_error 3.80e-08 erg/cm² Fermi_GBM
redshift 1.7520 GCN_circulars,Optical
T100 25.6 s
GBM_located False
mjd 60900.95221337963 Fermi_GBM
Fermi GBM table
GRB_name_Fermi GRB250813952
trigger_name bn250813952
ra 336.7279°
decl 12.4981°
datum 2025-08-13
t_trigger 22:51:11.236 UTC
T90 24.064 s
T90_error 0.362 s
T90_start 22:51:12.772 UTC
fluence 1.40e-05 erg/cm²
fluence_error 3.80e-08 erg/cm²
flux_1024 8.06e+00 erg/cm²/s
flux_1024_error 3.26e-01 erg/cm²/s
flux_1024_time 1.07e+01 erg/cm²/s
flux_64 1.03e+01 erg/cm²/s
flux_64_error 1.45e+00 erg/cm²/s
GCN 41353 table
GRB_name GRB250813B
GCN_number 41353
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41353 SUBJECT: GRB 250813B: Ondrejov D50 optical afterglow detection DATE: 25/08/14 00:09:05 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov)report:We observed the position of the SVOM-detected GRB 250813B (Xie et al., GCN 41352) with the D50 robotic telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We performed a series of 10s unfiltered exposuresstarting at 22:52:44.496 UT, i.e. 93.5s after the trigger.We detect the optical afterglow at 22:27:00.15 +12:27:44.5 (J2000), consistent with both the ECLAIRs localization (Xie et al., GCN 41352) and the refined MXTX-ray position. The source is clearly detected in single 10s unfiltered images.
GCN 41354 table
GRB_name GRB250813B
GCN_number 41354
Detection_method correction
Circular_text TITLE: GCN CIRCULAR NUMBER: 41354 SUBJECT: GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352). DATE: 25/08/14 00:40:48 GMT FROM: SVOM_group W.J. XIE (NAOC), B.T. WANG (YNAO, CAS), O. Godet, H. Yang (IRAP), H. Goto (CEA, Kanazawa univ.), F. Robinet (IJCLAB), L. Zhang (IHEP) This GCN circular is the correction version for the GCN 41352. We sorry for the mistake in the GCN 41352, where the GRB name shall be GRB 250813B but not GRB 250813A. At 2025-08-13T22:51:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250813B (SVOM burst-id sb25081303). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 92.23 in the [8-120] keV energy band over a time window of 20.4 seconds starting at 2025-08-13T22:51:15. The localization of the best alert is R.A., Dec. 336.728, 12.498 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-13T22:51:11 on a timescale of 1 second with an SNR of 8. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-13T22:54:00 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 336.7591, 12.4479 degrees: R.A. (J2000) = 22h27m02.19s Dec. (J2000) = 12d26m52.70s with a 90% C.L. radius of 71 arcseconds including systematics. This location is 3.51 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Wenjin XIE (xiewj@bao.ac.cn). Please contact the BA by email if you require additional information.
GCN 41355 table
GRB_name GRB250813B
GCN_number 41355
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41355 SUBJECT: GRB 250813B: Ondrejov D50 fast decay DATE: 25/08/14 00:46:58 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov) report: Further to our earlier report (GCN 41353), we provide refined photometric analysis of the optical afterglow of GRB 250813B (Xie et al., GCN 41352). Our photometry reveals an extremely rapid decay with the afterglow fading from the initial magnitude of ~14.4 at ~100s post-trigger to near magnitude 20 at 0.03 days (43 minutes) after the trigger. This represents a fade of approximately 5.6 magnitudes in less than one hour and an average decay rate of ~1.8. Potential observers should note the rapid evolution when planning follow-up observations.
GCN 41359 table
GRB_name GRB250813B
GCN_number 41359
Detection_method Swift-XRT Other
ra 336.7505°
decl 12.4613°
Circular_text TITLE: GCN CIRCULAR NUMBER: 41359 SUBJECT: GRB 250813B: Swift-XRT afterglow detection DATE: 25/08/14 08:09:11 GMT FROM: K.L. Page at U Leicester K.L. Page, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for GRB 250813B, from 9.6 to 16.3 ks after the SVOM/ECLAIRs trigger (GCN Circ. 41354). The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 336.7505, +12.4613 which is equivalent to: RA (J2000): 22 27 00.13 Dec(J2000): +12 27 40.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). There is no evidence for fading during this interval, with the X-ray source showing a mean count rate of 0.17 +/- 0.02 count s^-1. However, the localisation of this source is consistent with the fading optical afterglow found by Ondrejov D50 (GCN Circ. 41353, 41355) and SVOM/COLIBRI (GCN Circ. 41356), and so we consider it the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+0.4, -0.3). The best-fitting absorption column is 2.5 (+1.3, -1.1) × 10^21 cm^-2, in excess of the Galactic value of 6.2 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 6.2 x 10^-12 (9.3 x 10^-12) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.5 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Photon index: 2.1 (+0.4, -0.3) This circular is an official product of the Swift-XRT team.
GCN 41363 table
GRB_name GRB250813B
GCN_number 41363
Detection_method Optical
redshift 1.7520
Circular_text TITLE: GCN CIRCULAR NUMBER: 41363 SUBJECT: GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752 DATE: 25/08/14 10:29:14 GMT FROM: Gregory Corcoran at University College Dublin B. Schneider (LAM), G. Corcoran (UCD), E. Le Floc’h (CEA), A. de Ugarte Postigo (LAM), J. An (NAOC), A. L. Thakur (INAF-IAPS), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration: We observed the optical afterglow (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356) of GRB 250813B detected by SVOM/ECLAIRs (Xie et al., GCN 41352; Xie et al., GCN 42354) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In images taken with the acquisition camera on Aug 14 05:40 UT (6.82 hr after the ECLAIRs trigger), the optical afterglow is clearly detected in g, r, and z bands. We measured a preliminary magnitude r = 22.24 +/- 0.06 AB (calibrated against the Pan-STARRS PS1 catalog). Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-14 at approximately 05:50 UT (6.98 hr after the SVOM trigger). In a preliminary reduction of the spectra, we detect a faint continuum down to ~3590 AA at the blue end. From the detection of a multitude of absorption lines, which we interpret as due to C II, Si IV, Si II, C IV, C I, Al II, Al III, Mn I, Fe II, Fe II*, Mn II, Mg II, Mg I, Ca II, we infer a redshift of z = 1.752. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Romero, and Akke Corporaal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN 41368 table
GRB_name GRB250813B
GCN_number 41368
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41368 SUBJECT: Subject GRB 250813B: SVOM/MXT refined analysis DATE: 25/08/14 11:45:54 GMT FROM: Diego Gotz at CEA D. Götz (CEA), F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), M. Moita (CEA), C. Plasse (CEA), , C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 250813B (Xie et al. GCN 41352/41354) was observed by SVOM/MXT after an automatic SVOM slew, starting at T0 = 2025-08-13T22:54:01, 169 s after trigger time Tb. MXT observed for the remainder of the orbit, cumulating 188 s of useful data before entering Earth occultation. Using the full X-band dataset of the first orbit, the position of the MXT afterglow is refined to: R.A. (J2000) = 22h26m58.6s Dec (J2000) = +12d27m08s with a 90% C.L. radius of 54 arc sec (including 25 arcseconds systematic error added in quadrature). This position is at 47 arc sec from the optical counterpart reported in GCN 41353. The light curve exhibits an initial fast fading with temporal decay of -2.3+/-0.5. We analysed the early time (first orbit) spectrum and modelled it with a redshifted (z=1.75 GCN 41363) absorbed power-law, a photon index Gamma 1.4+-/0.3 at 90% C.L and a redshifted absorbing column of NH = <0.8x1e22 cm^-2 on top of a Galactic NH = 4.86x10^20 cm^-2. The source is still detected on the subsequent orbit between Tb+3900 and Tb+6100 s but not after. 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 burst is Wenjin Xie (xiewj@bao.ac.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN 41369 table
GRB_name GRB250813B
GCN_number 41369
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41369 SUBJECT: GRB 250813B: SVOM/VT optical observations DATE: 25/08/14 12:16:34 GMT FROM: Liping Xin at NAOC, SVOM L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), B. T. Wang (YNAO) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst GRB 250813B triggered by SVOM/ECLAIRs (Xie et al., GCN 41354). SVOM/VT start the observations at 278 seconds after the burst, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Jelinek et al., GCN 41353 & GCN 41355; Schneider et al., GCN 41363; de Ugarte Postigo et al., GCN 41356) at the position consistent with the locations of Swift/XRT (Page et al., GCN 41359), EP/FXT (Wu et al., GCN 41361) and SVOM/MXT(Xie et al., GCN 41354, Gotz et al., GCN 41368), was clearly detected in both VT_R and VT_B. During the X-band data available, the brightness was fading from VT_R=16.61+/0.02 mag and VT_B=17.73+/-0.03 mag at 303 seconds post the burst to VT_R=20.9+/-0.1 mag and VT_B=22.1+/-0.2 mag at 4.27 hours after the burst. 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. The SVOM point of contact for this burst is Wenjin Xie (xiewj@bao.ac.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN 41370 table
GRB_name GRB250813B
GCN_number 41370
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41370 SUBJECT: GRB 250813B: NOT observations of the optical afterglow DATE: 25/08/14 12:18:54 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group G. Corcoran (UCD), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), B. P. Gompertz (Birmingham), V. Vuolteenaho (Univ. of Oulu), report on behalf of a larger collaboration: We observed the field of the SVOM/ECLAIRs GRB 250813B (Xie et al., GCN 41352; Xie et al., GCN 42354), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 6x150 s exposures in the r-band and 5x200 s in the z-band, starting at 2025-08-14 00:05:04 UT (1.231 hr after the trigger). The optical afterglow reported by Jelinek et al. (GCN 41355), de Ugarte Postigo et al. (GCN 41356), Schneider et al. (GCN 41363) and Xin et al. (GCN 41369) is well detected with a preliminary magnitude of r = 21.00 +/- 0.08 (AB, mid-time 1.379 hr after trigger); z = 20.04 +/- 0.09 (AB, mid-time 1.689 hr after trigger). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction.
GCN 41376 table
GRB_name GRB250813B
GCN_number 41376
Detection_method Fermi GBM Det
t_trigger 22:51:11.240 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 41376 SUBJECT: GRB 250813B: Fermi GBM Observation DATE: 25/08/14 19:17:11 GMT FROM: Jacob Smith at Fermi-GBM Team Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 22:51:11.24 UT on 13 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250813B (trigger 776818276/250813952), which was also detected by SVOM/ECLAIRs (W.J. Xie, et al. 2025, GCN 41354). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. An optical afterglow was first reported by Ondrejov D50 (M. Jelinek, et al. 2025, GCN 41353) which also reports an extremely rapid decay (M. Jelinek, et al. 2025, GCN 41355). A redshift of z=1.752 was report by the VLT (B. Schneider, et al. 2025, GCN 41363). The angle from the Fermi LAT boresight is 99 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 24.1 s (50-300 keV). The time-averaged spectrum from T0-3.8 to T0+31.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.82 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 114 +/- 3 keV. A Band function fits equally well with Epeak = 112 +/- 4, alpha = -0.81 +/- 0.04, and beta = -3.67 +/- 0.79. The event fluence (10-1000 keV) in this time interval is (1.30 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+11 s in the 10-1000 keV band is 8.1 +/- 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/
GCN 41383 table
GRB_name GRB250813B
GCN_number 41383
Detection_method Swift-XRT Other
ra 336.7280°
decl 12.4980°
redshift 1.7520
Circular_text TITLE: GCN CIRCULAR NUMBER: 41383 SUBJECT: GRB 250813B: SVOM/GRM observation DATE: 25/08/15 07:23:53 GMT FROM: tanwj@ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250813B (SVOM burst-id sb25081303) at 2025-08-13T22:51:12UTC (T0), which is also detected by SVOM/ECLAIRs (W.J. XIE et al., GCN #41354), Swift-XRT (K.L. Page et al., GCN #41359), EP-FXT (Q. Y. Wu et al., GCN #41361), SVOM/MXT (D. Götz et al., GCN #41368) and FERMI/GBM (Jacob Smith et al., GCN #41376) With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 24.9 +/-0.76 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250813B.png With this localization given by SVOM/ECLAIRs (RA= 336.728, DEC= 12.498, GCN #41354), the time-averaged spectrum from T0-6 to T0+35 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.84 +/-0.07 and the cutoff energy, parameterized as Epeak, is 109 +6/-5 keV. The event fluence (10-1000 keV) in this time interval is (1.35 +/-0.20)E-05 erg/cm^2. With the redshift z = 1.752 by VLT/X-shooter (B. Schneider et al., GCN#41363), the Eiso (from 1 keV to 10 MeV in rest frame) of this burst is (1.16 +0.20/-0.18)E53 erg. GRB 250813B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250813B_amati.png 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 point of contact for this burst is: Wen-Jun Tan (IHEP)(tanwj@ihep.ac.cn)
GCN 41388 table
GRB_name GRB250813B
GCN_number 41388
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41388 SUBJECT: GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit DATE: 25/08/15 10:13:58 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We imaged the field of GRB 250813B detected by SVOM/ECLAIRs telescope (Xie et al. GCN 41352 - 41354), with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-08-14 00:02 UT (approximately 1.19 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with partially clear skies and Moon (illumination: 74%, distance: 42°). We co-added 93 exposures of 60 sec each. Start T0+ End T0+ CR lim 1.19 hour 4.44 hour 20.1 We did not found any optical counterpart in the error box of the XRTcandidate (Page et al. GCN 41359). Magnitudes were estimated with the PanSTARRS cat. and are not corrected for galactic dust extinction. Our observations are consistent with other already reported Jelinek et al. (GCN 41355), Gill et al. (GCN 41356), Corcoran et al. (GCN 41370). The message may be cited.
GCN 41394 table
GRB_name GRB250813B
GCN_number 41394
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 41394 SUBJECT: GRB 250813B: Liverpool Telescope optical upper limits DATE: 25/08/15 14:54:03 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report: Using the IO:O imager on the 2.0 m Liverpool Telescope, we observed the field of the SVOM/ECLAIRs–triggered GRB 250813B (Xie et al., GCNs 41352, 41354), also detected by EP–FXT (Wu et al., GCN 41361), SVOM/MXT (Götz et al., GCN 41368), Fermi/GBM (Smith et al., GCN 41376), and SVOM/GRM (Tan et al., GCN 41383). Observations in the r and z bands were obtained on 2025-08-15 at 02:42:32.1 UT and 03:13:37.8 UT, corresponding to ~1.16 and ~1.18 days post-trigger, respectively. Each band consisted of 3 × 600 s exposures. We do not detect the optical afterglow of GRB 250813B (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356; Schneider et al., GCN 41363; Xin et al., GCN 41369; Corcoran et al., GCN 41370) down to limiting magnitudes of r >22.0 and z >20.6. Photometric calibration was performed using Pan-STARRS stars. The quoted magnitudes are not corrected for Galactic extinction in the direction of the GRB.
GCN 41412 table
GRB_name GRB250813B
GCN_number 41412
Detection_method Fermi GBM Other
redshift 1.7520
Circular_text TITLE: GCN CIRCULAR NUMBER: 41412 SUBJECT: GRB 250813B: SVOM/ECLAIRs refined analysis DATE: 25/08/18 15:48:24 GMT FROM: SVOM_group M. Brunet, O. Godet, H. Yang (IRAP), W.J. Xie (NAOC), B.T. Wang (YNAO, CAS) report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250813B (SVOM burst-id sb25081303). The burst that triggered ECLAIRs onboard (Xie et al. GCN 41352/[41354](https://gcn.nasa.gov/circulars/41354?view=index&query=250813B&startDate=&endDate=&sort=circularID)) consists of multiple peaks. By considering only the data before the slew of the platform, the T90-value is 26.8 +0.4/-0.5 s in the 4-120 keV energy band. We note that ECLAIRs detected some emission up to at least T0+90s (T0 = 2025-08-13T22:51:12 UTC). The time-averaged spectrum from T0-5.5 s to T0+36 s in the energy range 4-120 keV is best fitted by a cutoff power law. The powerlaw index is -0.936 +0.031/-0.032 and the cutoff energy, parameterized as Epeak, is 104 +12/-10 keV. With this model, the total fluence in 4-120 keV is (1.10 +0.01/-0.03)e-5 erg/cm^2. With a redshift of z = 1.752 (Schneider et al., GCN 41363), the burst isotropic energy Eiso (from 1 keV to 10 MeV in its rest frame) is (1.34 +0.07/-0.08)e53 erg, which makes this GRB consistent with type II GRBs in the 'Amati' relation diagram (Amati et al. 2002). We note that the ECLAIRs results are consistent within the errors with those provided by both SVOM/GRM (Tan et al., GCN 41383) and Fermi/GBM (Smith et al., GCN 41376). All quoted errors are at the 68% confidence level. We note that the calibration of SVOM/ECLAIRs is ongoing thus these results are preliminary. 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 GCN circular is Marius Brunet: (marius.brunet AT irap.omp.eu).
GCN 41449 table
GRB_name GRB250813B
GCN_number 41449
Detection_method Swift-UVOT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 41449 SUBJECT: GRB 250813B: Swift/UVOT Upper Limit DATE: 25/08/20 15:17:24 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250813B 9.6 ks after the SVOM/ECLAIRs trigger (Xie et al., GCN Circ. 41352). We do not detect any afterglow consistent with the XRT position (Page et al., GCN Circ. 41359) or optical position (Jelinek et al., GCN Circ. 41355). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 9599 16347 1576 >21.07 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.072 in the direction of the burst (Schlegel et al. 1998).