TITLE: GCN CIRCULAR
NUMBER: 41346
SUBJECT: GRB250812a: STEP/T80S Indication of slow decay of afterglow
DATE: 25/08/13 15:31:30 GMT
FROM: André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos(a)gmail.com>
A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration:
We conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the faint, long gamma-ray burst GRB250812A discovered by the SVOM/ECLAIRs instrument (GCN 41322). The T80S observations started on Aug 13 08:36:48 UT (~30 hours after the trigger). We obtained images totaling 600s (2x300s) in r-band and in i-band with the T80S camera centered at the position of the optical afterglow detection reported in He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328) and Freeberg et al. (GCN 41331). Subtracting DECam template images from the T80S individual frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position.
MJD Filter Magnitude Uncertainty
60900.358890 r 19.816 0.127
60900.362940 r 19.925 0.111
60900.366880 i 19.438 0.087
60900.370920 i 19.589 0.094
The reported magnitudes in r and i-bands 30 hours post burst in template-subtracted images indicate a slow decay for the afterglow. We encourage further follow-up observations to better characterize the transient and the source of its optical emission.
We acknowledge the T80S technical team with the provided support during the night.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41346.
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TITLE: GCN CIRCULAR
NUMBER: 41345
SUBJECT: EP250812a: NOT, NTT, and GS observations
DATE: 25/08/13 15:23:05 GMT
FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com>
A. P. C. van Hoof (Radboud), J. A. Quirola-Vasquez (Radboud), J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), L. Cotter (UCD), M. Fraser (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP250812a (Zhang et al., GCN 41327, GCN 41339) using the Nordic Optical Telescope (NOT, equipped with the ALFOSC camera), the New Technology Telescope (NTT, with the EFOSC2 instrument), and the Gemini South Telescope (GS, with the FLAMINGOS2, F2, instrument).
Observations with NTT were also carried out in the r filter (3x600 s) starting on 2025-08-13 05:22:07.8 UT, i.e., ~16.2 hr after the trigger. Moreover, NOT and NTT observations were carried out in the z filters (15x80 s and 6x300 s) starting on 2025-08-13 05:31:57.8 and 2025-08-13 05:40:17.2 UT, i.e, ~16.4 and 16.5 hr after the X-ray trigger, respectively. The GS-F2 visited the field using the H filter (20x10 s) starting on 2025-08-13 07:35:11.0 UT, i.e.,~18.4 hr after the trigger.
At the location of the transient reported by Zhang et al. (GCN 41327) and the optical counterpart from SVOM/VT reported by Xin et al. (GCN 41340) and from COLIBRI (Ducoin et al., GCN 41342), also consistent with the EP/FXT (Zhang et al., GCN 41339) and Swift/XRT positions (Evans et al., GCN 41330), no source is detected, down to 3-sigma limiting magnitudes:
H > 22.0 (GS)
z > 22.5 (NOT)
z > 22.3 (NTT)
r > 22.6 (NTT)
These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS and 2MASS catalogues and not corrected by galactic extinction.
We thank the excellent support from the observing staff at Gemini (especially Cinthya Rodrigez), NOT (in particular Emil Knudstrup), and NTT (in particular Pablo Arias).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41345.
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TITLE: GCN CIRCULAR
NUMBER: 41344
SUBJECT: GRB 250812A: Swift/UVOT Detection
DATE: 25/08/13 15:15:44 GMT
FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu>
M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250812A 6.5 ks after the SVOM/ECLAIRs trigger (Xin et al., GCN Circ. 41322). An uncatalogued source consistent with the XRT position (Sbarrato et al., GCN Circ. 41325) and the optical transient (He et al., GCN Circ. 41324; Xin et al., GCN Circ. 41326; Rakotondrainibe et al., GCN Circ. 41328; Freeberg et al., GCN Circ. 41333) is detected in the UVOT exposures. However, we note that the source shows no evidence of fading in the 67 ks between the two Swift epochs.
The preliminary UVOT position is:
RA (J2000) = 02:11:13.68 = 32.80701 (deg.)
Dec (J2000) = -43:09:49.1 = -43.16363 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
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 6500 12380 1479 19.43+/-0.12
u 73801 90784 695 19.48+/-0.13
v 74444 91365 424 >19.24
white 74122 91182 695 19.96+/-0.10
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.012 in the direction of the burst
(Schlegel et al. 1998).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41344.
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TITLE: GCN CIRCULAR
NUMBER: 41342
SUBJECT: EP250813a: COLIBRÍ detection of the VT candidate and evidence of flattening
DATE: 25/08/13 13:44:03 GMT
FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it>
Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (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 the EP250812a (Zhang et al., GCN Circ. 41327, 41339) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-13 08:00
to 10:21 UTC (from 18.8 to 21.2 hours after the trigger) and obtained 96 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.
In the stacked image, we marginally detect the VT candidate (Xin et al., GCN Circ. 41330), which is also consistent with the XRT Source 1 position (Evans et al., GCN Circ. 41340), at:
i = 22.5 +/- 0.3
This value is similar to the second observation reported by VT (Xin et al., GCN Circ. 41330) at T + 14.34 h, but brighter than in the Legacy Survey DR10 catalog (Dey et al. 2019):
i = 23.5 +/- 0.1
Therefore, we suggest that the candidate is indeed the afterglow of EP250812a and that it showed evidence of a flattening in its evolution at the time of our observations.
Further observations and analysis are ongoing.
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/41342.
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TITLE: GCN CIRCULAR
NUMBER: 41341
SUBJECT: EP250812a: Liverpool Telescope upper limits
DATE: 25/08/13 10:28:50 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 the fast X-ray transient EP250812a (Zhang et al., GCN 41327) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x100s exposures in the SDSS r’ and z’ filters starting at 2025-08-13 03:13:06 UT, approximately 14 hours after the trigger.
We do not detect any new objects within the EP/FXT error region of the transient (Zhang et al., GCN 41327; Zhang et al., GCN 41339). The 3-sigma limiting magnitudes on the stacked images are r > 21.71 mag and z > 21.53 mag. This is in agreement with the detection of an optical counterpart candidate by SVOM/VT at VT_R = 22.74 ± 0.15 at 14.3 hours (Xin et al., GCN 41340).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41341.
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TITLE: GCN CIRCULAR
NUMBER: 41340
SUBJECT: EP250812a: SVOM/VT optical counterpart
DATE: 25/08/13 09:40:18 GMT
FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn>
L. P. Xin, H. L. Li, Y. N. Ma, Y. L. Qiu, C. Wu, Z. H. Yao, 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 two Target of Opportunity observations of EP250812a detected by EP/WXT (Zhang et al., GCN 41327). The first epoch is from 2025-08-12T20:32:53 UTC, 7.38 hours after the EP trigger time. The second epoch is from 2025-08-13T01:47:59, 12.64 hours post the trigger.
No any uncatalogued sources, compared to Lagecy survey, was found using VT X-band data, within the errorbox of EP/FXT (Zhang et al., GCN 41327, GCN 41339) or Swift/XRT (Evans et al., GCN 41330).
However, there is a cataloged source in Legacy survey within the errorbox of Swift/XRT source1 with a distance of 3.4 arcseconds at R.A.=30.993037 Dec=-9.318883 degrees:
RA (J2000) = 02:03:58.329
Dec (J2000) = -09:19:07.98
with an uncertainty of 0.5 arcsec.
The cataloged source was detected in both VT_B and VT_R images. The magnitudes are derived as below:
DeltaT(Mid time) | exposure time (s) | band | mag (AB) | mag err
---------------------- |-------------------|------|----------|--------
7.62 hours | 26*70 | VT_B | 22.52 | 0.15
7.62 hours | 26*70 | VT_R | 22.04 | 0.12
14.34 hours | 75*70 | VT_B | 23.10 | 0.16
14.34 hours | 67*70 | VT_R | 22.74 | 0.15
Our photometry is not corrected for Galactic extinction.
Given the fading of the source in our observations, we proposed that it is the counterpart of the transient.
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/41340.
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TITLE: GCN CIRCULAR
NUMBER: 41339
SUBJECT: EP250812a: refined analysis of the EP-WXT and EP-FXT observations
DATE: 25/08/13 08:57:14 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
M.H. Zhang (NAO, CAS), H. Zhou (PMO, CAS), W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:
The X-ray transient EP250812a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 41327). Refined analysis of the WXT data shows that the event started at T0=2025-08-12 13:10:18 (UTC) and lasted for about 37 s before the interruption of the autonomous follow-up. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 2.5 x 10^20 cm^-2 and a photon index of 1.0 (-0.3/+0.3). The derived average unabsorbed 0.5-4 keV flux is 6.7(-0.8/+0.8) x 10^(-10) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 111 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 30.9931, DEC = -9.3191 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 2.5 x 10^20 cm^-2 and a photon index of 2.21 (-0.18/+0.20). The absorption from the host galaxy cannot be constrained. The derived average unabsorbed 0.5-10 keV flux is 1.97 (-0.13/+0.21) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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/41339.
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TITLE: GCN CIRCULAR
NUMBER: 41338
SUBJECT: IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
DATE: 25/08/13 08:05:29 GMT
FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu>
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
On 2025-08-13 03:21:09.69 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.0759 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection.
After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141240_9390028.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:
Date: 2025-08-13
Time: 03:21:09.69 UT
RA: 275.36 (+0.84, -0.94 deg 90% PSF containment) J2000
Dec: 8.27 (+0.79, -0.75 deg 90% PSF containment) J2000
We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.
No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu
View this GCN Circular online at https://gcn.nasa.gov/circulars/41338.
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