GRB 250727A
GCN Circular 41208
Subject
GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
Date
2025-07-31T05:57:17Z (24 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato
(INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), S.
Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:
We have analysed 5.9 ks of XRT data for GRB 250727A, from 2.4 ks to
300.7 ks after the SVOM/ECLAIRs trigger. The data are entirely in
Photon Counting (PC) mode. During this second observation, source 1
(SWIFT J234539.1-811248) given in GCN Circ. 41180 is found to have
faded at the 3.7-sigma level, so we believe this to be the X-ray
afterglow. We also note that EP-FXT found this source to have faded
(GCN Circ. 41199).
Using 1353 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 = 356.41475, -81.21390 which is
equivalent to:
RA (J2000): 23h 45m 39.54s
Dec(J2000): -81d 12' 50.1"
with an uncertainty of 4.3 arcsec (radius, 90% confidence). The source
is fading with alpha >0.3.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00019965.
This circular is an official product of the Swift-XRT team.
GCN Circular 41199
Subject
GRB 250727A: EP-FXT follow-up observation
Date
2025-07-30T06:15:15Z (25 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (NJU), R. D. Liang, W. Yuan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250727A (SVOM/sb25072701) (Cao et al. GCN 41176) at 2025-07-29T10:57:54 (UTC), about 48 hours after the SVOM/ECLAIRs trigger, with an exposure time of 3878s. Three FXT candidate sources (Yin et al. GCN 41182) are not detected in this observation. The upper limits are listed as follows.
Source 1: EPF_J234436.3-810410
RA (J2000): 356.1514
Dec (J2000): -81.0694
Flux upper limit: 8.78 x 10^-14 erg/s/cm2 (0.5-10 keV)
Source 2: EPF_J234357.8-811244
RA (J2000): 355.9909
Dec (J2000): -81.2121
Flux upper limit: 1.03 x 10^-13 erg/s/cm2 (0.5-10 keV)
Source 3: EPF_J234541.4-811245
RA (J2000): 356.4225
Dec (J2000): -81.2124
Flux upper limit: 6.40 x 10^-14 erg/s/cm2 (0.5-10 keV)
Note: This source is spatially consistent with the candidate counterpart Source 1 (SWIFT J234539.1-811248) detected by Swift/XRT.
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).
GCN Circular 41193
Subject
GRB 250727A: SVOM/ECLAIRs refined analysis
Date
2025-07-29T08:16:33Z (25 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. G. Bernardini (INAF-OAB, LUPM), N. Dagoneau, D. Turpin (CEA), J.-L. Atteia, M. Brunet (IRAP), L. P. Xin (NAOC), J. X. Cao (GXU)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250727A (SVOM burst-id sb25072701).
The burst that triggered ECLAIRs onboard (Cao et al. GCN 41176) consists of a long soft bump detected mainly below 30 keV, with a duration of T90 = (115.1 -8.2 +14.2) s in the 4-30 keV energy band.
The time-averaged spectrum from T0-10 s to T0+100 s (T0 = 2025-07-27T10:55:41.923s) in the energy range 5-50 keV is best fitted by a powerlaw model with index 2.3+/-0.4. With this model, the total 4-50 keV fluence is (1.4+/-0.1)e-7 erg/cm^2.
The spectrum can be equally fit by a blackbody model with temperature 2.4+/-0.5 keV. With this model, the total 4-50 keV fluence is (1.1+/-0.1)e-7 erg/cm^2.
All the quoted errors are at the 68% confidence level.
We note that the calibration of SVOM/ECLAIRs is undergoing 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 burst is: Maria Grazia Bernardini (INAF-OAB, LUPM) (maria.bernardini at inaf.it)
GCN Circular 41184
Subject
GRB 250727A: AST3-2 Upper limit
Date
2025-07-28T10:02:21Z (a month ago)
From
Tianrui Sun at Purple Mountain Obs,CAS <trsun@pmo.ac.cn>
Via
Web form
Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Yi-Qiao Yang, Xiao-Yan Li(Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team:
Following the detection of GRB 250727A by ECLAIRs onboard SVOM (Cao et al., GCN 41176),
we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173°, Long. 77.0950°).
Observations began at 2025-07-27T11:09:43.449 UT.
No significant optical counterpart was detected within the ECLAIRs error circle (~9 arcmin radius), compared to the Gaia DR2 catalog. The stacked image (71 × 30 s exposures) in the i-band reached a 5σ limiting magnitude of ~18.9. This non-detection is consistent with the non-detection reported by SVOM/VT (Li et al., GCN 41181).
Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018).
We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2.
GCN Circular 41182
Subject
GRB 250727A: EP-FXT counterpart detection
Date
2025-07-28T04:00:11Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (NJU), R. D. Liang, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250727A (SVOM/sb25072701) (Cao et al. GCN 41176) at 2025-07-27T12:37:29 (UTC), about 1.7 hours after the SVOM/ECLAIRs trigger, with an exposure time of 4209s. Three uncatalogued sources are detected within the ECLAIRs error circle, among which Source 3 is spatially consistent with the candidate counterpart Source 1 (SWIFT J234539.1-811248) detected by Swift/XRT (Evans et al. GCN 41180). Preliminary analysis on these source are automatically conducted, and the details are listed as follows.
Source 1: EPF_J234436.3-810410
RA (J2000): 356.1514
Dec (J2000): -81.0694
Flux: 4.96 x 10^-14 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 2.00 x 10^-14 erg/s/cm^2 (1 sigma)
Source 2: EPF_J234357.8-811244
RA (J2000): 355.9909
Dec (J2000): -81.2121
Flux: 6.82 x 10^-14 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 2.18 x 10^-14 erg/s/cm^2 (1 sigma)
Source 3: EPF_J234541.4-811245
RA (J2000): 356.4225
Dec (J2000): -81.2124
Flux: 1.36 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 3.44 x 10^-14 erg/s/cm^2 (1 sigma)
Note: This source is spatially consistent with the candidate counterpart Source 1 (SWIFT J234539.1-811248) detected by Swift/XRT.
The Source 2, and 3 are detected by both FXT-A and FXT-B, while Source 1 is detected only by FXT-A. The positional uncertainty of the sources are about 10 arcsec in radius (90% C.L. statistical and systematic).
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).
GCN Circular 41181
Subject
GRB250727A: SVOM/VT optical upper limit
Date
2025-07-27T23:03:23Z (a month ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), J. X. Cao (GXU) report on behalf of the SVOM team.
SVOM/VT performed ToO follow-up observations on the GRB 250727A (SVOM burst-id sb25072701, Cao et al., GCN 41176) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started on 2025-07-27T12:45:24 UT, about 1.82 hours after the SVOM T0 time.
No uncatalogued sources are detected in single or stacked images at the position of the Swift/XRT (Evans et al., GCN 41180), compared to the Legacy survey. The 3 sigma upper limit magnitudes are derived as below:
Mid_time | Band | Exposure Time | Upper limit (AB)
2.16 hour VT_B 36*70 sec 23.5 mag
2.16 hour VT_R 35*70 sec 23.4 mag
Also no apparent variation is found for the catalogued sources that lie within the errorbox of the Swift/XRT source 2 (Evans et al., GCN 41180).
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.
GCN Circular 41180
Subject
GRB 250727A: Swift-XRT observations
Date
2025-07-27T21:03:14Z (a month ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
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 250727A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+2.2 ks
and T0+8.3 ks after the trigger. We have detected 2 sources. These have been
automatically classified as follows:
* 0 likely counterparts
* 0 candidate counterparts
* 2 uncatalogued X-ray sources
* 0 known X-ray sources
Uncatalogued X-ray sources
--------------------------
Source 1 (SWIFT J234539.1-811248):
==================================
RA (J2000.0): 356.4132 = 23h 45m 39.17s
Dec (J2000.0): -81.2136 = -81d 12' 49.0"
Error: 4.9 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 7.7 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0155 +/- 0.0041 ct s^-1
Mean flux: (5.2 +/- 1.4)e-13 erg cm^-2 s^-1
Peak rate: 0.0155 +/- 0.0041 ct s^-1
Peak flux: (5.2 +/- 1.4)e-13 erg cm^-2 s^-1
ECF: 3.37e-11 erg cm^-2 ct^-1, assuming NH=9.71e+20 cm^-2,
gamma=1.97; determined from a spectral fit.
XMM UL: 4.6e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 29.9-sigma below this 3-sigma upper limit.
There is no evidence for fading.
Source 2 (SWIFT J234406.8-810315):
==================================
RA (J2000.0): 356.0284 = 23h 44m 06.82s
Dec (J2000.0): -81.0543 = -81d 03' 15.5"
Error: 8.5 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 4.9 arcmin from the SVOM/ECLAIRs position.
Mean rate: (5.2 [+2.6, -2.0])e-3 ct s^-1
Mean flux: (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1
Peak rate: (5.2 [+2.6, -2.0])e-3 ct s^-1
Peak flux: (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1
ECF: 2.93e-11 erg cm^-2 ct^-1, assuming NH=3.26e+22 cm^-2,
gamma=4.66; determined from a spectral fit.
XMM UL: 1.9e-12 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 25.1-sigma below 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/SVOM_FIELD00025.
This circular is an official product of the Swift-XRT team.
GCN Circular 41176
Subject
GRB 250727A: SVOM detection of a burst
Date
2025-07-27T11:55:37Z (a month ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. X. Cao (GXU), W. J. Xie (NAOC), M. Brunet, J-L. Atteia (IRAP), M. G. Bernardini (INAF-OAB, LUPM), report on behalf of the SVOM mission team:
At 2025-07-27T10:55:41 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250727A (SVOM burst-id sb25072701).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.45 in the [8-50] keV energy band over a time window of 163.84 seconds starting at 2025-07-27T10:53:39.
The localization of the best alert is R.A., Dec. 355.7990, -81.1275 degrees:
R.A. (J2000) = 23h43m11.76s
Dec. (J2000) = -81d07m39.00s
with a 90% confidence level (C.L.) radius of 9.33 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a featureless structure with a T90 duration in the [5-120] keV energy band of about 70 (-14, +16) s.
This burst was also detected by SVOM/GRM with low significance.
No immediate slew was performed on this burst. A SVOM ToO has been requested.
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 Jiaxin Cao: cjx@st.gxu.edu.cn.
Please contact the BA by email if you require additional information.