TITLE: GCN CIRCULAR
NUMBER: 41289
SUBJECT: GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
DATE: 25/08/08 14:30:18 GMT
FROM: Ines Francesca Giudice <ines.giudice(a)inaf.it>
I. F. Giudice (INAF/OACn), M. Garnichey (LUX-Paris Obs.), A. L. Thakur (INAF-IAPS), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn & DARK/NBI), A. Martin-Carrillo (UCD), M. De Pasquale (U.Messina), N. R. Tanvir (U. Leicester), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud Univ.), report on behalf of the Stargate collaboration:
We observed the optical counterpart (Kingler et al., GCN 41268; van Dalen et al., GCN 41278) of GRB 250807B detected by Swift with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 A, and consist of 4 exposures of 600 s each. Observation started on 2025-08-08 at 08:42:42 UTC (17 hours after trigger).
In a preliminary reduction of the spectra, we identify several absorption features, which we interpret as Fe II, the Mg II doublet, and Mg I, from which we derive a redshift of z = 1.522. We notice the absence of emission or fine-structure lines. The presence of a continuum in the UVB arm supports the interpretation that this could be the GRB redshift.
The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
We acknowledge excellent support from the ESO observing staff in Paranal.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41289.
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TITLE: GCN CIRCULAR
NUMBER: 41288
SUBJECT: GRB 250806A: SVOM/MXT refined analysis
DATE: 25/08/08 14:08:03 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:
GRB 250806A (Xie et al. GCN 41243) was observed by SVOM/MXT after an automatic SVOM slew, starting at T0 = 2025-08-06T08:00:11, 117 s after trigger time Tb. MXT observed for the remainder of the orbit for 297s.
Using the full X-band dataset, the position of the MXT candidate afterglow is refined to:
R.A. (J2000) = 23h13m38.10s
Dec (J2000) = +01d21m59.0s
with a 90% C.L. radius of 66” (including 25 arcseconds systematic error added in quadrature). This is just outside the Swift/XRT afterglow identified by Evans et al. (GCN 41249) and observed with Einstein Probe/FXT (Liang et al., GCN 41260), but the light curve analysis below confirms that this is the same source.
We analysed the time-averaged spectrum, subtracting an appropriately-scaled blank sky background spectrum from the Lockmann Hole. Modelled with an absorbed power-law, a soft spectrum is found, with a photon index Gamma >2.2 at 90% C.L and an absorbing column NH = 4.1 (+4.5/-3.2) x1e21 cm2 on top of Galactic NH = 4.6 x 1e20 /cm2.
We derive a count rate conversion factor of 1 cps = 9.9e-11 erg/s/cm2
The light curve exhibits an initial fast decay with temporal index alpha~-3.5+/-0.6 (with count rate proportional to t^alpha). At t >Tb + 250s the source is no longer detected by MXT. Extending the light curve using Swift/XRT data in Photon Counting mode from the automatic follow-up suggests a transition to a shallower decay occurred at about 5 minutes post-trigger.
The source is below the MXT detection limit in subsequent orbits.
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(a)bao.ac.cn).
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41288.
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TITLE: GCN CIRCULAR
NUMBER: 41287
SUBJECT: GRB 250806A: SVOM/ECLAIRs refined analysis
DATE: 25/08/08 13:18:05 GMT
FROM: SVOM_group <svomgroup(a)bao.ac.cn>
L. Bouchet (IRAP), Y. Nourlil (CEA), S. Schanne (CEA), N. Dagoneau (CEA), J.-L. Atteia (IRAP) report on behalf of the SVOM/ECLAIRs team:
We performed further analysis of GRB 250806A (SVOM burst-id sb25080601), triggered by ECLAIRs onboard SVOM (Xie et al. GCN 41243).
Using the ECLAIRs event-by-event data downloaded through the X-band ground station, we confirm that the burst consists of a single peak, with a duration of about 20 s. The time-averaged spectrum from T0-10 s to T0+10 s (T0 = 2025-08-06T07:58:14 UTC) in the energy range 4-120 keV is best fitted by a powerlaw model with index -2.07 (-0.12, +0.12). With this model, the total flux in 4-120 keV is 1.2e-8 erg/cm^2/s. All quoted errors are at the 68% confidence level.
This prompt emission spectrum suggests that GRB 250806A is an X-Ray Flash (a low energy GRB with a soft spectrum) located at low redshift. This interpretation is consistent with the Swift/UVOT observation of the afterglow (GCN 41264) and the identification of a host galaxy candidate by NOT (GCN 41279).
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: Laurent Bouchet (laurent.bouchet(a)irap.omp.eu).
View this GCN Circular online at https://gcn.nasa.gov/circulars/41287.
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TITLE: GCN CIRCULAR
NUMBER: 41286
SUBJECT: EP250807a: NTT z-band optical upper limit
DATE: 25/08/08 12:10:28 GMT
FROM: Agnes van Hoof at Radboud University <agnes.vanhoof(a)ru.nl>
A.P.C. van Hoof (Radboud), J.N.D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (U of Leicester), A. Martin-Carrillo (UCD) and P. G. Jonker (Radboud) report on behalf of a larger collaboration:
We observed the field of EP250807a (Wang et al., GCN 41277) at 2025-08-08 from 05:17:33 (5.7 hr after the trigger) to 05:33:33 UTC, using the ESO NTT in La Silla (Chile), equipped with the EFOSC2 camera. Observations consisted of 5x200 s exposures in the Gunn z band.
We do not identify any new sources within the EP-WXT uncertainty region, down to a 3-sigma limiting magnitude of z > 20.4 (AB system). The upper limit is calculated using nearby stars from Pan-STARRS and not corrected for galactic extinction.
We also performed image subtraction using a reference image from Pan-STARRS. There are no conclusive signs of variability compared to the reference, but we note that the crowded field has impacted our preliminary subtraction and there are artefacts across the field.
Further observations are planned to investigate if any of the known sources do show variability.
We thank the excellent support from the NTT operator, Duncan Castex.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41286.
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TITLE: GCN CIRCULAR
NUMBER: 41285
SUBJECT: GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
DATE: 25/08/08 12:08:44 GMT
FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com>
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 250806A detected by SVOM/ECLAIRs (Xie et. al, GCN 41243) with the 1.5m AZT-33IK telescope of the Solar Sayan Observatory (Mondy). The series of 28x120 s images were ingested in the R-filter starting on 2025-08-06 at 16:59 UT, i.e. ~0.39 days after the SVOM trigger. In the co-add image of 26x120 we do not detect the optical source reported in (Breeveld, GCN 41264). We note the presence of a nearby SDSS-DR12 galaxy at the coordinates (J2000) 23:13:43.45 01:21:21.9 located at the photometric redshift ~ 0.3 and has the SDSS photometry r = 21.383 +/- 0.141, and i = 21.113 +/- 0.163. This SDSS galaxy is the brighter one of the Legacy Survey galaxies reported in Malesani et al., GCN 41279. The preliminary photometry of the galaxy in the co-add image is presented below:
Date UT start t-T0 Exp. Filter Mag Err UL
(mid, days) (n x s) (3sigma)
2025-08-06 16:59:03 0.39362 26x120 R 21.27 0.22 22.4
The photometry was calibrated using nearby stars from the SDSS-DR12 catalog (R mags were obtained via Lupton 2005 transformations) and not corrected for the Galactic extinction. At present we cannot say anything about the change in brightness of the galaxy. The second Legacy Survey faint galaxy (RA = 23:13:43.42, Dec = +01:21:19.8) is not detected in our image.
Our upper limits do not contradict the non-detections by other observations (Wu et. al, GCN 41244; Fortin et. al, GCN 41245; Freeberg et. al, GCN 41247; Xin et. al, GCN 41250; Zheng et. al, GCN 41251; Schneider et. al, GCN 41253).
Indeed the bright galaxy might be the host of GRB 250806A (Malesani et al., GCN 41279). Further comparison of the early observation is necessary and the SN monitoring.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41285.
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TITLE: GCN CIRCULAR
NUMBER: 41284
SUBJECT: GRB 250804B: Insight-HXMT detection
DATE: 25/08/08 11:41:51 GMT
FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn>
Chen-Wei Wang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2025-08-04T04:44:51.600 (T0), Insight-HXMT/HE detected the short burst GRB 250804B, which is also detected by SVOM/GRM (Wang et al., GCN #41229).
The Insight-HXMT/HE light curve mainly consists of a weak precursor and a single main pulse with a T90 of 0.47 +0.14/-0.18 s. The total counts from this burst is 2193 counts.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250804B.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41284.
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TITLE: GCN CIRCULAR
NUMBER: 41283
SUBJECT: GRB 250807A: SVOM/GRM observation
DATE: 25/08/08 11:07:22 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: Sebastien Guillot (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250807A (SVOM trigger reference: sb25080702) at 2025-08-07T10:46:06.700 UTC (T0), which is also detected by Swift/BAT (N. J. Klingler et al., GCN #41262), AstroSat (S.Salunke et al., GCN #41281) and Konus-Wind.
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 71.0 +4.5/-7.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250807A.png
In addition, the position of this burst, as determined by Swift/BAT (RA= 51.420, DEC= -47.877, GCN #41064), is located at about 69 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. Nonetheless, the burst is seen (via analysis of X-band data) in the ECLAIRs data above 50 keV at the T0 given by GRM, likely through the ECLAIRs shielding.
With this localization, the time-averaged spectrum from T0-15 to T0+130 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.19 +/-0.03 and the cutoff energy, parameterized as Epeak, is 547 +52/-45 keV. The event fluence (10-1000 keV) in this time interval is (1.00 +/-0.10)E-04 erg/cm^2. Thus GRB 250807A is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/grb250807A_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: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn)
View this GCN Circular online at https://gcn.nasa.gov/circulars/41283.
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TITLE: GCN CIRCULAR
NUMBER: 41282
SUBJECT: Swift GRB250807.45: Global MASTER-Net observations report
DATE: 25/08/08 09:58:24 GMT
FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru>
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB250807.45 (trigger No 1340514,03h 25m 40.80s , -47d 52m 37.2s, R=0.05) errorbox 83032 sec after notice time and 83048 sec after trigger time at 2025-08-08 09:50:17 UT, with upper limit up to 18.7 mag. The observations began at zenith distance = 21 deg. The sun altitude is -18.7 deg.
The galactic latitude b = -53 deg., longitude l = 258 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2962968
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
83139 | MASTER-OAFA | C | 180 | 18.7 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41282.
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TITLE: GCN CIRCULAR
NUMBER: 41281
SUBJECT: GRB 250807A: AstroSat CZTI detection of bright long burst
DATE: 25/08/08 09:48:16 GMT
FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in>
S.Salunke (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright long-duration GRB 250807A which was also detected by Swift/BAT (N. J. Klingler et.al, GCN Circ. 41262), and Konus-Wind (reported through GCN Notices).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-08-07 10:46:42.50 UTC. The measured peak count rate associated with the burst is 535 (+49, -47) counts/s above the background in the combined data of all quadrants, with a total of 6218 (+449, -269) counts. The local mean background count rate was 275 (+1, -4) counts/s. Using cumulative rates, we measure a T90 of 44 (+2, -3) s. In the preliminary analysis, we find 630 Compton events associated with this event.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-08-07 10:46:42.27 UTC. The measured peak count rate associated with the burst is 3662 (+110, -125) counts/s above the background in the combined data of all quadrants, with a total of 36237 (+1153, -1203) counts. The local mean background count rate was 1239 (+5, -6) counts/s. We measure a T90 of 48 (+1, -3) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
View this GCN Circular online at https://gcn.nasa.gov/circulars/41281.
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TITLE: GCN CIRCULAR
NUMBER: 41280
SUBJECT: GRB 250807B: Swift-XRT refined Analysis
DATE: 25/08/08 09:17:21 GMT
FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk>
A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Ferro
(INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea
(PSU), D.N. Burrows (PSU), M.A. Williams (PSU) and P.A. Evans report on
behalf of the Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 250807B, from 133 s to 50.6
ks after the trigger. The data comprise 188 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The late-time light curve (from T0+3.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.16 (+0.14, -0.13).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.96 (+/-0.07). The
best-fitting absorption column is 4.2 (+1.5, -1.4) x 10^20 cm^-2, in
excess of the Galactic value of 1.9 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.97 (+0.21, -0.19)
and a best-fitting absorption column of 5.8 (+4.7, -4.0) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.4 x 10^-11 (3.8 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 5.8 (+4.7, -4.0) x 10^20 cm^-2
Galactic foreground: 1.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.97 (+0.21, -0.19)
If the light curve continues to decay with a power-law decay index of
1.16, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x
10^-13 (2.4 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01340561.
This circular is an official product of the Swift-XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/41280.
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