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GRB 260515A

GCN Circular 44821

Subject
GRB 260515A: SVOM/VT optical detection at about 18 days post trigger
Date
2026-06-04T15:44:09Z (16 hours ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. R. Xu, 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, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio, A. Saccardi and D. Gotz (CEA/Irfu) report on behalf of the SVOM/VT team.

SVOM/VT performed further ToO observations of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622, GCN 44666). The burst was also detected by Konus-Wind (Frederiks et al., GCN 44647). The observation started at 2026-06-03T02:02:18 UTC, i.e., 18.28 days post trigger  in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.  

The counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Wang et al., GCN 44642; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al. GCN 44646; Moskvitin et al., GCN 44652;  Bochenek et al., GCN 44658) with redshift z=0.764 (Malesani et al., GCN 44629) was faintly detected VT_R. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time | Brightness  
18.38 d   VT_R     108*70 s       23.5 +/- 0.3 mag
18.38 d   VT_B     110*70 s       >24.0 mag (3 sigma upper limit)

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 44666

Subject
GRB 260515A: SVOM/ECLAIRs refined analysis
Date
2026-05-19T14:14:04Z (17 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, L. Bouchet (IRAP), A. Saccardi (CEA/ Irfu), 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 SVOM/ECLAIRs observations of GRB 260515A (SVOM burst-id sb26051504 – GCN 44622, trigger time T0 = 2026-05-15T19:08:19 UTC), which was also detected by Konus-Wind (GCN 44647). 

The burst that triggered ECLAIRs shows a FRED like shape light curve preceded by a faint hard precursor at T0-4.2s. The burst duration is T90 = 16.33 +0.54/-0.35 s in the 4-120 keV energy band.

The time-averaged spectrum from T0-0.31 s to T0+16.0 s in the energy range 5-120 keV is best fitted by a powerlaw model with alpha = -1.69 +/-0.04. With this model, the 4-120 keV fluence is (1.09 -0.07/+0.04)e-6 erg/cm² and the 4-120 keV photon flux is 2.26 -0.06/+0.04 ph/cm²/s. 

All the quoted errors are at the 68% confidence level.
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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr)

GCN Circular 44658

Subject
GRB 260515A: further Liverpool Telescope observations
Date
2026-05-17T08:10:40Z (19 days ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU), report:

We observed the field of GRB 260515A (Brunetet al., GCN 44622) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x110s exposures in SDSS r and i filters, starting at 2026-05-12 00:42:25 UT, approximately 5.55 hours after trigger.

We detect a source in the stacked images in both filters at the position reported by He et al. (GCN 44623), and observed also by Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628, Dennefeld et al., GCN 44633; Li et al., GCN 44634, Antier et al., GCN 44643; Dimple et al. GCN 44646; and Moskvitin et al., GCN 44652:

MJD (mid)          T_mid-T_0       Filter       Mag. (AB)
61176.03308        5.64 h           r         21.32 ± 0.06
61176.04059        5.82 h           i         21.26 ± 0.07

The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.

GCN Circular 44652

Subject
GRB 260515A: CrAO ZTSh BVRI optical observations
Date
2026-05-16T23:52:00Z (19 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO),
N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN.


We observed the field of the GRB 260515A (Brunet et al., GCN 44622;
Wang et al., GCN 44642; Frederiks et al., GCN 44647) with the Shajn
2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory
(CrAO). We obtained  series of 120 s exposures in BVRI filters
starting on 2026-05-15  22:10:11 UT (about 3 hours after trigger).


The OT (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij
et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628;
Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al.,
GCN 44634; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645;
Dimple et al., GCN 44646) is clearly detected in the stacked frames.
Details of the photometry is the following.

Start_UT,  t_mid-T0, exp, filter, mag,   err,  UL(3 sigma)
 

2026-05-15T22:54:33  4.79 15*120 B 21.53  0.04 23.9
2026-05-15T22:56:41  4.75 13*120 V 21.30  0.05 23.7
2026-05-15T22:10:11  3.12  5*120 R 20.56  0.04 23.4
2026-05-15T22:20:40  3.29  5*120 R 20.57  0.04 23.4
2026-05-15T22:31:09  3.46  5*120 R 20.65  0.04 23.5
2026-05-15T22:41:44  3.66  6*120 R 20.64  0.03 23.6
2026-05-15T22:56:41  4.26  7*120 R 20.87  0.03 23.7
2026-05-15T23:58:56  5.35  8*120 R 21.03  0.04 23.4
2026-05-15T23:00:57  4.89 15*120 I 20.75  0.05 22.8


This preliminary photometry is based on nearby SDSS stars
(using Lupton 2005 transformation equations) and  not corrected for Galactic extinction.

GCN Circular 44647

Subject
Konus-Wind detection of GRB 260515A
Date
2026-05-16T19:07:11Z (20 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

A long-duration GRB 260515A (SVOM detection: Brunet et al., GCN 44622)
was detected by Konus-Wind (KW)in the waiting mode at T0=T0(KW)~19:08:19UT.
A Bayesian block analysis of the KW data in the 20-1500 keV
band reveals a ~8 sigma count rate increase in the interval
from ~T0+0.4 s to ~T0+9.3 s from the SVOM detection time.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260515A/

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 = -1.37 (-0.17, + 0.17) and Ep = 95(-9,+10) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (7.70 ± 0.81)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (1.47 ± 0.22)x10^-7 erg/cm^2/s.

Assuming the redshift z=0.764 (Malesani et al., GCN 44629)
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 (1.25 ± 0.15)x10^52 erg,
the isotropic peak luminosity L_iso to (5.70 ± 0.85)x10^50 erg/s, and
the rest-frame peak spectral energy Ep,z to (168 ± 18) keV.
With the obtained estimates, GRB 260515A is consistent with 68% prediction bands
of both 'Amati' relation and 90% prediction bands of 'Yonetoku' relation 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/GRB260515A/GRB260515A_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.

GCN Circular 44646

Subject
GRB 260515A: Liverpool Telescope optical detection
Date
2026-05-16T14:32:40Z (20 days ago)
From
Dimple at University of Birmingham <dimplepanchal96@gmail.com>
Via
Web form
Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), P. O'Brien (U. Leicester), D. O'Neill  (U. Birmingham) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration:

We conducted follow-up observations of GRB 260515A (Brunet et al., GCN 44622) with the IO:O camera on the 2m robotic Liverpool Telescope (LT). Observations began at 22:42:40 UT on 2026-05-15,  ~3.57 hr after the burst, and consisted of 5 x 200 s exposures in each of the SDSS g and i filters.

We detect the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628, Dennefeld et al., GCN 44633; Li et al., GCN 44634, Antier et al., GCN 44643) in both filters, and measure an AB magnitude of g = 21.06 ± 0.04.

Magnitudes are calibrated against nearby Pan-STARRS stars and are not corrected for Galactic extinction.

GCN Circular 44645

Subject
GRB 260515A: LCO optical counterpart detection
Date
2026-05-16T14:16:15Z (20 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, 
I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL)

Following the detection of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622), detected also in Einstein Probe FXT follow-up observations (Wang et al., GCN 44642), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes, equipped with Sinistro cameras, located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 180 sec in the SDSS r' filter, started on 2026-05-15 at 21:17:54 UT, 2.16 hours after the SVOM trigger. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; 
Li et al., GCN 44634; and Antier et al., GCN 44643) with redshift of z = 0.764 (Malesani et al., GCN 44629) is clearly detected in our image with an AB magnitude of r' = 20.32 +/- 0.10, calibrated 
against the PanSTARRS-1 DR2 catalog and not corrected for Galactic extinction.

This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys).

This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).

GCN Circular 44643

Subject
GRB 260515A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2026-05-16T11:06:13Z (20 days ago)
Edited On
2026-05-17T22:46:56Z (18 days ago)
From
antier@ijclab.in2p3.fr
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of antier@ijclab.in2p3.fr
Via
Web form
Sarah Antier (IJCLAB), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Dalya Akl (NYUAD), William H. Lee (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM) and Antonio de Ugarte Postigo (LAM), and Andrea Saccardi (CEA/Irfu) report:

We imaged the field of the SVOM/ECLAIRs GRB 260515A (M. Brunet et al., GCN Circ. 44622) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-16 08:25 to 09:49 UTC (from to 13.3 hours after the trigger) and obtained 128 minutes of simultaneous exposure in r and z filters.

The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline.
The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

We detect the source reported by Saccardi et al. (GCN Circ. 44624) with preliminary unsubtracted magnitudes of:

r = 21.78 +/- 0.02
z = 21.50 +/- 0.05

We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.
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.

GCN Circular 44642

Subject
GRB 260515A: EP-FXT follow-up observation
Date
2026-05-16T09:39:53Z (20 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Z.M. Wang (BNU), X.X. Sun(NAO, CAS), Y.H.Cheng (SWIFAR, YNU), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed an automatic follow-up observation of GRB 260515A detected by SVOM/ECLAIRs (SVOM/sb26051504, Brunet et al., GCN 44622). The follow-up obervation started at 2026-05-15T20:51:27 UTC, approximately 1.7 hours after the SVOM trigger, with a total exposure time of 5.9 ks.

On-ground analysis of the FXT data found an uncatalogued fading source within the ECLAIRs error circle at R.A., Dec. = 227.6846, 24.5566 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Dennefeld et al., GCN 44633; Li et al., GCN 44634). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value of 3.47×10^20 cm^-2 and a photon index of 1.71(-0.09/+0.09). The derived average unabsorbed flux in the 0.3-10 keV band is 7.13(-0.19/+0.21) x 10^(-12) erg/s/cm^2.

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 44634

Subject
GRB 260515A: SVOM/VT optical observations
Date
2026-05-16T03:45:58Z (20 days ago)
Edited On
2026-05-17T22:42:49Z (18 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. L. Qiu, C. Wu,  L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio, A. Saccardi (CEA/Irfu) report on behalf of the SVOM/VT team.

SVOM/VT performed observations with automatic slew of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622). The observation started at 2026-05-15T19:10:54 UTC, i.e., 155 seconds post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.  An additional ToO observation was performed started at 2026-05-15T20:59:23 UTC, 1.85 hours post trigger.

The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Dennefeld et al., GCN 44633) with redshift z=0.764 (Malesani et al., GCN 44629) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time | Brightness
 3.00 m   VT_B        50 s        16.06 +/- 0.05 mag
 3.00 m   VT_R        50 s        15.49 +/- 0.04 mag    
 3.91 h   VT_B     26*70 s        21.27 +/- 0.08 mag
 3.92 h   VT_R     19*70 s        20.93 +/- 0.07 mag
  
During our observations the decay slope changed from 1.3 to 0.8.

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 44633

Subject
GRB 260515A: OHP/T193 optical observations
Date
2026-05-16T03:39:29Z (20 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
M. Dennefeld (IAP), B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu) report on behalf of a larger collaboration:

We observed the field of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622; He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Lipunov et al., GCN 44627; Wu et al., GCN 44628; Malesani et al., GCN 44629) using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL spectro-imager. We obtained two epochs: 2x5 minutes of exposure in the r-band starting at 2026-05-15T21:29:45 UT (2.36 hr after the trigger), and 3x10 minutes of exposure in the r-band starting at 2026-05-16T001045UT (5.04 hr after the trigger).

In the stacked images, the optical counterpart is visible with preliminary magnitudes of:

r = 20.42 +/- 0.13 mag (1st visit)
r = 21.34 +/- 0.12 mag (2nd visit)

The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Yoann Degot-Longhi.

GCN Circular 44629

Subject
GRB 260515A: GTC/OSIRIS+ spectroscopic redshift z = 0.764
Date
2026-05-16T01:11:21Z (20 days ago)
Edited On
2026-05-17T22:40:30Z (18 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), I. V. Yanes-Rizo (IAC), D. Pérez Valladares (GTC), F. Pérez Toledo (GTC) report:

We observed the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628) of GRB 260515A (Brunet et al., GCN 44622) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument.

In the 20-s acquisition image (beginning on 2026-05-15 at 23:48:49.010 UT, that is 4.67 hr after trigger), the optical afterglow is well detected with a magnitude r = 21.15 ± 0.10 (AB), calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction.

A total of 3 spectra of 1200 s were secured, starting on 2026-05-15 at 23:52:26.010 UT (4.73 hr after trigger), using grism R1000B. Continuum is visible over the range 3650-7800 AA. A number of metal absorption features are detected, which we interpret as due to Fe II, Mg II, and Mg I, all at a common redshift z = 0.764, which we suggest to be the redshift of GRB 260515A. We also detect emission due to the [O II] doublet at the same redshift.

This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774).

GCN Circular 44628

Subject
GRB 260515A: LCO optical observations
Date
2026-05-16T00:11:51Z (20 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
C. Wu (NAOC), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of the SVOM mission team:

We observed the field of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622) with the LCO 1m telescope at Teide Observatory equipped with the Sinistro instrument.

Our observation started on 2026-05-15 at 22:42:33 UT (about 3.57 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters.

The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626) is faintly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction:

r = 21.22 +/- 0.09 AB (mid-time 4.44 hr after the trigger);
z > 20.5 AB (3-sigma, mid-time 3.63 hr after the trigger).

A marginal detection is recovered through forced photometry in the z band as well, to the level of z = 20.6 +/- 0.4 AB.

This project is funded by the SVOM collaboration.

GCN Circular 44627

Subject
SVOM GRB 260515A: Global MASTER-Net observations report
Date
2026-05-15T21:53:05Z (20 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
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-Tavrida robotic telescope  [1]  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the SVOM GRB 260515A ( SVOM/ECLAIRs Commissioning Team et al., GCN 44622) errorbox  30 sec after notice time and 659 sec after trigger time at 2026-05-15 19:19:18 UT, with upper limit up to  19.9 mag. The observations began at zenith distance = 32 deg. The sun  altitude  is -18.8 deg. 

The galactic latitude b = 58 deg., longitude l = 36 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3316887

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

     719 | 2026-05-15 19:19:18 |      MASTER-Tavrida | (15h 10m 30.15s , +24d 42m 28.1s) |   C |   120 | 18.8 |        
     842 | 2026-05-15 19:21:20 |      MASTER-Tavrida | (15h 10m 30.34s , +24d 42m 18.6s) |   C |   120 | 19.1 |        
     965 | 2026-05-15 19:23:23 |      MASTER-Tavrida | (15h 10m 30.45s , +24d 42m 11.4s) |   C |   120 | 19.1 |        
    1087 | 2026-05-15 19:25:26 |      MASTER-Tavrida | (15h 10m 30.55s , +24d 42m 04.2s) |   C |   120 | 18.9 |        
    1210 | 2026-05-15 19:27:28 |      MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 58.5s) |   C |   120 | 19.4 |        
    1332 | 2026-05-15 19:29:31 |      MASTER-Tavrida | (15h 10m 30.65s , +24d 41m 52.9s) |   C |   120 | 19.4 |        
    1455 | 2026-05-15 19:31:33 |      MASTER-Tavrida | (15h 10m 30.66s , +24d 41m 47.7s) |   C |   120 | 19.5 |        
    1577 | 2026-05-15 19:33:36 |      MASTER-Tavrida | (15h 10m 30.65s , +24d 41m 42.7s) |   C |   120 | 19.5 |        
    1700 | 2026-05-15 19:35:38 |      MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 38.1s) |   C |   120 | 19.6 |        
    1822 | 2026-05-15 19:37:41 |      MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 33.2s) |   C |   120 | 19.6 |        
    1945 | 2026-05-15 19:39:44 |      MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 28.5s) |   C |   120 | 19.6 |        
    2068 | 2026-05-15 19:41:46 |      MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 24.0s) |   C |   120 | 19.6 |        
    2190 | 2026-05-15 19:43:49 |      MASTER-Tavrida | (15h 10m 30.62s , +24d 41m 19.0s) |   C |   120 | 19.6 |        
    2313 | 2026-05-15 19:45:52 |      MASTER-Tavrida | (15h 10m 30.63s , +24d 41m 14.6s) |   C |   120 | 19.5 |        
    2436 | 2026-05-15 19:47:54 |      MASTER-Tavrida | (15h 10m 30.61s , +24d 41m 09.9s) |   C |   120 | 19.6 |        
    2558 | 2026-05-15 19:49:57 |      MASTER-Tavrida | (15h 10m 30.58s , +24d 41m 05.5s) |   C |   120 | 19.6 |        
    2681 | 2026-05-15 19:51:59 |      MASTER-Tavrida | (15h 10m 30.55s , +24d 41m 00.9s) |   C |   120 | 19.6 |        
    2804 | 2026-05-15 19:54:02 |      MASTER-Tavrida | (15h 10m 30.53s , +24d 40m 56.5s) |   C |   120 | 19.7 |        
    2926 | 2026-05-15 19:56:05 |      MASTER-Tavrida | (15h 10m 30.51s , +24d 40m 52.0s) |   C |   120 | 19.6 |        
    3049 | 2026-05-15 19:58:07 |      MASTER-Tavrida | (15h 10m 30.50s , +24d 40m 47.5s) |   C |   120 | 19.7 |        
    3179 | 2026-05-15 20:00:18 |      MASTER-Tavrida | (15h 10m 34.07s , +24d 41m 17.5s) |   C |   120 | 19.7 |        
    3302 | 2026-05-15 20:02:20 |      MASTER-Tavrida | (15h 10m 34.06s , +24d 41m 13.1s) |   C |   120 | 19.7 |        
    3424 | 2026-05-15 20:04:23 |      MASTER-Tavrida | (15h 10m 34.06s , +24d 41m 08.9s) |   C |   120 | 19.7 |        
    3547 | 2026-05-15 20:06:26 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 41m 04.4s) |   C |   120 | 19.7 |        
    3670 | 2026-05-15 20:08:28 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 41m 00.1s) |   C |   120 | 19.7 |        
    3793 | 2026-05-15 20:10:31 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 55.8s) |   C |   120 | 19.7 |        
    3915 | 2026-05-15 20:12:34 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 51.4s) |   C |   120 | 19.7 |        
    4038 | 2026-05-15 20:14:36 |      MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 47.0s) |   C |   120 | 19.7 |        
    4161 | 2026-05-15 20:16:39 |      MASTER-Tavrida | (15h 10m 34.00s , +24d 40m 42.8s) |   C |   120 | 19.6 |        
    4283 | 2026-05-15 20:18:42 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 40m 38.5s) |   C |   120 | 19.8 |        
    4406 | 2026-05-15 20:20:44 |      MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 34.2s) |   C |   120 | 19.9 |        
    4529 | 2026-05-15 20:22:47 |      MASTER-Tavrida | (15h 10m 34.01s , +24d 40m 30.0s) |   C |   120 | 19.9 |        
    4651 | 2026-05-15 20:24:50 |      MASTER-Tavrida | (15h 10m 33.97s , +24d 40m 26.2s) |   C |   120 | 19.8 |        
    4774 | 2026-05-15 20:26:53 |      MASTER-Tavrida | (15h 10m 33.93s , +24d 40m 22.2s) |   C |   120 | 19.8 |        
    4897 | 2026-05-15 20:28:55 |      MASTER-Tavrida | (15h 10m 33.91s , +24d 40m 17.9s) |   C |   120 | 19.9 |        
    5020 | 2026-05-15 20:30:58 |      MASTER-Tavrida | (15h 10m 33.93s , +24d 40m 13.4s) |   C |   120 | 19.9 |        
    5143 | 2026-05-15 20:33:01 |      MASTER-Tavrida | (15h 10m 33.94s , +24d 40m 09.2s) |   C |   120 | 19.9 |        
    5265 | 2026-05-15 20:35:04 |      MASTER-Tavrida | (15h 10m 33.96s , +24d 40m 04.8s) |   C |   120 | 19.9 |        
    5388 | 2026-05-15 20:37:06 |      MASTER-Tavrida | (15h 10m 33.97s , +24d 40m 00.6s) |   C |   120 | 19.9 |        
    5510 | 2026-05-15 20:39:09 |      MASTER-Tavrida | (15h 10m 33.95s , +24d 39m 56.5s) |   C |   120 | 19.9 |        
    5633 | 2026-05-15 20:41:12 |      MASTER-Tavrida | (15h 10m 33.91s , +24d 39m 52.7s) |   C |   120 | 19.8 |        
    5756 | 2026-05-15 20:43:14 |      MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 48.3s) |   C |   120 | 19.9 |        
    5878 | 2026-05-15 20:45:17 |      MASTER-Tavrida | (15h 10m 33.94s , +24d 39m 43.8s) |   C |   120 | 19.9 |        
    6001 | 2026-05-15 20:47:20 |      MASTER-Tavrida | (15h 10m 33.96s , +24d 39m 39.5s) |   C |   120 | 19.9 |        
    6124 | 2026-05-15 20:49:23 |      MASTER-Tavrida | (15h 10m 33.99s , +24d 39m 35.1s) |   C |   120 | 19.9 |        
    6246 | 2026-05-15 20:51:25 |      MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 31.4s) |   C |   120 | 19.7 |        
    6369 | 2026-05-15 20:53:28 |      MASTER-Tavrida | (15h 10m 33.93s , +24d 39m 27.2s) |   C |   120 | 19.9 |        
    6492 | 2026-05-15 20:55:31 |      MASTER-Tavrida | (15h 10m 33.95s , +24d 39m 22.9s) |   C |   120 | 19.8 |        
    6615 | 2026-05-15 20:57:33 |      MASTER-Tavrida | (15h 10m 34.00s , +24d 39m 18.6s) |   C |   120 | 19.9 |        
    6737 | 2026-05-15 20:59:36 |      MASTER-Tavrida | (15h 10m 34.00s , +24d 39m 14.5s) |   C |   120 | 19.9 |        
    6860 | 2026-05-15 21:01:38 |      MASTER-Tavrida | (15h 10m 34.02s , +24d 39m 10.3s) |   C |   120 | 19.9 |        
    6983 | 2026-05-15 21:03:41 |      MASTER-Tavrida | (15h 10m 34.07s , +24d 39m 06.1s) |   C |   120 | 19.8 |        
    7105 | 2026-05-15 21:05:44 |      MASTER-Tavrida | (15h 10m 34.10s , +24d 39m 01.9s) |   C |   120 | 19.9 |        
    7228 | 2026-05-15 21:07:46 |      MASTER-Tavrida | (15h 10m 34.10s , +24d 38m 57.7s) |   C |   120 | 19.9 |        
    7350 | 2026-05-15 21:09:49 |      MASTER-Tavrida | (15h 10m 34.11s , +24d 38m 53.5s) |   C |   120 | 19.7 |        
    7472 | 2026-05-15 21:11:51 |      MASTER-Tavrida | (15h 10m 34.14s , +24d 38m 49.3s) |   C |   120 | 19.8 |        
    7595 | 2026-05-15 21:13:54 |      MASTER-Tavrida | (15h 10m 34.17s , +24d 38m 45.0s) |   C |   120 | 19.8 |        
    7718 | 2026-05-15 21:15:56 |      MASTER-Tavrida | (15h 10m 34.22s , +24d 38m 40.5s) |   C |   120 | 19.8 |        
    7840 | 2026-05-15 21:17:58 |      MASTER-Tavrida | (15h 10m 34.23s , +24d 38m 36.3s) |   C |   120 | 19.9 |        
    7962 | 2026-05-15 21:20:01 |      MASTER-Tavrida | (15h 10m 34.25s , +24d 38m 31.9s) |   C |   120 | 19.9 |        
    8085 | 2026-05-15 21:22:03 |      MASTER-Tavrida | (15h 10m 34.28s , +24d 38m 27.7s) |   C |   120 | 19.8 |        
    8207 | 2026-05-15 21:24:06 |      MASTER-Tavrida | (15h 10m 34.33s , +24d 38m 23.2s) |   C |   120 | 19.9 |        
    8330 | 2026-05-15 21:26:08 |      MASTER-Tavrida | (15h 10m 34.34s , +24d 38m 19.1s) |   C |   120 | 19.9 |        
    8452 | 2026-05-15 21:28:11 |      MASTER-Tavrida | (15h 10m 34.36s , +24d 38m 14.5s) |   C |   120 | 19.9 |        
    8575 | 2026-05-15 21:30:14 |      MASTER-Tavrida | (15h 10m 34.36s , +24d 38m 09.9s) |   C |   120 | 19.8 |        
    8698 | 2026-05-15 21:32:16 |      MASTER-Tavrida | (15h 10m 34.41s , +24d 38m 05.3s) |   C |   120 | 19.9 |        
    8820 | 2026-05-15 21:34:19 |      MASTER-Tavrida | (15h 10m 34.43s , +24d 38m 00.8s) |   C |   120 | 19.9 |        
    8943 | 2026-05-15 21:36:21 |      MASTER-Tavrida | (15h 10m 34.46s , +24d 37m 56.3s) |   C |   120 | 19.9 |        
    9065 | 2026-05-15 21:38:24 |      MASTER-Tavrida | (15h 10m 34.51s , +24d 37m 51.7s) |   C |   120 | 19.9 |        
    9188 | 2026-05-15 21:40:27 |      MASTER-Tavrida | (15h 10m 34.53s , +24d 37m 47.2s) |   C |   120 | 19.8 |        
    9311 | 2026-05-15 21:42:29 |      MASTER-Tavrida | (15h 10m 34.57s , +24d 37m 42.6s) |   C |   120 | 19.8 |        
    9433 | 2026-05-15 21:44:32 |      MASTER-Tavrida | (15h 10m 34.59s , +24d 37m 38.0s) |   C |   120 | 19.8 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html

GCN Circular 44626

Subject
GRB 260515A: NOT optical observations.
Date
2026-05-15T21:31:23Z (20 days ago)
Edited On
2026-05-17T22:44:57Z (18 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
L. B. He (NAOC), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Fuglsang (NOT), A. S. Mårtensson (NOT and DTU), report on behalf of a larger collaboration:

We observed the optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625) of the SVOM/ECLAIRs GRB 260515A (Brunet et al., GCN 44622) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC instrument.

In a single 300-s exposure commencing on May 15.8696 UT (1.73 hr after trigger), the optical afterglow is well detected in our images, with an AB magnitude of r = 20.22 +- 0.04 (calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction).

GCN Circular 44625

Subject
SVOM GRB 260515A: MASTER OT J151044.43+243321.7 optical counterpart detection
Date
2026-05-15T20:41:12Z (20 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email

A.Sosnovskij, A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, K.Zhirkov, E.Gorbovskoy,
G.Antipov, N.Tiurina, Ya.Kechin, V.Senik, A.Chasovnikov, V.Topolev,D.Vlasenko, A.Sankovich, I.Gorbunov, V.Fedorova, A.Telnova (Lomonosov MSU),
N.Budnev, O.Gress (ISU),
F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU),
D.Buckley (SAAO),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich  (Blagoveschensk Educational StateUniversity)
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)

MASTER-Tavrida robotic telescope of MASTER Global Robotic Net [1-4]
was pointed to the SVOM GRB260516A (Brunet et al. GCN 44622) error-box at 2026-05-15 19:19:18UT (notice time=2026-05-15 19:18:47)
with upper limit up to  19.6m at single images.

 MASTER OT J151044.43+243321.7 / AT2026msu  detection by Lomonosov MSU:

MASTER-Tavrida auto-detection system discovered OT source
at (RA, Dec) = 15h 10m 44.43s +24d 33m 21.7s on 2026-05-15.80648 UT.

The OT magnitude (unfiltered) is 17.4m (mlim=19.1).

The OT is seen in all images. There is no minor planet at this place.

We have reference image on 2024-03-17.95291 UT with unfiltered mlim=19.5m.

Spectral observations are required.

Optical counterpart first was publishied by JinShan 100B Telescope (He et al. GCN 44623) and observed by Svom/VT (GCN 44624)

Real time updated cover map and OT are available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3316865


[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel
Astrophysics,Lomonosov MSU PRESS, 591pp.
 http://www.pereplet.ru/lipunov/625.html#625

GCN Circular 44624

Subject
GRB 260515A: SVOM/VT optical candidate from VHF data
Date
2026-05-15T20:26:50Z (20 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form

A. Saccardi, J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team.

After the trigger by SVOM/ECLAIRs at 2026-05-15T19:08:19 UTC (T0), SVOM performed an automatic slew on the burst location (Brunet et al., GCN 44622

Loading...
 
 
). SVOM/VT began observing the field at 2026-05-15T19:12:34, 254.71 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.

VT_ID 32: The position of this candidate is R.A., Dec. 227.6852, 24.5562 degrees, corresponding to: R.A. (J2000) = 15h10m44.4s Dec. (J2000) = 24d33m22.4s with an uncertainty of 0.50 arcsec. This location is consistent with the optical afterglow reported by He et al. (GCN 44623

Loading...
 
 
).

This candidate was detected in both VT_R and VT_Band was flagged as an uncatalogued source. The candidate's magnitudes are:

| date-obs (UTC)  | mid-time  | exposure  | VT_B mag(AB)  | VT_R mag(AB)  | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-15T19:12:34  | 5.08 min  | 2*50 sec  | 16.16 ± 0.01  | 15.78 ± 0.01  |

Magnitudes were not corrected for Galactic reddening.

The mean color of VT_B - VT_R = 0.38 is in line with the expectations of an event at redshift z < 4.

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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.

The Burst Advocate (BA) on shift for this alert is Andrea Saccardi: andrea.saccardi@cea.fr. Please contact the BA by email if you require additional information.

GCN Circular 44623

Subject
GRB 260515A: JinShan optical counterpart candidate
Date
2026-05-15T19:51:51Z (20 days ago)
Edited On
2026-05-17T22:48:07Z (18 days ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, Z.P. Zhu, X. Liu, D. Xu, J. An, S.Q. Jiang (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report:

We observed the field of GRB 260515A (sb26051504; Brunet et al., GCN 44622) using the JinShan 100B telescope located at Altay, Xinjiang, China. We obtained a series of frames in the Sloan i-band.

An uncatalogued and varying source is detected within the SVOM/ECLAIRs error circle at coordinates
R.A. (J2000) = 227.6852 deg
Dec. (J2000) = 24.5562 deg
with an uncertainty of ~ 1.0 arcsec. The source had i ~ 16.5 mag at a median time of ~ 11 min post-trigger, calibrated with Pan-STARRS1 DR2 and not corrected for Galactic extinction.

We acknowledge the excellent support from T.Q. Chen, and J.F. Zhang for enabling these observations.

GCN Circular 44622

Subject
GRB 260515A: SVOM detection of a burst
Date
2026-05-15T19:36:12Z (21 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, L. Bouchet (IRAP), A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu) report on behalf of the SVOM mission team:

At 2026-05-15T19:08:19 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260515A (SVOM burst-id sb26051504).

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 17 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 24.06 in the [5-20] keV energy band over a time window of 10.20 seconds starting at 2026-05-15T19:08:19.

The localization of the best alert is R.A., Dec. 227.6800, 24.5706 degrees:
R.A. (J2000) = 15h10m43.20s
Dec. (J2000) = 24d34m14.13s
with a 90% confidence level (C.L.) radius of 3.77 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of 16.6 +/-1.5 s in the 5-120 keV.

This burst was also detected by SVOM/GRM with a significance of 10.2 .

SVOM slewed to the burst.

MXT and 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 Andrea Saccardi (CEA): andrea.saccardi@cea.fr
Please contact the BA by email if you require additional information.
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