GRB 260727A — All Circulars

Ziming Wang (BNU), Ruizhi Li (YNAO), An Li (BNU), Yifang Liang (PMO), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Clara Plasse (HKU) report on behalf of the SVOM mission team:

EP-FXT performed a second epoch of follow-up observation of GRB 260727A (Li et al., GCN 45220; Harsha K. H. et al., GCN 45225; Cheung et al., GCN 45233; Svinkin et al., GCN 45242; Wang et al. GCN 45247). The follow-up observation started at 2026-07-30 00:38:00 (UTC), about 72.3 hours after the SVOM-ECLAIRs trigger, with a total exposure time of around 2.5 ks. 

A faint X-ray source was detected at the position of the uncatalogued X-ray source (Li et al., GCN 45236). The 0.5-10 keV spectrum can be fitted by an absorbed powerlaw model with a Galactic hydrogen column density of 0.55 x 10^22 cm^-2 and a photon index of 2.09 +1.07/-1.29. The average unabsorbed flux is 1.58 (+2.52, -0.93) x 10^(-13) erg/s/cm^2 in the 0.5-10 keV energy band (90% C.L.).

The Burst Advocate (BA) on shift for this alert is Ziming Wang: 202421101144@mail.bnu.edu.cn.
Please contact the BA by email if you require additional information.

M. Brunet (IRAP), R. Li (YNAO), Z. Wang (BNU) 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 260727A (SVOM burst-id sb26072701 – GCN 45220, trigger time T0 = 2026-07-27T00:22:02 UTC), which was also detected by SVOM/GRM (GCN 452457), AstroSat/CZTI  (GCN 45225), Glowbug (GCN 45233), and Konus-Wind (GCN 45242). 

The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 66.5+/-2.5 s in the 4-120 keV energy band.

The time-averaged spectrum from T0-3.5 s to T0+112 s in the 5-120 keV energy range is best fitted by a powerlaw with an exponential cutoff model with alpha = -1.03 +/-0.03 and a peak energy = 72 +4/-3 keV. With this model, the 4-120 keV fluence is (1.38 +/-0.02)e-5 erg/cm^2 and the 4-120 keV photon flux is 3.17 +/-0.03 ph/cm^2/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)

N. Pankov (IKI), A. Moskvitin (SAO RAS), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), M. Zhuzhunadze (AbAO) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 260727A (Li et al., GCN 45220; Harsha. et al., GCN 45225; Cheung et al., GCN 45233; Li et al., GCN 45236; Svinkin et al., GCN 45242; Wang et al., GCN 45247) with the 0.7m AS-32 telescope of Abastumani Observatory (AbAO) and the Zeiss-1000 1m telescope of the Special Astrophysical Observatory of the RAS (SAO RAS). The observations started on 2026-07-27 at 19:15:15 UT (~0.81 days after the SVOM trigger) at AbAO. The series of 70x60 s exposures in the R-band was obtained using the CCD-photometer. The observations continued at SAO RAS starting 2026-07-28 at 00:12:38 UT (~ 1.0 days since trigger). The series of 6x300 s exposures was obtained in the Rc-band using the CCD-photometer. We performed catalog search and image subtraction (against the PS1 r-band template image) on co-add images from both observatories. The observational properties are provided further.

Date       UT start  t-T0         Exp.    Filter  UL(3sigma) Site/Telescope
                     (mid, days)  (s)
2026-07-27 19:15:15  0.81092      69x60   R       20.9       AbAO/AS-32
2026-07-28 00:12:38  1.00509      6x300   Rc      22.9       SAO RAS/Zeiss-1000

No optical candidates were found in the EP-FXT error circle (Li et al., GCN 45236) up to limiting magnitude presented above.

The field was also observed in optical by (Shi et al., GCN 45223; Freeberg et al., GCN 45224; Starling et al., GCN 45226; Lechapelain&Midavaine, GCN 45228; Mohan et al., GCN 45231; Bochenek et al., GCN 45240) but no candidate transients were reported.

The photometry is based on nearby stars from USNO-B1.0. No correction has been made for the Galactic extinction.

SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Feliu Lacreu (IAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in flight by GRB 260727A at 2026-07-27T00:22:01.000 UTC (T0), which is also detected by SVOM/ECLAIRs (Li et al., GCN #45220), AstroSat/CZTI (Harsha K. H. et al., GCN #45225), Glowbug (Cheung et al., GCN #45233) and Konus-Wind (Svinkin et al., GCN #45242).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple broad peaks with a T90 of 53 +3/-2 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/svgrb260727A.png

In addition, the position of this burst, as determined by EP/FXT (RA = 331.7702 deg, Dec = 74.5296 deg, Err = 10 arcsec; GCN #45236), is located at about 23.7 degrees from the SVOM optical axis.

With this localization, the time-averaged spectrum from T0-3 to T0+70 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.64 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 81.7 +3.0/-2.7 keV. The event fluence (10-1000 keV) in this time interval is (1.352 +0.034/-0.032)E-05 erg/cm^2.

The localization of GRB 260727A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn/gcn/2026/svgrb260727A_amati.png
The localization of GRB 260727A in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn/gcn/2026/svgrb260727A_yonetoku.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/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang@ihep.ac.cn)

D. Svinkin, D. Frederiks, A. Lysenko, V. Panteleeva,
A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 260727A
(SVOM-ECLAIRs detection: Li et al., GCN 45220;
AstroSat-CZTI detection: Harsha et al., GCN 45225;
Glowbug detection: Cheung et al., GCN 45233)
triggered Konus-Wind at T0=1327.631 s UT (00:22:07.631).

The burst light curve shows a multi-peaked structure
which starts at ~T0-11 s and has a total duration of ~30 s (75-1200 keV).
The emission is seen up to ~300 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260727_T01327/

As observed by Konus-Wind, the burst
had the total fluence of 1.15(-0.03,+0.03)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.072 s,
of 1.61(-0.30,+0.30)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.20(-0.11,+0.11)
and Ep = 85(-2,+2) keV (chi2 = 107/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -4.2
(chi2 = 107/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
with alpha = 0.02(-0.14,+0.14)
and Ep = 93(-3,+3) keV (chi2 = 80/82 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.8
(chi2 = 80/81 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

A. Bochenek, D. A. Perley (LJMU), report:

We observed the field of GRB 260727A (Li et al. GCN 45220) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS r and i filters, starting at 2026-07-28 01:07:14 UT, approximately 24.75. hours after trigger.

The images were stacked, and the stacks were subtracted from PanSTARRS reference images, using PSF matching through PSF convolution, with the help of PSFEx. We do not detect any new sources in the SVOM/IMT error region (Li et al. GCN 45220) down to 3-sigma limiting magnitudes of r > 22.17 and i > 22.05 mag. We note that the image subtraction is partially affected by two bright stars located close to the edge of the error region.

The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.

Ruizhi Li (YNAO), Ziming Wang (BNU), An Li (BNU), Yifang Liang (PMO), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Clara Plasse (HKU) and Andrea Saccardi (CEA) report on behalf of the SVOM mission team:

EP-FXT performed a follow-up observation of GRB 260727A detected by SVOM/ECLAIRs (Li et al., GCN 45220), which also triggered AstroSat CZTI (Harsha K. H. et al., GCN 45225) and Glowbug (Cheung et al., GCN 45233). The follow-up observation started at 2026-07-27T05:27:41 (UTC), about 5.09 hours after the SVOM-ECLAIRs trigger, with a total exposure time of around 6.1 ks. 

An uncatalogued X-ray source was found within the ECLAIRs error circle. The position of the source is at R.A., Decl. = 331.7702, 74.5296 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The 0.5-10 keV spectrum can be fitted by an absorbed powerlaw model with a Galactic hydrogen column density of (0.55 +/-0.10) x 10^22 cm^-2 and a photon index of 2.61 +/- 0.07. The average unabsorbed flux is 2.65 (+0.55, -0.35) x 10^(-12) erg/s/cm^2 in the 0.5-10 keV energy band (90% C.L.).

Optical follow-up observations of the burst were carried out by LCO (Shi et al., GCN 45223), Kilonova-Catcher (Freeberg et al., GCN 45224), GOTO (Starling et al., GCN 45226), RAPAS (Lechapelain et al., GCN 45228), and WINTER (Mohan et al., GCN 45231).

The Burst Advocate (BA) on shift for this alert is Ziming Wang: 202421101144@mail.bnu.edu.cn.
Please contact the BA by email if you require additional information.

C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:

The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260727A, which was also detected by SVOM (GCN 45220) and AstroSat (GCN 45225). 

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-07-27 00:21:57.592 with a duration of 22.5 s and a total significance of about 24.2 sigma.  The emission seen by Glowbug corresponds to the brightest portion of the burst seen in the AstroSat light curve, and is a subset of the full emission episode observed by SVOM.

The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.

Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.  It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. 

[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O 
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 

Distribution Statement A: Approved for public release.  Distribution is unlimited.

Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:

We observed the field of GRB 260727A (Li et al., GCN 45220; Harsha et al., GCN 45225) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2026-07-27T04:17:32.122 UTC in the J band (3.93 hr after the SVOM/ECLAIRs trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).

We do not detect any new source in the SVOM localization (Shi et al., GCN 45223; Freeberg et al., GCN 45224; Starling et al., GCN 45226; RAPAS network, GCN 45228) in our stacked image. We obtain the following 5-sigma upper limit: J = 19.19 mag (AB).

WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.

Pierre-Yves Lechapelain and Thierry Midavaine report on behalf of the RAPAS network:

We observed the field of GRB 260727A (SVOM/ECLAIRs trigger sb26072701; Li et al., GCN 45220) in response to the overlapping SVOM broker alert sb26072702 (RA = 331.626 deg, Dec = +74.549 deg, J2000, 2.5 arcmin error radius). Observations were obtained with the RAPAS 0.25 m f/3 robotic telescope and IMX533 sensor at Observatoire de Bretagne Sud (Y80), using RAPAS filters matched to the Gaia G, Gbp, and Grp bands. Data were reduced with the STDPipe/stdweb pipeline; photometry and astrometry are calibrated to Gaia DR3 with spatially varying zero points and color terms.

Observations began at 2026-07-27 00:48 UTC (T_GRB + 26 min, with T_GRB = 2026-07-27 00:22:02 UTC from GCN 45220) and continued in a G / Gbp / Grp cycle with 30 s exposures until approximately 02:44 UTC (T_GRB + 2.4 hr).

We detect no optical afterglow at the sb26072702 position. Forced aperture photometry at RA = 331.626 deg, Dec = +74.549 deg shows no significant excess on the earliest G exposure (flux S/N = 1.8) or on the deep G co-add (flux S/N = 3.6, below our 5σ detection threshold). No Gaia-uncatalogued source is found within the 2.5 arcmin SVOM error circle. A comparison to Gaia DR3 in a 12 arcmin (0.2 deg) radius around the alert on the first G frame yields five marginal transient candidates at 7–11 arcmin offset; none are confirmed in deeper co-added images. Searches over the full unvignetted RAPAS field (~0.62 deg radius) reveal no plausible afterglow at the SVOM coordinates.

We report 5σ limiting magnitudes (Vega, Gaia-calibrated) from the global detection limits of each reduction:

Earliest epoch per band (single frame or shortest stack in the sequence):

| T_mid - T_GRB | Exp        | Band | Limit (5σ) | Note        |
|---------------|------------|------|------------|-------------|
| +25 min       | 1 × 30 s   | G    | >18.3      |             |
| +31 min       | 2 × 30 s   | G_BP | >18.6      |2-frame stack|
| +36 min       | 2 × 30 s   | G_RP | >17.4      |2-frame stack|

Co-added images from the ToO night:

| Band | Co-add      | Limit (5σ) |
|------|-------------|------------|
| G    | 17 × 30 s   | >20.1      |
| G_BP | 18 × 30 s   | >19.9      |
| G_RP | 14 × 30 s   | >18.6      |

Mid-exposure times correspond to the first useful epoch in each band and to the weighted mean epoch of each co-added stack, respectively.

Acknowledgements :
RAPAS ( https://gemini.obspm.fr/20220101-rapas/ ) is a ProAm collaboration created by T. Midavaine (SAF), W. Thuillot (LTE, Obs. de Paris-PSL) and M. Dennefeld (IAP/CNRS and Sorbonne Univ.) and funded by the Paris Observatory under API ProAm of the Scientific Council. It aims at homogenizing observing procedures and filters, and is delivering to a network of french amateur observatories a set of 3 filters which have been chosen to meet the Gaia G, Gbp and Grp spectral bands. This network produces data on  astrophysical alerts delivered by various Alert systems (Gaia Alerts, Atlas, ZTF, etc…) and collected by Astro-COLIBRI ( https://astro-colibri.science ). It is similarly progressing towards an homogeneous spectroscopic equipment to deliver SED. Paris Observatory PADC which is on the way to archive all the FITS files with attached processing pipeline.

R. Starling, M. Kennedy, D. O'Neill, B. P. Gompertz, G. Ramsay, A. Kumar, S. Belkin, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, I. Worssam on behalf of the GOTO collaboration

We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM/ECLAIRs detected GRB 260727A (sb26072701, Li et al. 2026, GCN 45220), also detected by AstroSat (Harsha et al.2026, GCN 45225).

Observations at the ECLAIRs position began at 2026-07-27 00:27:22 UT (+5.8 minutes post trigger) and continued to 2026-07-27 01:47:11 UT (+1.4h post trigger). Images consisted of 4x90s exposures in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Any source candidates are initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs (Lyman et al. 2026).

We found no new transients that could be credibly associated with 260727A within the localisation down to a 5-sigma depth of L<20.2 AB mag.

GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).

Harsha K. H. (IUCAA), S.Salunke(IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 long GRB 260727A which was also detected by SVOM/ECLAIRs (An Li et.al., GCN Circ. 45220).

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 2026-07-27 00:22:10.26 UTC. The measured peak count rate associated with the burst is 72 (+26, -7) counts/s above the background in the combined data of two quadrants (out of four), with a total of 743 (+158, -105) counts. The local mean background count rate was 118 (+1, -2) counts/s. We measure a T90 of 20 (+3, -1) s from the cumulative CZT light curve. 

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 2026-07-27 00:22:01.23 UTC. The measured peak count rate associated with the burst is 149 (+43, -18) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1666 (+284, -314) counts. The local mean background count rate was 476 (+3, -4) counts/s. We measure a T90 of 20 (+2, -3) s from the cumulative Veto light curve.

CZTI data products like interactive and downloadable light curves for this GRB can be found at: 
https://astrosat.iucaa.in/cift/cift_products/ET20260727T002157/ET20260727T002157_details.html

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

M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:

We observed the field of GRB 260627A detected by SVOM/ECLAIRs (Li et al., GCN 45220) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a TEC 180  telescope operated by M. Freeberg. Our observations started at TGRB+3.12 hours and were taken with the sdssr filter.

In our stacked frames, subtracted from the PanSTARRS DR2 template image, we do not detect any optical counterpart.

We report our follow-up results in the table below:

| Tmid-TGRB (hr)| Exp (s)      | Filter         | Magnitude      | Instrument  |
| ------------  | ------------ |------------    |------------    |------------ |
| 3.38          | 10 x 180s    | r (AB)         | 19.8 (5 sigma) | TEC180      | 

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022).  Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog.

We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). 

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).

Y.Y. Shi (GXU), C. Wu, L.P. Xin (NAOC), A. Saccardi, D. Turpin (CEA/Irfu), Z.M. Wang, R.Z. Li (BA-F) report on behalf of the SVOM mission team:


We observed the field of GRB 260727A (SVOM burst-id sb26072701) detected by SVOM (Li et al., GCN 45220) with the LCO 1m telescope at Tenerife Observatory equipped with the Sinistro instrument.

Our observation started on 2026-07-27 at 02:31:21 UT (about 2.16 hr after the trigger) and we obtained 3x200 s exposures in the Pan-STARRS z filters.

In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:

z > 20.2 AB (5-sigma, mid-time 2.25 hr after the trigger).

This project is funded by the SVOM collaboration.

An Li (BNU), Yifang Liang (PMO), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Clara Plasse (HKU), Ruizhi Li (YNAO), Ziming Wang (BNU) report on behalf of the SVOM mission team:
At 2026-07-27T00:22:02 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260727A (SVOM burst-id sb26072701).

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 41 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 111.24 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2026-07-27T00:21:34.

The localization of the best alert is R.A., Dec. 331.6445, 74.5406 degrees:
R.A. (J2000) = 22h06m34.69s
Dec. (J2000) = 74d32m25.98s
 with a 90% confidence level (C.L.) radius of 2.12 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a multiple peak structure with long duration. The SVOM/GRM light curve showed a multiple broad peak structure with long duration.

This burst does not satisfy the SVOM pointing constraints due to its angular separation from the Sun, and therefore no ToO follow-up observations will be performed by SVOM.

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 Ziming Wang: 202421101144@mail.bnu.edu.cn.
Please contact the BA by email if you require additional information.

An Li (BNU), Yifang Liang (PMO), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Clara Plasse (HKU), Ruizhi Li (YNAO), Ziming Wang (BNU) report on behalf of the SVOM mission team:
At 2026-07-27T00:22:02 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260727A (SVOM burst-id sb26072701).

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 41 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 111.24 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2026-07-27T00:21:34.

The localization of the best alert is R.A., Dec. 331.6445, 74.5406 degrees:
R.A. (J2000) = 22h06m34.69s
Dec. (J2000) = 74d32m25.98s
 with a 90% confidence level (C.L.) radius of 2.12 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a multiple peak structure with long duration. The SVOM/GRM light curve showed a multiple broad peak structure with long duration.

This burst does not satisfy the SVOM pointing constraints due to its angular separation from the Sun, and therefore no ToO follow-up observations will be performed by SVOM.

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 Ziming Wang: 202421101144@mail.bnu.edu.cn.
Please contact the BA by email if you require additional information.