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GRB 260511A

GCN Circular 44686

Subject
GRB 260511A: iTelescope T-75 optical detection
Date
2026-05-21T22:55:39Z (4 months ago)
From
Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>
Via
Web form
H. Ban, T. Kato, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU)

We observed the field of GRB 260511A detected by
the Fermi/GBM (Fermi GBM Team, GCN Circ. 44529),
the SVOM/ECLAIRs (Godet et al., GCN Circ. 44532),
the NuSTAR CsI anti-coincidence shields (Waratkar et al., GCN Circ. 44555),
the Konus-Wind (Ridnaia et al., GCN Circ. 44585),
the Glowbug (Woolf et al., GCN Circ. 44586), and
the GRID (Li et al., GCN Circ. 44664)
with the iTelescope.Net (http://www.itelescope.net) T75 (ASAN250) telescope
located at Rio Hurtado Valley, Chile.

We took 20 images of 60 sec exposures in the Red filter starting from 
May 11 at 06:37:27 (UT), about 24 minutes after the Fermi/GBM trigger 
and stopped at 07:07:42.

The afterglow (Jiang et al., GCN Circ. 44533; Akl et al., GCN Circ. 44534;
Saccardi et al., GCN Circ. 44535; Zheng et al., GCN Circ. 44536;
Wu et al., GCN Circ. 44538; Harper et al., GCN Circ. 44545; 
Brivio et al., GCN Circ. 44562; Li et al., GCN Circ. 44575; 
Fu et al., GCN Circ. 44579; Zhu et al., GCN Circ. 44584) is detected
in the stacked image of the first eight images (total exposure of 480 s) 
collected between 06:37:27 and 06:49:12. The afterglow magnitude is 
19.3 +- 0.6 using the USNO-B1 catalog. No afterglow was detected in 
the following twelve images collected between 06:49:44 and 07:07:42.
The 5-sigma upper limit of the stacked image of the last twelve images 
(total exposure of 720 s) is 18.3 mag.

GCN Circular 44664

Subject
GRID detection of GRB 260511A
Date
2026-05-19T08:18:09Z (4 months ago)
From
GRID Student Team at Tsinghua University <grid@tsinghua.edu.cn>
Via
Web form
Longhao Li, Siqi Wu, Chenyu Wang, report on behalf of the GRID Collaboration:

GRID-10B and GRID-11B reports the detection of the long-duration GRB 260511A, which was also detected by Fermi GBM (GCN Circular 44529), SVOM (GCN Circular 44532), NuSTAR(GCN Circular 44555), MASS-Cube(GCN Circular 44584), Konus-Wind (GCN Circular 44585), Glowbug(GCN Circular 44586).

The event was triggered with GRID on 2026-05-11 at 06:13:30 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately T90 = 26.0 +/- 1.3 seconds. 

The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260511A/GRID_260511A_ltcv.pdf. 

GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4.

GCN Circular 44586

Subject
GRB 260511A: Glowbug gamma-ray detection
Date
2026-05-12T17:03:10Z (4 months ago)
From
Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ@us.navy.mil>
Via
Web form
R. Woolf, C.C. Cheung, 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 260511A, which was also detected by Fermi GBM (GCN 44529), SVOM (GCN 44532), NuSTAR (GCN 44555), and Konus–Wind (GCN 44585).

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-11 06:13:28.904 with a duration of 11.3 s and a total significance of about 41.6 sigma. The light curve comprises three primary peaks from T0 to ~T0+11s. 

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.

GCN Circular 44585

Subject
Konus-Wind detection of GRB 260511A
Date
2026-05-12T16:55:02Z (4 months ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 260511A
(Fermi-GBM detection: Fermi GBM team, GCN 44529;
Roberts et al., GCN 44548; 
BALROG localization: Preis & Greiner, GCN 44531;
SVOM detection: Godet et al., GCN 44532;
NuSTAR detection: Waratkar et al., GCN 44555) 
triggered Konus-Wind at T0=22416.401 s UT (06:13:36.401).

The burst light curve shows a multipeaked structure
which starts at ~T0-4.6 s and has a total duration of ~20.5 s.
The emission is seen up to ~6 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260511_T22416/

As observed by Konus-Wind, the burst
had a fluence of 1.72(-0.05,+0.05)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.482 s,
of 6.96(-0.71,+0.71)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 = -0.79(-0.08,+0.09)
and Ep = 187(-8,+8) keV (chi2 = 107/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.1
(chi2 = 107/98 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:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.66(-0.08,+0.08)
and Ep = 187(-6,+7) keV (chi2 = 88/86 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.9
(chi2 = 87/85 dof).

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

GCN Circular 44584

Subject
MASS-Cube (GRID 2.0) detection of GRB 260511A
Date
2026-05-12T16:35:13Z (4 months ago)
From
GRID Student Team at Tsinghua University <grid@tsinghua.edu.cn>
Via
Web form
Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration:

MASS-Cube reports the detection of the long-duration GRB 260511A, which was also observed by Fermi/GBM (GCN #44548, #44548), SVOM (GCN #44532) and GRID. The optical counterpart was detected by TRT (GCN #44533).

The event was triggered by MASS-Cube on 2026-05-11 at 06:13:29.2 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 9.7 +/- 2.3 seconds. The second peak is not clearly detected by MASS-Cube due to its limited sensitivity.

The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260511A/MASS_Cube_260511A_ltcv.pdf.

MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4.

GCN Circular 44579

Subject
GRB 260511A: EP-FXT follow-up observation
Date
2026-05-12T13:12:09Z (4 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
S.-Y. Fu (HUST), X. Tian (GXU), H.-N. Yang, Z.-X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260511A (SVOM/sb26051101, Godet et al., GCN 44532), which also triggered Fermi-GBM (Fermi GBM team, GCN 44529). The follow-up obervation started at 2026-05-11T07:00:13 UTC, approximately 46.7 minutes after the SVOM trigger, with a total exposure time of 2.2ks.

On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 197.8992, -33.8042 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) near the ECLAIRs error circle. This position is consistent with the optical counterpart reported by TRT (Jiang et al., GCN 44533) and FM-GFT (Akl et al. GCN 44534). 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, adittional hydrogen column density of 5.9 (+-1.3) ×10^20 cm^-2, and a photon index of 1.93 +- 0.05. The derived average unabsorbed flux in the 0.3-10 keV band is 6.33 (+-0.18)×10^-11 erg s^-1 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 44575

Subject
GRB 260511A: SVOM/VT optical observations
Date
2026-05-12T09:53:21Z (4 months ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, C. Wu, Y. L. Qiu, 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 (CEA/Irfu) report on behalf of the SVOM/VT team.

SVOM/VT performed ToO observations of GRB260511A triggered by SVOM/ECLAIRs (sb26051101, Godet et al., GCN 44532). The burst was also detected by Fermi/GBM (Fermi GBM team, GCN 44529; Preis et al., GCN 44531; Preis et al., GCN 44531; Roberts et al., GCN 44548) and NuSTAR (Waratkar et al. GCN 44555). The observation started at 2026-05-11T22:13:58 UTC, about 16.0 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

The afterglow (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538, Harper et al., GCN 44545; Brivio et al., GCN 44562) was detected in stack images of both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time | Brightness
 18.00 h   VT_B     35*70 s     23.43 +/- 0.27 mag
 18.00 h   VT_R     39*70 s     21.82 +/- 0.13 mag    

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 44562

Subject
GRB 260511A: REM near-infrared detection
Date
2026-05-11T18:00:39Z (4 months ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB), A. Melandri (INAF-OAR) report on behalf of the REM team:

We observed the field of GRB 260511A, detected by SVOM/ECLAIRs (Godet et al., GCN 44532) and Fermi/GBM (Fermi GBM Team, GCN 44529) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile).                 
The observations were carried out in the H band, started on 2026-05-11 at 06:15:22 UT (i.e. 110 s after the burst) and lasted for about 10 minutes.

From preliminary photometry, we  detect the optical/NIR counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538, Harper et al., GCN 44545) with the following magnitude:


H = 12.9 +/- 0.2 (Vega; calibrated against the 2MASS catalogue),
 at a mid-time of 115 s after the trigger.

GCN Circular 44555

Subject
GRB 260511A: NuSTAR detection of prompt emission
Date
2026-05-11T16:06:48Z (4 months ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:

The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260511A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper.

The NuSTAR SINGS algorithm, triggered at 2026-05-11T06:13:30.0 UTC, shows a detection of GRB 260511A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44529) and SVOM (Godet et al., GCN 44532).

The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~10-s burst consistent with Fermi/GBM. The peak count rate is ~3500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. 

The optical counterpart candidate (Akl et al., GCN 44534) at RA = 197.8996, Dec = -33.80446 implies an offset from the NuSTAR boresight of 57-deg and an offset from the geocenter of 144-deg.

Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260511A       

Information on NuSTAR SINGS can be found here: 
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/     

NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.

GCN Circular 44548

Subject
GRB 260511A: Fermi GBM Detection
Date
2026-05-11T13:25:00Z (4 months ago)
From
oliver.roberts@universityofgalway.ie
Via
Web form
O.J. Roberts (Uni. Of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 06:13:30.286 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260511A (trigger 800172815/260511259), which was 
also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44532), with 
an optical counterpart was initially detected by Colibri (Akl et al. 2026, GCN 44534).
The angle from the Fermi LAT boresight is 118 degrees.

The GBM light curve consists of a two bright emission episodes with a duration (T90)
of about 14 s (50-300 keV). The time-averaged spectrum from T0-0.26 to T0+18.43 s is 
best fit by a Band function, with Epeak = 166 +/- 9 keV, alpha = -0.66 +/- 0.05,  
and beta = -2.31 +/- 0.07.

The event fluence (10-1000 keV) in this time interval is
(1.973 +/- 0.032) E-05 erg/cm^2. The 1-s peak photon flux measured
starting from T0+2.6 s in the 10-1000 keV band is 27.3 +/- 0.5 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

GCN Circular 44545

Subject
GRB 260511A: UTGO H50 optical afterglow observation
Date
2026-05-11T12:13:03Z (4 months ago)
Edited On
2026-05-20T13:06:20Z (4 months ago)
From
Harrison at University of Tasmania <hgharper9962@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Harrison at University of Tasmania <hgharper9962@gmail.com>
Via
Web form

H. Harper (UTAS), K. Siellez (UTAS), B. Emptage (UTAS), K. Hill (UTAS), T. Plunkett (UTAS), A. Cole (UTAS), J.-P. Beaulieu (IAP/UTAS) report:

We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN 44532; Fermi GBM Team, GCN 44529) with the Harlingten 50cm (H50) at Greenhill Observatory, University of Tasmania (UTGO).

Our observation started on 2026-05-11 at 08:58:59UT, ~165 minutes after Fermi trigger Observations. We obtained 11 x 120s exposure in the SDSS r’ filter.

The optical counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538) is clearly detected in our stacked images at RA = 13:11:35.9244 (J2000) (197.8996850 deg) and Dec = -33:48:15.887 (J2000) (-33.8044130 deg) with an uncertainty of ~0.4 arcsec.

All the data have been reduced by our UTGO pipeline (Plunkett et al. 2025), image subtraction was performed using STDpipe (Karpov 2025). We measured the following magnitude not corrected for Galactic extinction:

r = 20.68 +/- 0.12 AB (mid time ~176minutes after trigger)

Refined processing and more observations are still ongoing.

GCN Circular 44538

Subject
GRB 260511A: SVOM/VT optical observation with VHF data
Date
2026-05-11T09:18:19Z (4 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form

C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), Y.N. Ma, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), L. Zhang (IHEP), D. F. Kong (GXU) on behalf of the SVOM/VT team.

After the trigger by SVOM/ECLAIRs at 2026-05-11T06:13:32 UTC (T0), SVOM performed an automatic slew on the burst location ( Godet et al., GCN 44532

Loading...
 
 
; Fermi GBM team, GCN 44529;Preis et al., GCN44531). SVOM/VT took images of the field 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, the candidate (Jiang et al., GCN 44533

Loading...
 
 
; Akl et al., GCN 44534; Saccardi et al., GCN 44535; Zheng et al., GCN 44536) was clearly detected in VT-VHF data. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded over the course of the VT observations. The candidate's magnitudes are:

date-obs (UTC)mid-timeexposureVT_B mag(AB)VT_R mag(AB)
2026-05-11T06:26:52.00013.32 min6*50 sec--18.61 ± 0.02
2026-05-11T07:42:49.00089.27 min6*50 sec21.15 ± 0.0819.65 ± 0.07

Magnitudes were not corrected for Galactic reddening. ( Note: The missing VT_B magnitude is likely caused by onboard processing interference. )

The color of VT_B - VT_R = 1.5 is in line with the expectations of an event at redshift z < 4. Further follow-up is encouraged.

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.

GCN Circular 44537

Subject
Fermi GRB 260511A: Global MASTER-Net observations report
Date
2026-05-11T08:30:44Z (4 months 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-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260511A ( Fermi GBM team, GCN 44529) errorbox  5184 sec after notice time and 5215 sec after trigger time at 2026-05-11 07:40:25 UT, with upper limit up to  20.5 mag. The observations began at zenith distance = 64 deg. The sun  altitude  is -45.2 deg. 

MASTER-OAGH robotic telescope  located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260511A errorbox  6822 sec after notice time and 6853 sec after trigger time at 2026-05-11 08:07:44 UT, with upper limit up to  19.5 mag. The observations began at zenith distance = 77 deg. The sun  altitude  is -39.6 deg. 

The galactic latitude b = 29 deg., longitude l = 310 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3306895

We obtain a following upper limits.  

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

    5246 | 2026-05-11 07:40:25 |         MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.4s) |   C |    60 | 19.5 |        
    5306 | 2026-05-11 07:40:25 |         MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) |   C |   180 | 20.0 |  Coadd 
    5366 | 2026-05-11 07:40:25 |         MASTER-OAFA | (13h 10m 55.68s , -33d 35m 27.5s) |   C |   300 | 20.0 |  Coadd 
    5636 | 2026-05-11 07:40:25 |         MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) |   C |   840 | 20.5 |  Coadd 
    5322 | 2026-05-11 07:41:42 |         MASTER-OAFA | (13h 10m 55.74s , -33d 37m 08.5s) |   C |    60 | 19.4 |        
    5400 | 2026-05-11 07:43:00 |         MASTER-OAFA | (13h 10m 59.00s , -33d 35m 34.7s) |   C |    60 | 19.2 |        
    5475 | 2026-05-11 07:44:14 |         MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) |   C |    60 | 19.5 |        
    5535 | 2026-05-11 07:44:14 |         MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) |   C |   180 | 20.0 |  Coadd 
    5554 | 2026-05-11 07:45:34 |         MASTER-OAFA | (13h 10m 53.06s , -33d 35m 26.1s) |   C |    60 | 19.3 |        
    5631 | 2026-05-11 07:46:51 |         MASTER-OAFA | (13h 10m 59.98s , -33d 36m 26.7s) |   C |    60 | 19.4 |        
    5708 | 2026-05-11 07:48:07 |         MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.2s) |   C |    60 | 19.3 |        
    5768 | 2026-05-11 07:48:07 |         MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.1s) |   C |   180 | 19.9 |  Coadd 
    5781 | 2026-05-11 07:49:21 |         MASTER-OAFA | (13h 11m 00.12s , -33d 37m 27.8s) |   C |    60 | 19.3 |        
    5858 | 2026-05-11 07:50:37 |         MASTER-OAFA | (13h 10m 56.28s , -33d 35m 51.6s) |   C |    60 | 19.4 |        
    5935 | 2026-05-11 07:51:54 |         MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) |   C |    60 | 19.3 |        
    5995 | 2026-05-11 07:51:54 |         MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) |   C |   180 | 19.9 |  Coadd 
    6012 | 2026-05-11 07:53:11 |         MASTER-OAFA | (13h 10m 58.63s , -33d 35m 39.5s) |   C |    60 | 19.3 |        
    6087 | 2026-05-11 07:54:27 |         MASTER-OAFA | (13h 10m 52.96s , -33d 36m 32.8s) |   C |    60 | 19.2 |        
    6163 | 2026-05-11 07:55:43 |         MASTER-OAFA | (13h 10m 53.42s , -33d 35m 33.6s) |   C |    60 | 19.2 |        
    6223 | 2026-05-11 07:55:43 |         MASTER-OAFA | (13h 10m 53.41s , -33d 35m 33.6s) |   C |   180 | 19.9 |  Coadd 
    6239 | 2026-05-11 07:56:59 |         MASTER-OAFA | (13h 10m 59.31s , -33d 36m 35.2s) |   C |    60 | 19.2 |        
    6313 | 2026-05-11 07:58:13 |         MASTER-OAFA | (13h 10m 52.93s , -33d 37m 36.1s) |   C |    60 | 19.2 |        
    6391 | 2026-05-11 07:59:31 |         MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.1s) |   C |    60 | 19.2 |        
    6451 | 2026-05-11 07:59:31 |         MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.2s) |   C |   180 | 19.8 |  Coadd 
    6464 | 2026-05-11 08:00:44 |         MASTER-OAFA | (13h 10m 57.03s , -33d 35m 54.4s) |   C |    60 | 19.1 |        
    6541 | 2026-05-11 08:02:01 |         MASTER-OAFA | (13h 10m 57.13s , -33d 37m 22.1s) |   C |    60 | 19.1 |        
    6617 | 2026-05-11 08:03:16 |         MASTER-OAFA | (13h 10m 59.39s , -33d 35m 57.2s) |   C |    60 | 19.2 |        
    6677 | 2026-05-11 08:03:16 |         MASTER-OAFA | (13h 10m 59.40s , -33d 35m 57.2s) |   C |   180 | 19.8 |  Coadd 
    6692 | 2026-05-11 08:04:32 |         MASTER-OAFA | (13h 10m 53.41s , -33d 36m 41.7s) |   C |    60 | 19.2 |        
    6766 | 2026-05-11 08:05:46 |         MASTER-OAFA | (13h 10m 54.96s , -33d 35m 42.7s) |   C |    60 | 19.0 |        
    6840 | 2026-05-11 08:07:00 |         MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) |   C |    60 | 19.1 |        
    6900 | 2026-05-11 08:07:00 |         MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) |   C |   180 | 19.7 |  Coadd 
    6884 | 2026-05-11 08:07:44 |         MASTER-OAGH | (13h 11m 20.18s , -33d 45m 22.0s) |   C |    60 | 18.2 |        
    6944 | 2026-05-11 08:07:44 |         MASTER-OAGH | (13h 11m 20.19s , -33d 45m 21.9s) |   C |   180 | 19.0 |  Coadd 
    6884 | 2026-05-11 08:07:44 |         MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) |   C |    60 | 18.8 |        
    6944 | 2026-05-11 08:07:44 |         MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) |   C |   180 | 19.5 |  Coadd 
    6917 | 2026-05-11 08:08:17 |         MASTER-OAFA | (13h 10m 54.11s , -33d 37m 45.2s) |   C |    60 | 19.0 |        
    6953 | 2026-05-11 08:08:52 |         MASTER-OAGH | (13h 11m 26.44s , -33d 45m 03.2s) |   C |    60 | 18.4 |        
    6953 | 2026-05-11 08:08:52 |         MASTER-OAGH | (13h 09m 55.72s , -33d 12m 16.6s) |   C |    60 | 18.8 |        
    6990 | 2026-05-11 08:09:30 |         MASTER-OAFA | (13h 11m 01.38s , -33d 37m 35.3s) |   C |    60 | 19.0 |        
    7021 | 2026-05-11 08:10:01 |         MASTER-OAGH | (13h 11m 22.36s , -33d 43m 39.0s) |   C |    60 | 18.3 |        
    7021 | 2026-05-11 08:10:01 |         MASTER-OAGH | (13h 09m 51.74s , -33d 10m 53.0s) |   C |    60 | 18.7 |        
    7066 | 2026-05-11 08:10:46 |         MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) |   C |    60 | 19.1 |        
    7126 | 2026-05-11 08:10:46 |         MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) |   C |   180 | 19.6 |  Coadd 
    7091 | 2026-05-11 08:11:11 |         MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) |   C |    60 | 18.2 |        
    7151 | 2026-05-11 08:11:11 |         MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) |   C |   180 | 18.9 |  Coadd 
    7091 | 2026-05-11 08:11:11 |         MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.6s) |   C |    60 | 18.5 |        
    7151 | 2026-05-11 08:11:11 |         MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.5s) |   C |   180 | 19.4 |  Coadd 
    7143 | 2026-05-11 08:12:03 |         MASTER-OAFA | (13h 10m 58.00s , -33d 37m 28.1s) |   C |    60 | 19.1 |        
    7161 | 2026-05-11 08:12:21 |         MASTER-OAGH | (13h 11m 25.40s , -33d 43m 36.4s) |   C |    60 | 18.2 |        
    7161 | 2026-05-11 08:12:21 |         MASTER-OAGH | (13h 09m 54.89s , -33d 10m 50.9s) |   C |    60 | 18.6 |        
    7217 | 2026-05-11 08:13:17 |         MASTER-OAFA | (13h 11m 02.04s , -33d 35m 52.5s) |   C |    60 | 18.9 |        
    7231 | 2026-05-11 08:13:31 |         MASTER-OAGH | (13h 11m 18.85s , -33d 44m 19.2s) |   C |    60 | 18.2 |        
    7231 | 2026-05-11 08:13:31 |         MASTER-OAGH | (13h 09m 48.37s , -33d 11m 33.8s) |   C |    60 | 18.6 |        
    7294 | 2026-05-11 08:14:34 |         MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.2s) |   C |    60 | 18.9 |        
    7354 | 2026-05-11 08:14:34 |         MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.1s) |   C |   180 | 19.6 |  Coadd 
    7300 | 2026-05-11 08:14:40 |         MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) |   C |    60 | 18.3 |        
    7360 | 2026-05-11 08:14:40 |         MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) |   C |   180 | 18.8 |  Coadd 
    7300 | 2026-05-11 08:14:40 |         MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.7s) |   C |    60 | 18.6 |        
    7360 | 2026-05-11 08:14:40 |         MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.5s) |   C |   180 | 19.2 |  Coadd 
    7370 | 2026-05-11 08:15:49 |         MASTER-OAGH | (13h 11m 25.51s , -33d 44m 17.0s) |   C |    60 | 18.2 |        
    7370 | 2026-05-11 08:15:49 |         MASTER-OAGH | (13h 09m 55.12s , -33d 11m 31.7s) |   C |    60 | 18.6 |        
    7371 | 2026-05-11 08:15:51 |         MASTER-OAFA | (13h 10m 55.41s , -33d 35m 51.5s) |   C |    60 | 18.9 |        
    7438 | 2026-05-11 08:16:58 |         MASTER-OAGH | (13h 11m 19.31s , -33d 45m 15.5s) |   C |    60 | 18.1 |        
    7438 | 2026-05-11 08:16:58 |         MASTER-OAGH | (13h 09m 48.97s , -33d 12m 30.0s) |   C |    60 | 18.5 |        
    7449 | 2026-05-11 08:17:09 |         MASTER-OAFA | (13h 11m 00.93s , -33d 36m 53.0s) |   C |    60 | 18.9 |        
    7507 | 2026-05-11 08:18:07 |         MASTER-OAGH | (13h 11m 24.61s , -33d 45m 00.1s) |   C |    60 | 18.2 |        
    7567 | 2026-05-11 08:18:07 |         MASTER-OAGH | (13h 11m 24.62s , -33d 44m 60.0s) |   C |   180 | 18.8 |  Coadd 
    7507 | 2026-05-11 08:18:07 |         MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) |   C |    60 | 18.6 |        
    7567 | 2026-05-11 08:18:07 |         MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) |   C |   180 | 19.4 |  Coadd 
    7523 | 2026-05-11 08:18:23 |         MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) |   C |    60 | 18.9 |        
    7583 | 2026-05-11 08:18:23 |         MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) |   C |   180 | 19.6 |  Coadd 
    7577 | 2026-05-11 08:19:17 |         MASTER-OAGH | (13h 11m 21.64s , -33d 43m 38.5s) |   C |    60 | 18.0 |        
    7577 | 2026-05-11 08:19:17 |         MASTER-OAGH | (13h 09m 51.53s , -33d 10m 53.2s) |   C |    60 | 18.5 |        
    7598 | 2026-05-11 08:19:38 |         MASTER-OAFA | (13h 11m 00.75s , -33d 37m 31.6s) |   C |    60 | 18.8 |        
    7647 | 2026-05-11 08:20:26 |         MASTER-OAGH | (13h 11m 21.58s , -33d 44m 48.6s) |   C |    60 | 18.1 |        
    7647 | 2026-05-11 08:20:26 |         MASTER-OAGH | (13h 09m 51.49s , -33d 12m 02.7s) |   C |    60 | 18.6 |        
    7676 | 2026-05-11 08:20:55 |         MASTER-OAFA | (13h 10m 58.71s , -33d 36m 14.3s) |   C |    60 | 18.9 |        
    7722 | 2026-05-11 08:21:42 |         MASTER-OAGH | (13h 11m 24.04s , -33d 43m 24.1s) |   C |    60 | 18.1 |        
    7782 | 2026-05-11 08:21:42 |         MASTER-OAGH | (13h 11m 24.03s , -33d 43m 24.0s) |   C |   180 | 18.6 |  Coadd 
    7722 | 2026-05-11 08:21:42 |         MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.6s) |   C |    60 | 18.5 |        
    7782 | 2026-05-11 08:21:42 |         MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.5s) |   C |   180 | 19.1 |  Coadd 
    7752 | 2026-05-11 08:22:12 |         MASTER-OAFA | (13h 10m 58.85s , -33d 37m 45.7s) |   C |    60 | 18.9 |        
    7792 | 2026-05-11 08:22:51 |         MASTER-OAGH | (13h 11m 17.55s , -33d 44m 06.7s) |   C |    60 | 18.0 |        
    7792 | 2026-05-11 08:22:52 |         MASTER-OAGH | (13h 09m 47.49s , -33d 11m 21.0s) |   C |    60 | 18.3 |        
    7826 | 2026-05-11 08:23:26 |         MASTER-OAFA | (13h 11m 02.50s , -33d 36m 10.9s) |   C |    60 | 18.9 |        
    7861 | 2026-05-11 08:24:01 |         MASTER-OAGH | (13h 11m 18.56s , -33d 43m 05.0s) |   C |    60 | 18.0 |        
    7861 | 2026-05-11 08:24:01 |         MASTER-OAGH | (13h 09m 48.54s , -33d 10m 19.5s) |   C |    60 | 18.4 |        
    7903 | 2026-05-11 08:24:43 |         MASTER-OAFA | (13h 10m 56.54s , -33d 36m 58.6s) |   C |    60 | 18.9 |        
    7931 | 2026-05-11 08:25:11 |         MASTER-OAGH | (13h 11m 24.27s , -33d 44m 03.0s) |   C |    60 | 18.1 |        
    7931 | 2026-05-11 08:25:11 |         MASTER-OAGH | (13h 09m 54.32s , -33d 11m 17.1s) |   C |    60 | 18.5 |        
    8000 | 2026-05-11 08:26:20 |         MASTER-OAGH | (13h 11m 17.71s , -33d 45m 00.9s) |   C |    60 | 18.1 |        
    8000 | 2026-05-11 08:26:20 |         MASTER-OAGH | (13h 09m 47.79s , -33d 12m 14.9s) |   C |    60 | 18.5 |        
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 44536

Subject
GRB 260511A: KAIT optical afterglow observations
Date
2026-05-11T07:56:17Z (4 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and

Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, observed the field of GRB 260511A (Fermi GBM Team,

GCN Circ. 44529; Godet et al., GCN Circ. 44532) starting at 06:15:44,

132 seconds after SVOM trigger. Observations were performed in

3 x 3 tiling mode, and a set of clear (roughly R) filter images

were obtained. The first image covered the optical afterglow

(Jiang et al., GCN 44533; Akl et al. GCN 44534 Saccardi et al.,

GCN 44535) was at 06:16:57, 205 seconds after the burst, in which

we measure the afterglow brightness to be 16.7 +/- 0.1 mag (Vega)

calibrated to APASS catalog. Observations are on going.

GCN Circular 44535

Subject
GRB 260511A: LCO optical afterglow detection
Date
2026-05-11T07:20:44Z (4 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi (CEA/Irfu), C. Wu (NAOC), L. Zhang (IHEP), D. Kong (GXU), report on behalf of the SVOM mission team:

We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN 44532; Fermi GBM Team, GCN 44529) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument.

Our observation started on 2026-05-11 at 06:24:46 UT (about 11 min 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 (Jiang et al., GCN 44533; Akl et al. GCN 44534) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:

r = 18.88 +/- 0.02  AB (mid-time 21 min after the trigger);
z = 18.05 +/- 0.04 AB (mid-time 15 min after the trigger).

This project is funded by the SVOM collaboration.

GCN Circular 44534

Subject
GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart
Date
2026-05-11T07:11:33Z (4 months ago)
From
Dalya Akl at New York University Abu Dhabi <dka2010@nyu.edu>
Via
Web form
Dalya Akl (NYUAD), Camila Angulo (UNAM), Alan M. Watson, Rosa L. Becerra (UNAM),  (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), 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), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM), L. Zhang (IHEP), and D. Kong (GXU) report:

We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 06:14:45 to 06:27:52 UTC (from 72 seconds to 14 minutes after the trigger) and obtained 520 seconds of simultaneous exposure in r and z filters.

The data were reduced, coadded, calibrated, and analyzed 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 a bright, fading source at:

  RA(J2000) = 13:11:35.90 = 197.89960 degrees
  Dec(J2000) = -33:48:16.1 = -33.80446 degrees

with an uncertainty of 0.5 arcsec. The preliminary, unsubtracted magnitudes derived for that source are:

r = 16.86 +/- 0.01,

z = 16.43 +/- 0.01.

This position is 3.25 arcmin and 0.87 arcmin away from the ECLAIRs and MXT positions, respectively, released via notices. 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 44533

Subject
GRB 260511A: TRT optical counterpart detection
Date
2026-05-11T06:45:10Z (4 months ago)
From
sqjiang at NAOC <sqjiang@bao.ac.cn>
Via
Web form
S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), J. An, L.B. He, X. Liu, Z.P. Zhu, D. Xu (NAOC) report:

We observed the field of GRB 260511A detected by Fermi GBM (GCN 44529) and SVOM (GCN 44532) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT) located at Cerro Tololo Inter-American Observatory, Chile (CTO). We obtained a series of frames in the Sloan r-band.

An uncatalogued and varing source is detected near the SVOM MXT error circle at coordinates
R.A. (J2000) = 13:11:35.94 (197.8997 deg)
Dec. (J2000) = -33:48:16.3 (-33.8045 deg)
with an uncertainty of ~ 1.0 arcsec. The source had r ~ 17.9 mag at a median time of 2026-05-11T06:19:37.771, calibrated with Legacy DR10 and not corrected for Galactic extinction.

No NEO would be at the above position at the observational time by checking MPC.

We thus think the source could be the optical counterpart of GRB 260511A.

GCN Circular 44532

Subject
GRB 260511A: SVOM detection of a bright burst
Date
2026-05-11T06:37:49Z (4 months ago)
Edited On
2026-05-12T13:42:44Z (4 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
O. Godet, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM mission team:

At 2026-05-11T06:13:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260511A (SVOM burst-id sb26051101).

This transient was also detected by Fermi/GM (GCN Circular 44529).

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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 55.22 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2026-05-11T06:13:32.

The localization of the best alert is R.A., Dec. 197.929, -33.853 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.44 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of 13.5 (-0.4/ +0.6) s in the 5-120 keV.

This burst also triggered SVOM/GRM at 2026-05-11T06:13:30 on a timescale of 1 seconds with an SNR of 12.10.

The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of 14.3 (-0.4 / +0.8) s in the 8-1100 keV.

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2026-05-11T06:16:38 UTC, 186 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 197.9145, -33.8120 degrees:
R.A. (J2000) = 13h11m39.48s
Dec. (J2000) = -33d48m43.09s
with a 90% C.L. radius of 39.05 arcseconds.

This location is 2.54 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

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 zhangli: zhangli at ihep.ac.cn
Please contact the BA by email if you require additional information.

GCN Circular 44531

Subject
GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259)
Date
2026-05-11T06:37:48Z (4 months ago)
From
Jochen Greiner at MPE <jcgrog@mpe.mpg.de>
Via
email
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:

The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
800172815 at 06:13:30 on 11 May 2026 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).

The best-fit position is:
RA(2000.0) = 197.3 deg
Decl.(2000.0) = -33.7 deg
The 1 sigma statistical error radius is 1.3 deg.
We estimate an additional systematic error of 1 deg.

Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260511259/

The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260511259/healpix

The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260511259/json

GCN Circular 44529

Subject
GRB 260511A: Fermi GBM Final Real-time Localization
Date
2026-05-11T06:22:11Z (4 months ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB

At 06:13:30 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511A (trigger 800172815.286154 / 260511259).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 199.1, Dec = -33.0 (J2000 degrees, equivalent to J2000 13h 16m, -33d 00'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 117.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/quicklook/glg_skymap_all_bn260511259.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/quicklook/glg_healpix_all_bn260511259.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/quicklook/glg_lc_medres34_bn260511259.gif
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