GRB 260411B
GCN Circular 44684
Subject
GRB 260411B: TERI Gamma-ray detection
Date
2026-05-21T14:08:14Z (5 months ago)
From
nicholasjkirschner@gmail.com
Via
Web form
Nicholas Kirschner (a), Daniel Shy (b), C.C. Cheung (b), Bernard Phlips (b), Michael Streicher (c), James Mason (c), Douglas M. Groves (c), Feng Zhang (c), and Willy Kaye (c)
(a) National Research Council Research Associate resident at the U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375
(b) U.S. Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375
(c) H3D, Inc., 812 Avis Dr., Ann Arbor, MI 48108, USA
The cadmium zinc TElluride Radiation Imager (TERI) gamma-ray telescope [1], operating on
the International Space Station, reports the detection of GRB 260411B, which was also detected
by Fermi GBM (GCN 44262, 44266), SVOM/GRM (GCN 44268), Fermi LAT (GCN 44277),
GECAM (GCN 44285), Glowbug (GCN 44312), and Konus-Wind (GCN 44332).
Using 1 Hz binning, and adopting T0 = 2026-04-11T08:04:43.568 Z, we observe one peak at
T0+1.5s, with peak excess count rate of 69 above the 192 cps baseline rate observed in nearby
off-source intervals.
The analysis results presented here are preliminary and currently lack a detailed response
function.
TERI is an Office of Naval Research funded technology demonstrator for large-volume pixelated
CdZnTe detectors developed, built, and operated by the U.S. Naval Research Laboratory (NRL)
in conjunction with H3D, Inc. The pixelated CdZnTe detectors have an energy range of 40 keV
to 3 MeV per pixel. It was launched on 2025 April 21 aboard the Department of Defense Space
Test Program STP-H10 to the ISS. On the ISS, it is located on the SOX external payload facility
on the Columbus module. Analysis of TERI data at NRL is supported by the Office of Naval
Research 6.1.
[1] Shy, Daniel, et al. "Development of the cadmium zinc TElluride Radiation Imager." Journal
of Astronomical Telescopes, Instruments, and Systems 10.4 (2024): 044009-044009
(arXiv:2408.04559).
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 44332
Subject
Konus-Wind detection of GRB 260411B
Date
2026-04-17T17:11:27Z (6 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 260411B
(Fermi-GBM detection: The Fermi GBM team, GCN 44262,
Pathak & Sonawane, GCN 44266;
BALROG localization: Preis & Greiner, GCN 44263;
SVOM-GRM detection: Wang et al., GCN 44268;
Fermi-LAT detection: Longo et al., GCN 44277;
GECAM-B detection: Zao et al., GCN 44285;
Glowbug detection: Woolf et al., GCN 44312;
IPN triangulation: Kozyrev et al., GCN 44329)
triggered Konus-Wind at T0=29079.388 s UT (08:04:39.388).
The burst light curve shows a multipeaked structure
which starts at ~T0-8.7 s and has a total duration of ~55.6 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260411_T29079/
As observed by Konus-Wind, the burst
had a fluence of 4.50(-0.50,+0.50)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.440 s,
of 1.15(-0.14,+0.14)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+49.408 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.62(-0.18,+0.19),
the high energy photon index beta = -2.12(-0.19,+0.12),
the peak energy Ep = 290(-38,+52) keV
(chi2 = 82/98 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 the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.16(-0.15,+0.16),
the high energy photon index beta = -2.19(-0.10,+0.08),
the peak energy Ep = 248(-19,+23) keV
(chi2 = 87/82 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 44329
Subject
IPN triangulation of GRB 260411B
Date
2026-04-17T15:16:20Z (6 months ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi-GBM team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The long-duration GRB 260411B
(Fermi-GBM detection: The Fermi GBM team, GCN 44262,
Pathak & Sonawane, GCN 44266;
BALROG localization: Preis & Greiner, GCN 44263;
SVOM-GRM detection: Wang et al., GCN 44268;
Fermi-LAT detection: Longo et al., GCN 44277;
GECAM-B detection: Zao et al., GCN 44285;
Glowbug detection: Woolf et al., GCN 44312)
was detected by Fermi (GBM, LAT), Konus-Wind,
SVOM (GRM), GECAM-B, Glowbug,
and Mars-Odyssey (HEND) at about 29075 s UT (08:04:35).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
85.558 (05h 42m 14s) +2.297 ( +2d 17' 50")
Corners:
85.572 (05h 42m 17s) -0.527 ( +0d 31' 39")
85.610 (05h 42m 26s) -0.425 ( +0d 25' 29")
85.523 (05h 42m 05s) +5.509 ( +5d 30' 32")
85.486 (05h 41m 57s) +5.372 ( +5d 22' 20")
---------------------------------------------
The error box area is 844 sq. arcmin, and its maximum
dimension is 6.0 deg (the minimum one is 2.4 arcmin).
The Sun distance was 65 deg.
This localization may be improved.
The OT reported by GOTO (GOTO26dam, GCN 44265)
is inside the IPN box, strengthening the association of the OT and GRB 260411B.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB260411_T29079/IPN/
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
GCN Circular 44312
Subject
GRB 260411B: Glowbug gamma-ray detection
Date
2026-04-16T13:36:13Z (6 months ago)
Edited On
2026-04-16T13:46:04Z (6 months ago)
From
Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ@us.navy.mil>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of 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 260411B, which was also detected by Fermi GBM (GCN 44262, 44266), SVOM/GRM (GCN 44268), Fermi LAT (GCN 44277), and GECAM (GCN 44285).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-11 08:04:43.568 with a duration of 3.1 s and a total significance of about 22.6 sigma. At the time of the detection, the ISS was entering a high background region and Glowbug captured the second, brighter peak visible in the GBM lightcurve. The initial, fainter peak near the GBM T0 may be detected by Glowbug at low significance.
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 44285
Subject
GRB 260411B: GECAM-B observation of a long burst
Date
2026-04-13T10:33:45Z (6 months ago)
From
xueyuan zao <zaoxueyuan@gmail.com>
Via
Web form
Xue-Yuan Zao, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered on-ground by GRB 260411B, at 2026-04-11T08:04:42.550 UTC, which is also detected by Fermi/GBM (Fermi GBM team, GCN #44262 and #44266), SVOM/GRM (Chen-Wei Wang et al., GCN #44268) and Feimi/LAT (F. Longo et al., GCN#44277).
According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of two emission episodes with a total duration (T90) of 18.8 +3.8/-2.0 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260411B.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 44277
Subject
GRB 260411B: Fermi-LAT detection
Date
2026-04-12T16:41:28Z (6 months ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
F. Longo (Univ. and INFN Trieste), D. Depalo (Politecnico and INFN Bari), R. Gupta (NASA/GSFC), A. Holzmann Airasca (UniTrento and INFN Bari), N. Omodei (Stanford University), and N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT team:
At 08:04.35.31 UT on April 11th, 2026, Fermi-LAT detected high-energy emission from GRB 260411B, which was also detected by Fermi-GBM (trigger 797587480/260411337, GCN #44262 and #44266), and SVOM (Wang et al. 2026, GCN #44268). An optical counterpart candidate was detected by GOTO (O'Neill et al. 2026, GCN #44265), DOT (Gupta et al. 2026, GCN #44271), Ondrejov D50 (Jeiinek et al. 2026, GCN #44272), and COLIBRI' (Sánchez Álvarez et al. 2026, GCN #44274).
The GBM location was initially inside the LAT field of view at an angle of 60 degrees to the LAT boresight, and remained in the LAT field of view until ~T0+500 s. No significant excess is seen using standard >100 MeV likelihood analysis procedures.
Using the LAT Low Energy (LLE) data selection, over 190 counts above background were detected within a 20 s interval coinciding with the time of the GBM emission. This data selection has insufficient spatial resolution to provide a reliable LAT localization. Since an excess of events was not seen using the standard analysis selection, this detection is likely due to low-energy gamma-rays (below 100 MeV).
The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.infn.it).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 44274
Subject
GRB 260411B: COLIBRÍ optical observations
Date
2026-04-12T05:49:16Z (6 months ago)
From
freddalvarez@astro.unam.mx
Via
Web form
Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM),Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (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), Benjamin Schneider (LAM) report:
We imaged the possible optical counterpart (O’Neill et al., GCN Circ. 44265) of the Fermi GRB 260411B (Fermi GBM Team, GCN Circ. 44262) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-12 02:56 to 2026-04-12 04:43 (from 18.86 to 20.68 hours after the trigger) and obtained 25/35/24/84 minutes of exposure in the g/r/i/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.
In the stacked image, we detect the optical counterpart reported by O’Neill et al. (GCN Circ. 44265), Gupta et al. (GCN Circ. 44271), and Jelinek et al. (GCN Circ.44272) and obtain the following preliminary magnitudes:
g = 21.44 +/- 0.04
r = 20.69 +/- 0.02
i = 20.35 +/- 0.03
z = 20.10 +/- 0.03
After correcting for Galactic extinction (A_g ≈ 0.92 and A_z ≈ 0.41), the g-z colour is 0.85 +/- 0.05. This and the other colours are consistent with an afterglow with moderate reddening from its host galaxy.
Furthermore, the detection in g-band suggests that the redshift of the transient is likely z < 3.5, assuming typical IGM absorption.
Comparing our r magnitude to the one reported by DOT (Gupta et al. GCN Circ. 44271), we estimate that the temporal decay index between 12.4 and 19.6 hours is α ≈ -2.3. The transient appears to show an initially rapid decay in the early GOTO observations (O’Neill et al. GCN Circ. 44265) at about 0.9 hours, followed by a shallower phase (α ≈ −0.8) between 0.9 and 12.4 hours, and a subsequent steepening at later times. In the Pan-STARRS DR1 images, there is an extended source at about 2” from the position of the transient with preliminary magnitudes of:
g = 24.12 +/- 0.23
r = 24.06 +/- 0.31
i = 24.64 +/- 0.53
z = 23.44 +/- 0.38
After correcting for Galactic extinction, we estimate a probability of chance coincidence of about 2%, which suggests that this source is the host galaxy of GRB 260411B. We encourage spectroscopic observations of the source. Further observations are planned.
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 44272
Subject
GRB 260411B: Ondrejov D50 optical afterglow detection
Date
2026-04-12T01:09:43Z (6 months ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
M. Jelinek, J. Strobl, F. Novotny, A. Malenakova, R. Hudec (ASU CAS Ondrejov)
report:
We observed the position of the optical afterglow of GRB 260411B (Fermi GBM team, GCN 44262; O'Neill et al., GCN 44265) with the D50 robotic telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We performed a series of 80x60s exposures in the SDSS r' filter.
We faintly detect the optical afterglow (O'Neill et al., GCN 44265) in the 80x60s combined image with exposure mean time 11.45 h after the trigger. The AB magnitude of the object is:
r' = 20.0 +/- 0.3
Photometric calibration was performed using the ATLAS REFCAT2 (Tonry et al.) catalog. The magnitude is not corrected for Galactic extinction in the direction of the burst.
Comparing with the GOTO detection at t = 0.89 h (L = 17.55 +/- 0.02; O'Neill et al., GCN 44265), this would imply a temporal decay index of alpha ~ 0.9 (where F_nu ~ t^-alpha).
GCN Circular 44271
Subject
GRB260411B: 3.6m DOT optical observation
Date
2026-04-11T20:40:36Z (6 months ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Aayushi Verma, Pankaj Pawar, Debalina Kar, Dhruv Jain, and Kuntal Misra (ARIES) report:
We observed the field of GRB260411B detected by Fermi/GBM (Fermi GBM Team, GCN 44262) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-04-11 at 20:29:45.480 UT, i.e., ~12.41 hours after the Fermi/GBM trigger. We have two frames with an exposure time of 200s in the r filter. We stacked the images after the alignment. We detect an optical counterpart in our stacked image at the position given by O'Neill et al. (GCN 44265). We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (hours) Filter Exp time (s) Magnitude
==================================================================
2026-04-11 20:29:45.480 ~12.41 r 200s*2 19.74 +/-0.01
Our detection is consistent with O'Neill et al. (GCN 44265).
The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the Pan-STARRS catalog.
GCN Circular 44268
Subject
GRB 260411B: SVOM/GRM observation of a long burst
Date
2026-04-11T16:24:34Z (6 months ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Frédéric Daigne (IAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight GRB 260411B (SVOM trigger reference: sb26041103) at 2026-04-11T08:04:37.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN#44262).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two emission episodes with a T90 of 16.2 +2.1/-1.4 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260411B.png
In addition, the position of this burst, as determined by GOTO (RA= 85.567893 deg, DEC= 1.984983 deg, GCN#44265), is located at about 81 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-2.5 to T0+16.4 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.81 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 385 +44/-37 keV. The event fluence (10-1000 keV) in this time interval is (2.37 +0.09/-0.09)E-05 erg/cm^2.
The 1s peak spectrum, measured from T0+6.7 to T0+7.7 s, is also best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.41 +0.09/-0.09 and the cutoff energy, parameterized as Epeak, is 331 +20/-17 keV. The flux (10-1000 keV) in this time interval is (6.34 +0.20/-0.20)E-06 erg/cm^2/s.
The localization of GRB 260411B in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260411B_amati.png
And the localization in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260411B_yonetoku.png
With the brightness of the prompt emission, the predicted soft X-ray afterglow [1] is shown at:
https://www.bursthub.cn//admin/static/svgrb260411B_xag_pre.png
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
[1] Chen-Wei Wang et al. ApJ 997 353 https://doi.org/10.3847/1538-4357/ae2eae
GCN Circular 44266
Subject
GRB 260411B: Fermi GBM Detection
Date
2026-04-11T13:46:30Z (7 months ago)
From
Utkarsh Pathak at IIT Bombay <utkarshpathak.07@gmail.com>
Via
Web form
U. Pathak (IITB) and R. Sonawane (IISER TVM) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 08:04:35.31 UT on 11 April 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260411B (trigger 797587480/260411337).
The Fermi GBM final real-time Localization is reported in GCN 44262.
An optical counterpart is also detected by GOTO (O'Neill et al. 2026 GCN 44265).
The angle from the Fermi LAT boresight is 60 degrees.
The GBM light curve consists of two spikes in a single emission episode, with a duration (T90)
of about 33 s (50-300 keV). The time-averaged spectrum
from T0-2.9 to T0+29.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.62 +/- 0.02 and the cutoff energy,
parameterized as Epeak, is 348 +/- 4 keV.
The event fluence (10-1000 keV) in this time interval is
(2.31 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+8.3 s in the 10-1000 keV band is 21.8 +/- 0.4 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 293 +/- 3 keV, alpha = -0.54 +/- 0.05 and beta = -2.3 +/- 0.1.
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 44265
Subject
GRB 260411B: GOTO optical counterpart candidate
Date
2026-04-11T10:56:59Z (7 months ago)
From
d.s.oneill@bham.ac.uk
Via
Web form
D. O'Neill, R. Starling, G. Ramsay, 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. Gompertz, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, on behalf of 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 Fermi/GBM alert GRB 260411B (Fermi GBM team, GCN #44262).
Observations covering the localisation area began at 2026-04-11 08:57:53 UT (t0 +0.89h). 8 images consisting of 4 x 90s exposures were taken in the L band (400-700 nm), covering 38.5 sq deg within the 90% localisation contour. ~32.3% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.4 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
A new optical source GOTO26dam is identified within the GBM 90% localisation region (22% contour) with co-ordinates:
RA,DEC (J2000) = 85.567893, 1.984983,
05:42:16.29, +01:59:05.94
The source was detected with L = 17.55 ± 0.02 AB mag (+0.89h) and is rapidly fading with a decay index alpha ~ -2.1±0.4. We find no evidence of the source prior to the GRB trigger time in previous ATLAS observations at 2026-04-07 17:36:17.597 (t0 -86.47h) down to c > 19.37 mag using the forced photometry server (Shingles et al. 2021).
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).
GCN Circular 44263
Subject
GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
Date
2026-04-11T08:50:14Z (7 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
797587480 at 08:04:35 on 11 April 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) = 85.7 deg
Decl.(2000.0) = 3.1 deg
The 1 sigma statistical error radius is 2.5 deg.
We estimate an additional systematic error of 2 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260411337/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260411337/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260411337/json
GCN Circular 44262
Subject
GRB 260411B: Fermi GBM Final Real-time Localization
Date
2026-04-11T08:15:05Z (7 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 08:04:35 UT on 11 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260411B (trigger 797587480.306254 / 260411337).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 83.2, Dec = 2.8 (J2000 degrees, equivalent to J2000 05h 32m, 2d 47'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 60.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/quicklook/glg_skymap_all_bn260411337.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/bn260411337/quicklook/glg_healpix_all_bn260411337.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260411337/quicklook/glg_lc_medres34_bn260411337.gif