GRB 260708A — All Circulars

R.-Z. Li (YNAO, CAS), J. Mao (YNAO, CAS), S. Antier (IJCLAB), M. Pillas (IAP), D. Turpin (CEA/Irfu), O. Pyshna (Caltech) report on behalf of a larger collaboration:

We report two EP/FXT Target of Opportunity (ToO) observations of the Fermi long GRB 260708A (Fermi/GBM Team, GCN 45115; Fermi/LAT, Holzmann Airasca et al., GCN 45117; GECAM-B, Ren et al., GCN 45126; Glowbug, Cheung et al., GCN 45130).


The first EP/FXT follow-up observation started at 2026-07-11T01:06:38 (UTC), approximately 2.62 days after the Fermi/GBM trigger, with a total exposure time of 2.7 ks.

EP/FXT detected an uncatalogued X-ray source at the following coordinates (J2000):
R.A., Decl. = 225.6537, -43.8844
with a localization uncertainty of 10 arcsec radius (90% confidence level, including both statistical and systematic uncertainties). The X-ray position is consistent with that of AT 2026stf reported by MASTER (Shilova et al., GCN 45123).

The average 0.5-10 keV EP/FXT spectrum can be fitted by an absorbed power law with a Galactic hydrogen column density of (0.36 +/- 0.12) x 10^22 cm^-2 and a photon index of 2.25 +/- 0.32. The derived average unabsorbed 0.5-10 keV flux is (1.31 +/- 0.13) x 10^-12 erg cm^-2 s^-1.


The second EP/FXT follow-up observation started at 2026-07-13T12:09:39 (UTC), approximately 5.08 days after the Fermi/GBM trigger, with a total exposure time of 6 ks. On-ground analysis of the EP/FXT data again detected an uncatalogued X-ray source consistent with the source detected in the first observation. The average 0.5-10 keV EP/FXT spectrum can be fitted by an absorbed power law with a Galactic hydrogen column density of (0.40 +/- 0.5) x 10^22 cm^-2 and a photon index of 2.36 +/- 0.38. The derived average unabsorbed 0.5-10 keV flux is (5.46 +/- 0.68) x 10^-13 erg cm^-2 s^-1.

The temporal decay index of X-ray emission between the two observations is 1.32 +/- 0.24. Given the slow temporal evolution observed in both the optical band (Shilova et al., GCN 45123; Freeberg et al., GCN 45127; Shi et al., GCN 45140; Sheng et al., GCN 45147) and the X-ray band, optical spectroscopy is strongly encouraged to determine the classification of the source.

All quoted uncertainties correspond to the 1-sigma confidence level.

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).

X. Sheng (QUB), D. Turpin (CEA/Irfu), O. Pyshna (Caltech), R. Strausbaugh (EIU), A. Iskandarova (ShAO), S. Rahimli (Sumgayit State Uni), V. Morozov (KU Leuven), S. Antier (IJCLAB), A. Simon (TShNU of Kyiv), L. Wyrzykowski (Uni. Warsaw/NCBJ), J. Hambsch (VVS, GEOS, BAV), M. Freeberg (KNC), R. Hellot (KNC), A. Klotz (IRAP), E. Jehin (ULiège), M. Ferrais (ULiège), Rui-Zhi (YNAO), J. Mao (YNAO) on behalf of on GRANDMA collaboration: 
 
We observed the field of the Fermi Long GRB 260708A (Fermi GBM team, GCN 45115; Fermi/LAT, Holzmann Airasca et al., GCN45117,; GECAM-B, Ren et al., GCN45126; Glowbug, Cheung et al., GCN 45130). The observations started at 14:30:42 UTC on the 9 of July 2026, 1.18 days post the Fermi Trigger.

We detected the optical afterglow candidate, reported by MASTER (Shilova et al, GCN 45123), in several epochs, using the 60cm telescope at les Makes Observatory, the LCO 0.4m telescope at the SAA Observatory, the TRAPPIST-South telescope at la SIlla Observatory, and Kilonova Catcher. However, we observed after template subtraction a softer decay than usual for the GRBs.

A subset of the photometry corrected for Galactic extinction is reported in the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GRB-260708A. To access, one simply needs to create an account using your ORCID id. 

The data were 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. Images obtained with the Johnson-Cousins filters were calibrated using the Gaia DR3 Synphot catalog. 

Our results are consistent across GRANDMA but not totally with LCO (GCN 45140). Further template taken at later time are needed.

The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. 

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/).

X. Sheng (QUB), D. Turpin (CEA/Irfu), O. Pyshna (Caltech), R. Strausbaugh (EIU), A. Iskandarova (ShAO), S. Rahimli (Sumgayit State Uni), V. Morozov (KU Leuven), S. Antier (IJCLAB), A. Simon (TShNU of Kyiv), L. Wyrzykowski (Uni. Warsaw/NCBJ), J. Hambsch (VVS, GEOS, BAV), M. Freeberg (KNC), R. Hellot (KNC), A. Klotz (IRAP), E. Jehin (ULiège), M. Ferrais (ULiège), Rui-Zhi (YNAO), J. Mao (YNAO) on behalf of on GRANDMA collaboration: 
 
We observed the field of the Fermi Long GRB 260708A (Fermi GBM team, GCN 45115; Fermi/LAT, Holzmann Airasca et al., GCN45117,; GECAM-B, Ren et al., GCN45126; Glowbug, Cheung et al., GCN 45130). The observations started at 14:30:42 UTC on the 9 of July 2026, 1.18 days post the Fermi Trigger.

We detected the optical afterglow candidate, reported by MASTER (Shilova et al, GCN 45123), in several epochs, using the 60cm telescope at les Makes Observatory, the LCO 0.4m telescope at the SAA Observatory, the TRAPPIST-South telescope at la SIlla Observatory, and Kilonova Catcher. However, we observed after template subtraction a softer decay than usual for the GRBs.

A subset of the photometry corrected for Galactic extinction is reported in the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GRB-260708A. To access, one simply needs to create an account using your ORCID id. 

The data were 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. Images obtained with the Johnson-Cousins filters were calibrated using the Gaia DR3 Synphot catalog. 

Our results are consistent across GRANDMA but not totally with LCO (GCN 45140). Further template taken at later time are needed.

The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. 

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) report on behalf of the SVOM mission team:


We observed the field of the GRB 260708A detected by Fermi/GBM(Fermi GBM team, GCN 45115; GCN 45124) and Fermi/LAT (Holzmann Airasca et al., GCN 45117) with the LCO 1m telescope at Cerro Tololo Inter-American Observatory equipped with the Sinistro instrument.

Our observation started on 2026-07-11 at 23:37:53 UT (about 3.56 day after the trigger) and we obtained 3x200 s exposures in the SDSS g, r and i filters.

The optical counterpart (Shilova et al., GCN 45123; Freeberg et al., GCN 45127) is clearly detected in our images. We measure the following magnitudes calibrated against the UCAC4 catalog, and not corrected for Galactic extinction:

g = 19.56 +/- 0.02 AB (mid-time 3.56 day after the trigger);
r = 19.21 +/- 0.02 AB (mid-time 3.60 day after the trigger);
i = 19.17 +/- 0.03 AB (mid-time 3.59 day after the trigger).

It appears to be fading compared with the results reported by Shilova et al. (GCN 45123) and  Freeberg et al.(GCN 45127).

This project is funded by the SVOM collaboration.

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 260708A, which was also detected by Fermi/GBM (GCN 45115, 45124), Fermi/LAT (GCN 45117), and GECAM-B (GCN 45126), and has a proposed optical counterpart (GCN 45123, 45127).

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-07-08 10:11:15.952 with a duration of 12.3 s and a total significance of about 7.7 sigma.  The emission seen by Glowbug corresponds to the brightest portion of the GBM and GECAM-B light curves.

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.

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 260708A detected by Fermi/GBM (Fermi GBM team, GCN 45115; GCN 45124) and Fermi/LAT (Holzmann Airasca et al., GCN 45117) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with a iTtelescope T30 located at Siding Spring Observatory operated by M. Freeberg. Our observations started at TGRB+1.17 days and were taken with the Johnson/Cousins R filter. 

In our stacked frames, we clearly detect the optical counterpart reported by MASTER (Shilova et al., GCN 45123).

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

| Tmid-TGRB (days) | Exp (s)     | Filter         | Magnitude     | Instrument       |
| ------------ | ------------ |------------ |------------ |------------ |
| 1.18            | 3 x 300s | R (Vega)     | 18.93 +/- 0.14  |  iT30     | 

Given the significant fading behavior compared to the previous MASTER epoch, we considered this optical candidate is the optical afterglow of the energetic burst GRB 260708A. Further observations are ongoing.

All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot 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/).

Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by GRB 260708A, at 2026-07-08T10:11:17.650 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45115), and Fermi/LAT (Fermi LAT team, GCN #45117). 

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 46.5 +5.0/-6.5 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260708A.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).

C. Malacaria (INAF-OAR) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: 

"At 10:11:16.89 UT on 08 July 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260708A (trigger 805198281/260708424).
The Final real-time localization was reported in GCN 45115.
Fermi-LAT also detected GRB 260708A (GCN 45117).

The GBM light curve displays a sharp peak with a duration (T90)
of about 62 s (50-300 keV). The time-averaged spectrum
from T0+0.5 to T0+49.7 s is best fit by
a power law function with a power law index of -1.86 +/- 0.01 . 

The event fluence (10-1000 keV) in this time interval is
(2.14 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.5 s in the 10-1000 keV band is 19.6 +/- 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/"

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

MASTER-OAFA and MASTER-SAAO robotic telescopes of MASTER Global Robotic
Net [1-4] was pointed to the Fermi LAT GRB 260708A
(Holzmann Airasca et al. GCN 45117, trigger 2026-07-08 10:11:16.89 UT, RA, Dec = 225.61, -44.07 +-0.27 (J2000))
at 2026-07-08 22:40:00 UT (Lipunov et al. 45119).

There is optical counterpart of GRB 260708A
MASTER OT J150237.02-435307.7 https://www.wis-tns.org/object/2026stf
discovered by MASTER auto-detection system [1-4] at 2026-07-08 22:42:34.272UT with unfiltere m~17.6m.
The typical light curve points to GRB source.

spectral observations is required.


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

A. Holzmann Airasca (UniTrento and INFN Bari), D. Depalo (Politecnico and INFN Bari) and P. Loizzo (UniTrento and INFN Bari) report on behalf of the Fermi-LAT collaboration:

At 10:11:16.89 UT on July 8th, 2026, Fermi-LAT detected high-energy emission from GRB 260708A, which was also detected by Fermi-GBM (trigger 805198281/260708424, GCN #45115).

The best LAT on-ground location is found to be
RA, Dec = 225.61, -44.07 (J2000)
with an error radius of 0.27 deg (90 % containment, statistical error only).

This was 43 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance.
The photon flux above 100 MeV in the time interval 0 - 400 s after the GBM trigger is (1.9 ± 0.4)E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.5 ± 0.3. The highest energy photon has an energy of 2.1 GeV and occurs at 65.8 s after trigger time.

The Fermi-LAT point of contact for this burst is Pierpaolo Loizzo (pierpaolo.loizzo@ba.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.

The Fermi GBM team reports the detection of a likely LONG GRB

"At 10:11:16.89 UT on 08 July 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260708A (trigger 805198281/260708424).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 227.4, Dec = -44.5 (J2000 degrees, equivalent to J2000 15h 09m, -44d 30'),
with a statistical uncertainty of 1.6 degrees.

The angle from the Fermi LAT boresight is 43 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260708424/quicklook/glg_skymap_all_bn260708424.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/bn260708424/quicklook/glg_healpix_all_bn260708424.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260708424/quicklook/glg_lc_medres34_bn260708424.gif"