GRB 260705A
GCN Circular 45105
Subject
GRB 260705A: Candidate Optical Counterpart from SOAR and Gemini-South and Possible Association with GRB 260705B
Date
2026-07-07T15:52:15Z (3 days ago)
From
James Freeburn at University of North Carolina at Chapel Hill <jamesfreeburn54@gmail.com>
Via
Web form
James Freeburn (UNC), Tomás Ahumada (NOIRLab), Jillian Rastinejad (UMD), Gokul Srinivasaragavan (UMD/Northwestern), Huei Sears (Rutgers), Anirudh Salgundi (UNC), report on behalf of a larger collaboration:
We observed the field of GRB 260705A (SVOM burst-id sb26070502) detected by SVOM (Saccardi et al., GCN 45079) and Fermi (Hamburg et al., GCN 45080) using the SOAR and Gemini-South telescopes. We obtained 8 x 300 s of i-band imaging with SOAR using the Goodman High Throughput Spectrograph (SOAR2026A-018; PI: Andreoni) in imaging mode with the Red camera at a mid-time of 2026-07-07 10:19 UT, corresponding to ~45 hrs after the trigger. We performed SOAR data reduction with a custom pipeline using pre-reduced images from the Goodman pipeline (Torres et al. 2018). We obtained 4 x 120 s of r-band imaging at three different pointings using GMOS on Gemini-South (PI: Srinivasaragavan) at a mid-time of 2026-07-07 09:35 UT and performed image reduction with DRAGONS (Labrie et al. 2019). For both images, we performed image subtraction using SFFT (Hu et al. 2022) against DECam Legacy Survey images. The GMOS image covers ~77% of the SVOM localization (Saccardi et al., GCN 45079), while the resampled Goodman image covers ~65% of the localization.
We detect a candidate optical counterpart at:
R.A. (J2000) = 03:53:12.49 (58.30204 d) +/- 0.5’’
Dec. (J2000) = -31:39:08.61 (-31.65239 d) +/- 0.5’’
with AB magnitudes, calibrated with SkyMapper DR4 (Onken et al., 2024), of:
r = 21.48 +/- 0.08
i = 21.44 +/- 0.04
These magnitudes have not been corrected for Galactic extinction of A_V = 0.028 mag. The brightness of this source is consistent with the upper limits found by LCO (Shi et al., GCN 45084), though these observations were taken ~30 hours prior.
This candidate optical counterpart is embedded in a catalogued source, WISEA J035312.50-313908. WISEA J035312.50-313908.7 has no reported proper motion in Gaia DR3 (Gaia Collaboration 2022) and is classified as a ‘high-confidence galaxy’ in DES DR2 (Abbott et al. 2021), therefore we conclude the source is a galaxy. WISEA J035312.50-313908.7 has a photometric redshift of z = 0.178 +/- 0.009 from Legacy Survey DR10 (Duncan et al. 2022). The candidate optical counterpart is consistent with a nuclear origin with an offset of ~0.4” from the host center. We disfavor this counterpart as an AGN given the WISE color of W1-W2 = -0.05 (Cutri et al. 2013) and the absence of an AGN match in the Milliquas catalog (Flesch et al. 2023).
We note that GRB 260705B, detected by Fermi (GCN 45081), has a localization consistent with GRB 260705A and was detected ~ 11 hr (~ 40,000 s) after. If these bursts are connected to the same source, this suggests a possible identification as an ultra-long GRB. The extended gamma-ray duration and nuclear location are also reminiscent of jetted TDEs (e.g., Swift J1644+57, Bloom et al. 2011; Swift J2058+05, Cenko et al. 2012; Swift J1112-82, Brown et al. 2015).
Further observations are planned to assess the variability of this source. We thank the staff at Gemini-South and SOAR for their assistance with the observations.
GCN Circular 45090
Subject
GRB 260705A: SVOM/ECLAIRs refined analysis
Date
2026-07-06T17:19:11Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
N. Dagoneau, A. Saccardi (CEA), 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 ECLAIRs observations of GRB 260705A (SVOM burst-id sb26070502).
The burst that triggered ECLAIRs onboard (GCN 45079) consists of a single broad peak lightcurve with a duration of T90 = 35.55 -9.04 / +6.05 (4-80 keV).
The time-averaged spectrum (from T0-5.49 s to T0+29.72 s) in the energy range 5-120 keV is best fit by a powerlaw with an index of -1.68 ± 0.09. With this model, the 4-120 keV fluence is (1.053 ± 0.087)*E-6 erg/cm² and the 4-120 keV photon flux is 1.002 ± 0.059 ph/cm²/s.
All the quoted errors are at the 68% confidence level.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
The SVOM/ECLAIRs point of contact for this burst is: N. Dagoneau (nicolas.dagoneau at cea.fr)
GCN Circular 45084
Subject
GRB 260705A: LCO optical upper limits
Date
2026-07-06T08:47:12Z (4 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Y.Y. Shi (GXU), A. Saccardi (CEA/Irfu), C. Wu (NAOC), L.P. Xin (NAOC), D. Turpin (CEA/Irfu), X. Tian (GXU), Z. Liu (GZNU) report on behalf of the SVOM mission team:
We observed the field of GRB 260705A (SVOM burst-id sb26070502) detected by SVOM (Saccardi et al., GCN 45079) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.
Our observation started on 2026-07-06 at 03:52:16 UT (about 14.76 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 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 limits calibrated against the DESI Legacy Imaging Surveys DR10 catalog, and not corrected for Galactic extinction:
r > 20.9 AB (5-sigma, mid-time 14.85 h after the trigger);
z > 19.9 AB (5-sigma, mid-time 15.06 h after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 45080
Subject
Fermi GBM Sub-Threshold Detection of GRB 260705A
Date
2026-07-05T20:33:37Z (5 days ago)
Edited On
2026-07-06T16:27:26Z (4 days ago)
From
rhamburg@usra.edu
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of rhamburg@usra.edu
Via
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R. Hamburg (USRA) and P. Veres (UAH) report on behalf of the Fermi-GBM Team:
SVOM ECLAIRs detected GRB 260702A on 2026-07-05 at 13:06:46 UTC (Saccardi et al 2026; GCN 45079). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates.
The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient starting about 8 seconds after the SVOM ECLAIRs best SNR time of 2026-07-05 13:06:28 UTC. The Fermi-MET for this transient is 804949601.573 s. The transient is found most significantly on the 32 s timescale with a false alarm rate of 1.4e-04 Hz. The Targeted Search localization is found to be spatially consistent with the SVOM ECLAIRs localization.
The GBM Targeted Search event was found with the highest significance using a "normal" spectrum (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular 45079
Subject
GRB 260705A: SVOM detection of a burst
Date
2026-07-05T14:25:13Z (5 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi (CEA/Irfu), N. Dagoneau (CEA/Irfu), D. Turpin (CEA/Irfu), X. Tian (GXU), Z. Liu (GZNU), report on behalf of the SVOM mission team:
At 2026-07-05T13:06:46 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260705A (SVOM burst-id sb26070502).
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. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 11.38 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2026-07-05T13:06:28.
The localization of the best alert is R.A., Dec. 58.2851, -31.6391 degrees:
R.A. (J2000) = 3h53m08.43s
Dec. (J2000) = -31d38m20.61s
with a 90% confidence level (C.L.) radius of 7.06 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a broad peak structure with a T90 duration of about 18.387 (-3.43 +11.095).
This burst was also detected by SVOM/GRM with a significance of 10.40.
The SVOM/GRM light curve showed a broad peak structure with a T90 duration of about 33.216 (-8.32 +11.914).
Due to sun constraint, no immediate slew was performed on this burst.
No X-ray observation could be performed by SVOM/MXT for the time being.
No optical observation could be performed by SVOM/VT for the time being.
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 Xiao Tian: tianxiao@st.gxu.edu.cn
Please contact the BA by email if you require additional information.