GRB 260705A
GCN Circular 45189
Subject
GRB 260705A: Retraction of optical counterpart
Date
2026-07-20T20:02:38Z (12 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 obtained further imaging of the optical counterpart to GRB 260705A (Saccardi et al., GCN 45079; Hamburg & Veres, GCN 45080) reported in Freeburn et al., GCN 45105. We observed with the Goodman High Throughput Spectrograph (GHTS) in imaging mode at a midpoint of UT 2026-07-11 10:15:00 corresponding to 5.88 days after the trigger and with the Gemini Multi-object Spectrograph (GMOS) mounted on Gemini south at UT 2026-07-08 09:08:46 corresponding to 2.83 days after the trigger. We obtain the following upper limits:
| Instrument | MJD | Filter | Upper limit |
|---|---|---|---|
| GMOS | 61229.381 | r | 23.7 |
| GHTS | 61232.423 | i | 23.0 |
| GHTS | 61232.434 | r | 23.3 |
We also obtained imaging and spectroscopic data using the GMOS-S instrument mounted on the Gemini South telescope. The acquisition images consisted of a sequence of 20 s and 30 s exposures in the r-band. We acquired 4 x 900 s spectroscopic observations using the B480 grating centered at 520 nm. Data were reduced using DRAGONS.
The spectrum is host dominated and shows no prominent transient features. We identify several narrow absorption and emission features at a common redshift of z = 0.1840 +/- 0.0005.
Motivated by the photometric and spectroscopic non-detections, we conducted more careful analysis of the images taken on the night of 2026-07-07, detailed in Freeburn et al., GCN 45105. Despite a convincing detection in the coadded image, we found that the source was not present when differencing the individual GMOS exposures. Similarly, in the SOAR data, the source was not reliably recovered when varying the subtraction parameters. We therefore conclude that the source is likely spurious.
GCN Circular 45155
Subject
GRB 260705A: ATCA radio observations
Date
2026-07-14T14:38:03Z (18 days ago)
From
James Leung at U. Toronto / HUJI <jamesk.leung@utoronto.ca>
Via
Web form
J. K. Leung (U. Toronto/HUJI), G. E. Anderson (CSIRO), S. Chastain (TTU), L. Rhodes (TSI/McGill), A. Gulati (U. Sydney), A. J. van der Horst (GWU) on behalf of the PanRadio GRB collaboration
We performed observations of GRB 260705A, which was detected by SVOM/ECLAIRs (Saccardi et al., GCN 45079) and Fermi/GBM (Hamburg, GCN 45080), using the Australia Telescope Compact Array (ATCA) from 14:30 - 23:00 UT on 11 July 2026 (~6.3 days post-burst) using the 4cm (4-12 GHz) receiver. Our observations were centred on the position of the candidate optical counterpart detected by SOAR and Gemini-South telescopes (Freeburn et al., GCN 45105).
In our preliminary analysis, we do not detect any radio source with a position consistent with the candidate optical counterpart. The rms noise of the observation at 8 GHz was 8 microJy/beam. However, we find multiple radio sources within the SVOM/ECLAIRs error circle (Saccardi et al., GCN 45079) that were not detected in the Rapid ASKAP Continuum Survey (RACS; McConnell et al., PASA, 37, e048) and will continue to monitor these sources.
In regards to the possible association with GRB 260705B (Freeburn et al., GCN 45105), we note that the separation between the reported positions for GRB 260705A (Saccardi et al., GCN 45079) and GRB 260705B (Fermi GBM Team, GCN 45081) is ~11 deg; with the uncertainties on the positions being 7.06 arcmin and 3.0 deg, respectively; the positions of these GRBs are not statistically consistent.
Further observations are planned.
We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
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 (25 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 (a month 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 (a month 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 (a month ago)
Edited On
2026-07-06T16:27:26Z (a month ago)
From
rhamburg@usra.edu
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of rhamburg@usra.edu
Via
Web form
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 (a month 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.