GRB 250702C, GRB 250702E, GRB 250702B, GRB 250702D, EP250702a
GCN Circular 41309
B. O’Connor (CMU), D. Pasham (Eureka/George Washington), I. Andreoni (UNC), J. Hare (Catholic/GSFC), X. Hall (CMU), J. Carney (UNC), A. Palmese (CMU), M. Busmann (LMU), D. Gruen (LMU), report on behalf of a larger collaboration:
We observed the position of the ultra-long X-ray and gamma-ray transient GRB 250702B (GCN #40883, #40886, #40890), also known as EP250702a (GCN #40906), with the Chandra X-ray Observatory (CXO) through Director's Discretionary Time (PI: O'Connor). Observations were carried out with ACIS-S starting on 2025-08-09 at 05:49:28 UT, corresponding to ~38 d after the initial Fermi trigger, for a total of 27.7 ks.
We detect a clear X-ray source at the position of the infrared and radio counterparts of GRB 250702B (GCNs #40924, #41053). Adopting the best-fit spectrum from Swift/XRT (GCN #40919), we derive an unabsorbed 0.3-10 keV flux of ~3.3e-14 erg/cm^2/s. This is consistent with the extrapolation of the decay observed by Swift/XRT at earlier times (<10 days), and favors a powerlaw with temporal slope ~-1.9 as measured from the initial Fermi trigger time (GRB 250702D; GCN #40886).
Further analysis is underway.
We thank Pat Slane for approving our DDT request, and the entire staff of the Chandra X-ray Observatory for scheduling the observations.
GCN Circular 41215
L. Rhodes (McGill), P. Atri (Astron), J.S. Bright (Oxford), F. Carotenuto (INAF, Romę), M. Gurwell (Harvard), G.K. Keating (Harvard) and N. Sarin (Cambridge) report:
We observed the position of GRB 250702B (GCN #40883, #40886, #40890) with the Submillimeter Array (SMA) at a central frequency 225.5GHz for 4.5hours beginning at 06:51UT on 31 July 2025. Vesta and MWC349A were used as the flux calibrator, while 3C84 was used to calibrate the bandpass response. 1743-038 and 1911-201 were used as interleaved complex gain calibrators.
The data was processed using the COMPASS pipeline (Keating et al, in prep). We do not detect any emission at the position of GRB 250702B (GCN #40924) with a 3sigma upper limit of 0.84mJy/beam.
We thank the staff at the SMA for carrying out these observations.
GCN Circular 41147
Author: N. Grollimund, S. Corbel (Univ. Paris Cité & CEA Saclay), A. Coleiro, F. Cangemi (Univ. Paris Cité), J. Rodriguez (CEA Saclay) on behalf of a larger team.
We observed the field of EP250702a (GCN 40906) with the MeerKAT radio telescope (proposal ID MKT-24172; PI: Corbel) using the S-band receivers, at a central frequency of 3.06 GHz. We conducted our observations from 2025-07-21 23:34:37 UTC, with a total on-source time of 11 min. We used J1939-6342 for flux and bandpass calibration, and J1822-0938 for complex gain calibration.
We detect a point source with a flux density of 147 +/- 19 uJy at the position of EP250702a, with an RMS noise level of ~15 uJy/beam. Our observation, in combination with the detection of a ~100 uJy point source reported in GCN 40985, implies that the flux of EP250702a increased by ~50% at 3 GHz between 2025-07-04 and 2025-07-21.
Averaging the fitted positions from all of our S-band observations, we find a refined radio position for the source: R.A. = 18:58:45.549 +/- 0.01s, Dec. = -7:52:26.54 +/- 0.15’'. This position is consistent with the radio position reported by VLA in GCN 41053, as well as the NIR and X-ray counterparts (GCNs 40924, 40906).
Further observations are planned.
We thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the "MPIfR S-band receiver system" designed, constructed and maintained by funding of the MPI für Radioastronomie and the Max-Planck-Society.
GCN Circular 41145
A. Balasubramanian (IIA), L. Resmi (IIST), D. Eappachen (IIA), S K Jagan (IIST), V. Bhalerao (IITB), B. Zhang (HKU), G.C. Anupama (IIA), H Sun (NAO, CAS), D. K. Sahu (IIA), and W. Yuan (NAO, CAS) report:
We observed the field of the X-ray transient EP250702a/GRB250702 B,D,E (GCNs 40906, 40883, 40886, 40890, 40891) with upgraded Giant Metrewave Radio Telescope under the joint uGMRT ToO proposals 48_059 (PI: D. Eappachen) and 48_167 (PI: L. Resmi) on 12th July 2025 in band 5 (1.26 GHz) for a total of 4 hours starting from 19:30 UTC.
In our preliminary analysis, we detect a point source with a flux density of ~90 uJy at the position of EP250702a. We used 3C48 for the flux calibration and J1911+201 for complex gain and phase calibration. The CAPTURE-CASA6 pipeline was used for data calibration and imaging.
We thank the staff of the GMRT that made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research.
GCN Circular 41122
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM mission team.
SVOM/VT conducted two ToO follow-up observations of EP250702a (Cheng et al., GCNs 40906, 40917), which was likely associated with the long burst GRB250702B,D,E (Fermi GBM Team, GCNs 40883, 40886, 40890; DeLaunay et al., GCN 40903; Frederiks et al., GCN 40914; Wang et al., GCN 40923).
The first observation was made on July 3, 2025 in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously, between 10:54:08 and 15:10:00 (UTC), 32.0 to 36.3 hours after the EP/WXT trigger (Cheng et al., GCN 40906). The second one was made on July 5, 2025, between 08:56:18 and 15:41:13, 3.25 days to 3.53 days after the EP/WXT trigger (Cheng et al., GCN 40906).
The counterpart detected by VLT (Martin-Carrillo et al., GCN 40924; Levan et al., GCN 40961), MOSFIRE (Sharma et al., GCN 41044), HST (Levan et al., GCN 41096), MeerKAT (Bright et al., GCN 40985), VLA (Sfaradi et al., GCN 41053) and ALMA (Alexander et al., GCN 41059) was not detected in our images for both observations.
The 3 sigma upper limit magnitudes were estimated:
Mid-time | Exposure time | Band | upper limit (AB)
34.2 hours | 80*100 sec | VT_R | 23.6 mag
34.2 hours | 81*100 sec | VT_B | 23.8 mag
3.53 days | 81*100 sec | VT_R | 23.6 mag
3.53 days | 81*100 sec | VT_B | 23.8 mag
The Mid-time above is the relative time from the trigger time of EP/WXT (Cheng et al., GCN 40906).
The result is consistent with the optical upper limit from GOTO (Kumar et al., GCN 40908), MASTER (Lipunov et al., GCN 40912), Colibri (Becerra et al., GCN 40918), CAHA (Pérez-García et al., GCN 40929), WFST (Hua et al., GCN 40943), FTW (Busmann et al., GCN 40949), UVOT (Siegel et al., GCN 40952), SYSU (Li et al., GCN 40986) and GRANDMA(Akl et al., GCN 41016).
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 41096
EP250702a / GRB 250702BD,D,E: Hubble Space Telescope Observations
A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Saccardi (CEA/Irfu), P. O’Brien (Univ. of Leicester), R. A. J. Eyles-Ferris (Univ. of Leicester), A. de Ugarte Postigo (LAM), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), N. R. Tanvir (U. Leicester), B. P. Gompertz (U. Birmingham) report for the Stargate collaboration:
We observed the location of EP250702a / GRB 250702B,D,E (Cheng et al., GCNs 40906, 40917; Fermi GBM Team, GCNs 40883, 40886, 40890; DeLaunay et al., GCN 40903; Frederiks et al., GCN 40914) with the Hubble Space Telescope on 15 July 2025. A total of 2196 s of observations were obtained using WFC3 and the F160W (broad-band H) filter.
At the location of the infrared counterpart (Martin-Carrillo et al., GCN 40924; Levan et al., GCN 40961) we clearly resolve a galaxy, whose nucleus is offset 0.7” from the transient location. The galaxy has an edge-on morphology, and either a disturbed disc or prominent dust lane. The transient lies on the stellar field of this galaxy, and the low probability of chance alignment (0.05%: Levan et al., GCN 40961) strongly implies that EP250702a / GRB 250702BDE is indeed an extragalactic transient. A weak excess of emission over the smooth disc is present at the transient location, but it appears likely the flux is now dominated by galaxy light.
If extragalactic in origin the very long duration of the outburst is extremely unusual. Only relativistic TDEs have been seen to have such long-lived emission in gamma-rays. However, the non-nuclear nature of the transient is not in keeping with the expected location of a supermassive black hole, although is consistent with the expectations for white-dwarf - intermediate mass black hole disruptions.
We thank Bill Januszewski, Joel Green, Claus Leitherer and Jennifer Lotz for their rapid work in approving and scheduling these observations.
GCN Circular 41095
The H.E.S.S. array of imaging atmospheric Cherenkov telescopes conducted follow-up observations of the transient EP250702a, at the localization provided by the EP-WXT (Cheng et al., GCN 40906). H.E.S.S. observed this source position for a total of 6 hours over 4 consecutive nights, starting on 2025-07-04, under fairly good observing conditions. A preliminary off-site analysis shows no evidence for a significant signal in either the full dataset or the four nights individually, consistent with the non-detection reported by the LST-1 and MAGIC telescopes (Paneque et al., GCN 41067). Our upper limits are expected to be compatible with the H.E.S.S. sensitivity curves (e.g., Fig. 6 of https://doi.org/10.22323/1.236.0847), scaled to the observation duration.
The observations took place during the following times:
2025-07-04, 00:06 - 03:01 UTC
2025-07-05, 00:48 - 02:19 UTC
2025-07-06, 01:41 - 03:08 UTC
2025-07-07, 02:36 - 03:00 UTC
H.E.S.S. is an array of five imaging atmospheric Cherenkov telescopes that detects very-high-energy gamma rays (>100 GeV) and is located in the Khomas Highland in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, France, Germany, Ireland, Japan, the Netherlands, Poland, South Africa, Sweden, UK, and the host country, Namibia. For more details see https://hess.in2p3.fr/.
GCN Circular 41067
D. Paneque (MPP Munich), M. Teshima (MPP Munich), Arnau Aguasca-Cabot (UB, ICCUB, and IEEC-UB), Alessio Berti (MPP Munich), Sweta Menon (UNIROMA2 & INAF), Edna Ruiz-Velasco (LAPP Annecy), Monica Seglar-Arroyo (IFAE Barcelona) and Andrea Simongini (UNIROMA2 & INAF), on behalf of the CTAO-LST and MAGIC Collaborations report:
We observed the field of EP250702a / GRBs 250702B,D,E (GCN 40883, 40886, 40890, 40891, 40906). A total of 2.94 hours of observations were conducted with the MAGIC telescopes, beginning at 2025-07-04 01:25:53 UTC. The final 1.79 hours of this period were carried out jointly with LST-1.
A preliminary offline analysis of the LST-1 and MAGIC dataset shows no excess of gamma rays above 200 GeV in the field of EP250702a (GCN 40906). These results have been obtained using the LST analysis software, lst-chain (LST Collaboration, 2023 ApJ 956 80, v0.10.7), and the MAGIC analysis software MARS (Zanin et al. 2013, v 3.2.1). Observations were affected by reduced atmospheric transparency. A more in-depth analysis of this data set is ongoing.
Subsequent observations are planned after the moonbreak, subject to the nature of upcoming detections.
LST-1 is a prototype of the Large-Sized Telescope (LST) for the Cherenkov Telescope Array Observatory, and is located on the Canary island of La Palma, Spain. The telescope design is optimized for observation of gamma rays in the range from 20 GeV to 3 TeV.
MAGIC is a system of two 17m-diameter Imaging Atmospheric Cherenkov Telescopes located on the Canary island of La Palma, Spain, and designed to perform gamma-ray astronomy in the energy range from 50 GeV to greater than 50 TeV.
GCN Circular 41061
A.J. Tetarenko (ULethbridge), J. Bright (Oxford), G. Bower (EAO/JCMT), S. Graves (EAO/JCMT):
The James Clerk Maxwell Telescope (JCMT) observed the position of GRB 250702B,D,E/EP250702A (GCNs 40906, 40883, 40885, 40886, 40890, 40891, ATels 17259, 17261) on 2025 July 08 between ~08:50 - 12:30 UTC for 3 scans totalling 0.55 hrs on-source and 2025 July 09 between ~08:15 - 09:20 UTC for 2 scans totalling 1.05 hrs on-source. The observations were made at a central frequency of 850 um (350 GHz) with the SCUBA-2 instrument. We do not detect a target source at the previously reported VLA radio position (RA: 18:58:45.565, Dec: -07:52:26.42; GCN 41053), yielding a 3-sigma upper limit of 6.3 mJy from stacking all of the data.
Extrapolating the previous radio detections with MeerKAT/VLA at 1.28/10 GHz of ~0.1/0.5 mJy (which imply a spectral index of ~1.3; GCN 41053), we would expect a clear detection at 350 GHz of ~50 mJy, suggesting a break in the spectrum between the cm and mm/sub-mm regions for this source. However, the recent ALMA detection at 97.5 GHz of ~2 mJy (GCN 41059), taken nearly simultaneously with our JCMT observations, implies a flatter spectral index of ~0.6. Therefore, a more accurate estimate of the expected 350 GHz flux density at the time of our JCMT observations would be ~4 mJy, consistent with our 3-sigma upper limit. Given these constraints, the source appears to likely have an inverted optically thick spectrum extending into the sub-mm bands.
We thank the JCMT staff for rapidly scheduling these observations. The JCMT is operated by the EAO on behalf of ASIAA and NARIT. Additional funds for the construction of SCUBA-2 were provided by the Canada Foundation for Innovation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
GCN Circular 41059
Kate D. Alexander (U of Arizona), James Miller-Jones (Curtin U), Adelle Goodwin, (Curtin U), Noah Franz (U of Arizona), Raffaella Margutti (UC Berkeley) Ryan Chornock (UC Berkeley), Dheeraj Pasham (Eureka Scientific/George Washington), Edo Berger (Harvard), Yvette Cendes (U of Oregon), and Collin Christy (U of Arizona) report on behalf of a larger collaboration:
We observed the location of the unusual transient GRB 250702B,D,E / EP250702a (GCNs 40906, 40883, 40885, 40886, 40890, 40891) with the Atacama Large Millimeter/submillimeter Array (ALMA) at multiple frequencies (program 2023.1.01731.T, PI: Miller-Jones). On 2025 July 9 02:09:03 UT, 6.97 days after the first detection with the Einstein Probe (GCN 40906) and 6.51 days after the first Fermi trigger (GCN 40883), we clearly detected the source at a mean frequency of 97.5 GHz with a preliminary flux density of ~2 mJy. Further ALMA observations are planned.
We thank the ALMA staff for quickly scheduling these observations and for providing the quick-look reduction.
GCN Circular 41054
Pikky Atri (Astron), Lauren Rhodes (TSI/McGill), Rob Fender (Oxford), Andrew Hughes (Oxford),and Sara Motta (INAF-OAB) report on behalf of the XKAT Collaboration.
The MeerKAT radio telescope observed the position of GRB 250702B,D,E/EP250702A (GCNs 40906, 40883, 40885, 40886, 40890, 40891) as part of the XKAT program on 06-07-2025 starting at 18:53:41 UT for 15 minutes. The observation was made at a central frequency of 1.28GHz with a bandwidth of 856MHz. We detect a point source with a flux density of ~100uJy at the coordinates R.A.: 18:58:45.5, Dec: -07:52:28.2 with a positional uncertainty of ~1" (please note the slight offset in declination).
The proximity of EP250702a on the sky to the neutron star X-ray Swift J1858.6-0814 allowed us to check archival observations from MeerKAT of the new transient’s position. Using our most recent observation of the Swift J1858.6-0814 from 02-03-2020 (Rhodes et al 2020), we place a 3-sigma upper limit of 114uJy/beam at the position of the EP250702a.
Further observations are planned.
We thank the SARAO staff for rapidly scheduling these observations. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.
X-KAT is a large MeerKAT open-time programme to observe X-ray binaries in the radio band, performing weekly monitoring of bright, active systems, with capacity for higher cadence observations, and in coordination with large X-ray and optical monitoring programmes. For further information on this programme contact Rob Fender.
GCN Circular 41053
Authors: I. Sfaradi (UC Berkeley), Y. Yao (UC Berkeley), H. Sears (Rutgers), E. Wiston (UC Berkeley), R. Margutti (UC Berkeley), R. Chornock (UC Berkeley), K.D. Alexander (U of Arizona), T. Laskar (Utah), E. Hammerstein (UC Berkeley), W. Lu (UC Berkeley)
We report here a radio detection of GRB 250702B,D,E / EP250702a (GCNs 40906, 40883, 40885, 40886, 40890, 40891) with the Karl G. Jansky Very Large Array (VLA program 25A-109; PI: Yao). We conducted our observation from 2025-07-08 05:29:18 (UTC) to 2025-07-08 06:29:03 (UTC), 6.13 days after the first detection with the Einstein Probe (GCN 40906) and 5.7 days after the first Fermi trigger (GCN 40883). Calibration and imaging were performed in CASA using the VLA calibration pipeline, with 3C286 as a bandpass and flux density calibrator, and J1832-1035 as the complex gain calibrator.
Our observation in X-band, with a 3.9 GHz bandwidth centered around 10 GHz, results in a detection of a point source with a flux density of 0.49 +/- 0.05 mJy (including 10% systematic flux calibration uncertainties) at R.A.: 18:58:45.565 +/- 0.015s, Dec.: -07:52:26.42 +/- 0.35’’ (J2000), consistent within 1 sigma uncertainty with the NIR counterpart (GCN 40924) and the EP X-ray counterpart (GCN 40906). The in-band spectral slope of F_nu ~ nu^1.3 implies optically thick emission. Radio detection with the MeerKAT telescope of a 0.1 mJy point source at 3 GHz was previously reported in GCN 40985.
We plan to continue monitoring this source and encourage further multi-wavelength observations.
We thank the VLA and the NRAO staff for scheduling and performing this observation.
GCN Circular 41016
D. Akl (AUS), K. Noysena, A. Manasanun (NARIT), M. Freeberg, R. Hellot (KNC), C. Andrade (UMN), W. Corradi (LNA), M. Pillas (Uliege), S. Antier (OCA/IJCLAB), N. Kochiashvili (AbAO), M. Lamoureux (UCLouvain), on behalf of GRANDMA:
We observed the field of EP250702a (GCN 40906; associated with GRBs 250702/B/D/E) with GRANDMA and Kilonova Catcher and did not detect any optical counterpart.
All our measurements can be downloaded from: https://skyportal-icare.ijclab.in2p3.fr/public/sources/EP250702a/
All the data have been 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-Cousin 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).
Our observations are consistent with previously reported measurements (refer to SkyPortal for a subset of GCN measurements we collected).
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/).
GCN Circular 41014
Brendan O’Connor (CMU), Dheeraj Pasham (Eureka Scientific/George Washington), Igor Andreoni (UNC), Jeremy Hare (Catholic/GSFC) report on behalf of a larger collaboration:
We observed the X-ray transient EP250702a (GCN 40906), which is also associated with the multiple gamma-ray triggers designated as GRB 250702B/D/E (GCNs 40883, 40886, 40890, 40891, 40931, 40903, 40914, 40923), with the NuSTAR X-ray Telescope through a Target of Opportunity observation through GO program 11282 (PI: Pasham). The observation occurred between 2025-07-03 20:45:21 and 2025-07-04 09:15:00 UTC for an on-source exposure of ~21.5 ks, simultaneous with Swift/XRT observations (ObsID: 19906002).
The source is clearly detected at an average rate of ~0.4 cts/s. The 3-79 keV X-ray lightcurve shows short term variability throughout the full exposure in both FPMA and FPMB, but no flaring is observed. The source varies in count rate by a factor of 2-3 on timescales as short as a few ks. Compared to NuSTAR observations of GRB 221009A at a similar count rate (GCNs 32695, 32788), the source shows more significant variability, which we suggest disfavors an ultralong GRB origin, especially in conjunction with the July 1st onset reported by the Einstein Probe (GCN 40906).
The X-ray spectra are featureless and do not show any Fe lines or reflection features. This is consistent with the lack of features in the Swift/XRT spectra. The 3-79 keV spectrum (FPMA+FPMB) is well fit by an absorbed powerlaw with a photon index of Gamma~1.81+/-0.03, which is consistent with the initial Swift/XRT spectral index within errors (GCN 40919). The hydrogen column density was fixed to 1e22 cm^-2 as per the best-fit Swift/XRT spectra (see https://www.swift.ac.uk/LSXPS/transients/9377). The unabsorbed 3-79 keV flux (time-averaged) is (2.35+/-0.05)e-11 erg/cm^2/s during our observation.
We also performed a fit with an absorbed cutoff powerlaw and find a cutoff energy >60 keV. In this case, the best-fit photon index is Gamma~1.67+/-0.08. This has better agreement with the EP/FXT result, although the FXT observation was obtained at an earlier time (GCN 40917). The C-stat between both fits to the NuSTAR data was nearly identical and the cutoff powerlaw is not a statistically significant improvement. We suggest that the lack of Fe lines, and lack of cutoff in the powerlaw spectra (out to at least 60 keV), is atypical for an X-ray binary.
We performed a Lomb-Scargle analysis on the barycenter corrected X-ray data, and did not identify any periodic signals over the frequency range 1e-3 to 100 Hz, consistent with the EP/FXT report (GCN 40917). The periodogram becomes red noise dominated below 3e-3 Hz.
Further analysis is underway and additional NuSTAR and Swift observations are planned.
We thank the NuSTAR SOC, and in particular Karl Forster and Brian Grefenstette, for promptly implementing these observations.
GCN Circular 40986
Xia Li, Chun Chen, Zhong-nan Dong, Duo-le Cao, Wei-Sen Huang, Jin-Ji Li, Jia-Qi Lin, Pu Lin, Yan Yu, Hao-Nan Yang, Hao-Ran Zhang, Xiang-Tao Zeng, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team:
We observed the field of GRBs 250702B,C,D,E / EP250702a (H. Q. Cheng et al., GCN 40906