GRB 250515A
GCN Circular 40462
Subject
GRB 250515A: Fermi GBM Final Localization
Date
2025-05-15T21:34:47Z (14 days ago)
From
R. Hamburg at CNRS/IJCLab <rachel.k.hamburg@gmail.com>
Via
Web form
The Fermi GBM team reports the detection of a likely SHORT GRB
"At 20:46:21.91 UT on 15 May 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250515A (trigger 769034786/250515866).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 154.35, Dec = 23.19 (J2000 degrees, equivalent to J2000 10h 17m, +23d 11'),
with a statistical uncertainty of 7.76 degrees.
The angle from the Fermi LAT boresight is 69 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/quicklook/glg_skymap_all_bn250515866.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/quicklook/glg_healpix_all_bn250515866.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/quicklook/glg_lc_medres34_bn250515866.gif"
GCN Circular 40464
Subject
GRB 250515A: GOTO candidate optical counterpart
Date
2025-05-16T09:20:14Z (13 days ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, R. Starling, D. O’Neill, G. Ramsay, A. Kumar, 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. Godson, T. Killestein, and M. Pursiainen report 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 short GRB 250515A (Fermi GBM team, GCN 40462).
Targeted observations were performed by GOTO-North (La Palma) beginning at May 15 2025 21:21:20 UT, (+0.58h post trigger) and continuing through to May 16 2025 00:15:21 UT (+3.48h post trigger). 232 images were taken, across 10 unique pointings, covering 471.6 square degrees within the 90% localisation contour. ~60.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.8 mag in the GOTO L-band (400-700nm).
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, GOTO25cqo, is identified within the GBM 90% localisation region at RA 10:38:32.5, Dec +19:25:03.1 (J2000). This position is on the 37% probability contour of the Fermi/GBM localisation map. The source was initially detected with magnitude L = 20.17 ± 0.21 mag (+0.71h after the GBM trigger), rising to L = 19.79 ± 0.15 mag at +1.85h post trigger. In a 3rd epoch, taken at t0+2.99 hours, we obtain a 3-sigma upper limit of L > 19.21.
We find no strong evidence of this source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). However, we caution that observations to sufficiently constraining depths are not available in the weeks prior to the GRB. We note a marginal flux excess in two ATLAS images taken on 2025-05-01 and 2025-05-03. Visual inspection of these images does not reveal any compelling source, and no significant flux excess was seen in the 7 epochs between these dates and GRB 250515A.
From available observations, we cannot confirm whether GOTO25cqo is associated with GRB 250515A, but given its time coincidence and apparent rapid evolution, we encourage further follow-up observations.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing.
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 and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 40470
Subject
GRB 250515A: Swift ToO observations
Date
2025-05-16T21:26:55Z (13 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/GBM-detected event
GRB 250515A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021829
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/GBM event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular 40474
Subject
GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
Date
2025-05-17T01:24:43Z (13 days ago)
Edited On
2025-05-19T13:08:20Z (10 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Y. Wang (PMO, CAS), R. Z. Li (YNAO, CAS), J. X. Cao, D. F. Kong (GXU), J. R. Mao (YNAO, CAS), X. W. Liu (YNU) report on behalf of the SVOM/VT team:
SVOM/VT conducted ToO follow-up observations of the optical transient (B. P. Gompertz et al., GCN 40464) which was proposed to be the optical candidate of the GRB 250515A (Fermi GBM team, GCN 40462). The observation started from 2025-05-16T12:16:52 UTC (15.50 hours after the Fermi GBM trigger) to 2025-05-16T19:20:30 UTC in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical candidate (B. P. Gompertz et al., GCN 40464) was clearly detected in VT both channels, which is not found in the legacy survey.
The brightness in AB magnitude was estimated to be:
Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error
22.27 | VT_B | 32x70 | 20.25 | 0.03
22.27 | VT_R | 32x70 | 20.56 | 0.05
Our photometry was not corrected for Galactic extinction.
The source shows no significant fading or brightening in both channels during our observations. However, given the blue color and the possible association to the likely short GRB (Fermi GBM team, GCN 40462), more multiband follow-up observations are encouraged.
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 40476
Subject
GRB 250515A: 1.6m Mephisto optical detection
Date
2025-05-17T05:06:22Z (13 days ago)
From
zhjh@nao.cas.cn
Via
Web form
Jinghua Zhang, Yu Pan, Xiangkun Liu, Yiheng Xie, Guowang Du, Yuan Fang, Xinlei Chen, Xingzhu Zou, Helong Guo, Xufeng Zhu, Tao Wang, Brajesh Kumar, Xinzhong Er, Yuanpei Yang, Xiaowei Liu (SWIFAR, YNU) report on behalf of Mephisto Team:
We conducted simultaneous multi-band photometric observations of the optical candidate of the likely short GRB 250515A (Fermi GBM team, GCN 40462) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. Mephisto was triggered ~17 hours post-alert and commenced observations starting from 13:47:01 UTC 2025-05-16 in moderate sky conditions. Multiple frames across uvgriz bands were acquired. The optical candidate (B. P. Gompertz et al., GCN 40464; Xin et al., GCN40474) was clearly detected in the stacked images of g and r bands while marginally detected in the u, v, i, z -bands. The preliminary photometry (AB magnitude system) are listed below:
| Time-Mid
(2025-05-16 UT)
| Filter | Exposure | Mag | Mag Err |
| 15:02:22 | u | 300sec*3 | 21.17 | 0.27 |
| 13:54:44 | v | 300sec*3 | 21.46 | 0.47 |
| 15:02:22 | g | 300sec*3 | 20.21 | 0.07 |
| 13:54:44 | r | 300sec*3 | 19.91 | 0.08 |
| 15:02:22 | i | 300sec*3 | 20.74 | 0.20 |
| 13:54:44 | z | 300sec*3 | 20.22 | 0.47 |
-------------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
-------------------------------------------------------------------------------------------------------
GCN Circular 40478
Subject
GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
Date
2025-05-17T06:16:42Z (12 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Kin Ocelotl López (UNAM), Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GOTO candidate afterglow (Gompertz et al., GCN Circ. 40464) of the Fermi GRB 250515A (Fermi GBM team., GCN Circ. 40462) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-17 03:23 to 05:27 UTC (median epoch 1.30 days after the trigger) and obtained 32 minutes of exposure in the i filter and 3 minutes in each of the g and r filters.
The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical candidate at preliminary magnitudes of:
g = 20.31 +/- 0.03
r = 20.24 +/- 0.04
i = 20.45 +/- 0.03
This source was also detected by SVOM/VT (Xin et al., GCN Circ. 40474) and Mephisto (Zhang et al., GCN Circ. 40476).
Our magnitudes are similar in g, fainter in r, and brighter in i than those reported at 0.71 days by Zhang et al. (GCN Circ. 40746), and these changes are not obviously compatible with the temporal evolution of a GRB afterglow after about 1 day.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
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 40480
Subject
GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
Date
2025-05-17T08:32:02Z (12 days ago)
Edited On
2025-05-19T13:08:30Z (10 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. Martin-Carrillo (UCD), Z. P. Zhu (NAOC), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), B. P. Gompertz (U. Birmingham), G. Corcoran (UCD), N. R. Tanvir (Leicester), R. Rautio (Univ. Oulu), report on behalf of a larger collaboration.
We observed the position of GOTO25cqo (Gompertz et al., GCN 40464), a candidate optical counterpart to GRB 250515A (Fermi GBM team, GCN 40462), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS r band (3x300 s) starting at 23:44:29 UT on 2025-05-16 (27 hours after the Fermi trigger). The candidate is detected in single exposures with an AB magnitude of r = 20.18 +/- 0.02, calibrated against nearby Pan-STARRS stars.
We further obtained 4x600 s of spectroscopic observations. The flux-calibrated spectrum shows features not consistent with typical GRB afterglows. Using SNID (Blondin & Tonry 2007, doi:10.1086/520494), the spectrum matches well several normal rising type-Ia supernovae at z = 0.18 +/- 0.01. This excludes the association of GOTO25cqo with GRB 250515A, as already suggested by Xin et al. (GCN 40474) and Lopez et al. (GCN 40478).
The slit was oriented so to cover the bright galaxy 5.3” NW of GOTO25cqo. We detect several emission lines which we identify Halpha, Hbeta, [O III] and [O II] at a common redshift of z = 0.169. With a 15 kpc projected separation, this galaxy is thus a plausible host of GOTO25cqo.
We acknowledge excellent support from the NOT staff, in particular Joonas Viuho and Amanda Djupvik.
GCN Circular 40481
Subject
GRB 250515A: Swift-XRT observations
Date
2025-05-17T08:43:22Z (12 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC &
INAF-OAR), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU),
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Fermi/GBM-detected burst GRB 250515A, centred on the location of
GOTO25cqo (GCN 40464) collecting 4.5 ks of Photon Counting (PC) mode
data between T0+88.8 ks and T0+117.8 ks.
No X-ray sources have been detected within the estimated 3-sigma GOTO
error region (4.9 arcsec). The 3-sigma upper limit in the field ranges
from ~0.002 to ~0.003 ct s^-1, corresponding to a 0.3-10 keV observed
flux of 9.2e-14 to 1.4e-13 erg cm^-2 s^-1 (assuming a typical GRB
spectrum).
GOTO25cqo has since been classified as a type Ia supernova.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021829.
This circular is an official product of the Swift-XRT team.