GRB 250403A
GCN Circular 40164
Subject
Konus-Wind detection of GRB 250403A
Date
2025-04-17T17:43:37Z (7 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova,
M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report
The long GRB 250403A (Fermi GBM detection: Fermi GBM team, GCN 40025;
Veres et al., GCN 40060; SVOM detection: Julacanti et al., GCN 40026;
AstroSat CZTI detection: Tembhurnikar et al., GCN 40077)
was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a ~12 sigma count-rate increase in the interval
from T0-0.4 s to T0+11.5 s where T0 = 15:15:22 UT.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB250403A/
Modeling the time-integrated spectrum of the burst
by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.14 (-0.23, + 0.23) and Ep = 83(-6,+6) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the burst fluence is (2.55 ± 0.18)x10^-6 erg/cm^2
and the 2.944 s peak energy flux is (2.51 ± 0.22)x10^-7 erg/cm^2/s.
Assuming the redshift z=1.847 (de Ugarte Postigo et al., GCN 40162)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to (2.2 ± 0.2)x10^52 erg,
the isotropic peak luminosity L_iso to (6.3 ± 0.6)x10^51 erg/s, and
the rest-frame peak spectral energy Ep,z to (236 ± 11) keV.
With the obtained estimates, GRB 250403A is consistent (inside 68% prediction bands)
of both 'Amati' and 'Yonetoku' relations for the sample
of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB250403A/GRB250403A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 40162
Subject
GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
Date
2025-04-17T14:35:25Z (7 months ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
Web form
A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. Schneider (LAM), L. Izzo (INAF/OAC and DARK/NBI), J. P. U. Fynbo (DAWN/NBO), Y. Julakanti (Univ. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. T. Palmerio (CEA/Irfu), S. Savaglio (Univ. Calabria), N. R. Tanvir (Univ. Leicester), S. D. Vergani (LUX-Obs. de Paris, CNRS), report on behalf of the Stargate collaboration:
We observed the optical and NIR counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041; Pérez-Fournon et al., GCN 40043; Brivio et al., GCN 40044; Xin et al., GCN 40045; Shilling et al., GCN 40048; Zheng et al., GCN 40065; Leonini et al., GCN 40068) of the SVOM/ECLAIRs (Julakanti et al., GCN 40026), Fermi/GBM (Veres et al., GCN 40060), and AstroSat CZTI (Tembhurnikar et al., GCN 40077) GRB 250403A using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. The 300V grism with no order-blocking filter was adopted, covering the wavelength range 3300-9600 AA (with potential second-order contamination redward of 6600 AA). Observations started on 2025 April 4 at 02:15:01 UT (10.99 hr after the burst). Two exposures of 600 s each were obtained.
From a 60 s acquisition image obtained on 2025 April 4 at 02:01:37 UT (10.76 hr after the burst), we measure R ~ 21.1 +/- 0.2 mag (AB) calibrated against nearby Pan-STARRS objects.
From a preliminary reduction of the spectrum, continuum is detected over the wavelength range 3600-9600 AA. While the spectrum is noisy blueward of 3720 AA, we can set an upper limit to the redshift z < 2.06 due to the lack of Lyman forest. Four clear absorption features are apparent in clean regions of the spectrum, three of which match Si IV 1393, Si IV 1402 and the (blended) C IV doublet 1548,1550 at a common redshift z = 1.847. The fourth line seems marginally split and could be an intervening C IV doublet at z = 1.763, although no other features are seen to confirm this value.
The observed absorption system is somewhat peculiar (but not unprecedented), as some typically strong low-ionization features common in long GRB spectra (de Ugarte Postigo et al. 2012, doi:10.1051/0004-6361/201219894) are either non-detected or only marginally detected. This indicates a high-ionization environment, which has been previously linked to systems with low H I column density (e.g. Jakobsson et al. 2006, doi:10.1051/0004-6361:20066405; Thoene et al. 2011, doi:10.1111/j.1365-2966.2011.18408.x; Vielfaure et al. 2020, doi:10.1051/0004-6361/202038316). We thus consider z = 1.847 a viable possibility, and the most likely redshift of GRB 250403A.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Matias Jones, Claudia Paladini, Jesus Corral-Santana, and Cecilia Bustos.
GCN Circular 40077
Subject
GRB 250403A: AstroSat CZTI detection
Date
2025-04-05T10:38:20Z (7 months ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 250403A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 40025) and SVOM/ECLAIRs (Y. Julakanti et. al. GCN Circ. 40026).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-04-03 15:15:26.00 UTC. The measured peak count rate associated with the burst is 80 (+18, -23) counts/s above the background in the combined data of three quadrants (out of four), with a total of 343 (+110, -184) counts. The local mean background count rate was 225 (+3, -2) counts/s. Using cumulative rates, we measure a T90 of 9.1 (+1.3, -5.5) s.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 40068
Subject
GRB 250403A: Montarrenti Observatory optical detection
Date
2025-04-04T21:35:28Z (7 months ago)
From
Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini@iol.it>
Via
Web form
S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:
we observed the field of GRB 250403A detected by Fermi/GBM (Fermi team, GCN 40025), SVOM/ECLAIRs (Julakanti et al., GCN 40026) and SWIFT (Dichiara et al., GCN 40037; Shilling et al., GCN 40048) with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started at 2025-04-03 21:56:50 UT (approximately 7 hours after burst) stacking a set of Rc-band CCD images. The elevation of the field decreased from 19 degrees above the horizon.
The optical afterglow (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al, GCN 40039; Jiang et al., GCN 40041; Perez-Fournon et al., GCN 40043; Brivio et al., GCN 40044; Xin et al, GCN 40045 and Zheng et al., GCN 40065) was barely detected (S/N=2.4) at the following position:
RA (J2000.0) 12h 58m 27.72s +/-0.15
Decl. (J2000.0) -24° 22' 46.5" +/-0.19
Preliminary photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. UL (3-sigma)
2025-04-03 21:57:10 UT 6.68 94x40s Rc 20.10 S/N =2.4 >19.90
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.
GCN Circular 40065
Subject
GRB 250403A: KAIT optical observations
Date
2025-04-04T18:53:09Z (7 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of GRB 250403A (Julakanti
et al., GCN 40026; Fermi GBM team, GCN 40025) with a set of
120x60s images in the clear (roughly R) filters, at a mid time
of 16.0 hours after the trigger. We marginally detected the optical
afterglow (Starling et al., GCN 40028; Wu et al., GCN 40029;
Du et al., GCN 40031; Li et al., GCN 40032, Julakanti et al.,
GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041;
Pérez-Fournon et al., GCN 40043; Brivio et al., GCN 40044;
Xin et al., GCN Circ. 40045) in the coadd image with a brightness
of 21.2 +/- 0.4 mag (Vega).
GCN Circular 40060
Subject
GRB 250403A: Fermi GBM observations
Date
2025-04-04T16:31:50Z (7 months ago)
From
Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>
Via
Web form
P. Veres (UAH), M. Godwin (UAH), C. Meegan (UAH) and E. Bissaldi (Politecnico and INFN Bari)
report on behalf of the Fermi GBM Team:
"At 15:15:22.83 UT on 03 April 2025, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 250403A (trigger 765386127 / 250403636).
This GRB was also detected by the SVOM (Julakanti et al. 2025, GCN 40026).
The Fermi GBM Final Real-time Localization (GCN 40025) is consistent with the SVOM position.
The angle from the Fermi LAT boresight at the GBM trigger time is 59 degrees.
The GBM light curve consists of multiple pulses
with a duration (T90) of about 16.4 s (50-300 keV).
The time-averaged spectrum from T0-4.1 s to T0+14.3 s is
best fit by a simple power law function with index -1.65 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is
(6.7 +/- 0.2)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.3 s in the 10-1000 keV band
is 4.2 +/- 0.2 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/"
GCN Circular 40048
Subject
GRB 250403A: Swift/UVOT Detection
Date
2025-04-04T13:28:59Z (7 months ago)
Edited On
2025-04-04T16:16:20Z (7 months ago)
From
Sam Shilling at Lancaster University <shilling.sam@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Sam Shilling at Lancaster University <shilling.sam@gmail.com>
Via
Web form
S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on behalf of the Swift UVOT team:
Swift/UVOT observed the field of GRB 250403A detected by Fermi GBM (Fermi team, GCN Circ. 40025) and
SVOM/ECLAIRs (Julakanti et al., GCN Circ. 40026), starting at 17:22:59 UT on 24/04/03, ~2.1 hours after the initial detections.
An optical afterglow is initially detected in the U-band consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (Dichiara et al., GCN Circ. 40037) and the optical afterglow detected by various facilities (Starling et al., GCN Circ. 40028; Wu et al., GCN Circ. 40029; Du et al., GCN Circ. 40031; Li et al., GCN Circ. 40032; Ghosh et al., GCN Circ. 40039; Jiang et al., GCN Circ. 40041; Pérez-Fournon et al., GCN Circ. 40043; Xin et al., GCN Circ. 40045). At 00:02:02 UT on 25/04/04, ~6.7 hours later, the optical afterglow is no longer detected.
The preliminary detection and 3-sigma upper limits calculated using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial and subsequent exposures are:
Filter T_start(h) Exp(s) Mag
u 2.1 396 19.2 +/- 0.2
u 8.8 492 >20.3
b 8.8 386 >20.5
v 9.0 130 >19.0
w1 12.1 164 >19.3
m2 12.0 245 >19.7
w2 8.9 246 >19.8
The magnitudes given are calculated using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) and are not corrected for the Galactic extinction.
GCN Circular 40045
Subject
GRB 250403A: SVOM/VT optical observation
Date
2025-04-04T11:49:37Z (7 months ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L.P. Xin, Y. L. Qiu, C. Wu, H. L. Li, J . Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, Y. N. Yi, J. Y. Wei (NAOC), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM team:
SVOM performed a Target of Opportunity observation of GRB 250403A detected by Fermi/GBM (Fermi GBM team, GCN 40025) and SVOM/ECLAIRs (Julakanti et al., GCN 40026) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical afterglow (Starling et al., GCN. 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041, Pérez-Fournon et al., GCN 40043, Brivio et al., GCN 40044) was detected with a brightness of VT_R=21.26 +/- 0.07 (AB) mag and VT_B=21.78 +/- 0.07 (AB) at the mid time of 14.26 hours after the burst.
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 40044
Subject
GRB 250403A: REM NIR afterglow detection
Date
2025-04-04T10:49:24Z (7 months ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 April 03 at 23:27:03 UT (i.e. 8.2 hr after the burst), and lasted for about 1 hour.
From preliminary photometry, we detect the NIR counterpart at the position of the optical afterglow (Starling et al., GCN. 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039; Jiang et al., GCN 40041, Pérez-Fournon et al., GCN 40043) with the following magnitude:
H = 16.3 +/- 0.3 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 8.6 hours after the trigger.
The afterglow is not detected in our r-band observations down to the following 3sigma limit:
r > 20.7 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 8.7 hours after the trigger.
GCN Circular 40043
Subject
GRB 250403A: LCO optical counterpart detection
Date
2025-04-04T10:34:53Z (7 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL)
We report on Las Cumbres Observatory Global Telescope network (LCOGT) observations of GRB 250403A, detected by Fermi GBM (Fermi GBM team, GCN circ. 40025), SVOM/ECLAIRs (Julakanti et al., GCN circ. 40026), and Swift XRT (Dichiara et al., GCN circ. 40037)
We observed the field of GRB 250403A with two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa) in the SDSS r, i, g, and u filters, starting at 2025-04-03 22:00:46 UTC, about 6.76 hours after the Fermi and SVOM triggers.
A source is clearly detected in the four filters at the position of the optical counterpart
first reported by GOTO (Starling et al., GCN circ. 40028) and detected also by WU et al. (GCN circ. 40029), Du et al. (GCN circ. 40031), Li et al. (GCN circ. 40032), Julakanti et al. (GCN circ. 40034), Ghosh et al. (GCN circ. 40039), and Jiang et al. (GCN circ. 40041).
The r, i, and g images were calibrated against Pan-STARRS DR2 stars and the u image was calibrated against stars from the Gaia DR3 synthetic photometry catalog generated from the Gaia BP/RP mean spectra (Gaia Collaboration, 2022). We measure the following preliminary magnitudes, that are not corrected for Galactic extinction:
Date | UT start | mag | error | filter | exposure time (sec)
---------------------------------------------------------------------
2025-04-03 22:00:46 20.34 0.08 r 300
2025-04-03 23:00:56 20.39 0.08 i 300
2025-04-03 23:08:52 20.97 0.08 g 300
2025-04-04 00:14:01 21.44 0.16 u 600
We note that a faint source, morphologically classified as point-like, is detected in the Legacy Surveys (LS) DR10 images at the position of the optical counterpart of GRB 250403A, with coordinates RA, Dec (J2000) = 194.6157, -24.3795, and magnitudes in the LS DR10 catalog of g = 24.16, r = 24.17, i = 23.88, and z = 24.34.
This work makes use of observations from the Las Cumbres Observatory global telescope network
(LCOGT observing programme IAC2025A-009, SGLF).
GCN Circular 40041
Subject
GRB 250403A: JinShan optical observations
Date
2025-04-04T09:10:46Z (7 months ago)
From
sqjiang at NAOC <sqjiang@bao.ac.cn>
Via
Web form
S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, D. Xu (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of GRB 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 18:03:34.11 UT on 2025-04-03, i.e., 2.80 hr after the SVOM/ECLAIRs trigger, and a series of 600 s frames were obtained in the Sloan r- and i- bands.
The optical afterglow (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039) of GRB 250403A is clearly detected in our stacked images. Preliminary photometry results are as follows:
T_mid(hr) Filter Mag(AB) MagErr
4.06 r 19.77 0.05
4.73 i 20.11 0.06
calibrated with nearby Legacy Survey stars and not corrected for Galactic extinction.
We acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations.
GCN Circular 40039
Subject
GRB 250403A: Optical counterpart detection by LCO.
Date
2025-04-04T08:44:09Z (7 months ago)
Edited On
2025-04-04T13:40:53Z (7 months ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
Web form
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
We observed the field of the GRB 250403A triggered by Fermi (Fermi GBM team, GCN 40025) in the V, r filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Teide Observatory, Tenerife, Canary Islands, Spain. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on April 04, 2025, starting 8.93 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs (Julakanti et al. 2025, GCN 40026, Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032, Julakanti et al. 2025, GCN 40034) in our r band image.
-------------------------------------------------------------------------------------------------
|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
--------------------------------------------------------------------------------------------------
2025-04-04 00:11:21.696 8.93 1 x 900 r r = 20.83 +/- 0.07
--------------------------------------------------------------------------------------------------
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
GCN Circular 40037
Subject
GRB 250403A: Swift-XRT observations
Date
2025-04-04T03:32:07Z (7 months ago)
Edited On
2025-04-04T13:41:38Z (7 months ago)
From
Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Simone Dichiara at Pennsylvania State University <sbd5667@psu.edu>
Via
Web form
S. Dichiara (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB), K.L.
Page and P.A. Evans (U.Leicester) reports on behalf of the Swift-XRT team:
We have analysed 401 s of XRT data for the GRB 250403A detected by
Fermi GBM (Fermi team, GCN circ. 40025) and SVOM/ECLAIRs (SVOM trigger
sb25040305; Julakanti et al., GCN circ. 40026), from T0+7.62 ks to T0+8.02
ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting
(PC) mode.
We find an uncatalogued X-ray source 3.1 sigma above the RASS limit,
consistent with the reported optical counterpart (Starling et al.,
GCN 40028, Chao et al., GCN 40029, Guowang et al., GCN 40031, Li et al., GCN
40032). Details of this source are given below:
Source 1:
RA (J2000.0): 194.6162 = 12:58:27.90
Dec (J2000.0): -24.3800 = -24:22:47.9
Error: 3.7 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.29 (±0.07) ct s-1
Flux: 1.2 (±0.3) ×10-11 erg cm-2 s-1 (observed, 0.3-10 keV)
This XRT position is 2.5 arcsec away from the optical position (Starling et
al., GCN 40028).
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/SVOM/SVOM_FIELD00010/.
This circular is an official product of the Swift-XRT team.
GCN Circular 40035
Subject
Fermi GRB 250403A: Global MASTER-Net observations report
Date
2025-04-03T21:47:38Z (7 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250403A ( Fermi GBM team, GCN 40025) errorbox 22256 sec after notice time and 22291 sec after trigger time at 2025-04-03 21:26:53 UT, with upper limit up to 18.5 mag. The observations began at zenith distance = 27 deg. The sun altitude is -58.3 deg.
The galactic latitude b = 36 deg., longitude l = 316 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2832003
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
22321 | 2025-04-03 21:26:53 | MASTER-SAAO | (13h 38m 33.90s , -25d 30m 56.0s) | C | 60 | 18.5 |
22400 | 2025-04-03 21:28:13 | MASTER-SAAO | (13h 47m 18.63s , -25d 31m 56.8s) | C | 60 | 18.4 |
22559 | 2025-04-03 21:30:51 | MASTER-SAAO | (13h 34m 56.63s , -27d 26m 34.6s) | C | 60 | 18.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 40034
Subject
GRB 250403A: GOTO optical counterpart follow-up observations
Date
2025-04-03T19:34:36Z (7 months ago)
From
Yashaswi Julakanti at University of Leicester <skyj1@leicester.ac.uk>
Via
Web form
Y. Julakanti, A. Kumar, B. P. Gompertz, D. O'Neill, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on further observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) on GRB 250403A (Julakanti et al. 2025, GCN 40026; Fermi GBM team, GCN 40025). Images were processed immediately after acquisition using the GOTO pipeline. Observations consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
We continue to detect the optical counterpart (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032) with the following AB magnitudes:
+-------------------------------------------------------------------+
| Observation time (UT) | t-t0 | filter | mag (AB) |
+-------------------------------------------------------------------+
| 2025-04-03 16:20:24 | +1.08h | L | 18.99 ± 0.07 |
| 2025-04-03 16:27:28 | +1.2h | L | 19.10 ± 0.07 |
| 2025-04-03 16:34:48 | +1.32h | L | 19.30 ± 0.08 |
| 2025-04-03 17:41:22 | +2.44h | L | 19.35 ± 0.08 |
| 2025-04-03 17:51:00 | +2.60h | L | 19.47 ± 0.12 |
+-------------------------------------------------------------------+
Our observations can be fit with a broken power-law model with slopes of t^-0.90 and t^-0.44 on either side of a break at 1.32 hours.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
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 40032
Subject
GRB 250403A: GMG Optical Observation
Date
2025-04-03T17:52:32Z (7 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
Web form
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report:
We observed the field of GRB 250403A (Fermi/GBM team, GCN 40025, T0 at 2025-04-03T15:15:22; Julakanti et al., GCN 40026) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-04-03 17:24:07, about 2.15 hours after the trigger.
The optical counterpart of GRB 250403A (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031) was clearly detected in the r-band image with an exposure of 600 s.
The preliminary analysis results are shown as follows:
+---------------+------------+----------+--------------+----------------+
| Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma U.L. |
+===============+============+==========+==============+================+
| 2.23 | 600 | r | 19.23 ± 0.03 | 21.6 |
+---------------+------------+----------+--------------+----------------+
The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.1110 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).
GCN Circular 40031
Subject
GRB 250403A: 1.6m Mephisto multi-band optical detection
Date
2025-04-03T17:46:43Z (7 months ago)
Edited On
2025-04-03T18:50:06Z (7 months ago)
From
Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Chenxu Liu at Mephisto Team <cxliu@ynu.edu.cn>
Via
Web form
Guowang Du (SWIFAR, YNU), Ziwei Li (SWIFAR, YNU), Dezi Liu (SWIFAR, YNU), Yaosong Yu (SWIFAR, YNU), Chenxi Shang (SWIFAR, YNU), Chenxu Liu (SWIFAR, YNU), Jinghua Zhang (SWIFAR, YNU), Yuan Fang (SWIFAR, YNU), Xufeng Zhu (SWIFAR, YNU), Tao Wang (SWIFAR, YNU), Xinlei Chen (SWIFAR, YNU), Xingzhu Zou (SWIFAR, YNU), Xuhui Han (NAOC), Pinpin Zhang (NAOC), Liping Xin (NAOC), Chao Wu (NAOC), Yu Pan (SWIFAR, YNU), Brajesh Kumar (SWIFAR, YNU), Yuanpei Yang (SWIFAR, YNU), Xiangkun Liu (SWIFAR, YNU), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
We performed simultaneous multi-band photometric observations of GRB 250403A (SVOM burst-id sb25040305) detected by SVOM/ECLAIRs (Y. Julakanti et. al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 15:17:48UTC 2025-04-03 (i.e., 148s after the SVOM/ECLAIRs trigger) and are still ongoing at the time of this report. Multiple frames were obtained in uvgriz- bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is listed below:
UT start |Band | Exp | Mag (AB)
---------------------------|-------|----------------
2025/04/03T15:25:37 | u |180s |17.92 +/- 0.12
2025/04/03T15:17:48 | v |180s |16.51 +/- 0.03
2025/04/03T15:25:38 | g | 50s |17.16 +/- 0.05
2025/04/03T15:17:49 | r | 50s |15.64 +/- 0.01
2025/04/03T15:25:38 | i | 79s |16.68 +/- 0.04
2025/04/03T15:17:49 | z | 79s |15.27 +/- 0.02
Our results are consistent with the previously reported circulars (R. Starling et al., GCN 40028; Wu et al., GCN 40029). Further analysis of the additional images is ongoing.
----------------------------------------------------------
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 40029
Subject
GRB 250403A: SVOM/C-GFT optical observations
Date
2025-04-03T17:08:55Z (7 months ago)
Edited On
2025-04-03T17:21:44Z (7 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Chao WU (NAOC), Liping Xin(NAOC), Zhe Kang (CHO), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei, Qiu(NAOC), Jing Wang(NAOC), Jianyan Wei (NAOC), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 250403A detected by FERMI/GBM(FERMI team: GCN 40025) and SVOM/ECLAIRs/GRM (sb25040305, Julakanti et al., GCN 40026)with C-GFT. Our observations were started on 2025-04-03T15:16:17 UTC, ~57s after the trigger.
The optical counterpart (reported by Starling et al., GCN 40028) was clearly detected in our images. Its brightness is 15.60 +/- 0.13 mag in i band with the mid time of 62 sec after the burst.
The photometry was calibrated with nearby Pan-STARRS1 stars. Further observation and analysis is on-going.
We thank the observation assistants Shuai lui and Guangsheng Zhang at Jilin observatory for their excellent support.
Chinese Ground Follow-up Telescope of SVOM mission is located at Jilin, Changchun Observatory, National Astronomical Observatories, CAS. It has FOV of 1.28 deg x 1.28 deg with a 4k*4k CMOS detector mounted on the primary focus of 1.2-meter-aperure telescope.
GCN Circular 40028
Subject
GRB 250403A: GOTO detection of the optical afterglow
Date
2025-04-03T16:26:51Z (7 months ago)
From
Rhaana Starling at U of Leicester <rlcs1@leicester.ac.uk>
Via
Web form
R. Starling, Y. Julakanti, A. Kumar, D. O'Neill, B. P. Gompertz, J. Lyman, G. Ramsay, M. Kennedy, K. Ackley, M. J. Dyer, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250403A detected by SVOM (Julakanti et al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025). Targeted observations were performed using the GOTO-South starting at 15:25:31 UT on 2025-04-03 (10.12 minutes after the SVOM ECLAIRs trigger) to to 15:30:27 UT on 2025-04-03 (15.10 minutes after the SVOM ECLAIRs trigger). The images are 90s exposures in the GOTO L-band (400-700 nm).
A new optical source within the SVOM localisation region (Julakanti et al., GCN 40026) is identified at the position: RA, Dec: 194.61570 -24.37950 deg. We report four epochs of observations, showing a clear power-law-like decay with t^-1.1.
+------------------------------------------------------------------------------------------------+
| Observation time (UT) | t-t0 (min) | Mag (AB) |
+------------------------------------------------------------------------------------------------+
| 2025-04-03 15:25:31.182 | 10.12 | 17.02 ± 0.02 |
| 2025-04-03 15:27:09.645 | 11.82 | 17.16 ± 0.03 |
| 2025-04-03 15:28:48.308 | 13.47 | 17.35 ± 0.03 |
| 2025-04-03 15:30:26.677 | 15.10 | 17.50 ± 0.03 |
+------------------------------------------------------------------------------------------------+
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
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 40026
Subject
GRB 250403A : SVOM detection of a burst
Date
2025-04-03T15:58:17Z (7 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne, D. Turpin (CEA), M. Brunet (IRAP) report:
SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250403A (SVOM burst-id sb25040305) starting at 2025-04-03T15:15:20 UTC (Tb), also detected by Fermi (GCN 40025).
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 19 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 42.11 in the 8-120 keV energy band over a time window of 20.40 seconds starting at Tb. The downloaded light curve shows a single broad structure of duration of about 20 seconds.
The localization of the best alert is R.A., Dec 194.5927, -24.3762 degrees:
RA (J2000) = 12h58m22.24s
Dec (J2000) = -24d22m34.36s
with a 90% C.L. radius of 2.71 arcmin (including systematic error of 2 arcmin added in quadrature).
The burst was also detected by GRM as SVOM burst-id sb25040306.
No immediate slew was performed on this burst. A SVOM ToO has been programmed for follow-up.
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 Burst Advocate (BA) on shift for this burst is Y. Julakanti (skyj1@leicester.ac.uk).
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular 40025
Subject
GRB 250403A: Fermi GBM Final Real-time Localization
Date
2025-04-03T15:26:06Z (7 months ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 15:15:22 UT on 3 Apr 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250403A (trigger 765386127.830438 / 250403636).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 204.2, Dec = -25.4 (J2000 degrees, equivalent to J2000 13h 36m, -25d 23'), with a statistical uncertainty of 5.1 degrees.
The angle from the Fermi LAT boresight is 56.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250403636/quicklook/glg_skymap_all_bn250403636.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/bn250403636/quicklook/glg_healpix_all_bn250403636.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250403636/quicklook/glg_lc_medres34_bn250403636.gif