GRB 250403A
GCN Circular 40164
Subject
Konus-Wind detection of GRB 250403A
Date
2025-04-17T17:43:37Z (6 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 (6 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 (6 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 (6 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 (6 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 (6 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 (6 months ago)
Edited On
2025-04-04T16:16:20Z (6 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 (6 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 (6 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 (6 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 (6 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