GRB 250402A
GCN Circular 40082
Subject
GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
Date
2025-04-05T22:22:30Z (6 months ago)
From
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai@tiscali.it>
Via
Web form
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy
Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.
Report:
We observed the field of GRB 250402A (SVOM burst-id sb25040203, Chen et al., GCN 40014) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.
The observations were started at 2025-04-02 23:57 UT (approximately 49 min after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and fair visibility conditions.
The OT was detected at the following position (+/- 0.3 arcsec):
RA (J2000.0) 14h 13m 38.17s
Decl. (J2000.0) -05° 55' 48.8"
Photometry was obtained using nearby PanSTARRS stars as follows:
Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err.
2025-04-03 01:39:02 UT 2.52 180x60s CR 21.6 +/- 0.4
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations.
No correction for galactic dust extinction was applied.
Our observations are consistent with other already reported L.P. Xin et al. (GCN 40015), Pérez-Fournon et al. (GCN 40020), Brivio et al. (GCN 40021), Schneider et al. (GCN 40022), Magnani et al. (GCN 40023), Komesh et al. (GCN 40033), Shilling et al. (GCN 40047), Mazaeva et al. (GCN 40049).
The message may be cited.
GCN Circular 40062
Subject
GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
Date
2025-04-04T18:11:36Z (6 months ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form
James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250402A onboard (T0: 2025-04-02T23:08:01.467 UTC, SVOM trig sb25040203, Fermi trig 765328094)
The Fermi and SVOM notices, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 8.2 in a 4.096 s analysis time bin, starting at T0 + 7.168 s.
Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)
The 90% credible area is 5,905 deg2 and the 50% credible area is 1,632 deg2. The integrated probability inside the coded field of view is 1%.
The NITRATES skymap is consistent with the SVOM/ECLAIRS position (GCN 40014), and the afterglow position (SVOM/VT GCN 40015, SVOM/MXT GCN 40019, LCO GCN 40020, SVOM/COLIBRI GCN 40023, Swift/XRT GCN 40027, EP/FXT GCN 40040, Mondy GCN 40049)
A plot of the probability skymap can be viewed here:
The probability skymap file can be downloaded from the link here
Instructions on how to read and manipulate this map can be found here:
https://guano.swift.psu.edu/documentation
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=765328116
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular 40049
Subject
GRB 250402A: Mondy optical observations
Date
2025-04-04T14:24:06Z (6 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
E. Mazaeva (IKI), E. Klunko (ISTP), N. Pankov (HSE), A. Pozanenko (IKI)
report on behalf of IKI GRB-FuN:
We observed GRB 250402A (Chen et al. GCN 40014) with the AZT-33IK telescope
starting on 2025-04-03 (UT) 18:11:28. We found the optical counterpart (Xin
et al., GCN 40015; Pérez-Fournon et al., GCN 40020; Schneider et al., GCN
40022; Magnani et al., GCN 40023) at the position reported by Xin et al.,
GCN 40015.
Preliminary photometry of the optical counterpart is the following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2025-04-03 18:11:28 0.81567 R 29*120 21.9 0.2 22.3
The photometry is based on the nearby PS1 stars (R mag by Lupton
transformations).
GCN Circular 40047
Subject
GRB 250402A: Swift/UVOT Upper Limits
Date
2025-04-04T12:51:00Z (6 months ago)
From
Sam Shilling at Lancaster University <shilling.sam@gmail.com>
Via
Web form
S. P. R. Shilling (Lancaster U.) and S. R. Oates (Lancaster U.) report on behalf of the Swift UVOT team:
Swift/UVOT observed the field of SVOM/ECLAIRs GRB 250402A (Chen et al. GCN Circ. 40014) for 2521 seconds in the U-band starting at 12:48:12 UT on 25/04/03, ~13 hours after the detection by SVOM/ECLAIRs.
No optical afterglow is detected within a 5" radius of the position of the uncatalogued X-ray source
detected by Swift/XRT (Dichiara et al., GCN Circ. 40027) and SVOM/MXT (Maggi et al., GCN circ. 40019) or the optical afterglow detected by SVOM/VT (Xin et al., GCN Circ. 40015), LCOGT (Pérez-Fournon et al., GCN Circ. 40020), and the SVOM/COLIBRÍ (Magnani et al., GCN Circ. 40023).
The Swift/UVOT non-detection in the U-band has a preliminary 3-sigma upper limit of >21.1, calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).
GCN Circular 40040
Subject
GRB 250402A: EP-FXT afterglow detection
Date
2025-04-04T09:08:48Z (6 months ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
D. Turpin, B. Cordier (CEA), H. Q. Cheng (NAO, CAS), R.-Z. Li (YNAO, CAS), Q. C. Zhao, Z. H. Yang (IHEP, CAS), Y. Liu (NAO, CAS), W. Yuan (NAO, CAS) on behalf of the SVOM and Einstein Probe teams
We performed a follow-up observation of GRB 250402A (Chen et al., GCN 40014) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2025-04-03 20:30:51 (T-TGRB ~ 21.4 hr) for about 4.6ks of exposure in total.
A bright uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000) RA, DEC = 213.4094, -5.9295 (error=10", 90% C.L.), 2.1 arcminute away from the SVOM/ECLAIRs position (Chen et al., GCN 40014). This position is consistent with the x-ray and optical afterglow positions reported by SVOM/VT (Xin et al., GCN 40015), SVOM/MXT (Maggi et al., GCN 40019), the LCO telescope (Pérez-Fournon et al., GCN 40020), VLT/X-shooter (Schneider et al., GCN 40022), SVOM/COLIBRI (FM-GFT, Magnani et al., GCN 40023) and Swift/XRT (Dichiara et al., GCN 40027).
The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.2 x 10^21 cm^-2 and a photon index of 2.16 (-0.22/+0.25). The derived average observed 0.5-10 keV flux is 1.31 (-0.12/+0.16) x 10^(-12) erg/s/cm^2.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 40033
Subject
GRB 250402A: NUTTelA-TAO Early Optical Limits
Date
2025-04-03T19:02:42Z (6 months ago)
From
Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh@nu.edu.kz>
Via
Web form
T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), D. Berdikhan (NU), B. Grossan (UCB, NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB250402A on receipt of an automated GCN / SVOM position alert, observing in Sloan g' and r' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).
We started observations at 23:10:30 UT on 2025-04-02, 154 seconds after the SVOM/ECLAIRs trigger (X. Chen et al., GCN 40014). Observations were made in partially cloudy conditions. No source consistent with the SVOM/VT (L. P. Xin et al., GCN 40015) was detected. We report the following results:
start time t-t0(s) end time UL g' UL r' exposure_time (s)
--------------------------------------------------------------
23:10:30 154 23:11:30 18.01 18.35 60
23:12:13 257 23:22:13 18.58 18.67 600
t is the middle time, t0 is the SVOM/ECLAIRs trigger time, t-t0 is given in seconds. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images of the given exposure time. Calibration was done with 4 Pan-STARRS catalog stars on our images. No color or other corrections were applied to the values above.
----------------------------------
NU = Nazarbayev University, Astana, Kazakhstan
UCB = University of California, Berkeley, USA
FAI = Fesenkov Astrophysical Institute, Kazakhstan
This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
GCN Circular 40030
Subject
GRB 250402A: Fermi GBM Observation
Date
2025-04-03T17:29:10Z (6 months ago)
From
Matt Godwin <msg0028@uah.edu>
Via
Web form
Jacob Smith (UAH), Utkarsh Pathak(IIT Bombay), and Matt Godwin (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 23:08:09.09 UT on 02 April 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250402A (trigger 765328094/250402964).
which was also detected by SVOM (Chen et al. 2025, GCN 40014).
The Fermi GBM on-ground location is consistent with the SVOM position.
The angle from the Fermi LAT boresight is 57 degrees.
The GBM light curve consists of a double peak with a duration (T90)
of about 44 s (50-300 keV). The time-averaged spectrum
from T0-5.1 to T0+45.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.1 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 115 +/- 10 keV.
The event fluence (10-1000 keV) in this time interval is
(4.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+23 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 60 +/- 10 keV, alpha = -0.4 +/- 0.3 and beta = -2.1 +/- 0.1.
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 40027
Subject
GRB 250402A: Swift-XRT observations
Date
2025-04-03T16:01:19Z (6 months ago)
From
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 2.4 ks of XRT data for the SVOM/ECLAIRs-detected burst
GRB 250402A (SVOM trigger sb25040203; Chen et al., GCN circ. 40014), from
T0+49.2 ks to T0+51.5 ks after the SVOM/ECLAIRs trigger. The data are
entirely in Photon Counting (PC) mode.
We find an uncatalogued X-ray source consistent with the X-ray counterpart
identified by SVOM/MXT (Maggi et al., GCN circ. 40019) and the optical
counterpart (Xin et al., GCN 40015, Pérez-Fournon et al., GCN 40020,
Schneider et al., GCN 40022, Magnani et al., GCN 40023). We note that the
source is fading compared to the flux reported by previous MXT observations
(Maggi et al., GCN circ. 40019).
Details of this source are given below:
Source 1:
RA (J2000.0): 213.4089 = 14:13:38.13
Dec (J2000.0): -5.9302 = -05:55:48.5
Error: 3.4 arcsec (radius, 90% conf. [Enhanced position])
Count-rate:0.045 (±0.012) ct s-1
Flux: 1.9 (±0.5) ×10-12 erg cm-2 s-1 (observed, 0.3-10 keV)
This XRT position is 1.07 arcsec away from the optical position.
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_FIELD00009/.
This circular is an official product of the Swift-XRT team.
GCN Circular 40023
Subject
GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
Date
2025-04-03T10:48:39Z (6 months ago)
Edited On
2025-04-04T13:41:05Z (6 months ago)
From
Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Via
Web form
Francesco Magnani (CPPM), Camila Angulo (UNAM), Damien Dornic (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), , Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and X. Chen (YNU) report:
We imaged the field of the SVOM/ECLAIRs GRB 250402A (sb25040203, Chen et al. GCN 40014) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-04-03 04:37 to 06:49 UTC (between 5.49 and 7.69 hours after the trigger) and obtained 43 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
At the position of the previously reported optical afterglow (Xin et al., GCN 40015; Pérez-Fournon et al. GCN 40020; Schneider et al. GCN 40022), we detect a source with a magnitude of
i = 21.22 +/- 0.11
Further observations are ongoing.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
GCN Circular 40022
Subject
GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
Date
2025-04-03T09:52:28Z (6 months ago)
From
luca.izzo@inaf.it
Via
Web form
B. Schneider (LAM), A. Saccardi (CEA/Irfu), A. de Ugarte Postigo (LAM), L. Izzo (INAF-OACn and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester), A. Martin-Carrillo (UCD) report on behalf of the Stargate collaboration:
We observed the afterglow of the SVOM/ECLAIRs GRB 250402A (Chen et al., GCN 40014; Xin et al., GCN 40015, Maggi et al., GCN 40019; Pérez-Fournon et al., GCN 40020) using the ESO/VLT UT1 (Antu) equipped with the FORS2 spectrograph. Observations started on April 3 at 05:54:45 UT (6.78 hr after the SVOM trigger). Four exposures of 600 s were obtained.
From a 60 s acquisition image obtained on April 3 at 05:43:17 UT (6.59 hr after the SVOM trigger), we measure r ~ 21.1 +/- 0.2 (AB).
From a preliminary reduction of the 300V spectrum, a trough due to Lya absorption is visible at 4645 AA. From the detection of multiple absorption features, which we interpret as due to Si II, O I, C II, Si IV, Si II*, C IV, Fe II, and Al II, we infer a redshift of z = 2.823. Additionally, we note the presence of an intervening absorber at z = 1.409 with multiple Fe II absorption lines.
We acknowledge excellent support from the ESO observing staff in Paranal.
GCN Circular 40021
Subject
GRB 250402A: REM optical/NIR upper limits
Date
2025-04-03T09:46:37Z (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 the SVOM/ECLAIRs GRB 250402A (Chen et al., GCN 40014) 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 00:50:28 UT (i.e. 1.7 hr after the burst), and lasted for about 2 hours.
From preliminary inspection, we do not find any counterpart at the position of the reported optical afterglow candidate (Xin et al., GCN. 40015; Pérez-Fournon et al., GCN 40020) down to the following 3sigma limits:
r > 20.3 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 2.8 hours after the trigger,
H > 16.1 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 2.2 hours after the trigger.
GCN Circular 40020
Subject
GRB 250402A: LCO optical counterpart detection
Date
2025-04-03T09:09:55Z (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 Las Cumbres Observatory Global Telescope network (LCOGT) observations of the SVOM GRB 250402A (Chen et al., GCN circ. 40014; Maggi et al., GCN circ. 40019). We observed the field of GRB 250402A with the three LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Cerro Tololo Inter-American Observatory (Chile) in the SDSS r, g, and i filters, starting at 2025-04-03 02:58:50 UTC, about 3.85 hours after the SVOM trigger.
An uncatalogued source is clearly detected in the three filters at the position of the optical counterpart detected by SVOM/VT (Xin et al., GCN circ. 40015).
We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:
Date | UT start | mag | error | filter | exposure time (sec)
---------------------------------------------------------------------
2025-04-03 02:58:50 21.01 0.14 r 300
2025-04-03 03:15:44 21.91 0.17 g 300
2025-04-03 03:21:06 20.80 0.13 i 300
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
GCN Circular 40019
Subject
GRB 250402A: refined SVOM/MXT data analysis
Date
2025-04-03T07:20:33Z (6 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
P. Maggi (ObAS), D. Götz (CEA), H. Goto (Kanazawa University/CEA), M. Moita (CEA), C. Plasse (CEA), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team:
GRB 250402A (Chen et al. GCN 40014) was observed by SVOM/MXT after an automatic SVOM slew starting at T0 = 2025-04-02T23:10:59.278 (183s after trigger time Tb). MXT observed for 4.3 ks effective exposure.
Using the full X band dataset, we find a rapidly fading uncatalogued source with a light curve temporal index of -0.75+/-0.02. At times T0>500s the source is no longer detected and hence we restricted the analysis to the first 500s of data.
Its position is RA=213.4051, Dec=-5.94374
RA (J2000) = 14h13m37s
Dec (J2000) = -05d56m37s
with a statistical 90% C.L. radius of 38". The position is 51" away from, but consistent with, the one reported for the SVOM/VT afterglow candidate (Xin et al. GCN 40015) when including a 35" systematic uncertainty.
The X-ray spectrum (t<T0+500s) can be fit by an absorbed power law model with a photon index of 3.2 (-0.8, +1.3) and an NH value of 0.21 (-0.1, +0.2) x 1e22 /cm2 (90% C.L. uncertainties). The absorbed X-ray flux in the 0.3-10 keV range is 8.4e-11 (+/-0.5e-11) erg/cm2/s.
Follow-up observations at other wavelengths are encouraged.
The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE.
The SVOM point of contact for this burst is: X. Chen: xlchen@stu.ynu.edu.cn
GCN Circular 40015
Subject
GRB 250402A: SVOM/VT optical counterpart
Date
2025-04-03T00:26:36Z (6 months ago)
Edited On
2025-04-03T13:09:24Z (6 months ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of 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), J. T. Palmerio(CEA/Irfu), T. Sadibekova(CEA), X. Chen(YNU), Y. Hu(GXU) report on behalf of the SVOM team:
SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Chen et al., GCN 40014). SVOM/VT began observing the field automatically with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With VHF downlinked data, a bright uncatalogued source was found in both channels in the first sequence, and brightening with about 0.2 mag in the second sequence, compared to DESI catalog.
The coordinates are RA, Dec = 213.40915, -5.93013 which is equivalent to:
R.A.(J2000) = 14:13:38.20,
DEC.(J2000)= -05:55:48.5
Error=0.5 arcseconds.
The brightness are VT_B ~21.53 mag(AB) and VT_R ~20.61 mag(AB) in the first sequence with the mid time of 443 seconds after the burst.
We proposed that this is the optical counterpart of the burst. Given the VT color, it is likely a low/medium redshift 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 40014
Subject
GRB 250402A: SVOM detection of a burst
Date
2025-04-03T00:15:14Z (6 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
X. Chen(YNU), Y. Hu(GXU), H. Yang(IRAP), B. Cordier (CEA), L. Zhang(IHEP), P. Maggi (ObAS)
on behalf of the SVOM mission team.
At 2025-04-02T23:07:56 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250402A (SVOM burst-id sb25040203).
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 15 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 27.79 in the [8-120] keV energy band over a time window of 40.96 seconds starting at Tb.
The light curve showed a long GRB with a T90 duration of about 35 (+/-3) s.
The localization of the best alert is R.A., Dec 213.3783, -5.9457 degrees (J2000) with a 90% C.L. radius of 3.42 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
MXT began observing the field at 2025-04-02T23:10:58 UTC, 183 seconds after Tb.
Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec 213.3893, -5.9468 degrees:
RA (J2000) = 14h13m33.44s
DEC (J2000) = -5d56m48.59s
with a 90% C.L. radius of 45 arcseconds(including 25 arcseconds systematic error added in quadrature).
This location is 0.66 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.
VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.
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 X. Chen: xlchen@stu.ynu.edu.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.