GRB 250506A
GCN Circular 40798
Subject
GRB 250506A - SVOM/ECLAIRs Refined analysis
Date
2025-06-20T22:04:35Z (4 months ago)
Edited On
2025-06-21T21:50:39Z (4 months ago)
From
sebastien.guillot@irap.omp.eu
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>
Via
Web form
Authors: S. Guillot (IRAP), F. Cangemi, A. Coleiro (APC), M.-G. Bernardini (INAF-OAB, LUPM), O. Godet (IRAP), Chenwei WANG (IHEP), Lin LAN (NAOC)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250506A (SVOM burst-id sb25050601).
The burst that triggered ECLAIRs onboard (GCN 40358) consists of a single pulse with a duration of T90 = 6.4 +1.0/-0.6 s in the 4-120 keV energy band. We note that ECLAIRs only saw the first peak of this GRB since the source passed behind the Earth during the burst. Therefore, this T90 value is only for the first peak, and is shorter than those measured by Fermi/GBM (GCN 40362) and GECAM (GCN 40396).
The time-averaged spectrum of the burst from T0 + 4.12 sec to T0 + 12.12 sec (T0 = 2025-05-06T02:23:16.88) in the energy range 5-115 keV is best fit by a broken power-law model with a break energy of 14.2 +3.8/-1.9 keV, a photon index of -0.3 +/- 0.2 before the break, and of -0.97 +0.06/-0.08 after the break. The photon index after the break is broadly consistent with the PL index (50-300 keV) reported from the Fermi/GBM analysis (GCN 40362). With this model, the total 4-120 keV fluence, assuming the T90 measured, is 1.75 +0.28/-0.5 x 10^-6 erg/cm^2.
All the quoted errors are at the 90% confidence level.
Other models (power law, cutoff power law, blackbody + power law, gamma-ray burst continuum) do not satisfactorily fit the data. The comparison of the power-law and broken power-law fits yields a spectral break significance of 5.1 sigma (Gaussian two-sided).
We note that the calibration of SVOM/ECLAIRs is undergoing thus these results are preliminary.
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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.
The SVOM/ECLAIRs point of contact for this burst is: Sébastien Guillot (IRAP) (sebastien.guillot at irap.omp.eu)
GCN Circular 40453
Subject
Konus-Wind detection of GRB 250506A
Date
2025-05-13T10:36:33Z (5 months ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:
The long-duration GRB 250506A
(Fermi-GBM detection: The Fermi GBM team, GCN 40355;
SVOM detection: Wang et al., GCN 40358;
GECAM-B detection: Wang et al., GCN 40396;
GRBAlpha detection: Pal et al., GCN 40440;)
triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817).
The burst light curve shows a multi-peaked structure
which starts at ~T0-2.1 s and has a total duration of ~56 s.
The emission is seen up to ~7 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605
As observed by Konus-Wind, the burst
had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+33.728 s,
of 8.39(-0.74,+0.75)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+57.600 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.06(-0.04,+0.08),
the high energy photon index beta = -3.51(-6.49,+0.91),
the peak energy Ep = 284(-28,+28) keV
(chi2 = 123/97 dof).
The spectrum near the maximum count rate
(measured from T0+33.024 to T0+41.216 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.02(-0.07,+0.08)
and Ep = 278(-21,+25) keV (chi2 = 111/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 111/97 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 40440
Subject
GRB 250506A: GRBAlpha detection
Date
2025-05-12T14:45:14Z (5 months ago)
From
Andras Pal at Konkoly Observatory <apal@szofi.net>
Via
Web form
A. Pal (Konkoly Observatory), M. Dafcikova, J. Ripa, N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 250506A (Fermi/GBM detection: GCN 40355; SVOM/GRM and ECLAIRs detection: GCN 40358; GECAM-B detection: GCN 40396) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).
The detection was confirmed at the peak time 2025-05-06 02:23:56.5 UTC. The T90 duration measured by GRBAlpha is 41 s and the overall significance during T90 reaches 22 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250506A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
GCN Circular 40405
Subject
GRB 250506A: NOT optical upper limits
Date
2025-05-09T09:37:58Z (5 months ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
Z. P. Zhu (NAOC), B. Schneider (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), T. T. Hansen, W. M. Ali, P. H. Chan, N. Hölinger, E. Lamprou, R. Lesley, H. Lundberg, J. Pajak, L. Peschieras, and N. Valsamidis (all Stockholm University), report on behalf of a larger collaboration.
We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi/GBM (Sonawane et al., GCN 40362), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT) centered at the X-ray source detected by EP/FXT (Zhang et al. GCN 40365). We obtained exposures in the SDSS r (3x600 s) and z (4x300 s) bands starting at 23:44:29 UT on 2025-05-06 (21.35 hr after the SVOM/ECLAIRs trigger).
No new optical source is detected at a position consistent with the Swift/XRT error region (the best currently available for this event; Burrows et al., GCN 40378) in the stacked images of either band down to the 5-sigma limiting AB magnitudes of r > 23.6 and z > 22.5, calibrated against nearby Pan-STARRS stars.
GCN Circular 40396
Subject
GRB 250506A: GECAM detection
Date
2025-05-08T14:13:56Z (5 months ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by GRB 250506A at 2025-05-06T02:23:22.850 UTC (denoted as T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #40355) and SVOM (Wang et al., GCN #40358).
According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 34.6 +0.8/-1.9 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250506A.png
With the localization of RA, Dec = 219.28269, +28.87835, as determined by Swift/XRT (D.N. Burrows et al., GCN #40394), the time-averaged spectrum from T0-10s to T0+60 s is best fitted by a powerlaw with an alpha of -2.02 +/- 0.11. The event fluence (10-1000 keV) in this time interval is (2.60 +/- 0.14)E-05 erg/cm^2.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 40394
Subject
GRB 250506A: Swift-XRT afterglow detection
Date
2025-05-08T08:42:38Z (5 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the
SVOM/MXT-detected burst GRB 250506A. The observations now extend from
T0+63.4 ks to T0+138.3 ks and have a total exposure time of 6.3 ks. The
source previously reported, "Source 1", is fading with 2.8 sigma
significance and thus is believed to be the GRB afterglow. Using 2772 s
of PC mode data and 2 UVOT images, we find an enhanced XRT position
(using the XRT-UVOT alignment and matching UVOT field sources to the
USNO-B1 catalogue): RA, Dec = 219.28269, +28.87835 which is equivalent
to:
RA (J2000): 14h 37m 07.85s
Dec(J2000): +28d 52' 42.0"
with an uncertainty of 2.6 arcsec (radius, 90% confidence). This
position is 84 arcsec from the SVOM/MXT position.
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.7 (+0.5, -0.4).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.74 (+0.34, -0.21). The
best-fitting absorption column is 2.1 (+7.8, -0.4) x 10^20 cm^-2,
consistent with the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.8 x 10^-11 (3.9 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.1 (+7.8, -0.4) x 10^20 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.74 (+0.34, -0.21)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021828.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021828.
This circular is an official product of the Swift-XRT team.
GCN Circular 40392
Subject
GRB 250506A: SVOM/VT optical upper limit
Date
2025-05-08T07:22:50Z (5 months ago)
Edited On
2025-05-08T13:19:19Z (5 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
L. Lan(NAOC), C. W. Wang(IHEP), R. C. Chen(NJU), W. J. Tan(IHEP), 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, J. T. Palmerio (CEA), J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT instrument team.
SVOM/VT performed ToO observations on the GRB 250506A (Fermi GBM team, GCN 40355; Wang et al., GCN 40358) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started at 13.69 hours after the SVOM trigger.
No uncatalogued sources are detected in single or stacked images at the improved MXT position (Maggi et al., GCN Circ. 40364), the position of FXT (Zhang et al., GCN 40365) and XRT (Burrows et al., GCN 40378), compared to the Legacy survey.
The 3 sigma upper limits are derived below:
Mid_time | Band | Exposure Time (second) | Upper limit (AB)
15.64 hour | VT_B | 100*63 | 23.7
15.64 hour | VT_R | 100*73 | 23.6
This results are consistent with the report by Postigo et al. (GCN 40359), Liu et al. (GCN 40360), Ferro et al. (GCN 40363), Xin et al. (GCN 40366), Liu et al. (GCN 40373), Ducoin et al. (GCN 40382) and Oates et al. (GCN 40387).
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 40387
Subject
GRB 250506A: Swift/UVOT Upper Limits
Date
2025-05-07T20:04:42Z (5 months ago)
From
Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>
Via
email
S. R. Oates (Lancaster U.) and N. Klinger (GSFC/UMBC/CRESSTII)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250506A
63 ks after the of the SVOM and Fermi-detected GRB 250506A
(GCN Circs. 40355, 40358). No optical afterglow consistent with
the SVOM MXT (Maggi et al., GCN Circ. 40364) and the XRT position
(Burrows et al. GCN Circ. 40378) is detected in the initial UVOT exposures.
Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 64170 70154 1176 >22.1
v 64937 65102 163 >19.3
u 63403 69711 1530 >21.1
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 40382
Subject
GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
Date
2025-05-07T14:39:13Z (5 months ago)
From
J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr>
Via
Web form
Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Chenwei WANG (IHEP) and Lin LAN (NAOC):
We imaged the field of the SVOM GRB 250506A (Wang et al., GCN Circ. 40358) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-07T03:44:16 to 05:14:17 UTC (from 1.12 to 1.22 days after the trigger) and obtained 64 minutes of exposure in the i filter.
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 and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the improved MXT position (Maggi
et al., GCN Circ. 40364) and at the XRT position (Burrows et al., GCN Circ. 40378) down to the following 5-sigma limit (AB):
i > 22.4
This upper limit is consistent with the one reported by Xin et al. (GCN Circ. 40366), Ferro et al. (GCN Circ. 40363), Liu et al. (GCN Circ. 40360), Postigo et al. (GCN Circ. 40359), and Liu et al. (GCN Circ. 40373).
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 40378
Subject
GRB 250506A: Swift-XRT observations
Date
2025-05-07T09:35:26Z (5 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/MXT-detected
burst GRB 250506A at the revised position given in GCN Circ. 40364,
collecting 2.9 ks of Photon Counting (PC) mode data between T0+63.2 ks
and T0+70.1 ks.
One uncatalogued X-ray source has been detected, it is below the RASS
limit and shows no definitive signs of fading. Therefore, at the
present time we cannot confirm this as the afterglow. Details of this
source are given below:
Source 1:
RA (J2000.0): 219.28269 = 14:37:7.85
Dec (J2000.0): +28.87835 = +28:52:42.1
Error: 2.6 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.0586 +/- 0.0052 ct s^-1
Distance: 84 arcsec from SVOM/MXT position.
Flux: (2.16 +/- 0.19)e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV)
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/00021828.
This circular is an official product of the Swift-XRT team.
GCN Circular 40373
Subject
GRB 250506A: Mephisto optical upper limits
Date
2025-05-07T02:43:57Z (5 months ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Dezi Liu, Ziwei Li, Tao Wang, Shuang Lin, Xiangru Qian, Guowang Du, Xingzhu Zou, Yu Pan, Xinlei Chen, Xufeng Zhu, Helong Guo, Yuan Fang, Jinghua Zhang, Chenxu Liu, Edoardo Lagioia, Brajesh Kumar, Jianhui Lian, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We conducted simultaneous multi-band photometric observations of the GRB 250506A (SVOM burst-id sb25050601) detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and by Fermi (Fermi GBM team, GCN 40362) with the Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. Simultaneous u, g, and i band observations were initiated at 14:08:39 UTC on 2025-05-06 (~12.5 hours after the trigger). We obtained four exposures of 300 seconds each in ugi bands. No optical counterpart was detected at the refined position reported by the SVOM team (Maggi et al., GCN 40364). The preliminary 3-sigma upper limits are below:
| UT Start | T-T0 (hr) | Band | Exp | LimMag (AB) |
|-------------------|-----------|------|--------|-------------|
| 2025/5/6 14:08:40 | 12.53 | u | 4x300s | > 21.82 |
| 2025/5/6 14:08:40 | 12.53 | g | 4x300s | > 22.42 |
| 2025/5/6 14:08:39 | 12.53 | i | 4x300s | > 21.84 |
These limits are consistent with previously reported non-detections (Xin et al., GCN 40366; Ferro et al., GCN 40363; Liu et al., GCN 40360; Postigo et al., GCN 40359).
----------------------------------------------------------
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 40371
Subject
GRB 250506A: Swift ToO observations
Date
2025-05-06T19:55:53Z (5 months 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 SVOM/ECLAIRs-detected event
GRB 250506A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021828
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 SVOM/ECLAIRs 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 40366
Subject
GRB 250506A: Xinglong 2.16m optical upper limit
Date
2025-05-06T16:04:35Z (5 months ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, J. Zhen, J. Wang, H. L. Li, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, P. P. Zhang, Y. J. Xiao, L. Lan, W. J. Xie, J. S. Deng, J. Y. Wei (NAOC) report on behalf of SVOM follow-up team:
We observed the field of GRB 250506A (Wang et al., GCN 40358; Maggi et al., GCN 40364; Fermi team GCN 4035). using the 2.16-m telescope located at Xinglong observatory, China, equipped with the BFOSC camera. The weather is not good. We obtained 2*200s and 7x300s frames in R-band, starting at 14:00:19 UT on 2025-05-06,about 11.65 hrs after the trigger.
No any uncatalogued sources were detected within the error box of EP/FXT(Zhang et al., GCN 40365) or SVOM/Eclairs or SVOM/MXT (Maggi et al., GCN 40364) in our stacked image, down to a 3 sigma limiting magnitude of R~21.0 mag, calibrated with the nearby PanSTARRS field.
GCN Circular 40364
Subject
GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
Date
2025-05-06T14:47:41Z (5 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) on behalf of the SVOM/MXT Team report:
M. Brunet, S. Guillot (IRAP), S. Schanne (CEA) on behalf of the SVOM/ECLAIRs Team report:
Using the full X band dataset a corrected ECLAIRs position could be derived for GRB 250506A/sb25050601 (Wang et al., GCN 40358). The improved ECLAIRs position is RA=219.373, Dec=28.909 with a 90% c.l. of 6.4 arc min.
The burst appeared very close to the Earth limb and only part of the burst signal was considered by the onboard processing, explaining the localization error.
SVOM MXT observed the ECLAIRs error region starting at T0 = 2025-05-06T03:09:28.279 (46 min after trigger time Tb). MXT observed it during 5 orbits for a 10.9 ks effective exposure.
Using the full X band dataset, we find an uncatalogued source. The source is fading with time and not detected after the fourth orbit (t+T0 > 23 ks). The best position is obtained from first orbit data (t+T0 < 2.5ks), at RA=219.267, Dec=28.8593 corresponding to:
RA (J2000) = 14h37m04.
Dec (J2000) = +28d51m34.
with a statistical 90% C.L. radius of 32.5” to which a 35” systematic uncertainty is to be added in quadrature.
The afterglow spectrum is modelled by an absorbed power law fading with time. The absorption column is NH = 3+/-1 x 1e21 /cm2 (90% C.L. uncertainties) and a photon index of 2.3 (+0.7/-0.6) in first orbit softening to 3.3 (+2.5/-1.2) in the second orbit. The average observed flux in the 0.3-8 keV band is 6.8 (+3.4/-2.2) x1e-11 erg/cm2/s during the first orbit and 1.4 (<2.7) x1e-11 erg/cm2/s during the second one.
The ECLAIRs and MXT position are consistent, confirming that the MXT source is the afterglow of the GRB 250506A.
This position corrects and supersedes the one reported by Wang et al. (GCN 40358).
The active QSO detected by TRT (Liu et al., GCN 40360) and Swift XRT (Beardmore et al., GCN 40361) is thus unrelated to GRB 250506A.
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. ECLAIRs was developed jointly by CNES, IRAP, APC and CEA.
The Burst Advocate (BA) on shift for this burst is Chenwei Wang: cwwang@ihep.ac.cn
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular 40363
Subject
GRB 250506A: REM optical/NIR upper limits
Date
2025-05-06T14:25:25Z (5 months ago)
From
Matteo Ferro at INAF-OAB <matteo.ferro@inaf.it>
Via
Web form
M. Ferro, R. Brivio, P. D'Avanzo, M. G. Bernardini, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi GBM (Fermi GBM team, GCN 40355; Sonawane et al., GCN 40362) 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 May 06 at 02:43:22 UT (i.e. 20 minutes after the burst), and lasted for about 3 hours.
From preliminary inspection, we do not detect any possible counterpart inside the SVOM error circle, in agreement with other follow-up observations (de Ugarte Postigo et al., GCN 40359; Liu et al., GCN 40360; Beardmore et al., GCN 40361), down to the following 3sigma limits:
r > 19.8 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 54 minutes after the trigger;
H > 16.4 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 31 minutes after the trigger.
GCN Circular 40362
Subject
GRB 250506A: Fermi GBM Observation
Date
2025-05-06T13:07:40Z (5 months ago)
From
Rushikesh Sonawane at IISER, TVM <rushikesh23@iisertvm.ac.in>
Via
Web form
R. Sonawane (IISER, TVM), S. Bala (USRA), and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 02:23:22.60 UT on 06 May 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250506A (trigger 768191007/250506100).
which was also detected by SVOM/ECLAIRs (Wang et al. 2025, GCN 40358).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
The angle from the Fermi LAT boresight is 116 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 48 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+61.441 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.07 +/- 0.04 and the cutoff energy,
parameterized as Epeak, is 280 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is
(2.36 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+34 s in the 10-1000 keV band is 27.4 +/- 0.5 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 40361
Subject
GRB 250506A: Swift XRT observations and possible counterpart detection
Date
2025-05-06T10:03:08Z (5 months ago)
From
P.A. Evans at U. Leicester <pae9@leicester.ac.uk>
Via
email
A.P. Beadmore, K.L. Page and P.A. Evans (U. Leicester) report on behalf
of the Swift-XRT team,
Swift-XRT has observed the location of the SVOM and Fermi-detected GRB 250506A
(GCN Circs. 40355, 40358), gathering 1.7 ks of data between 1.5 ks and 13.7ks
after the Fermi trigger. The observations are centred on the SVOM/ECLAIRs
position.
We find a single, uncatalogued X-ray source with an enhanced XRT position of RA,
Dec = 219.64184, 29.21742 which is equivalent to:
RA (J2000) = 14h 38m 34.04s
Dec (J2000) = +29° 13′ 02.7
with an uncertainty of 4.6 arcsec (radius, 90% confidence). This source shows
evidence for fading at the 2.2-sigma level.
As noted by Liu et al. (GCN Circ. 50360), this is spatially consistent with an
optical source which Gaia classifies as a "quasar with 100.00% probability”
(Gaia DR3 1281175103580872064). The source also appears in the ALLWISEAGN
catalogue (Secrest et al., 2015, ApJS, 221, 12).
The XRT observations show a mean count-rate of 2.9 (+/- 0.007) ct sec and the
spectrum can be modelled with an absorbed power-law with photon index 1.8 (+0.8,
-0.5). The intrinsic absorption is <1.8e21 cm^-2, in addition to the Galactic
column of 1.44e20 cm^-2. Using these paramters the mean 0.3-10 keV flux is 8.2
(+1.8, -1.7)e-13 erg cm^-2 s^-1.
No other X-ray sources are detected, to an upper limit of ~6e-3 ct/sec which
corresponds to 2.6e-13 erg cm^-2 s^-1 (0.3-10 keV) assuming a standard power-law
spectrum (photon index 1.7, absorption column 3e20 cm^-2).
Given the lack of other sources and how early the XRT observations started,
combined with the apparent fading of the XRT afterglow, we consider it likely
that this source is the counterpart to the Fermi and SVOM triggers; however,
follow up observations are encouraged to determine the nature of this event.
Automated analysis of the observations is available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00014/.
This circular is an official product of the Swift-XRT team.
GCN Circular 40360
Subject
GRB 250506A: TRT optical observations
Date
2025-05-06T09:28:48Z (5 months ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), Z.P. Zhu, S.Q. Jiang, J. An, D. Xu (NAOC) report on behalf of a large collaboration:
We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and probably by Fermi/GBM as well (Fermi GBM team, GCN 40355), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile.
Within the Swift/XRT error circle (https://www.swift.ac.uk/SVOM/SVOM_FIELD00014/), a brightening, catalogued, and seemingly round source is detected at coordinates
R.A. (J2000) = 14:38:34.03
Dec. (J2000) = +29:13:02.10
which has r = 18.41+/- 0.01 in the TRT image (calibrated with PanSTARRS) at a median time of 4.48 hrs after the SVOM trigger, while it has has r = 19.00 +/- 0.01 mag in PanSTARRS.
This source is also covered by SDSS, Legacy Survey, and GAIA. In GAIA, it is classified as a QSO. The source has a photometric redshift of z ~ 0.46+/-0.10 from SDSS and z ~ 0.49+/-0.26 from Legacy Survey.
No new source is detected within the Swift/XRT error circle, down to a limiting magnitude of r ~ 21.8 mag.
GCN Circular 40359
Subject
GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
Date
2025-05-06T04:50:55Z (5 months ago)
From
Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>
Via
email
Antonio de Ugarte Postigo (LAM), William H. Lee (UNAM), Sarah Antier (OCA), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM); Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Chenw ei Wang (IHEP) report:
We imaged the field of GRB 250506A (Wang et al. GCN 40358) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We started observations at 2025-05-06 03:29:48 (1.106 hours after the trigger). An initial stack with 16 minutes of exposure in the i filter was obtained with a mean epoch 1.266 hrs after the burst. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.
No credible counterpart is detected down to an AB 5-sigma limit of i > 22.2 mag.
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 40358
Subject
GRB 250506A: SVOM detection of a burst
Date
2025-05-06T03:20:58Z (5 months ago)
Edited On
2025-05-06T13:17:59Z (5 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
Chenwei WANG (IHEP), Lin LAN, Wenjin XIE, Donghua ZHAO (NAOC), Li ZHANG (IHEP), Pierre MAGGI (ObAS) on behalf of the SVOM mission team.
SVOM/ECLAIRs trigger on the gamma-ray burst GRB 250506A (SVOM burst-id sb25050601) starting at 2025-05-06T02:23:22 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alert. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 12.51 in the [8-120] keV energy band over a time window of 2.50 seconds starting at Tb.
The localization of the best alert is R.A., Dec. 219.61, 29.28 degrees:
R.A. (J2000) = 14h38m27.02s
Dec. (J2000) = 29d16m38.09s
with a 90% confidence level (C.L.) radius of 6.47 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM with 3 GRDs but only the first pulse is detected, since the other part is in occultation. The lightcurve of GRM could be found in the link below:
https://www.bursthub.cn//admin/static/svgrb250506A.png
SVOM slewed to the burst. It was occulted by the Earth after slew, thus neither MXT nor VT data are available for the early time.
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 Chenwei Wang: cwwang@ihep.ac.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular 40355
Subject
GRB 250506A: Fermi GBM Final Real-time Localization
Date
2025-05-06T02:33:50Z (5 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 02:23:22 UT on 6 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250506A (trigger 768191007.604196 / 250506100).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.9, Dec = 26.9 (J2000 degrees, equivalent to J2000 14h 39m, 26d 53'), with a statistical uncertainty of 2.1 degrees.
The angle from the Fermi LAT boresight is 107.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250506100/quicklook/glg_skymap_all_bn250506100.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/bn250506100/quicklook/glg_healpix_all_bn250506100.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250506100/quicklook/glg_lc_medres34_bn250506100.gif