GRB 250430A
GCN Circular 40384
Subject
GRB 250430A / EP250430a: AstroSat CZTI detection
Date
2025-05-07T15:16:23Z (5 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 the long duration GRB 250430A which was also detected by Swift/BAT (Moss et al., GCN Circ. 40356), Konus/Wind (Svinkin et al., GCN Circ. 40367), and associated with the detection of EP250430a by EP/WXT (Wang et al., GCN Circ. 40299).
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-04-30 17:31:00.84 UTC. The measured peak count rate associated with the burst is 279 (+66, -70) counts/s above the background in the combined data of all quadrants, with a total of 761 (+210, -232) counts. The local mean background count rate was 1336 (+7, -8) counts/s. We measure a T90 of 7.1 (+0.5, -2.5) s from the cumulative Veto light curve.
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 40367
Subject
GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
Date
2025-05-06T16:17:44Z (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 250430A
(Swift-BAT detection: Parsotan et al., GCN 40292;
Moss et al., GCN 40356;
EP-WXT detection: Wang et al., GCN 40299)
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 ~16 sigma count-rate increase in the interval
from T0-0.581 s to T0+5.307 s, where T0 = T0(BAT) = 17:31:00.28 UT.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB250430A/
To derive broad-band spectral parameters of this burst,
we performed a joint spectral analysis of the Swift/BAT data
(15-150 keV) and the KW 3-channel spectral data (20-1600 keV).
A fit to the time-averaged spectrum, measured from T0-0.581 s
to T0+5.307 s, by the Band GRB function results in
alpha = -0.99(-0.31,+0.70),
beta = -2.01(-0.39,+0.19), and
Ep = 107(-44,+86) keV (chi2/dof= 57.7/59).
The total burst fluence is 3.21(-0.92,+1.09)x10^-6 erg/cm^2,
and the 64-ms peak energy flux, measured from T0+0.446 s,
is 1.63(-0.50,+0.58)x10^-6 erg/cm^2.
(both in the 20 keV - 10 MeV energy range).
Assuming the redshift z=0.767 (Garnichey et al., GCN 40301)
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 5.26(-1.50,+1.78)x10^51 erg,
the isotropic peak luminosity L_iso to 2.35(-0.72,+0.84)x10^51 erg/s,
and the rest-frame peak spectral energy Ep,z to 189(-77,+151) keV.
With the obtained estimates, GRB 250430A is inside 68% prediction bands for both
the 'Amati' and the 'Yonetoku' relations derived 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/GRB250430A/GRB250430A_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 40356
Subject
GRB 250430A: Swift-BAT refined analysis
Date
2025-05-06T02:50:20Z (5 months ago)
From
Mike Moss at NASA GSFC <mikejmoss3@gmail.com>
Via
Web form
M. J. Moss (GSFC), S. D. Barthelmy (GSFC),
R. Gupta (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC),
T. Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250430A (trigger #1308754)
(Parsotan, et al., GCN Circ. 40292). The BAT ground-calculated position is
RA, Dec = 233.395, -18.101 deg which is
RA(J2000) = 15h 33m 34.7s
Dec(J2000) = -18d 06' 03.2"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 72%.
The mask-weighted light curve displays a double peaked structure.
The T90 (15-350 keV) is 9.17 +- 1.70 sec (estimated error including systematics).
The time-averaged spectrum from T+0.10 to T+11.86 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.66 +- 0.11. The fluence in the 15-150 keV band is 8.9 +- 0.6 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.31 sec in the 15-150 keV band
is 2.3 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1308754
GCN Circular 40323
Subject
GRB 250430A: Swift-XRT refined Analysis
Date
2025-05-02T13:27:07Z (5 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
R. Brivio (INAF-OAB), M. A. Williams (PSU), S. Dichiara (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
We have analysed 1.4 ks of XRT data for GRB 250430A, from 166 s to 1.9
ks after the BAT trigger. The data are entirely in Photon Counting
(PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.37 (+0.13, -0.14).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.89 (+0.26, -0.24). The
best-fitting absorption column is 1.7 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 9.6 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 (4.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.7 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 9.6 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index: 1.89 (+0.26, -0.24)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01308754.
This circular is an official product of the Swift-XRT team.
GCN Circular 40321
Subject
GRB 250430A: Swift/UVOT Detection
Date
2025-05-02T12:22:02Z (5 months ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250430A 118 s after the BAT trigger (Parsotan et al., GCN Circ. 40292).
The optical source detected in the UVOT white filter reported in that circular (and also detected by Oden & Guessoum, GCN Circ. 40295; Garnichy et al., GCN Circ. 40301; Komesh et al., GCN Circ. 40307; Zheng et al., GCN Circ. 40310 and Li et al., GCN Circ. 40311) was also detected in the UVOT U-band filter, but has since faded.
Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 141 291 147 19.08 ± 0.1
white 843 1856 264 19.40 ± 0.1
v 118 1733 169 >18.9
b 473 1831 156 >19.8
u 448 468 20 17.91 ± 0.3
u 621 1117 59 18.67 ± 0.3
w1 424 1782 156 >19.0
m2 1393 1413 19 >17.3
w2 696 1364 58 >18.6
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.092 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 40318
Subject
GRB 250430A: Enhanced Swift-XRT position
Date
2025-05-02T11:57:52Z (5 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1722 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 250430A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 233.38699, -18.11851 which is equivalent
to:
RA (J2000): 15h 33m 32.88s
Dec (J2000): -18d 07' 06.6"
with an uncertainty of 2.3 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 40316
Subject
GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
Date
2025-05-02T11:22:42Z (5 months ago)
From
Gianluca Masi at Virtual Telescope Project <gianluca@bellatrixobservatory.org>
Via
Web form
Gianluca Masi, Virtual Telescope Project (Italy), reports:
We attempted to observe the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum.
We collected 7, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 30 April, 22:19 UTC, that is about 4.75 hours after the burst.
We detected a faint object at the following position (J2000.0):
RA: 15 33 32.94s
Decl.: -18 07 06.5
R= 20.8 (assuming R-mags from Gaia DR2 for the reference stars).
This position is consistent with Odeh et al., GCN 40295.
At the position above, there is a very faint source on Panstarrs DR1 images, as well as on DESI Legacy DR10 images (the latter mentioned by Garnichey et al., GCN 40301), likely the host galaxy of GRB 250430A.
The image is available here:
https://www.virtualtelescope.eu/2025/05/02/grb-250430a-detection-of-the-optical-afterglow-30-apr-2025/
GCN Circular 40312
Subject
GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
Date
2025-05-02T06:35:58Z (5 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 imaged the field of GRB 250430A detected by Swift/BAT (Parsotan et al. GCN 40292), with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.
The observations were started at 2025-04-30 21:32 UT (approximately 4.02 hours after burst) stacking a set of unfiltered CCD image.
We co-added 80 exposures of 60 sec each.
Start T0+ End T0+ CR lim
4.02 hour 6.85 hour 19.9
We did not found any optical uncatalogued object within the Swift error circle.
Magnitudes were estimated with the PanSTARRS cat. and are not corrected for galactic dust extinction.
Our upper limit is consistent with other observations reported by Kawabata et al. (GCN 40294), Odeh et al. (GCN 40295), Saccardi et al. (GCN 40301), Hagio et al. (GCN 40302), Quadri et al. (GCN 40303), Moretti et al. (GCN 40304), Atri et al. (GCN 40305), Komesh et al. (GCN 40307), Mo et al. (GCN 40308), Zheng et al. (GCN 40310), Li et al. (GCN 40311).
The message may be cited.
GCN Circular 40311
Subject
GRB 250430A: SVOM/VT optical observations
Date
2025-05-02T03:29:23Z (5 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. L. Li, , L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), L. Zhang(IHEP), W. K. Zheng (UCB) report on behalf of the SVOM/VT team:
SVOM/VT conducted ToO follow-up observations for GRB 250430A. The observation started on 2025 Apr 24 04:54:31 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
The optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295;Garnichey et al., GCN 40301; Komesh et al., GCN 40307; Zheng et al., GCN 40310) was clearly detected in our observations.
The afterglow was fading during our observations and the brightness was estimated to be 21.69+/-0.05 mag in VT_R, and 22.96+/-0.10 mag in VT_B, at the mid time of 13.39 hours post the burst. The photometry was estimated in AB magnitude and not corrected for Galactic extinction. Considering the host galaxy's brightness and red color (Garnichey et al., GCN 40301),the photometry might be contaminated by the host galaxy's light, particularly in the VT_R band.
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 40310
Subject
GRB 250430A: KAIT optical observations
Date
2025-05-01T21:27:09Z (5 months ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng 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 (Parsotan et
al., GCN 40292; Wang et al., GCN 40299) with a set of 120x60s
images in the clear (roughly R) filters, at a mid time of 13.9
hours after the trigger. We marginally detected the optical
afterglow (Parsotan et al., GCN 40292; Odeh et al., GCN 40295