GRB 250430A
GCN Circular 40292
Subject
GRB 250430A: Swift detection of a burst with optical counterpart
Date
2025-04-30T18:07:07Z (a month ago)
From
Tyler Parsotan at NASA GSFC <tyler.parsotan@nasa.gov>
Via
email
T. M. Parsotan (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC),
N. J. Klingler (GSFC/UMBC/CRESSTII), M. J. Moss (GSFC),
K. L. Page (U Leicester), M. H. Siegel (PSU) and M. A. Williams (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 17:31:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250430A (trigger=1308754). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA, Dec 233.428, -18.083 which is
RA(J2000) = 15h 33m 43s
Dec(J2000) = -18d 04' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multi peak
structure with a duration of about 20 sec. The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 17:33:37.5 UT, 157.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 233.38611, -18.11784 which is
equivalent to:
RA(J2000) = 15h 33m 32.67s
Dec(J2000) = -18d 07' 04.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 190 arcseconds from the BAT onboard position, outside the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (9.57 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+2.62/-2.27) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 161 seconds after the BAT trigger. There is a candidate afterglow in
the list of sources generated on-board at
RA(J2000) = 15:33:32.85 = 233.38688
DEC(J2000) = -18:07:06.2 = -18.11840
with a 90%-confidence error radius of about 1.10 arc sec. This position is 3.65
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.44 with a 1-sigma error of about 0.35. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.092.
Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular 40294
Subject
GRB 250430A: Kanata optical upper limit
Date
2025-04-30T18:52:29Z (a month ago)
From
Koji Kawabata at HASC,Hiroshima U <kawabtkj@hiroshima-u.ac.jp>
Via
email
K. S. Kawabata, T. Hori, T. Nakaoka (Hiroshima Univ.) report on
behalf of Kanata team:
We performed optical imaging polarimetry to the field of the
GRB 180720B (Parsotan et al. GCN 40292; Lipunov et al. GCN 40291) from
2025-04-30 17:34:03 UT (162 seconds after the trigger) with HONIR
attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory,
Japan. We did not detect any new optical source up to a limiting
magnitude of Rc = 16.0 (3-sigma; Vega mag) at the position of the UVOT
source in our first 30 second exposure.
GCN Circular 40295
Subject
GRB 250430A: AKO Optical Afterglow Detection
Date
2025-04-30T19:20:09Z (a month ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Via
email
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International
Astronomical Center in Abu Dhabi, UAE), and Nidhal Guessoum (American
University of Sharjah, UAE), report:
We observed the field of GRB 250430A detected by Swift/BAT (Parsotan et al.,
GCN 40292), using our 0.36m f/7.7 robotic telescope. The observation session
began on 30 April 2025 at 17:52 UT, 21 minutes after the trigger.
We obtained multiple 180-second exposures using the Ic filter. An
uncatalogued object is faintly visible at the location below, which could be
the optical afterglow:
R.A. (J2000): 15:33:32.95
Dec. (J2000): -18:07:05.9
The following observation was calculated using the Atlas catalogue as a
reference:
----------------------------------------------------------------------------
-
ObsTime (mid), Exposure (sec), Filter, Mag
----------------------------------------------------------------------------
-
2025-04-30T18:29:42Z, 15 x 180s (stacked), Ic, 18.6 +/- 0.22
----------------------------------------------------------------------------
-
The magnitude is not corrected for galactic extinction.
GCN Circular 40301
Subject
GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
Date
2025-05-01T10:00:04Z (a month ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
M. Garnichey (LUX-Paris Obs.), A. Saccardi (CEA/Irfu), B. Schneider (LAM), G. Corcoran (UCD), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (Leicester), A. L. Thakur (INAF/IAPS), A. de Ugarte Postigo (LAM) report on behalf of the Stargate collaboration:
We observed the optical counterpart (Parsotan et al., GCN 40292; Odeh et al., GCN 40295) of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000 - 21000 AA, and consist of 4 exposures of 600 s each. The observation mid time was 2025 May 01 at 04:00:11 UT (10.87 hr after the Swift/BAT trigger).
In a 3x30-s image, taken in the r band at a mid time of 10.34 hr after the trigger, the optical counterpart is detected at RA, Dec 233.3872, -18.1184 which is equivalent to:
RA (J2000) = 15:33:32.93
Dec (J2000) = -18:07:06.3
These coordinates are in good agreement with those reported by Odeh et al. (GCN 40295). We measure a preliminary AB magnitude r = 21.97 +/- 0.06, calibrated against nearby stars from the Pan-STARRS catalog.
In a preliminary reduction of the spectra, we observe a continuum over the entire covered wavelength range, fainter in the UVB and VIS arms than in the NIR. A few absorption features are detected, which we interpret as the Mg II doublet (2796, 2804) and Fe II (2374, 2383, 2587, 2600), all at the common redshift z = 0.767. No emission lines are observed across the whole covered spectrum.
We note the presence of a catalogued object in the Legacy Survey DR10 at a position consistent with the optical afterglow. The magnitudes of the galaxy are g = 24.59 +/- 0.25, r = 23.22 +/- 0.10, i = 21.96 +/- 0.05, and z = 21.35 +/- 0.04, and its centroid is 0.5" away from the optical afterglow position. Our spectroscopic redshift measurement is consistent with the photometric redshift value provided of 0.89 +/- 0.11. This object is the likely host galaxy of GRB 250430A, though we notice that its red colors and lack of emission lines are not typical of a long (collapsar) GRB host.
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Palominos, and Camila de Sa Freitas. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular 40302
Subject
GRB 250430A : MITSuME Akeno optical upper limits
Date
2025-05-01T11:06:05Z (a month ago)
From
hagio.h.ffca@m.isct.ac.jp
Via
Web form
H. Hagio, I. Takahashi, M. Sasada, H. Seki, S. Joshima, Y. Kubo, A. Ochi, R. Kato, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration:
We observed the field of GRB 240430A detected by Swift/BAT (Parsotan et al. GCN 40292) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno.
The observation started at 2025-04-30 17:31:53 UT (32 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Parsotan et al., GCN 40292, Odeh et al., GCN 40295, Wang et al., GCN 40299, and Garnichey et al., GCN 40301. We obtained the 5-sigma limits of the stacked images as follows:
T0+[min] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
15.1 | 2025-04-30 17:46:27 | 620 | g'>18.2, Rc>18.2, Ic>17.8
78.5 | 2025-04-30 18:29:51 | 2880 | g'>19.3, Rc>19.6, Ic>19.0
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time
We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire).
GCN Circular 40303
Subject
GRB 250430A: Bassano Bresciano Observatory upper limit
Date
2025-05-01T13:33:33Z (a month ago)
From
Ulisse Quadri at Bassano Bresciano Observatory <osservatoriobassano@gmail.com>
Via
Web form
U.Quadri, L.Strabla and P.Madurini (Bassano Bresciano Astronomical Observatory)
Members of:
GRB/UAI - Gamma ray Burst section of Unione Astrofili Italiani.
AAVSO - American Association of Variable Star Observers.
GAC - Gruppo Astrofili Cremonesi.
In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report:
We imaged the field of GRB 250430A detected by Swift with the robotic telescope of (IAU station 565) Bassano Bresciano Observatory, Italy.
The observations started 5h 01m after the GRB trigger with our Newton telescope D=250 mm F/D=4.8.
We co-added 2 series of 150 exposures of 30 sec each.
Start T0+ End T0+ Rc lim. Err.
5h 01m 6h 30m 20.3 +/- 0.2
6h 31m 8h 01m 20.3 +/- 0.2
We did not found any optical uncatalogued object within the Swift error circle.
Our upper limit is consistent with other observations reported by K. S. Kawabata et al. (GCN Circular 40294), Mohammad Odeh et al. (GCN Circular 40295), Andrea Saccardi et al (GCN Circular 40301), H. Hagio et al. (GCN Circular 40302).
Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations.
Not corrected for galactic dust extinction.
Reference:
http://www.osservatoriobassano.altervista.org
The message may be cited.
GCN Circular 40304
Subject
GRB 250430A: Leavitt Observatory optical upper limit
Date
2025-05-01T14:02:45Z (a month ago)
From
leavittob@gmail.com
Via
Web form
L. Moretti, E. Pavoni (Leavitt Observatory, Italy)
Members of:
GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani
ATA - Associazione Tuscolana di Astronomia
In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
report:
We observed the field of the GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) with our RC telescope (D=250 mm, F/D=8) of Leavitt Observatory, Manciano, Italy.
The observations started approximately 6 hours after the Swift/BAT trigger time, with good weather conditions. We utilized the astropy package (Astropy Collaboration et al., 2022ApJ...935..167A) to align and stack 25 individual frames of 120 sec each, with a median time of 2025-04-30T23:29:41 (UTC). All images are unfiltered and were processed by a single data processing pipeline based on astropy package (Astropy Collaboration et al., 2022ApJ...935..167A).
In the stacked frame, we did not found any optical uncatalogued object within the Swift error circle.
Mid-Time (UTC) Rc limit Error
2025-04-30T23:29:41 >20.32 +/- 0.01
This upper limit is consistent with other observations reported by K. S. Kawabata et al. (GCN Circular 40294), Mohammad Odeh et al. (GCN Circular 40295), Andrea Saccardi et al (GCN Circular 40301), H. Hagio et al. (GCN Circular 40302), Quadri et al. (GCN 40303).
Our photometry is in the AB system and is not corrected for galactic dust extinction. Magnitudes were estimated with the Pan-STARRS cat. and converted using Lupton (2005) equations.
The message may be cited.
Reference:
https://leavittobservatory.altervista.org
GCN Circular 40305
Subject
GRB 250430A: DDOTI Optical Observations
Date
2025-05-01T14:06:36Z (a month ago)
From
sahil.atri@students.uniroma2.eu
Via
Web form
Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Sahil Atri (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), and Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of the Swift/BAT GRB 250430A (Parsotan et al., GCN Circ. 40292) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-01 UTC.
DDOTI observed the Swift/UVOT error region (Parsotan et al., GCN Circ. 40292) from 05:23 UTC to 10:43 UTC (from T+11.9 h to T+17.4 h after the trigger) with a total exposure of 2.3 hours, alternating with other scientific programs.
Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no any uncatalogued source at the position reported by Parsotan et al., (GCN Circ. 40292); Odeh et al., (GCN Circ. 40295); Wang et al., (GCN Circ. 40299); Garnichey et al., (GCN Circ. 40301); Hagio et al., (GCN Circ. 40302); Quadri (GCN Circ. 40303) and Moretti (GCN Circ. 40304) down to a 3-sigma limiting AB magnitude of:
w > 20.6
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular 40307
Subject
GRB 250430A: NUTTelA-TAO Early Measurements
Date
2025-05-01T17:08:43Z (a month ago)
From
Toktarkhan Komesh at Nazarbayev University <toktarkhan.komesh@nu.edu.kz>
Via
Web form
T. Komesh (NU), Z. Abdullayev (NU), Z. Maksut (NU), B. Grossan (UCB, NU), D. Berdikhan (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 GRB 250430A on receipt of an automated GCN / BAT 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 17:31:53 UT on 2025-04-30, 32 s after the BAT trigger. Observations were made in clear conditions for the first ~1 hour, followed by cloudy weather. Note that these observations provide essentially full-time coverage, simultaneous in two bands. A new and changing source consistent with the XRT/EP position (T. M. Parsotan et al., GCN 40292; C. Y. Wang et al., GCN 40299) was detected. We report the results for the earliest co-added images, without color corrections or corrections for galactic reddening, as following:
filter tc-t0(s) mag err exposure_time (s)
-------------------------------------------------------------------------------
r' 59 18.44 0.13 54
g' 55 UL18.10 45
r’ 162 18.56 0.14 120
g’ 227 19.23 0.11 300
… … … …
tc-t0 = image center time minus trigger time. Calibration was done with 4 bright Pan-STARRS catalog stars on our images. A light curve of the optical transient is presented in Figure 1: https://ecl.nu.edu.kz/research/observations/gamma-ray-bursts/grb250430a
We welcome opportunities for collaboration and data-sharing.
----------------------------------
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 40308
Subject
GRB 250430A / EP250430a: J-band upper limits with WINTER
Date
2025-05-01T17:50:27Z (a month ago)
From
Geoffrey Mo at MIT <gmo@mit.edu>
Via
Web form
Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 250430A / EP250430a (Parsotan et al., GCN 40292; Wang et al., GCN 40299) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2025-05-01T08:49:52 UTC (15.3 hours after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar
(https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We do not detect a source at the optical and X-ray counterpart position (Parsotan et al., GCN 40292; Kawabata et al., GCN 40294; Odeh et al., GCN 40295; Garnichey 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). We obtain the following 5-sigma upper limit: J ~ 19.7 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 40310
Subject
GRB 250430A: KAIT optical observations
Date
2025-05-01T21:27:09Z (a month 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;
Garnichey et al., GCN 40301; Komesh et al., GCN 40307) in the
coadd image with a brightness of 21.7 +/- 0.3 mag (Vega).
GCN Circular 40311
Subject
GRB 250430A: SVOM/VT optical observations
Date
2025-05-02T03:29:23Z (a month 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 40312
Subject
GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
Date
2025-05-02T06:35:58Z (a month 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 40316
Subject
GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
Date
2025-05-02T11:22:42Z (a month 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 40318
Subject
GRB 250430A: Enhanced Swift-XRT position
Date
2025-05-02T11:57:52Z (a month 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 40321
Subject
GRB 250430A: Swift/UVOT Detection
Date
2025-05-02T12:22:02Z (a month 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 40323
Subject
GRB 250430A: Swift-XRT refined Analysis
Date
2025-05-02T13:27:07Z (a month 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 40356
Subject
GRB 250430A: Swift-BAT refined analysis
Date
2025-05-06T02:50:20Z (24 days 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 40367
Subject
GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
Date
2025-05-06T16:17:44Z (23 days 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 40384
Subject
GRB 250430A / EP250430a: AstroSat CZTI detection
Date
2025-05-07T15:16:23Z (22 days 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