GRB 250331D
GCN Circular 39961
Subject
GRB 250331D: Fermi GBM Final Real-time Localization
Date
2025-03-31T05:59:53Z (2 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 05:49:17 UT on 31 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250331D (trigger 765092962.014718 / 250331243).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 21.1, Dec = 55.7 (J2000 degrees, equivalent to J2000 01h 24m, 55d 42'), with a statistical uncertainty of 13.9 degrees.
The angle from the Fermi LAT boresight is 12.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/quicklook/glg_skymap_all_bn250331243.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/bn250331243/quicklook/glg_healpix_all_bn250331243.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250331243/quicklook/glg_lc_medres34_bn250331243.gif
GCN Circular 39979
Subject
GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
Date
2025-03-31T17:36:04Z (2 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250331D onboard (T0: 2025-03-31T05:49:17 UTC, Fermi GCN 39961).
The Fermi notice, 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 burst occurred during a Swift slew. The imaging is performed using BatAnalysis tools (Parsotan et al. 2025 [https://arxiv.org/abs/2502.00278](https://arxiv.org/abs/2502.00278)).
A confident location is found for the burst with SNR of 11.6
The BAT position is
RA, Dec = 48.52543, 62.30596 deg which is
RA(J2000) = 03h 14m 06.10s
Dec(J2000) = +62d 18’ 21.5″
with an estimated uncertainty of 5 arcmin.
This position is consistent with the Ferm/GBM localization (GCN 39961).
XRT and UVOT follow-up has been requested. Results of follow-up
observations will be reported in future circulars.
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 39982
Subject
GRB 250331D: Swift ToO observations
Date
2025-03-31T18:37:26Z (2 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 Swift/BAT-detected event
GRB 250331D. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021825
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 Swift/BAT 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 39990
Subject
Fermi GRB 250331D: Global MASTER-Net observations report
Date
2025-04-01T00:03:05Z (2 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin,
V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250331D ( Fermi GBM team, GCN 39961) errorbox 62486 sec after notice time and 62523 sec after trigger time at 2025-03-31 23:11:20 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 71 deg. The sun altitude is -35.8 deg.
The galactic latitude b = -7 deg., longitude l = 128 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2829033
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
62554 | 2025-03-31 23:11:20 | MASTER-Kislovodsk | (02h 54m 34.96s , +65d 33m 33.8s) | C | 60 | 17.7 |
63431 | 2025-03-31 23:25:58 | MASTER-Kislovodsk | (02h 54m 36.68s , +65d 33m 23.8s) | C | 60 | 17.9 |
64508 | 2025-03-31 23:43:54 | MASTER-Kislovodsk | (02h 53m 45.13s , +65d 44m 21.5s) | C | 60 | 17.7 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 39998
Subject
GRB 250331D: Swift-XRT observations
Date
2025-04-01T08:59:42Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB),
S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester)
reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 250331D, collecting 5.3 ks of Photon
Counting (PC) mode data between T0+45.2 ks and T0+68.1 ks.
Two uncatalogued X-ray sources have been detected within the estimated
3-sigma Swift/BAT error region (493 arcsec), however none of them is
above the RASS limit or shows definitive signs of fading. Therefore, at
the present time we cannot identify which, if any, is the afterglow.
Details of these sources are given below:
Source 2:
RA (J2000.0): 48.6572 = 03:14:37.72
Dec (J2000.0): +62.2833 = +62:16:59.7
Error: 3.5 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: (7.4 [+1.6, -1.4])e-3 ct s^-1
Distance: 235 arcsec from Swift/BAT position.
Flux: (3.18 [+0.67, -0.61])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Source 4:
RA (J2000.0): 48.7705 = 03:15:4.93
Dec (J2000.0): +62.3734 = +62:22:24.1
Error: 5.9 arcsec (radius, 90% conf.)
Count-rate: (1.77 [+0.95, -0.72])e-3 ct s^-1
Distance: 476 arcsec from Swift/BAT position.
Flux: (1.19 [+0.64, -0.49])e-10 erg cm^-2 s^-1 (observed, 0.3-10 keV)
A catalogued source was also detected within the estimated 3-sigma
Swift/BAT error region (493 arcsec).
Two uncatalogued sources were also detected too far from the GRB
position to be likely afterglow candidates.
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/00021825.
This circular is an official product of the Swift-XRT team.
GCN Circular 40004
Subject
GRB 250331D: Fermi GBM observation
Date
2025-04-01T13:33:45Z (2 months ago)
From
Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>
Via
Web form
E. Bissaldi (Politecnico and INFN Bari), C. Meegan (UAH)
and A. Holzmann Airasca (Univ. Trento and INFN Bari)
report on behalf of the Fermi GBM Team:
"At 05:49:17.01 UT on 31 March 2025, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 250331D (trigger 765092962 / 250331243),
which was also detected by the Swift/BAT-GUANO (Ronchini et al. 2025, GCN 39979).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 27 degrees.
The GBM light curve consists of a single emission episode
with a duration (T90) of about 9 s (50-300 keV).
The time-averaged spectrum from T0-2.5 s to T0+6.4 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.12 +/- 0.27 and
the cutoff energy, parameterized as Epeak, is 91 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is
(6.1 +/- 0.8)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.64 s in the 10-1000 keV band
is 2.2 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 40005
Subject
GRB250331D: AbAO optical observations
Date
2025-04-01T14:15:27Z (2 months ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
email
N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report
on behalf of IKI GRB-FuN:
We observed the entire localisation region of BAT-GUANO/Swift of GRB250331D
(Ronchini et al., GCN 39979), initially detected by GBM/Fermi (Fermi GBM
team, GCN 39961) with AS-32 telescope of AbAO starting on 2025-03-31 (UT)
18:56:37. We report the results of optical transient searches in five
XRT/Swift localisations reported in
https://www.swift.ac.uk/ToO_GRBs/00021825/ and (Melandri et al., GCN
39998). Details of the preliminary photometry of the stacked image and the
sources detected so far are given below.
Date UT start t-T0 Filter Exp. UL(3sigma) Telescope
(mid, d) (s)
2025-03-31 18:56:37 0.56447 R 61x60 20.8 AS-32
XRT #1
------
RA = 48.26026d
Dec = 62.30756d
Err90 = 5.1"
Inside the XRT error circle the single source is detected:
RA = 48.25957d +/- 0.05"
Dec = 62.30756 +/- 0.02"
R(AbAO) = 13.24 +/- 0.05
USNO-B1.0 R2 = 13.39
XRT #2
------
RA = 48.65718d
Dec = 62.28326d
Err90 = 3.5"
Inside the XRT error circle the single source is detected:
RA = 48.66142d +/- 0.14"
Dec = 62.28324d +/- 0.07"
R(AbAO) = 18.72 +/- 0.07
USNO-B1.0 R2 = 18.97
XRT #3
------
RA = 48.86152d
Dec = 62.34017d
Err90 = 7.0"
Inside the XRT error circle the single source is detected:
RA = 48.85897d +/- 0.12"
Dec = 48.85897d +/- 0.06"
R(AbAO) = 18.64 +/- 0.07
USNO-B1.0 R2 = 18.93
XRT #4
------
RA = 48.77053d
Dec = 62.37337d
Err90 = 5.9"
Inside the XRT error circle the single source is detected:
RA = 48.76831d +/- 0.3"
Dec = 62.37292d +/- 0.3"
R(AbAO) = 19.68 +/- 0.26
USNO-B1.0 R2 = 19.94
XRT #5
------
RA = 48.3703896d
Dec = 62.10607d
Err90 = 6.9"
Inside the XRT error circle the single source is detected:
RA = 48.37039d +/- 0.3"
Dec = 62.10664d +/- 0.3"
R(AbAO) ~ 21.0
PS1 r = 21.17 +/- 0.15, i = 20.21 +/- 0.06
We did not identify any variable sources in any of the XRT localisations (
https://www.swift.ac.uk/ToO_GRBs/00021825/).
GCN Circular 40079
Subject
GRB 250331D: Swift-XRT afterglow detection
Date
2025-04-05T12:24:26Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB),
S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester) 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
Swift/BAT-detected burst GRB 250331D. The observations now extend from
T0+45.3 ks to T0+406.9 ks and have a total exposure time of 8.6 ks.
Of the sources previously reported, "Source 2" is fading with >3-sigma
significance, and is therefore likely the GRB afterglow. Using 3064 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 = 48.65718, +62.28326 which is equivalent
to:
RA (J2000): 03h 14m 37.72s
Dec(J2000): +62d 16' 59.8"
with an uncertainty of 3.5 arcsec (radius, 90% confidence). This
position is 3.9 arcmin from the Swift/BAT position. There is evidence
that the source may be fading, however we cannot constrain the decay at
the current time.
The results of the XRT-team automatic analysis of the likely afterglow
are at https://www.swift.ac.uk/ToO_GRBs/00021825/Source2.php.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021825.
This circular is an official product of the Swift-XRT team.