- GCN/BACODINE POSITION NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 25 Feb 25 19:42:47 UT
NOTICE_TYPE: Swift-BAT GRB Position
TRIGGER_NUM: 1291459, Seg_Num: 0
GRB_RA: 306.145d {+20h 24m 35s} (J2000),
306.567d {+20h 26m 16s} (current),
305.304d {+20h 21m 13s} (1950)
GRB_DEC: -41.484d {-41d 29' 03"} (J2000),
-41.401d {-41d 24' 04"} (current),
-41.647d {-41d 38' 48"} (1950)
GRB_ERROR: 3.00 [arcmin radius, statistical only]
GRB_INTEN: 416 [cnts] Image_Peak=60 [image_cnts]
TRIGGER_DUR: 0.064 [sec]
TRIGGER_INDEX: 10420 E_range: 25-100 keV
BKG_INTEN: 17586 [cnts]
BKG_TIME: 70740.85 SOD {19:39:00.85} UT
BKG_DUR: 8 [sec]
GRB_DATE: 20731 TJD; 56 DOY; 25/02/25
GRB_TIME: 70753.65 SOD {19:39:13.65} UT
GRB_PHI: -51.54 [deg]
GRB_THETA: 33.40 [deg]
SOLN_STATUS: 0x20000003
RATE_SIGNIF: 25.76 [sigma]
IMAGE_SIGNIF: 8.46 [sigma]
MERIT_PARAMS: +1 +0 +0 -4 +2 -1 -105 +0 -72 +0
SUN_POSTN: 339.15d {+22h 36m 36s} -8.77d {-08d 46' 09"}
SUN_DIST: 43.49 [deg] Sun_angle= 2.2 [hr] (West of Sun)
MOON_POSTN: 311.63d {+20h 46m 31s} -22.07d {-22d 04' 20"}
MOON_DIST: 19.79 [deg]
MOON_ILLUM: 6 [%]
GAL_COORDS: 359.49,-34.45 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 298.36,-21.54 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Coordinates.
COMMENTS: This Notice was delayed by more than 60 sec past the end of the
trigger integration interval;
COMMENTS: probably due to it occurring during a Malindi downlink session.
COMMENTS: This is a rate trigger.
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
COMMENTS: This trigger occurred at longitude,latitude = 177.15,18.46 [deg]
.
COMMENTS:
COMMENTS: NOTE: This BAT event is temporally(0.0<100sec) coincident with t
he INTEGRAL_SPIACS event (trignum=11068).
- red DSS finding chart
ps-file
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Tue 25 Feb 25 19:39:43 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 47
TRIGGER_NUM: 762205158
GRB_RA: 287.633d {+19h 10m 32s} (J2000),
288.100d {+19h 12m 24s} (current),
286.703d {+19h 06m 49s} (1950)
GRB_DEC: -47.367d {-47d 22' 00"} (J2000),
-47.324d {-47d 19' 24"} (current),
-47.449d {-47d 26' 55"} (1950)
GRB_ERROR: 7.90 [deg radius, statistical plus systematic]
GRB_INTEN: 934 [cnts/sec]
DATA_SIGNIF: 23.60 [sigma]
INTEG_TIME: 0.256 [sec]
GRB_DATE: 20731 TJD; 56 DOY; 25/02/25
GRB_TIME: 70753.83 SOD {19:39:13.83} UT
GRB_PHI: 36.00 [deg]
GRB_THETA: 45.00 [deg]
DATA_TIME_SCALE: 0.2560 [sec]
HARD_RATIO: 0.54
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 52% GRB
2nd_MOST_LIKELY: 45% Distant Particles
DETECTORS: 0,1,0, 0,0,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN: 339.15d {+22h 36m 36s} -8.77d {-08d 46' 12"}
SUN_DIST: 57.77 [deg] Sun_angle= 3.4 [hr] (West of Sun)
MOON_POSTN: 311.60d {+20h 46m 23s} -22.08d {-22d 04' 55"}
MOON_DIST: 31.52 [deg]
MOON_ILLUM: 6 [%]
GAL_COORDS: 349.95,-22.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 283.05,-24.72 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250225819/quicklook/glg_lc_medres34_bn250225819.gif
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 92.27,-25.05 [deg].
COMMENTS: The LC_URL file will not be created until ~15 min after the trigger.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Tue 25 Feb 25 19:39:52 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 60
TRIGGER_NUM: 762205158
GRB_RA: 303.450d {+20h 13m 48s} (J2000),
303.873d {+20h 15m 29s} (current),
302.607d {+20h 10m 26s} (1950)
GRB_DEC: -40.833d {-40d 49' 59"} (J2000),
-40.756d {-40d 45' 19"} (current),
-40.985d {-40d 59' 05"} (1950)
GRB_ERROR: 4.37 [deg radius, statistical plus systematic]
GRB_INTEN: 916 [cnts/sec]
DATA_SIGNIF: 61.20 [sigma]
INTEG_TIME: 2.048 [sec]
GRB_DATE: 20731 TJD; 56 DOY; 25/02/25
GRB_TIME: 70753.83 SOD {19:39:13.83} UT
GRB_PHI: 25.00 [deg]
GRB_THETA: 55.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO: 0.68
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 69% Distant Particles
2nd_MOST_LIKELY: 29% GRB
DETECTORS: 0,1,0, 0,0,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN: 339.15d {+22h 36m 36s} -8.77d {-08d 46' 12"}
SUN_DIST: 44.71 [deg] Sun_angle= 2.4 [hr] (West of Sun)
MOON_POSTN: 311.60d {+20h 46m 24s} -22.08d {-22d 04' 53"}
MOON_DIST: 19.78 [deg]
MOON_ILLUM: 6 [%]
GAL_COORDS: 359.90,-32.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 296.42,-20.41 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250225819/quicklook/glg_lc_medres34_bn250225819.gif
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 92.27,-25.05 [deg].
COMMENTS: The LC_URL file will not be created until ~15 min after the trigger.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 25 Feb 25 19:43:27 UT
NOTICE_TYPE: Swift-BAT GRB Lightcurve
TRIGGER_NUM: 1291459, Seg_Num: 0
GRB_RA: 306.145d {+20h 24m 35s} (J2000),
306.567d {+20h 26m 16s} (current),
305.304d {+20h 21m 13s} (1950)
GRB_DEC: -41.484d {-41d 29' 03"} (J2000),
-41.401d {-41d 24' 04"} (current),
-41.647d {-41d 38' 48"} (1950)
GRB_DATE: 20731 TJD; 56 DOY; 25/02/25
GRB_TIME: 70753.82 SOD {19:39:13.82} UT
TRIGGER_INDEX: 10420
GRB_PHI: -51.54 [deg]
GRB_THETA: 33.40 [deg]
DELTA_TIME: -15.00 [sec]
TRIGGER_DUR: 0.064 [sec]
SOLN_STATUS: 0x3
RATE_SIGNIF: 25.76 [sigma]
IMAGE_SIGNIF: 8.46 [sigma]
LC_URL: sw01291459000msb.lc
SUN_POSTN: 339.15d {+22h 36m 37s} -8.77d {-08d 46' 08"}
SUN_DIST: 43.49 [deg] Sun_angle= 2.2 [hr] (West of Sun)
MOON_POSTN: 311.63d {+20h 46m 32s} -22.07d {-22d 04' 13"}
MOON_DIST: 19.80 [deg]
MOON_ILLUM: 6 [%]
GAL_COORDS: 359.49,-34.45 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 298.36,-21.54 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Lightcurve.
COMMENTS:
COMMENTS: The next comments were copied from the BAT_POS Notice:
COMMENTS: This is a rate trigger.
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
COMMENTS: This trigger occurred at longitude,latitude = 177.15,18.46 [deg].
- GCN Circular #39473
M. A. Williams (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC),
H. A. Krimm (NSF), M. J. Moss (GSFC), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 19:39:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250225B (trigger=1291459). Swift could not slew immediately
due to an observing constraint.
The BAT on-board calculated location is
RA, Dec 306.145, -41.484 which is
RA(J2000) = 20h 24m 35s
Dec(J2000) = -41d 29' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multiple-peaked
structure (well-separated peaks at T+1, T+60, T+110) with a total
duration of about 120 sec. The peak count rate was ~13000 counts/sec
(15-350 keV), at ~1 sec after the trigger.
Due to a Moon observing constraint, Swift cannot slew to the BAT
position until 05:11 UT on 2025 February 26. There will thus be no XRT
or UVOT data for this trigger before this time.
We note the presence of the Emission-line Galaxy ESO 340-26
in the BAT error box. This is a bright (B=14.8, R=10.9) extended
(1.4 arcmin) galaxy at z ~ 0.018 .
Burst Advocate for this burst is M. A. Williams (mjw6837 AT psu.edu).
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 #39483
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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 250225B ( M. A. Williams et al., GCN 39473) errorbox 41481 sec after notice time and 41703 sec after trigger time at 2025-02-26 07:14:16 UT, with upper limit up to 16.6 mag. The observations began at zenith distance = 83 deg. The sun altitude is -37.0 deg.
The galactic latitude b = -35 deg., longitude l = 360 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2791924
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
41793 | MASTER-OAFA | C | 180 | 16.6 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #39493
SVOM/GRM team: Yan-Qiu Zhang, Chao Zheng, Chen-Wei Wang, Shi-Jie Zheng, Wen-Jun Tan, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP)
report on behalf of the SVOM team:
SVOM/GRM was triggered on-ground by a long burst GRB 250225B at 2025-02-25T19:39:14.000 (T0), which was also observed by Swift/BAT (M.A. Williams et al., GCN #39473), Fermi/GBM (triNum #762205158) and INTEGRAL/SPI-ACS (triNum #11068).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 293.0 +/- 31.2 s in the 15-5000 keV band.
In addition, the position of this burst, as determined by Swift/BAT (GCN #39473, RA: 306.145 deg, DEC: -41.4845 deg, Error: 3 arcmin), is located at about 113 degrees from the SVOM optical axis, and outside the ECLAIRs field of view.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250225B.png
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Yan-Qiu Zhang (IHEP) (zhangyanqiu@ihep.ac.cn)
- GCN Circular #39494
B. Schneider (LAM), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), R. A. J. Eyles-Ferris (Leicester), N. R. Tanvir (Leicester), L. Izzo (INAF/OACn and DARK/NBI), A. Martin-Carrillo (UCD), P. D’Avanzo (INAF/OAB), S. D. Vergani (CNRS, Paris Obs./LUX), report on behalf of the Stargate collaboration:
We observed the location of the Swift/BAT GRB 250225B (Williams et al., GCN 39473) with the FORS2 instrument on the VLT UT1. Observations began on 2025 Feb 26.40 UT (13.94 hr after the GRB), and a total of 5x50 s of observations were obtained, at large airmass ~2.3 and deep in twilight.
Image subtraction against the z-band template from the Legacy Survey reveals a transient source at coordinates:
RA(J2000) = 20:24:33.81
DEC(J2000) = -41:28:25.4
This source is consistent with a faint, extended object visible in the Legacy Survey (with a reported photometric redshift 1.12 +/- 0.18), and photometry suggests it has brightened by about 0.6 magnitudes from the time of the Legacy Survey observations. We consider this a candidate afterglow for GRB 250225B, although we note that detection of fading or an X-ray association will be required to robustly establish its nature.
The source is offset by ~3 arcmin (65 kpc in projection) from the bright galaxy ESO 340-26. Although this is well within the range of offsets seen for merger-driven GRBs, if this transient is indeed the afterglow of GRB 250225B, the presence of an underlying source in the Legacy Survey suggests the proximity to ESO 340-26 is a chance association.
Our subtraction shows no sign of any other transients within the BAT error circle, including within or close to ESO 340-26. The 5-sigma limiting magnitude for any such transient corresponds to z > 22.7 (M_z > -12 at redshift z = 0.018).
We thank the staff at ESO, among which Marco Berton, for their assistance in obtaining these challenging observations.
- GCN Circular #39495
Yu-Han Yang (U Rome), Brendan O’Connor (CMU), Eleonora Troja (U Rome), Rosa Becerra (U Rome) and Muskan Yadav (U Rome) report:
We observed the field of GRB 250225A (Williams et al., GCN 39473) with the FORS2 imager on the ESO VLT UT1 (Antu) and the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+13.7 hours and were carried out at an average airmass of about 2.6 in the I filter and in the J filter, respectively.
We detect the source reported by Schneider et al. (GCN 39494) at a preliminary magnitude J~21.4 AB mag calibrated using nearby stars in the 2MASS Catalogue. In comparison with archival imaging, the source appears brighter by ~0.5 mag in both the i- and the J-band, thus confirming the brightening reported by Schneider et al. (GCN 39494).
Although the probability of a chance alignment with the nearby galaxy ESO 340-26 remains small (P_cc<3%; Dichiara et al. 2020), we note that the observed color and magnitude of the candidate counterpart do not match the behavior of the kilonova AT2017gfo, if placed at a distance of 78 Mpc. If confirmed as the GRB afterglow, our observations favor the association with the underlying fainter galaxy, visible in the Legacy Survey (P_cc ~0.8%; Bloom et al. 2002)
We thank the staff at the VLT, for the rapid execution of these observations.
- GCN Circular #39498
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 250225B
(Swift-BAT detection: Williams et al., GCN 39473;
SVOM/GRM detection: Zhang et al., GCN 39493)
triggered Konus-Wind at T0=70750.895 s UT (19:39:10.895).
The burst light curve shows a bright initial pulse
which starts at ~T0-2.2 s and has a total duration of ~3.3 s,
followed by two weaker emission episodes centered
around ~T0+60 s and T0+108 s.
The emission is seen up to ~6 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250225_T70750/
As observed by Konus-Wind, the burst
had a fluence of 1.54(-0.18,+0.28)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.262 s,
of 1.14(-0.24,+0.35)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the initial pulse
(measured from T0 to T0+8.448 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 = -1.14(-0.16,+0.18)
and Ep = 634(-181,+393) keV (chi2 = 66/84 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.7
(chi2 = 66/83 dof).
The time-averaged spectrum of the second emission episode
(measured from T0+57.600 to T0+65.792 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with alpha = -1.23(-0.21,+0.28)
and Ep = 361(-118,+292) keV (chi2 = 97/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.7
(chi2 = 95/98 dof).
The time-averaged spectrum of the third emission episode
(measured from T0+106.752 to T0+114.944 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with alpha = -0.91(-0.69,+1.12)
and Ep = 187(-74,+228) keV (chi2 = 110/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.7
(chi2 = 110/98 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
- GCN Circular #39500
M. Ferro, R. Brivio, P. D'Avanzo, S. Covino, D. Fugazza, S. Campana (INAF-OAB), and L. Izzo (INAF-OACn and DARK/NBI) report on behalf of the REM team:
We observed the field of Swift detected GRB250225B (Williams et al., GCN 39473), also seen by SVOM (Zhang et al., GCN 39493) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the J, H, and K bands, started on 2025 February 26 at 08:27:46 UT (i.e. 12.8 hr after the burst), and lasted for about 1 hour.
From preliminary inspection inside the BAT error circle, we do not find any counterpart at the position of the reported optical/NIR candidate counterpart (Schneider et al., GCN 39494, Yang et al., GCN 39495) down to the following 3sigma limit:
H > 17.5 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 13.2 hours after the trigger
J > 17.1 (Vega; calibrated against the 2MASS catalogue)
at a mid-time of 13.4 hours after the trigger.
- GCN Circular #39502
M. Godwin (UAH), C. Meegan (UAH), P. Veres (UAH) and R. Hamburg (USRA) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 19:39:13.83 UT on 25 February 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250225B (trigger 762205158/250225819).
which was also detected by Swift BAT (H. A. Krimm et al. 2025, GCN 39473), Konus-Wind (A. Tsvetkova et al. 2025, GCN 39498), and VLT/FORS2 (Schneider et al. 2025, GCN 39494)
The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 55 degrees.
The GBM light curve consists of one bright peak followed my multiple short peaks with a duration (T90)
of about 335 s. The time-averaged spectrum
from T0-3.6 to T0+340.5 s is best fit by
a power law function with an exponential high-energy cutoff.The power law index is -1.30 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 218 +/- 28 keV.
The event fluence (10-1000 keV) in this time interval is
(2.14 +/- 0.11)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.3 s in the 10-1000 keV band is 21.9 +/- 0.3 ph/s/cm^2.
The time-averaged spectrum of the first peak from T0 to T0+3.6 s is best fit by
a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 568 +/- 42 keV. The Band function fits the spectrum equally well, with an Epeak of 547 +/- 46 keV, alpha = -1.05 +/- 0.03 and beta = -2.85 +/-0.67.
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 #39517
Aishwarya Linesh Thakur(a), Patrizia Barria(a,b), James Craig Rodi(a), Giulia Gianfagna(a), Luigi Piro(a), Lorenzo Natalucci(a,b) report:
GRB 250225B was discovered by Swift/BAT (GCN 39479) at 2025-02-25T19:39:13 (UTC) and has also been detected by SVOM/GRM (GCN 39493), Konus Wind (GCN 39498) and Fermi/GBM (GCN 39502).
In a SPI-ACS light curve above 80 keV, we find a signal temporally coincident with these detections, having an approximate duration of ~ 3 sec. The signal consists of a single pulse over this duration.
The approximate peak count rate in SPI-ACS is 90,000 cts/s for E>80 keV, over a median background rate of 70,800 cts/s.
This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany.
-----
(a) INAF/IAPS-Rome
(b) ICSC National Research Centre for High-Performance Computing
- GCN Circular #39521
Yu-Han Yang (U Rome), Eleonora Troja (U Rome), and Rosa Becerra (U Rome) report on behalf of the ERC BHianca team:
We observed the field of GRB 250225B (Williams et al., GCN 39473) with the Xshooter spectrograph on the ESO VLT UT3 (Melipal). Observations began at T+38.0 hours and, due to visibility constraints, only 2x600s spectra were acquired.
Using the acquisition and guiding (A&G) camera, imaging in the I filter was carried out at an average airmass of about 2.1. No source is detected at the position of the optical and nIR candidate counterpart (Schneider et al. GCN 39494, Yang et al. GCN 39495) down to a 3-sigma limit I>22.4 AB mag calibrated using nearby stars in the Legacy Survey DR10 (Dey et al. 2019) catalogue. Compared to our previous measurement (Yang et al. GCN 39495), these observations provide tentative evidence for fading by ~0.3 mag.
Further observations are planned.
We thank the staff at the VLT, for the rapid execution of these observations.
- GCN Circular #39535
B.C. Rayson (U. Leicester), N. Habeeb (U. Leicester), N. R. Tanvir (U. Leicester), R. A. J. Eyles-Ferris (U. Leicester), R. Brivio (INAF-OAB), M. Ferro (INAF-OAB), A J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the Stargate collaboration:
We observed the field of the GRB 250225B (Williams et al., GCN 39473) with the ESO Very Large Telescope UT4, equipped with the HAWK-I near-infrared camera. We obtained a 20 min exposure Ks band, starting at 09:12:18.45 UT on 2025-02-27, i.e. 1.56 days after the Swift trigger. The observations were obtained under good seeing conditions, with a measured seeing of 0.96″ in the Ks band.
We detect the optical afterglow candidate reported by Schneider et al. (GCN 39494) and Yang et al. (GCN 39495) at coordinates:
RA(J2000) = 20:24:33.81
DEC(J2000) = -41:28:25.4
Its Vega magnitude is Ks = 19.382 +- 0.057, calibrated using nearby stars in the 2MASS catalogue.
From VISTA survey images, we measured a 2-sigma upper limit to be Ks(Vega) > 19.56. No other obviously variable sources are seen, to the depth of the VISTA comparison images.
We thank the staff at the VLT, for the rapid execution of these observations.
- GCN Circular #39541
G. Finneran, C. McKenna, D. Murphy, C. de Barra, A. Ulyanov, P. McDermott, M. Doyle, R. Dunwoody, J. Mangan, G. Corcoran, L. Cotter, A. Empey, J. Fisher, F. Gibson Kiely, J. Thompson, D. McKeown, A. Martin-Carrillo, L. Hanlon, S. McBreen, on behalf of the EIRSAT-1 team:
EIRSAT-1 reports the detection of the long gamma-ray burst GRB250225B by the Gamma-ray Module (GMOD) instrument, which was also detected by Swift BAT (GCN 39473), SVOM GRM (GCN 39493), Konus-Wind (GCN 39498), Fermi GBM (GCN 39502) and INTEGRAL SPI-ACS (GCN 39517). The GMOD detection was made starting at 2025-02-25 19:39:13.1 UTC.
The GMOD light-curve for GRB250225B with 1.2s binning shows a peak consistent with the first peak seen by SVOM GRM, with a tentative detection of the second peak at around 60 seconds.
The spacecraft location at the time of detection was 31.703 N, 135.873 W, at an altitude of 425.8km.
The GMOD light curve for this event can be found here:
https://grb.eirsat1.ie/250225B/250225B_LC_onboard_preliminary.png
EIRSAT-1 is Ireland’s first satellite (Doyle et al. Proceedings of the 4th SSEA, 2022). It is a 2U CubeSat and carries onboard a number of experiments including the Gamma-Ray Module (GMOD), a novel, compact, gamma-ray detector (Murphy et al, Experimental Astronomy, 53, 961–990, 2022). GMOD consists of a 25 mm × 25 mm × 40 mm Cerium Bromide scintillator coupled to SiPMs and is designed to detect gamma-ray bursts in the ~ 60 keV - 1.5 MeV range. EIRSAT-1 was developed in University College Dublin with support from ESA’s Fly Your Satellite! programme and was launched on 1st December 2023.
- GCN Circular #39544
Yu-Han Yang (U Rome), Muskan Yadav (U Rome), Eleonora Troja (U Rome) on behalf of the ERC BHianca team:
We re-observed the field of GRB 250225B (Williams et al., GCN 39473) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations began at T+3.6 d days and were carried out at an average airmass of about 2.4 in the J filter.
In comparison to our first epoch of observations, the candidate counterpart (Schneider et al. GCN 39494, Yang et al. GCN 39495, Rayson et al. GCN 39535) appears to have substantially faded by about 1 mag. Image subtraction between the two epochs, reveals no other credible counterpart within the BAT error circle. We therefore confirm that this is the GRB afterglow.
We thank the staff at the VLT, for the rapid execution of these observations.
- GCN Circular #39668
T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
R. Gupta (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), M. A. Williams (PSU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+160 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250225B (trigger #1291459)
(Williams et al., GCN Circ. 39473). The BAT ground-calculated position is
RA, Dec = 306.134, -41.481 deg which is
RA(J2000) = 20h 24m 32.2s
Dec(J2000) = -41d 28' 50.8"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 47%.
The mask-weighted BAT light curve shows a bright peak around the trigger time, followed by multiple fainter peaks. After approximately 160 seconds, the GRB was no longer in the BAT field of view (FOV).
T90 (15-350 keV) is 110.46 +- 2.12 sec (estimated error including systematics).
The time-averaged spectrum from T-0.02 to T+122.46 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.60 +- 0.07. The fluence in the 15-150 keV band is 6.5 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+1.31 sec in the 15-150 keV band
is 10.4 +- 0.5 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/1291459
- GCN Circular #39830
Jia-Cong Liu, Shao-Lin Xiong, Peng Zhang, Yan-Qiu Zhang, Chen-Wei Wang (IHEP) report on behalf of the GECAM team:
GECAM-A detected a long burst, GRB 250225B, at 2025-02-25T19:39:13 UTC (denoted as T0), which was also observed by Swift/BAT (H. A. Krimm et al. 2025, GCN 39473),
SVOM/GRM (Yan-Qiu Zhang et al. 2025, GCN 39493), Fermi/GBM (M. Godwin et al. 2025, GCN 39502), and Konus-Wind (A. Tsvetkova et al. 2025, GCN 39498).
According to the GECAM-A light curves in about 50-200 keV, this burst mainly consists of multiple pulses with a T90 of about 63.2 ± 2.5 s.
The GECAM light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250225B.png
We note that these results are preliminary. Refined analysis will be reported.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (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 #40024
A. Saccardi (CEA/Irfu), G. Corcoran (UCD), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick) report on behalf of the Stargate collaboration:
We observed with the ESO VLT UT3 (Melipal) the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (Schneider et al., GCN 39494; Yang et al., GCN 39495, 39521; Rayson et al., GCN 39535; Yang et al., GCN 39544) of GRB 250225B (Williams et al., GCN 39473; Zhang et al., GCN 39493; Ridnaia et al., GCN 39498; Godwin et al., GCN 39502; Thakur et al., GCN 39517; Finneran et al., GCN 39541; Liu et al., GCN 39830). Due to its spatial coincidence, this is the likely GRB host galaxy.
We obtained two spectra of 1000 s each with the X-shooter instrument, starting at 07:08:05 UT on 2025 April 3, i.e. about 36.5 days after the Swift trigger. The observations were obtained under good conditions, with a measured seeing of 0.5".
Emission lines are detected in the visible and near-infrared arms, which we identify as H-alpha, [O III] 5007 and the [O II] 3726,3729 doublet at a common redshift of z = 0.950. This value is consistent with the photometric solution z_phot = 1.12 +/- 0.18 from the Legacy Survey (Zhou et al. 2021, doi:10.1093/mnras/staa3764). The absolute magnitude of the galaxy is M_B ~ -21, which is at the bright end of the distribution of long-duration (collapsar) GRB hosts. Our redshift measurement rules out an association between the object in the Legacy Survey and ESO 340-26 at z = 0.018. Considering the low chance association probability (Schneider et al., GCN 39494; Yang et al., GCN 39495), we consider this to be the likely redshift of GRB 250225B.
We acknowledge the excellent support from the ESO staff in Paranal, in particular Matias Jones, Rob van Holstein, and Rodrigo Palominos.
Previous IAU Circulars 
