- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sun 09 Mar 25 07:38:34 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 46
TRIGGER_NUM: 763198715
GRB_RA: 213.700d {+14h 14m 48s} (J2000),
214.008d {+14h 16m 02s} (current),
213.089d {+14h 12m 21s} (1950)
GRB_DEC: +10.650d {+10d 39' 00"} (J2000),
+10.534d {+10d 32' 01"} (current),
+10.882d {+10d 52' 57"} (1950)
GRB_ERROR: 9.00 [deg radius, statistical plus systematic]
GRB_INTEN: 554 [cnts/sec]
DATA_SIGNIF: 21.30 [sigma]
INTEG_TIME: 0.512 [sec]
GRB_DATE: 20743 TJD; 68 DOY; 25/03/09
GRB_TIME: 27510.66 SOD {07:38:30.66} UT
GRB_PHI: 227.00 [deg]
GRB_THETA: 65.00 [deg]
DATA_TIME_SCALE: 0.5120 [sec]
HARD_RATIO: 1.01
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 98% GRB
2nd_MOST_LIKELY: 1% Generic SGR
DETECTORS: 0,0,0, 0,0,0, 0,1,0, 0,0,1, 0,0,
SUN_POSTN: 349.87d {+23h 19m 30s} -4.36d {-04d 21' 25"}
SUN_DIST: 135.85 [deg] Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN: 114.21d {+07h 36m 52s} +26.50d {+26d 29' 43"}
MOON_DIST: 93.91 [deg]
MOON_ILLUM: 77 [%]
GAL_COORDS: 356.90, 64.38 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 207.56, 22.73 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 249.97,-5.28 [deg].
COMMENTS: The LC_URL file will not be created until ~15 min after the trigger.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sun 09 Mar 25 07:38:42 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 58
TRIGGER_NUM: 763198715
GRB_RA: 213.367d {+14h 13m 28s} (J2000),
213.686d {+14h 14m 45s} (current),
212.733d {+14h 10m 56s} (1950)
GRB_DEC: +2.300d {+02d 17' 60"} (J2000),
+2.183d {+02d 10' 59"} (current),
+2.533d {+02d 32' 00"} (1950)
GRB_ERROR: 6.20 [deg radius, statistical plus systematic]
GRB_INTEN: 510 [cnts/sec]
DATA_SIGNIF: 54.60 [sigma]
INTEG_TIME: 4.096 [sec]
GRB_DATE: 20743 TJD; 68 DOY; 25/03/09
GRB_TIME: 27510.66 SOD {07:38:30.66} UT
GRB_PHI: 220.00 [deg]
GRB_THETA: 70.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO: 1.38
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 98% GRB
2nd_MOST_LIKELY: 1% Generic SGR
DETECTORS: 0,0,0, 0,0,0, 0,1,0, 0,0,1, 0,0,
SUN_POSTN: 349.87d {+23h 19m 30s} -4.36d {-04d 21' 25"}
SUN_DIST: 136.21 [deg] Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN: 114.22d {+07h 36m 52s} +26.50d {+26d 29' 43"}
MOON_DIST: 97.48 [deg]
MOON_ILLUM: 77 [%]
GAL_COORDS: 344.77, 58.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 210.33, 14.80 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 249.97,-5.28 [deg].
COMMENTS: The LC_URL file will not be created until ~15 min after the trigger.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sun 09 Mar 25 07:38:48 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 57
TRIGGER_NUM: 763198715
GRB_RA: 212.080d {+14h 08m 19s} (J2000),
212.421d {+14h 09m 41s} (current),
211.405d {+14h 05m 37s} (1950)
GRB_DEC: -13.540d {-13d 32' 23"} (J2000),
-13.659d {-13d 39' 30"} (current),
-13.303d {-13d 18' 11"} (1950)
GRB_ERROR: 2.52 [deg radius, statistical only]
DATA_SIGNIF: 44.60 [sigma]
DATA_INTERVAL: 2.048 [sec]
GRB_DATE: 20743 TJD; 68 DOY; 25/03/09
GRB_TIME: 27510.66 SOD {07:38:30.66} UT
GRB_PHI: 207.00 [deg]
GRB_THETA: 80.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 4173 (Gnd S/W Version number)
SUN_POSTN: 349.87d {+23h 19m 30s} -4.36d {-04d 21' 25"}
SUN_DIST: 134.10 [deg] Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN: 114.22d {+07h 36m 52s} +26.49d {+26d 29' 42"}
MOON_DIST: 103.26 [deg]
MOON_ILLUM: 77 [%]
GAL_COORDS: 329.98, 45.26 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 214.53, -0.54 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif
POS_MAP_URL: http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_763198715.fits
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: This Notice was ground-generated -- not flight-generated.
COMMENTS: The LC_URL file will not be created/available until ~15 min after the trigger.
COMMENTS: The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sun 09 Mar 25 07:39:19 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 0
TRIGGER_NUM: 763198715
GRB_RA: 212.830d {+14h 11m 19s} (J2000),
213.172d {+14h 12m 41s} (current),
212.152d {+14h 08m 36s} (1950)
GRB_DEC: -14.190d {-14d 11' 23"} (J2000),
-14.308d {-14d 18' 26"} (current),
-13.955d {-13d 57' 18"} (1950)
GRB_ERROR: 2.09 [deg radius, statistical only]
DATA_SIGNIF: 38.70 [sigma]
DATA_INTERVAL: 3.072 [sec]
GRB_DATE: 20743 TJD; 68 DOY; 25/03/09
GRB_TIME: 27510.66 SOD {07:38:30.66} UT
GRB_PHI: 207.00 [deg]
GRB_THETA: 81.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 41731 (Gnd S/W Version number)
SUN_POSTN: 349.87d {+23h 19m 30s} -4.36d {-04d 21' 25"}
SUN_DIST: 133.19 [deg] Sun_angle= 9.1 [hr] (West of Sun)
MOON_POSTN: 114.22d {+07h 36m 53s} +26.49d {+26d 29' 39"}
MOON_DIST: 104.19 [deg]
MOON_ILLUM: 77 [%]
GAL_COORDS: 330.52, 44.36 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 215.44, -0.91 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif
POS_MAP_URL: http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_763198715.fits
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: This is likely a Long GRB.
COMMENTS: This Notice was ground-generated -- not flight-generated.
COMMENTS: The LC_URL file will not be created/available until ~15 min after the trigger.
COMMENTS: The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sun 09 Mar 25 07:39:29 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 1
TRIGGER_NUM: 763198715
GRB_RA: 211.330d {+14h 05m 19s} (J2000),
211.668d {+14h 06m 40s} (current),
210.661d {+14h 02m 39s} (1950)
GRB_DEC: -11.460d {-11d 27' 35"} (J2000),
-11.580d {-11d 34' 45"} (current),
-11.221d {-11d 13' 16"} (1950)
GRB_ERROR: 1.60 [deg radius, statistical only]
DATA_SIGNIF: 55.40 [sigma]
DATA_INTERVAL: 6.144 [sec]
GRB_DATE: 20743 TJD; 68 DOY; 25/03/09
GRB_TIME: 27510.66 SOD {07:38:30.66} UT
GRB_PHI: 208.00 [deg]
GRB_THETA: 78.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 41731 (Gnd S/W Version number)
SUN_POSTN: 349.88d {+23h 19m 30s} -4.36d {-04d 21' 24"}
SUN_DIST: 135.48 [deg] Sun_angle= 9.2 [hr] (West of Sun)
MOON_POSTN: 114.22d {+07h 36m 54s} +26.49d {+26d 29' 37"}
MOON_DIST: 101.72 [deg]
MOON_ILLUM: 77 [%]
GAL_COORDS: 330.27, 47.45 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 213.14, 1.17 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif
POS_MAP_URL: http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_763198715.fits
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: This is likely a Long GRB.
COMMENTS: This Notice was ground-generated -- not flight-generated.
COMMENTS: The LC_URL file will not be created/available until ~15 min after the trigger.
COMMENTS: The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.
- GCN Circular #39629
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
763198715 at 07:38:30 on 09 March 2025 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
RA(2000.0) = 210.5 deg
Decl.(2000.0) = -7.6 deg
The 1 sigma statistical error radius is 1.3 deg.
We estimate an additional systematic error of 1 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB250309318/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB250309318/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB250309318/json
- GCN Circular #39633
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the
Fermi/GBM GRB 230509B. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00134
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the Fermi/GBM event is high: 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 #39634
P.A. Evans reports on behalf of the Swift-XRT team,
There was an error in GCN Circ. 39633 — Swift is not observing a 22-month old GRB, but is in fact
observing combined error locatlisation of GRB 250309B and IceCube 250309A.
Apologies for any confusion caused by my errant fingers, and thanks to Kim Page for spotting this.
We will request a correction in the GCN archives.
- GCN Circular #39635
The Fermi GBM team reports the detection of a likely LONG GRB
"At 07:38:30.66 UT on 09 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250309B (trigger 763198715/250309318).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 210.58, Dec = -10.86 (J2000 degrees, equivalent to J2000 14h 02m, -10d 51'),
with a statistical uncertainty of 1.2 degrees.
The angle from the Fermi LAT boresight is 77 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_skymap_all_bn250309318.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/bn250309318/quicklook/glg_healpix_all_bn250309318.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250309318/quicklook/glg_lc_medres34_bn250309318.gif"
- GCN Circular #39639
Robert Stein (JSI), Tomas Ahumada (Caltech), Jannis Necker, Akshay Eranhalodi (DESY), and Anna Franckowiak (Ruhr University Bochum), Jesper Sollerman (Stockholm) report:
On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the localisation of Gamma-Ray Burst GRB 250309B (McDermott et al., GCN 39635) with the Palomar 48-inch telescope equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). This GRB was reported to be in spatial/temporal coincidence with high-energy neutrino IC250309A (Zegarelli et. al, GCN 39631), and our observations included ToO observations (Stein et al., GCN 39638) conducted as part of the ZTF neutrino follow up program (Stein et al. 2023).
We started serendiptious observations of the GRB skymap in the g- and r-band beginning at 2025-03-09 07:51 UTC, approximately 0.3 hours after event time. We covered 80% of the reported localization region. This estimate accounts for chip gaps.
The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). After applying standard candidate vetting procedures, we identified the following candidate optical afterglow:
±–––––––––––––––––––––––––––––––––––––––-+
| ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr |
±–––––––––––––––––––––––––––––––––––––––-+
| ZTF25aaitvjt | AT2025dws | 210.801761 | -8.502842 | r | 18.48| 0.107 |
±–––––––––––––––––––––––––––––––––––––––-+
Using the smaller BALROG localisation (Greiner et al, GCN 39629), we covered 76.8% (1.9 sq deg) of the reported localization region. This estimate accounts for chip gaps. Repeating the same search, AT2025dws is again the only candidate found within the error contour of the GRB.
AT2025dws is red (g−r>0.4 mag) and is coincident with a faint Legacy Survey source that appears to be a possible host galaxy. From the ATLAS forced photometry service, we find that the transient had deeper upper limit (m>19.2) 1.67 hours before the GRB trigger. This suggests that AT2025dws is both fast-evolving, and temporally coincident with the GRB. Given this, we consider AT2025dws to be the likely afterglow counterpart.
We encourage spectroscopic observations to confirm the nature of AT2025dws as an afterglow. ToO observations have been requested with the Neil Gehrels Swift Observatory.
We note that none of ZTF25aaitvjt/AT2025dws is located 2.24 degrees from the center of the neutrino localisation. If this is indeed the afterglow, then the offset to the reported neutrino uncertainty region is >5 sigma, suggesting that the neutrino and GRB are not associated.
We will continue to observe this field as part of our standard ToO cadence for high-energy neutrinos (Stein et al. 2023).
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.
GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ).
- GCN Circular #39641
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 250309B ( Fermi GBM team, GCN 39635) errorbox 53228 sec after notice time and 53238 sec after trigger time at 2025-03-09 22:25:49 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 61 deg. The sun altitude is -48.7 deg.
The galactic latitude b = 44 deg., longitude l = 331 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2805642
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
53269 | 2025-03-09 22:25:49 | MASTER-Kislovodsk | (13h 59m 30.46s , -13d 45m 18.7s) | C | 60 | 17.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #39642
P. McDermott (UCD), P. Veres (UAH) and L. Scotton (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 07:38:30.66 UT on 09 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250309B (trigger 763198715/250309318).
The Fermi GBM on-ground location was reported in GCN 39635.
The angle from the Fermi LAT boresight is 77 degrees.
The GBM light curve consists of an emission episode with
multiple peaks, with a duration (T90)
of about 6.4 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+8.192 s is best fit by
a Band function with Epeak = 93 +/- 5 keV,
alpha = -0.98 +/- 0.06 and beta = -2.40 +/- 0.08.
The event fluence (10-1000 keV) in this time interval is
(1.07 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.8 s in the 10-1000 keV band is 23 +/- 0.4 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 #39643
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)
We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of ZTF25aaitvjt / AT 2025dws, that has been proposed by Stein et al. (GCN circ. 39639) as the candidate optical counterpart of the Fermi GBM likely long Gamma-Ray Burst GRB 250309B (Preis & Greiner, GCN circ. 39629; Fermi GBM team, GCN circ. 39635; and McDermott et al., GCN circ. 39642), that may be related with the IceCube high-energy neutrino IceCube-250309A (The IceCube Collaboration, GCN circ. 39631).
We observed the field of ZTF25aaitvjt / AT 2025dws with one of the LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). We obtained a 180-sec exposure in each of the SDSS g', r', and i' filters starting at about 21.77 hours after the Fermi trigger. We detect ZTF25aaitvjt / AT 2025dws in the three filters.
We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:
Date | UT start | t_mid - t0 (hours) | mag | error | filter |
----------------------------------------------------------------------
2025-03-09 22:28:06 21.79 20.38 0.15 g'
2025-03-09 22:31:46 21.85 20.12 0.14 r'
2025-03-09 22:35:16 21.91 19.87 0.14 i'
The fast fading in the g' and r' bands compared with the Zwicky Transient Facility (ZTF) detections reported by Stein et al. (GCN circ. 39639 and TNS Astronomical Transient Report No. 247224) supports that ZTF25aaitvjt / AT 2025dws is the likely optical afterglow of GRB 250309B.
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
- GCN Circular #39644
Robert Stein (JSI), Tomas Ahumada (Caltech) report,
On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We requested observations of AT2025dws (Stein et al., GCN 39639), the candidate counterpart to GRB 250309B (Preis & Greiner, GCN 39629; McDermott et al., GCN 39635), with the Neil Gehrels Swift Observatory.
Observations were conducted beginning 2025-03-09 20:26:46 UT, ~13 hours after the GRB time (2025-03-09 07:38:30.66 UT). These observations had an exposure time of 30 minutes, in the U-band filter.
We reduced the Swift UVOT data (Roming et al. 2005) using HEASoft. A source is clearly visible at the position of AT2025dws, with an apparent magnitude of m = 21.5 +/- 0.2 [AB Mag]. These observations had a limiting magnitude of m = 22.4 [AB Mag]. While we have not performed host subtraction, the source is marginally detected in archival SDSS imaging with a u-band magnitude of m=24.02. This suggests our detection is dominated by transient light.
AT2025dws has been already been confirmed to be fast-fading by recent optical observations with LCO (Perez-Fournon et al., GCN 39643). While there are no earlier U-band detection of this transient, our UVOT detection is fainter than the optical detections reported in GCNs 39639 and 39643. This confirms the red nature of the transient, and is consistent with the expected red/fast-fading behaviour of a GRB aferglow.
- GCN Circular #39645
A. S. Moskvitin, O. I. Spiridonova (SAO RAS), A. S. Pozanenko (IKI),
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg),
Yu. V. Sotnikova (SAO RAS) report on behalf of a larger collaboration.
We partially covered the error circle of the GRB 250309B (Preis
and Greiner, GCN 39629; Fermi GBM team, GCN 39635; McDermott et al.,
GCN 39642) with 1-m telescope of SAO RAS, Zeiss-1000,
equipped with the CCD-photometer.
The fields of ZTF25aaitvjt / AT2025dws (Stein et al.,
GCN 39639), XRT sources #1 and #3 (Evans et al., GCN 39633) were
observed in Rc band on March 9/10 night. The AT2025dws source
does not fit into the error circle of ground-based GBM localization
(Fermi GBM group, GCN 39635), but falls into the BALROG localization
field (Preis et al., GCN 39629).
We obtained two epochs of observations for ZTF25aaitvjt / AT2025dws
field. The 1st: on March 9, 21:58:17 -- March 9, 22:29:28 UT,
t_mid - T0 = 14.5893 h = 0.60789 days (5 x 300 sec. exposure);
the 2nd: on March 9, 23:52:03 -- March 10, 00:47:22 UT,
t_mid - T0 = 16.6865 h = 0.69527 days (10 x 300 sec. exposure).
We clearly detected ZTF25aaitvjt / AT2025dws (Stein et al.,
GCN 39639; Pérez-Fournon et al., GCN 39643; Stein and Ahumada,
GCN 39644) in the stacked images. Preliminary photometry is the following.
Date UT start t-T0 Exptime Filter OT Err UL
(mid, days) (s) (3sigma)
2025-03-09 21:58:17 0.60789 5 x 300 Rc 19.52 +/- 0.04 22.0
2025-03-09 23:52:03 0.69527 10 x 300 Rc 19.66 +/- 0.02 22.6
The above photometry includes the OT and a possible host galaxy.
The photometry is based on nearby stars from the USNO-B1.0 catalog
(R2 magnitudes) and has not been corrected for the Galactic extinction.
USNO-B1.0 reference stars
RA Dec R2
14:03:06.24 -08:27:38.9 15.67
14:03:08.07 -08:26:47.1 17.30
- GCN Circular #39646
D. A. Perley (LJMU), A. Bochenek (LJMU), and A. Y. Q. Ho (Cornell) report:
We obtained imaging observations of AT2025dws (Stein et al., GCN 39639), a possible optical counterpart of GRB 250309B (Preis & Greiner, GCN 39629; McDermott et al., GCN 39635) with IO:O on the Liverpool Telescope on UT 2025 March 10 between 01:46:53 and 02:01:08 UT. Two 100s exposures were acquired in each of the g, r, i, and z bands. The source was weakly detected in all four filters. We report the following photometry, calibrated relative to SDSS standards (dt is reported relative to the GRB 250309B GBM trigger time; McDermott et al., GCN 39642):
MJD dt filter mag err
60744.07423 0.7558 g 20.47 0.19
60744.07708 0.7587 r 20.30 0.14
60744.07991 0.7615 i 20.07 0.19
60744.08274 0.7643 z 19.44 0.17
The red colours and significant fading are consistent with the interpretation of this source as the afterglow (see also Pérez-Fournon et al., GCN 39643; Stein et al., GCN 39644; Alexander et al., 39645).
No host galaxy subtraction or extinction correction has been performed.
- GCN Circular #39647
D. B. Malesani (DAWN/NBI and Radboud Univ.), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), C. C. Thoene (AbAO), J. F. Agui Fernandez (CAHA), N. R. Tanvir (Univ. Leicester), L. Izzo (INAF/OACn and DARK/NBI), J. P. U. Fynbo (DAWN/NBI), S. Geier (GTC), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), F. Perez Toledo (GTC), and A. Perez (GTC) report:
We observed the afterglow of GRB 250309B (Preis et al. GCN 39629; Fermi GBM team GCN 39635; Stein et al. GCN 39639; McDermott
et al. GCN 39642; Perez-Fournon et al. GCN 39643; Stain et al. GCN 39644; Moskvitin et al. GCN 39645; Perley et al. GCN 39646) with OSIRIS+, mounted on te 10.4.m GTC telescope at the Roque de los Muchachos Observatory in the island of La Palma (Spain). The observation started at 2025-03-10T03:28:33.011 UT (19.83 h after the burst) and consisted of 2x900 s spectroscopy with grism R1000B, covering the range between 3600 and 7880 AA.
A preliminary reduction shows a continuum across the complete spectral range with multiple spectral features which we interpret as due to SiII, SiIV, OI, CII, CIV, FeII, AlII, AlIII, ZnII, and MnII at a common redshift of 1.898, which we identify as the redshift of the GRB. Additionally, we detect a strong intervening system with features of CIV, AlII, FeII, MgII and MgI at a a redshift of 1.634.
- GCN Circular #39648
Yue Wang, Jia-Cong Liu, Jin-Peng Zhang, Chen-Wei Wang, Wen-Jun Tan, Wang-Chen Xue, Shao-Lin Xiong (IHEP), report on behalf of the GECAM team:
GECAM-B was triggered on-ground by a long burst, GRB 250309B, at 2025-03-09T07:38:31.050 UTC (T0), which was also observed by Fermi/GBM (McDermott et al., GCN 39642).
According to GECAM-B light curve, this burst mainly consists of multiple pulses with a duration (T90) of about 6.74 (+/-0.15) sec (50-300 keV). The GECAM-B light curve of GRB 250309B could be found at:
https://www.bursthub.cn//admin/static/gecamgrb250309B.png
The GECAM-B localization of GRB 250309B is consistent with the Fermi/GBM localization of this burst (McDermott et al., GCN 39642) and the position of optical counterpart AT 2025dws (Stein et al., GCN 39639) as well as the IceCube-250309A (The IceCube Collaboration, GCN 39631). Thus, we confirm that GRB 250309B is spatially and temporally coincident with IceCube-250309A.
The time-integrated spectrum of GRB 250309B from T0-1.0 s to T0+6.0 s is best fitted by
a cutoff-powerlaw function with Epeak = 109.3 +/- 6.8 keV and alpha = -1.00 +/- 0.27. The event fluence (10-1000 keV) in this time interval is (7.65 +/- 0.56)E-06 erg/cm^2.
With the measured redshift z=1.898 (D. B. Malesani et al., GCN 39647), we calculate the isotropic energy Eiso is (7.4 ± 0.8)x10^52 erg. Then we note that GRB 250309B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/grb250309B_amati.png
Further, we note that there is no GECAM-B trigger just around the event time of IceCube-250309A (2025-03-09 at 07:36:04.75 UT, The IceCube Collaboration, GCN 39631). We implemented a targeted search [1] for burst activities from T0-330 s to T0-30 s embracing this IceCube event, but identified no candidate above 3 sigma.
Thus, we calculated the upper limit of a potential precursor of GRB 250309B which is simultaneously associated with IceCube-250309A. Considering three typical GRB spectral models (i.e. soft, normal and hard Band functions), three timescales and the center region of GRB localization (RA= 211.07, Dec = -10.73), the 3 sigma upper limits of the potential GRB precursor energy flux (15 keV-5000 keV, in units of 10^-7 erg/s/cm^2) are reported below:
|Timescale (s)|Soft|Normal|Hard|
| ------------ | ------------ | ------------ | ------------ |
|0.1|3.86|3.92|6.33|
|1 |1.22|1.24|2.00|
|10 |0.38|0.39|0.63|
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 #39649
K.L. Page and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 3.9 ks of XRT data for the Fermi/GBM-detected GRB
250309B, from 46.1 to 57.7 ks after the Fermi trigger (GCN Circs. 39635,
39642). The data are entirely in Photon Counting (PC) mode.
We detect a previously uncatalogued X-ray source at the following
coordinates: RA/Dec(J2000) = 210.80129, -8.50302, which is equivalent to
RA (J2000): 14 03 12.31
Dec(J2000): -08 30 10.9
with an uncertainty of 3.0 arcsec (radius, 90% confidence). This source
is 1.8 arcsec from the optical counterpart AT2025dws discovered by the
Zwicky Transient Facility (GCN Circ. 39639), and also detected by LCO (GCN
Circ. 39643), SAO RAS (GCN Circ. 39645), the Liverpool telescope (GCN
Circ. 39646) and the Swift UVOT (GCN Circ. 39644). A redshift of 1.898 has
been reported from OSIRIS+/GTC spectroscopy in GCN Circ. 39647.
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.7 (+1.1, -2.6).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.74 (+0.24, -0.23). The
best-fitting absorption column is consistent with the Galactic value of
3.0 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 (4.0 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground column: 3.0 x 10^20 cm^-2
Photon index: 1.74 (+0.24, -0.23)
If the light curve continues to decay with a power-law decay index of 2.7,
the count rate at T+24 hours will be 0.015 count s^-1, corresponding to an
observed (unabsorbed) 0.3-10 keV flux of 5.7 x 10^-13 (6.0 x 10^-13) erg
cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
- GCN Circular #39650
Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Stéphane Basa (UAR Pytheas), Benjamin Schneider (LAM), Alan M. Watson (UNAM), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM)
We observed the field of GRB 250309B (Preis et al., GCN 39629) using the OGSE engineering camera on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-10T07:34:55 to 2025-03-10T08:46:13 UTC (23h 56min after the trigger) and obtained 3000 seconds of exposure in the r filter. The data were analyzed in STDWeb/STDPipe (Karpov 2021), 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.
In our stacked image, after the subtraction, we clearly detect a source at the position of the optical candidate AT2025dws (reported by Stein et al., GCN 39639, Pérez-Fournon et al. GCN 39643, Moskvitin et al. GCN 39645, Perley et al. GCN 39646) with magnitude:
r = 20.76 +/- 0.10
Further observations are planned to monitor the evolution of the transient.
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 #39652
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The long-duration GRB 250309B
(Fermi-GBM BALROG localization: Preis and Greiner, GCN 39629;
Fermi-GBM detection: The Fermi GBM team, GCN 39635;
McDermott et al., GCN 39642;
GECAM-B detection: Wang et al., GCN 39648)
was detected by Fermi (GBM trigger 763198715), Konus-Wind,
Mars-Odyssey (HEND), and GECAM-B at about 27510 s UT (07:38:30).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
-------------------------------
RA(2000), deg Dec(2000), deg
------------------------------
Center:
208.8101 -12.9141
Corners:
204.1541 -23.3442
204.3621 -23.0319
213.4312 -2.9483
213.5345 -2.5970
-------------------------------
The error box area is 1.3 sq. deg, and its maximum
dimension is 23 deg (the minimum one is 3.5 arcmin).
The Sun distance was 135 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of,
the final Fermi-GBM (GCN 39635) and BALROG (GCN 39629) localizations.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250309_T27513/IPN/
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.
The localization of IceCube-250309A (IceCube Collaboration, GCN 39631) is inconsistent with the IPN localization. The optical transient ZTF25aaitvjt/AT2025dws (Stein et al., GCN 39639) is inside the IPN box, which further strengthen the interpretation of transient as the burst afterglow.
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
- GCN Circular #39654
Min-Su Shin (Korea Astronomy and Space Science Institute; KASI),
Jae-Woo Kim (KASI), and Seo-Won Chang (Seoul National University)
report on behalf of the KMTNet neutrino ToO program:
We observed the area corresponding to the neutrino event IceCube-250309A
with the KMTNet-CTIO for the initial coordinates of Zegarelli et. al, GCN 39631.
The KMTNet-CTIO observation started at 2025-03-09 09:44 (UTC), and
we acquired I-band images for four pointings covering the entire
90% uncertainty area for the alert. The source AT2025dws
(Stein et al., GCN 39639, Pérez-Fournon et al. GCN 39643,
Moskvitin et al. GCN 39645, Perley et al. GCN 39646)
is clearly found in the images with the following photometric measurements:
MJD mag err
60743.40574 17.88 0.02
60743.40723 17.87 0.02
We thank the KMTNet operators for their support.
- GCN Circular #39655
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 250309B ( Fermi-GBM BALROG localization:
Preis and Greiner, GCN 39629; Fermi-GBM detection:
The Fermi GBM team, GCN 39635; McDermott et al., GCN 39642;
GECAM-B detection: Wang et al., GCN 39648;
IPN triangulation: Kozyrev et al., GCN 39652)
triggered Konus-Wind (KW) at T0=27513.791 s UT (07:38:33.791).
The burst light curve shows a multi-peaked structure
which starts at ~T0-0.5 s and has a total duration of ~8 s.
The emission is seen up to ~1 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250309_T27513/
As observed by Konus-Wind, the burst had
a fluence of (5.79 ± 0.48)x10^-6 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 1.024 s,
of (4.35 ± 0.43)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.03(-0.20,+0.22) and Ep = 106(-7,+8) keV (chi2 = 80/79 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -3.1 (chi2 = 79/78 dof).
Assuming the redshift z=1.898 ( Malesani et al., GCN 39647)
of ZTF25aaitvjt/AT 2025dws, the candidate counterpart to GRB 250309B
(Stein et al., GCN 39639), 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 (5.3 ± 0.4)x10^52 erg,
the isotropic peak luminosity L_iso to (1.2 ± 0.12)x10^53 erg/s, and
the rest-frame peak spectral energy Ep,z to (306 ± 21) keV.
With the obtained estimates, GRB 250309B is consistent with
68% prediction band of the 'Amati' relation and
90% prediction band of the 'Yonetoku' relation
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/GRB250309_T27513/GRB250309B_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
- GCN Circular #39658
A. S. Moskvitin, O. I. Spiridonova (SAO RAS), A. S. Pozanenko (IKI),
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg),
Yu. V. Sotnikova (SAO RAS) report on behalf of a larger collaboration.
We observed the field of GRB 250309B / AT2025dws (Preis and Greiner,
GCN 39629; Fermi GBM team, GCN 39635; McDermott et al., GCN 39642;
Wang et al., GCN 39648; Page and Evans, GCN 39649; Kozyrev et al.,
GCN 39652; Frederiks et al., GCN 39655; Scotton, GCN 39657)
with Zeiss-1000 1-m telescope of SAO RAS, equipped
with the CCD-photometer. We obtained 19 x 300 sec. images in Rc band
on March 10, 21:37:13 -- 23:23:40 UT (t_mid - T0 = 1.6194 days).
The optical candidate ZTF25aaitvjt / AT2025dws (Stein et al.,
GCN 39639; Pérez-Fournon et al., GCN 39643; Stein and Ahumada,
GCN 39644; Moskvitin et al., GCN 39645; Perley et al., GCN 39646;
Malesani et al., GCN 39647; Ducoin et al., GCN 39650; Shin et al,
GCN 39654) is clearly detected in the stacked image
with the brightness of R = 20.65 +/- 0.13.
We do not performed host galaxy subtraction.
The photometry is based on nearby stars from the USNO-B1.0 catalog
(R2 magnitudes) and has not been corrected for the Galactic extinction.
- GCN Circular #39661
Z. M. Wang, A. Li (BNU), Y. F. Liang (PMO), L. P. Xin, Y. L. Qiu, H. L. Li, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM team:
The SVOM/VT conducted a ToO follow-up observation of ZTF25aaitvjt / AT2025dws (Stein et al., GCN 39639) which is considered as the optical candidate of Fermi GRB 250309B (Preis & Greiner, GCN 39629; McDermott et al., GCN 39635; McDermott et al., GCN circ. 39642) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously,
The optical candidate ZTF25aaitvjt / AT2025dws (Stein et al., GCN 39639; Pérez-Fournon et al., GCN 39643; Stein and Ahumada, GCN 39644; Moskvitin et al., GCN 39645; Perley et al., GCN 39646; Malesani et al., GCN 39647; Ducoin et al., GCN 39650; Shin et al, GCN 39654) is clearly detected in images.
The brightness in AB manigutude was estimated to be 20.20+/0.04 mag in VT_R, and 20.72+/-0.05 mag in VT_B stacked images, with an exposure time of 46*60 seconds, at the mid time of 0.974 days post the burst.
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 #39670
GRB 250309B: PRIME near-infrared detection
O. Guiffreda (UMD), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC)
Following the Fermi GBM trigger (GCN 39635), we observed the transient field in J and H filters with PRIME ~1.5 days after the Fermi detection.
At the position of the optical counterpart AT2025dws (Stein et al., GCN 39639), we detect an uncatalogued source in both J-band and H-band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we estimate J~20 AB mag.
Further observations are planned.
PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024).
We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
- GCN Circular #39679
TITLE: GCN CIRCULAR
NUMBER: 39679
SUBJECT: GRB 230509B: 1.3m DFOT Optical observations
DATE: 25/03/12 06:18:47 GMT
FROM: Amit Kumar Ror at ARIES
Amit K. Ror, Anshika Gupta, Pranshu, Shashi B. Pandey, Kuntal Mishra
(ARIES) report:
We observed the field of GRB 230509B detected by the Swift and Fermi (Evans
et al. 2025, GCN 39633; Fermi GBM team, GCN 39635, 39642) with the 1.3m
Devasthal Fast Optical Telescope (DFOT), located at the Devasthal
Observatory of the Aryabhatta Research Institute of Observational Sciences
(ARIES), India. The observations were started on 2025-03-10 at 20:25:19 UT,
i.e., ~ 1.53 days after the Ferm-GBM trigger. We have taken multiple frames
with an exposure time of 300s in the R filter. We stacked the images after
the alignment. We detected an optical afterglow reported by Stein et al.
2025 (GCN 39639) in our stacked image. We obtain the following preliminary
magnitude in the stacked image:
Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude
=========================================================
2025-03-10 20:25:19 ~1.53 R 300s*24 20.36 +/- 0.10
Our detection is consistent with Stein et al. 2025 (GCN 39639); Lipunov et
al. 2025 (GCN 39641); Pérez-Fournon et al. 2025 (GCN 39643); Stein et al.
2025 (GCN 39644); Moskvitin et al. 2025 (GCN 39645); Perley et al. 2025
(GCN 39646); Malesani et al. 2025 (GCN 39647); Ducoin et al. 2025 (GCN
39650); Shin et al. 2025 (GCN 39654); Moskvitin et al. 2025 (GCN 39658);
Wang et al. 2025 (GCN 39661) and Guiffreda et al. 2025 (GCN 39670).
The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue. This circular may be cited.
- GCN Circular #39687
S.Q. Jiang (NAOC), S.H. Wang (THU), J. An, X. Liu, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu (HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the optical counterpart AT 2025dws (Stein et al., GCN 39639, 39644; Pérez-Fournon et al., GCN 39643; Moskvitin et al., GCN 39645, 39658; Perley et al., GCN 39646; Malesani et al., GCN 39647; Page and Evans, GCN 39649; Ducoin et al., GCN 39650; Shin et al., GCN 39654; Wang et al., GCN 39661; Guiffreda et al., GCN 39670) of GRB 250309B (GBM team, GCN 39635; Preis and Greiner, GCN 39629; McDermott et al., GCN 39642; Wang et al., GCN 39648; Kozyrev et al., GCN 39652; Frederiks et al., GCN 39655), using the 0.33 m diameter telescope RC-10 located at Daochen, Sichuan, China. Observations started at 18:53:25.836 on 2025-03-09, i.e., 11.247 hrs after the Fermi/GBM trigger time, a series of 600 s frames in sloan r-band were obtained.
The optical transient was detected in our stacked image with mag_r= 19.7 +/- 0.2 at a median time of 12.260 hrs after the trigger time, calibrated with the nearby Pan-STARRS field and not corrected for Galactic extinction.
- GCN Circular #39699
Tao An, Yuanqi Liu (SHAO, China), Jinjun Geng, Xuefeng Wu (PMO, China), Ailing Wang (IHEP, China) report on behalf of a large collaboration.
We report the detection of a radio counterpart to GRB 250309B-AT2025dws (GCN 39629, 39637, 39639) with the Australia Telescope Compact Array (ATCA).
We conducted ATCA observations at 5.5 and 9 GHz on UT14:00-20:59 March 10, 2025 (~T0+1 day) targeting both the optical counterpart position of GRB 250309B-AT2025dws (GCN 39639) and a reported possible neutrino event position XRT1 (GCN 39631, 39633). No significant radio emission was detected above our 5σ detection threshold at either position, with a 1σ sensitivity of approximately 30 μJy/beam.
Subsequent ATCA observations on UT14:00-20:59 March 12, 2025 (~T0+3 days) revealed a clear detection of radio emission at the position of GRB 250309B-AT2025dws with 0.322 ± 0.009 mJy at 5.5 GHz.
The detection of this relatively bright radio afterglow (comparable to some of the brighter GRB radio afterglows) provides an excellent opportunity for continued monitoring of the spectral and temporal evolution of the afterglow emission. We plan to continue monitoring this source with ATCA.
We thank the Jamie Stevens for rapid response in scheduling these observations.
We thank the CSIRO Space and Astronomy staff for supporting these observations. The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
- GCN Circular #39705
O. Guiffreda (UMD), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC)
Following up the initial PRIME detection (GCN 39670), the transient field was observed a second time ~3.5 days after the initial Fermi GBM trigger (GCN 39635).
At the position of the optical counterpart AT2025dws (Stein et al., GCN 39639), we no longer detect any uncatalogued sources in either J-band or H-band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive limiting magnitudes of J <21.0 AB mag and H <20.9 AB mag, not corrected for galactic extinction.
PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024).
We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.
- GCN Circular #39773
J. K. Leung (U. Toronto/HUJI), G. E. Anderson (Curtin University), A. J. van der Horst (GWU), L. Rhodes (TSI/McGill), Maria Drout (U. Toronto), Andrew Hughes (U. Oxford) report on behalf of a larger collaboration:
We report a second epoch of Australia Telescope Compact Array (ATCA) radio observations centred in the direction of the candidate optical counterpart AT2025dws (Stein et al., GCN 29639; Pérez-Fournon et al., GCN 29643; Alexander et al., GCN39645; Stein et al, GCN 39644; Perley et al. GCN 39646; Wang et al., GCN 39648; Ducoin et al., GCN 39650; Shin et al., GCN 39654) to GRB 250309B (Preis and Greiner, GCN 39629; McDermott et al., GCN 39642; Page and Evans, GCN 39649; Kozyrev et al., GCN 29652; and Frederiks et al., GCN 39655). These observations follow an earlier detection of the radio counterpart by the ATCA (An et al., GCN 39699).
The observations were taken at a mean epoch of UT12:57 on 2025-03-13T12:57 at central frequencies 5.5, 9, and 16.7 GHz. In our preliminary analysis, we detect a clear radio source at the position of the candidate optical and radio counterparts in both the 5.5 and 9 GHz images (0.24+/-0.04 mJy and 0.30+/-0.03 mJy, respectively) and attain a 5-sigma non-detection limit of <0.45 mJy/beam at 16.7 GHz.
We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.
- GCN Circular #39791
T. Ahumada (Caltech), E. C. Bellm (UW), L. Yan, T. du Laz, M. M. Kasliwal (Caltech), Q. Y. Wu, S. Q. Jiang (NAOC, CAS), J. H. Wu (GZHU), Y. Liu, C. Jin, W. Yuan (NAOC, CAS)
report on behalf of the Zwicky Transient Facility Partnership and Einstein Probe Team
Starting Feb 27, 2025, the Zwicky Transient Facility (ZTF) partnership is collaborating with the Einstein Probe (EP) team to map multiple EP pointings concurrently every night with ZTF. By cross-matching ZTF alerts with EP alerts, we report our first proof-of-concept cross-match.
On March 9, 2025, Fermi-GBM detected GRB 250309B at 07:38:30 UTC (Preis and Greiner, GCN 39629; Fermi GBM team, GCN 39635; McDermott et al., GCN 39642). As part of the regular schedule, EP was set to cover the region, with ZTF scheduled to shadow EP. Both EP and ZTF subsequently observed the afterglow, ZTF25aaitvjt/AT2025dws.
The Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission began observations from 2025-03-09T10:38:05(UTC) (~T0+3h) with an exposure time of 4.8 ks. The WXT position of the source is R.A. = 210.800 deg, DEC = -8.500 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic), which is consistent with the optical counterpart AT2025dws (Stein et al., GCN 39639) and the X-ray counterpart (Page and Evans, GCN 39649). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 3.0 x 10^20 cm^-2 and a photon index of 1.8 (-1.2/+1.6). The derived average unabsorbed 0.5-4 keV flux is 9.2 (-5.3/+10.8) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
In this particular example, we clarify that ZTF was double-triggered to observe this field - once by the joint ZTF+EP experiment and once by the IceCube neutrino experiment. Both experiments recovered AT2025dws. We observed a fading rate of 2.5 mag / hour in the r-band. This source was promptly reported by ZTF in Stein et al. GCN 39639.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC.
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