GRB250309B

This page lists all entries on GRB250309B in GRBweb

Summary Fermi GBM IPN GCN 39629 GCN 39631 GCN 39634 GCN 39635 GCN 39637 GCN 39639 GCN 39641 GCN 39642 GCN 39643 GCN 39644 GCN 39645 GCN 39646 GCN 39647 GCN 39648 GCN 39649 GCN 39652 GCN 39654 GCN 39655 GCN 39657 GCN 39658 GCN 39661 GCN 39670 GCN 39687 GCN 39705 GCN 39773 GCN 39791

Summary table
Variable Value Source
GRB_name_Fermi GRB250309318
T0 7:38:30 UTC GCN_circulars,Fermi GBM Det
ra 210.8000° IPN
decl -8.5000° IPN
pos_error 1.67e-03° IPN
T90 6.4 s Fermi_GBM
T90_error 0.389 s Fermi_GBM
T90_start 7:38:31.303 UTC Fermi_GBM
fluence 7.59e-06 erg/cm² Fermi_GBM
fluence_error 3.08e-08 erg/cm² Fermi_GBM
redshift 1.8980
T100 7.703 s
GBM_located False
mjd 60743.318402777775 GCN_circulars,Fermi GBM Det
Fermi GBM table
GRB_name_Fermi GRB250309318
trigger_name bn250309318
ra 210.5800°
decl -10.8600°
pos_error 4.55e+00°
datum 2025-03-09
t_trigger 7:38:30.663 UTC
T90 6.4 s
T90_error 0.389 s
T90_start 7:38:31.303 UTC
fluence 7.59e-06 erg/cm²
fluence_error 3.08e-08 erg/cm²
flux_1024 2.30e+01 erg/cm²/s
flux_1024_error 4.49e-01 erg/cm²/s
flux_1024_time 3.84e+00 erg/cm²/s
flux_64 3.30e+01 erg/cm²/s
flux_64_error 2.06e+00 erg/cm²/s
IPN table
GRB_name GRB250309B
ra 210.8000°
decl -8.5000°
pos_error 1.67e-03°
GCN 39629 table
GRB_name GRB250309B
GCN_number 39629
Detection_method Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39629 SUBJECT: GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318) DATE: 25/03/09 08:04:59 GMT FROM: Jochen Greiner at MPE 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 39631 table
GRB_name GRB250309B
GCN_number 39631
Detection_method Other
ra 211.0700°
decl -10.7300°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39631 SUBJECT: IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/03/09 11:48:28 GMT FROM: A. Zegarelli at Ruhr University Bochum The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-03-09 at 07:36:04.75 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD alert stream. The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.1759 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/140626_1288692.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2025-03-09 Time: 07:36:04.75 UT RA: 211.07 (+0.31 -0.30 deg 90% PSF containment) J2000 Dec: -10.73 (+0.26 -0.30 deg 90% PSF containment) J2000 The inferred neutrino energy of this alert is ~4 PeV, making it the fourth-highest energy known detection by IceCube over the past decade. The alert coincides with the Fermi GRB250309B (Fermi-GBM trigger 763198715 at 07:38:30.66 on 09 March 2025; https://gcn.gsfc.nasa.gov/other/763198715.fermi) with a time delay of 145.91 seconds relative to the GRB trigger time. The angular distance to the most updated reconstruction released by the GBM team, which has a 1σ statistical error of 1.60 deg, is 0.77 degrees. An alternative algorithm results in a shifted direction (https://gcn.nasa.gov/circulars/39629) with an angular distance from the best fit neutrino direction of 3.18 degrees and has a 1σ statistical error of 1.3 degree and a systematic error of 1 degree. We strongly encourage follow-up observations of the neutrino region of interest and the uncertainty region of GRB250309B. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu
GCN 39634 table
GRB_name GRB250309B
GCN_number 39634
Detection_method Swift Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39634 SUBJECT: Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A! DATE: 25/03/09 13:20:55 GMT FROM: P.A. Evans at U. Leicester 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 39635 table
GRB_name GRB250309B
GCN_number 39635
Detection_method Fermi GBM Other
ra 210.5800°
decl -10.8600°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39635 SUBJECT: GRB 250309B: Fermi GBM Final Localization DATE: 25/03/09 15:47:40 GMT FROM: Padraig McDermott at University College Dublin 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 39637 table
GRB_name GRB250309B
GCN_number 39637
Detection_method Fermi LAT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39637 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-250309A DATE: 25/03/09 17:38:48 GMT FROM: Sara Buson at DESY, Univ. of Wurzburg S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), N. Di Lalla (Stanford Univ.), M. Arimoto (Kanazawa University), R. Gupta (NASA GSFC) and A. Holzmann Airasca (UniTrento and INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250309A neutrino event (GCN 39631) with all-sky survey data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-03-09 07:36:04.75 UTC (T0) with J2000 position RA = 211.07 (+0.31, -0.30) deg, Decl. = -10.73 (+0.26, -0.30) deg 90% PSF containment. No cataloged gamma-ray sources are found within the 90% IC250309A localization error (The Fourth Fermi-LAT catalog, 4FGL-DR4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250309A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is <2.4e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), <6.8e-09 (<9.3 e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. The IceCube event IC250309A occurred near the GRB 250309B (GCN 39635), with a detection time 145.91 seconds after the Fermi-GBM trigger and a positional separation of 0.50 deg. An analysis of the LAT data conducted over a ±1000-second window centered on T0, shows no significant excess emission, neither associated with IC250309A nor GRB 250309B. The >100 MeV flux upper limit (95% confidence) at IC250309A best-fit position for this time interval is < 5.3 e-6 ph cm^-2 s^-1. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, the Fermi-LAT contact person is S. Buson (sara.buson at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN 39639 table
GRB_name GRB250309B
GCN_number 39639
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39639 SUBJECT: GRB250309B: One candidate counterpart from the Zwicky Transient Facility DATE: 25/03/09 18:25:09 GMT FROM: Robert David Stein at JSI 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 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 39641 table
GRB_name GRB250309B
GCN_number 39641
Detection_method Fermi GBM Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 39641 SUBJECT: Fermi GRB 250309B: Global MASTER-Net observations report DATE: 25/03/09 22:31:38 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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 39642 table
GRB_name GRB250309B
GCN_number 39642
Detection_method Fermi GBM Det
t_trigger 7:38:30.660 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 39642 SUBJECT: GRB 250309B: Fermi GBM Observation DATE: 25/03/10 00:47:24 GMT FROM: Lorenzo Scotton at UAH 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 39643 table
GRB_name GRB250309B
GCN_number 39643
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39643 SUBJECT: AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading DATE: 25/03/10 01:28:25 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias 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 39644 table
GRB_name GRB250309B
GCN_number 39644
Detection_method Swift-UVOT Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 39644 SUBJECT: GRB 250309B / AT2025dws: Swift-UVOT detection DATE: 25/03/10 02:12:00 GMT FROM: Robert David Stein at JSI 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 39645 table
GRB_name GRB250309B
GCN_number 39645
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39645 SUBJECT: GRB 250309B / AT2025dws: SAO RAS optical observations DATE: 25/03/10 02:45:01 GMT FROM: Moskvitin Alexander at SAO RAS 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 39646 table
GRB_name GRB250309B
GCN_number 39646
Detection_method correction
Circular_text TITLE: GCN CIRCULAR NUMBER: 39646 SUBJECT: Liverpool Telecope observations of AT 2025dws / GRB 250309B DATE: 25/03/10 03:52:06 GMT FROM: Daniel Perley at Liverpool JMU 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 39647 table
GRB_name GRB250309B
GCN_number 39647
Detection_method Fermi GBM Other
redshift 1.7660
Circular_text TITLE: GCN CIRCULAR NUMBER: 39647 SUBJECT: GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898 DATE: 25/03/10 05:47:31 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS 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 39648 table
GRB_name GRB250309B
GCN_number 39648
Detection_method Optical
ra 211.0700°
decl -10.7300°
redshift 1.8980
Circular_text TITLE: GCN CIRCULAR NUMBER: 39648 SUBJECT: GRB 250309B / IceCube-250309A: GECAM-B observations DATE: 25/03/10 07:04:11 GMT FROM: Yue Wang 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 39649 table
GRB_name GRB250309B
GCN_number 39649
Detection_method Swift-XRT Other
ra 210.8013°
decl -8.5030°
redshift 1.8980
Circular_text TITLE: GCN CIRCULAR NUMBER: 39649 SUBJECT: GRB 250309B: Swift-XRT refined Analysis DATE: 25/03/10 07:19:06 GMT FROM: K.L. Page at U Leicester 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 39652 table
GRB_name GRB250309B
GCN_number 39652
Detection_method IPN Triangulation
t_trigger 7:38:30 UTC
ra 208.8101°
decl -12.9141°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39652 SUBJECT: IPN triangulation of GRB 250309B DATE: 25/03/10 13:17:34 GMT FROM: Dmitry Svinkin at Ioffe Institute 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 39654 table
GRB_name GRB250309B
GCN_number 39654
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39654 SUBJECT: GRB 250309B / AT2025dws: KMTNet-CTIO optical observations DATE: 25/03/10 16:46:17 GMT FROM: Min-Su Shin at Korea Astronomy and Space Science Institute 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 39655 table
GRB_name GRB250309B
GCN_number 39655
Detection_method Konus-Wind Det
t_trigger 7:38:33.791 UTC
redshift 1.8980
Circular_text TITLE: GCN CIRCULAR NUMBER: 39655 SUBJECT: Konus-Wind detection of GRB 250309B DATE: 25/03/10 17:17:33 GMT FROM: Dmitry Frederiks at Ioffe Institute 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 39657 table
GRB_name GRB250309B
GCN_number 39657
Detection_method Fermi GBM Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 39657 SUBJECT: IceCube-250309A: Upper limits from Fermi-GBM Observations DATE: 25/03/10 23:19:19 GMT FROM: Lorenzo Scotton at UAH L. Scotton (UAH) reports on behalf of the Fermi-GBM Team: For the IceCube high-energy neutrino candidate event IceCube-250309A (GCN 39631), at the event time Fermi-GBM was observing the reported neutrino location at: RA: 211.07 (+0.31 -0.30 deg 90% PSF containment) J2000 Dec: -10.73 (+0.26 -0.30 deg 90% PSF containment) J2000 Fermi-GBM detected GRB 250309B (GCNs 39635, 39642) around 146s after the time of the neutrino candidate. However, the ZTF and GROWTH collaborations reported the detection of a potential optical counterpart ZTF25aaitvjt | AT2025dws (R. Stein et al, GCN 39639), suggesting that GRB 250309B and IceCube-250309A are unrelated. The IPN triangulation (Kozyrev A. S. et al, GCN 39652) also suggests that GRB 250309B and IceCube-250309A are unrelated. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around the neutrino candidate time. From this search, no significant signal was found related to IceCube-250309A. Using the representative soft, normal, and hard GRB-like templates described in arXiv:2308.13666, we set the following 3 sigma flux upper limits over 10-1000 keV (in units of 10^-7 erg/s/cm^2): Timescale Soft Normal Hard ------------------------------------------- 0.128 s: 1.0 1.8 3.7 1.024 s: 0.35 0.56 1.3 8.192 s: 0.11 0.11 0.24 These results are preliminary.
GCN 39658 table
GRB_name GRB250309B
GCN_number 39658
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39658 SUBJECT: GRB 250309B / AT2025dws: further SAO RAS optical observations DATE: 25/03/10 23:50:28 GMT FROM: Alexander Moskvitin at SAO RAS 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 39661 table
GRB_name GRB250309B
GCN_number 39661
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39661 SUBJECT: GRB 250309B: SVOM/VT optical observation DATE: 25/03/11 06:47:44 GMT FROM: SVOM_group 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 39670 table
GRB_name GRB250309B
GCN_number 39670
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39670 SUBJECT: GRB 250309B: PRIME near-infrared detection DATE: 25/03/11 19:46:22 GMT FROM: O. Guiffreda at UMD 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 39687 table
GRB_name GRB250309B
GCN_number 39687
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39687 SUBJECT: GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation DATE: 25/03/12 17:01:44 GMT FROM: sqjiang at NAOC 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 AT2025dws (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 39705 table
GRB_name GRB250309B
GCN_number 39705
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39705 SUBJECT: GRB 250309B: PRIME near-infrared upper limits in 2nd epoch DATE: 25/03/13 18:41:30 GMT FROM: O. Guiffreda at UMD 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 39773 table
GRB_name GRB250309B
GCN_number 39773
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 39773 SUBJECT: GRB 250309B/AT2025dws: further ATCA observations DATE: 25/03/18 17:15:37 GMT FROM: James Leung at U. Toronto / HUJI 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 39791 table
GRB_name GRB250309B
GCN_number 39791
Detection_method Fermi GBM Det
t_trigger 7:38:30 UTC
decl -8.5000°
Circular_text TITLE: GCN CIRCULAR NUMBER: 39791 SUBJECT: GRB250309B: Proof-of-concept for Joint ZTF+EP Experiment DATE: 25/03/20 20:29:02 GMT FROM: Tomas Ahumada Mena at Caltech 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.