February 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 37456] LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39444 SUBJECT: LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart DATE: 25/02/24 04:53:21 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), William H. Lee (UNAM), Océlotl López (UNAM), Camila Angulo Valdez (UNAM), Rosa L. Becerra (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), and Margarita Pereyra (UNAM), and Eleonora Troja (U Roma) report: We imaged the field of the Swift/BAT-GUANO trigger possibly associated with LIGO/Virgo/KAGRA S250223dk (GCN Circ. 39443) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico (http://ddoti.astroscu.unam.mx) We observed the whole BAT error region from 2025-02-24 03:56 UTC to 04:24 UTC (15.9 to 16.4 hours after the GW event) at extremely high airmass. We obtained a total exposure of 24 minutes. Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues, we detect no uncatalogued sources within the observed BAT error region to a 5-sigma AB limiting magnitude of w > 20.0. Our photometry is in the AB system and is not corrected for Galactic extinction. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37455] LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39443 SUBJECT: LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger DATE: 25/02/24 03:12:15 GMT FROM: minghuidu1993(a)gmail.com The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration along with the Swift/BAT-GUANO team report: We identified the compact binary merger candidate S250223dk during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at T0 = 2025-02-23 12:01:15.360 UTC (GPS time: 1424347293.360). The candidate was found by the GstLAL [1] analysis pipeline. S250223dk is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.4e-05 Hz, or about one in 19 hours. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250223dk The classification of the GW signal, in order of descending probability, is Terrestrial (92%), BBH (8%), NSBH (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. Five GW-only sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN notice about a minute after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 5 minutes after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 12 hours after the candidate event time. * bayestar.multiorder.fits,3, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 12 hours after the candidate event time. * bayestar.multiorder.fits,4, an initial localization generated by BAYESTAR [3], distributed via GCN notice about 13 hours after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,4. For the bayestar.multiorder.fits,4 sky map, the 90% credible region is 3203 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 6033 +/- 1778 Mpc (a posteriori mean +/- standard deviation). The LVK notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; [4]). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-45,+45] seconds around the time of the GW alert. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES [5], performed on the temporal window [T0-20 s, T0+20 s], detects a burst candidate with a sqrt(TS) of 8.0 in a 8.192 s analysis time bin, starting at T0 - 10.240 s The 90% credible area is 2666 deg2 and the 50% credible area is <1 deg2. The integrated probability inside the coded field of view is 83%. The joint LVK-Swift/BAT localization probability map peaks at RA = 85.341 deg, Dec = -47.554 deg. A circle with a radius of 5 arcmin around this position contains 52% of the integrated joint probability. Swift has already initiated TOO followup of this position with XRT and UVOT. Results will be reported in future circulars. We encourage followup by other, more sensitive, facilities. A plot of the Swift/BAT probability skymap can be viewed here: https://guano.swift.psu.edu/trigger_report?id=762004910/#:~:text=Probabilit… The Swift/BAT probability skymap file can be downloaded from the link here: https://guano.swift.psu.edu/files/762004910/0_n_PROBMAP Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=762004910 A search performed by the RAVEN pipeline [6] found a temporal coincidence between S250223dk and a sub-threshold Swift/BAT trigger with ID 762004910. The GRB trigger time is 10.24 seconds before the GW candidate event. The estimated joint false alarm rate for the coincidence using just timing info is 1.9e-07 Hz, or about one in a month. The GRB candidate was found during a joint targeted search between the LIGO/Virgo/KAGRA collaboration and Swift/BAT-GUANO, and has a false alarm rate of 7.4e-05 Hz, or about one in 3 hours.Combined sky maps are also available: * combined-ext.multiorder.fits,0, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,1, an initial localization, distributed via GCN notice about 12 hours after the candidate event time. * combined-ext.multiorder.fits,2, an initial localization, distributed via GCN notice about 13 hours after the candidate event time. For the combined-ext.multiorder.fits,2 sky map, the 90% credible region is <1 deg2. The joint localization is dominated by the Swift/BAT-GUANO candidate. Considering the overlap of the individual sky maps, the estimated joint false alarm rate for the spatial and temporal coincidence is 5.1e-09 Hz, or about one in 6 years. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 [4] Tohuvavohu et al. ApJ, 900, 1 (2020) [5] DeLaunay & Tohuvavohu, ApJ, 941, 169 (2022) [6] Urban, A. L. 2016, Ph.D. Thesis https://dc.uwm.edu/etd/1218 and Piotrzkowski, B. J. 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060 View this GCN Circular online at https://gcn.nasa.gov/circulars/39443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37454] The EP-WXT trigger 01709131882 is likely a flaring star
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39442 SUBJECT: The EP-WXT trigger 01709131882 is likely a flaring star DATE: 25/02/24 02:20:45 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), H. Z. Wu (HUST), H. He, S.-E. Xu (WHU), W. Yuan (NAOC, CAS) report on behalf of the Einstein Probe team: The EP-WXT trigger (ID: 01709131882) on 2025-02-23 21:47:14 (UTC) is likely a stellar flare associated with a BY Dra Variable V1217 Cen. The estimated flux of the flare is around 1.0 x 10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 5.1 x 10^31 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/39442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37453] EP250223a: OASDG optical observations
by GCN Circulars 24 Feb '25

24 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39441 SUBJECT: EP250223a: OASDG optical observations DATE: 25/02/24 00:06:24 GMT FROM: luca.izzo(a)inaf.it L. Izzo (INAF-OACn and DARK/NBI), and D. B. Malesani (DAWN/NBI and Radboud Univ.) report: We observed the field of EP250223a (Lian et al., GCN #39429) using the 0.5-m T1 telescope of the Osservatorio Astronomico S. Di Giacomo, located in Agerola, Italy. Our observations started on 2025 February 23 at 18:15 UT, approximately 3.19 hours after the GRB trigger. We acquired a series of 6x300 s images in the Rc filter. In the stacked image, we detect a faint source consistent with the X-ray afterglow reported by EP/FXT (Lian et al., GCN #39429), and by Swift-XRT (Kennea et al., GCN #39437), and with the optical counterpart reported by several other telescopes (Hauptmann et al., GCN #39436; Levan et al., GCN #39438; Wu et al., GCN #39439; Perez-Fournon et al., GCN #39440). We measure a preliminary magnitude of Rc = 19.6 +/- 0.2 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/39441. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37452] EP250223a: LCO detection of the afterglow
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39440 SUBJECT: EP250223a: LCO detection of the afterglow DATE: 25/02/23 23:49:41 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin, D. Aguado, J.A. Acosta-Pulido, A. López-Oramas, D. Nespral (IAC and ULL), F. Acero (CEA Saclay and IAC), N.C. Sun (UCAS), W. Li, Y. Wang, Z. Niu (NAOC), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL) We observed the location of EP250223a (Lian et al., GCN circ. 39429), detected also by Swift XRT (Kennea et al., GCN circ. 39437), with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). We obtained first a 600-sec exposure in the SDSS r' filter, that started at 2025-02-23 19:47:12 UT, e.g. 4.71 hr after the EP trigger, followed by 300-sec exposures in the SDSS i' and g' filters. The optical afterglow candidate reported by Hauptmann et al. (GCN circ. 39436) is clearly detected in the three images. We measured the following magnitudes, calibrated against PanSTARRS DR2 stars and not corrected for Galactic extinction: Date | UT start | T (mid) - T0 (hours) | mag | error | filter | ---------------------------------------------------------------------- 2025-02-23 19:47:12 4.79 19.73 0.03 r' 2025-02-23 21:38:41 6.61 19.74 0.06 i' 2025-02-23 21:42:28 6.67 20.77 0.10 g' A redshift of z = 2.756 has been reported by Levan et al. (GCN circ. 39438). This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/39440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37451] EP250223a: early optical detection by BOOTES-4
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39439 SUBJECT: EP250223a: early optical detection by BOOTES-4 DATE: 25/02/23 23:38:26 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S.-Y. Wu, I. Perez-Garcia, E. Fernandez-Garcia, M. D. Caballero-Garcia, G. Garcia-Segura, S. Guziy, R. Sanchez-Ramirez and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar (Univ. de Malaga), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXU), and D. R. Xiong, J. M. Bai, Y. F. Fan, C. J. Wang, Y. X. Xin, X. H. Zhao, J. R. Mao, B. K. Lun, K. Ye (Yunnan Observatories/CAS, Kunming) on behalf of a larger collaboration, report: Following the detection of EP250223a by EP/WXT (Lian et al. GCNC 39429), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this burst starting on Feb. 23, 15:16:38 UT (~12 min after trigger). At the position of the EP/FXT X-ray source (also recorded by Swift/XRT, Kennea et al. GCNC 39437), an optical counterpart is detected, for which we measure a magnitude of 18.4 +/- 0.1 (60s, clear filter, comparable with Gmag of Gaia DR3), which also consistent with the object reported by NOT at a later stage (Hauptmann et al. GCNC 39426, Levan et al. GCNC 39438). Further analysis of the additional images is ongoing. We thank the staff at Lijiang observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/39439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37450] EP250223a: NOT redshift z = 2.756
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39438 SUBJECT: EP250223a: NOT redshift z = 2.756 DATE: 25/02/23 23:17:57 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> Andrew J. Levan (Radboud and Warwick), Luca Izzo (INAF, Naples and DARK/NBI), Daniele B. Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud), Benjamin N. Hauptmann (NOT and DTU Space), Yfke Bethlehem (Kapteyn Astronomical Institute, Groningen, and ING), and Dong Xu (NAOC), report on behalf of a larger collaboration: Further to the identification of the likely optical counterpart (Hauptmann et al., GCN 39436) of EP 250223a (Lian et al., GCN 39429), we obtained spectroscopic observations with the Nordic Optical Telescope, beginning at 21:18 UT. A total of 4x900 s observations were obtained using grism #4. The observations reveal a strong continuum with a pronounced suppression at ~4550 AA, which we interpret as arising from damped Lyman-alpha absorption. In addition we detect a number of narrow metal lines, among which Fe II, Al II, C II, O I, Si II, which allow us to fix the redshift to z = 2.756. The spectral shape and redshift, as well as the detection of an X-ray counterpart at a consistent position with Swift (Kennea et al., GCN 39437), secure the source as the counterpart of EP250223a. View this GCN Circular online at https://gcn.nasa.gov/circulars/39438. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37449] EP250223a: Swift/XRT localization
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39437 SUBJECT: EP250223a: Swift/XRT localization DATE: 25/02/23 21:48:18 GMT FROM: Jamie Kennea at Penn State <jak51(a)psu.edu> J. A. Kennea, C. Gronwall (PSU) and P. A. Evans (Leicester) report on behalf of the Swift Team: At 16:36:15UT Swift began a target-of-opportunity observation of the transient EP250223a (GCN #39429), approximately 1.6 hours after the Einstein Probe trigger. We detect an an uncatalogued point source above the RASS limit at the following location: RA/Dec(J2000) = 98.27464, -22.4449, which is equivalent to: RA(J2000) = 06h 33m 05.91s, Dec(J2000) = -22° 26′ 41.8″, with an estimated uncertainty radius of 3.8 arc-seconds (90% confidence). This position lies 8.5 arc-seconds from the EP WXT position reported in GCN #39429. The peak flux during the XRT observation was 5.4 (±1.0) × 10^-12 erg cm^-2 s^-1 (0.3 - 10 keV). View this GCN Circular online at https://gcn.nasa.gov/circulars/39437. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37448] EP250223a: NOT optical afterglow candidate
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39436 SUBJECT: EP250223a: NOT optical afterglow candidate DATE: 25/02/23 21:46:49 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> Benjamin N. Hauptmann (NOT and DTU Space), Yfke Bethlehem (Kapteyn Astronomical Institute, Groningen, and ING), Andrew J. Levan (Radboud and Warwick), Daniele B. Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud) and Dong Xu (NAOC), report on behalf of a larger collaboration: We observed the location of EP250223a (Lian et al. GCN 39429) with the Nordic Optical Telescope (NOT). Observations in the r-band began at 20:36 UT, approximately 5.53 hr after the trigger time. In the first 300 s exposure we clearly detect a new point source, not visible in archival DSS and Pan-STARRS imaging of this field, at a location of RA(J2000) = 06:33:05.723 DEC(J2000) = -22:26:40.32 These coordinates are within the FXT X-ray uncertainty region, making this source the likely afterglow of EP250223a. The source has an AB magnitude r = 19.7, calibrated against nearby Pan-STARRS objects. Further observations are in progress. View this GCN Circular online at https://gcn.nasa.gov/circulars/39436. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 37447] GRB 250223B: Fermi GBM Final Localization
by GCN Circulars 23 Feb '25

23 Feb '25

TITLE: GCN CIRCULAR NUMBER: 39435 SUBJECT: GRB 250223B: Fermi GBM Final Localization DATE: 25/02/23 18:43:58 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely SHORT GRB "At 10:19:23.76 UT on 23 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250223B (trigger 761998768/250223430). This trigger was initially classified as Unreliable Location by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 3.54, Dec = +43.49(J2000 degrees, equivalent to J2000 00h 14m, +43d 29'), with a statistical uncertainty of 13 degrees. The angle from the Fermi LAT boresight is 56 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223430/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223430/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250223430/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/39435. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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