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

[vsnet-grb-info 39813] Fermi-LAT Gamma-ray Observations of IceCube-250905A
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41747 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250905A DATE: 25/09/08 12:34:22 GMT FROM: chiara.bartolini-1(a)unitn.it C.Bartolini (Univ. of Trento & INFN Bari), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250905A neutrino event (GCN 41731) 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 2025-09-05 at 20:08:36.00 UTC (T0) with J2000 position RA = 348.31 (+0.93, -1.09)deg, Decl. = 38.87 (+0.78, -0.86) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250905A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, 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 IC250905A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250905A best-fit position, the >100 MeV flux upper limit (95% confidence) is <3.4e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.7e-08 (<1.5e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is C. Bartolini (chiara.bartolini at ba.infn.it). 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/41747. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39812] GRB 250903A: Swift-XRT afterglow detection
by GCN Circulars 08 Sep '25

08 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41746 SUBJECT: GRB 250903A: Swift-XRT afterglow detection DATE: 25/09/08 09:47:11 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Perri (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 250903A. We searched for X-ray sources in 2.4 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 6.3 ks, obtained between T0+12.7 ks and T0+344.1 ks. Four uncatalogued X-ray sources are detected within the estimated 3-sigma SVOM/ECLAIRs error region (509 arcsec), of which one ("Source 1") is fading with >3-sigma significance and its position is consistent with the optical afterglow (An et al., GCN 41679). Therefore, this is the GRB afterglow. Using 2370 s of PC mode data and 3 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 356.79798, -75.96644 which is equivalent to: RA (J2000): 23h 47m 11.52s Dec(J2000): -75d 57' 59.2" with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.9 (+/-0.9). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.95 (+0.73, -0.21). The best-fitting absorption column is consistent with the Galactic value of 4.7 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 3.4 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4 (+/-10) x 10^20 cm^-2 Galactic foreground: 4.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.95 (+0.73, -0.21) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/03000070. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00034. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41746. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39811] LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
by GCN Circulars 07 Sep '25

07 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41745 SUBJECT: LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate DATE: 25/09/07 18:01:44 GMT FROM: Mayara Hilgert Pacheco at LIGO <mayara.pacheco(a)inpe.br> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250906ca during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-06 12:23:59.099 UTC (GPS time: 1441196657.099). Automated LVK preliminary notices as well as this initial circular were delayed by a day due to the consequences of a power outage in our main computing center for processing low-latency alerts. The candidate was found by the GstLAL [1] and MBTA [2] analysis pipelines. S250906ca is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250906ca The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 6%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin. Two 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 [4], distributed via GCN and SCiMMA notices about a day after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about a day after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 520 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1195 +/- 307 Mpc (a posteriori mean +/- standard deviation). 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. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41745. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39810] IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 07 Sep '25

07 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41744 SUBJECT: IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/09/07 03:51:25 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250905A (https://gcn.nasa.gov/circulars/41731) in a time range of 1000 seconds centered on the alert event time (2025-09-05 20:00:16.000 UTC to 2025-09-05 20:16:56.000 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250905A.We report a p-value of 1.00 in this time window. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250905A is 1.5e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 6e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-09-04 20:08:36.000 UTC to 2025-09-06 20:08:36.000 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90%spatial containment region of IceCube-250905A ranges from 1.7e-01 to 1.8e-01 GeV cm^-2 in a 2 day time window. 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(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/41744. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39809] SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41743 SUBJECT: SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40 DATE: 25/09/06 22:06:11 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. G. Bernardini (INAF, LUPM), M. Gnaoui (IAP), S. Schanne, N. Dagoneau (CEA/Irfu), F. Piron (LUPM), M. Moita (CEA/Irfu) At 2025-09-06T21:18:30 UTC (T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb25090605) from the LMXB 4U 0513-40, which is not present in the trigger onboard catalog. The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The source was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 14.14 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-09-06T21:18:25. The localization of the best alert is R.A., Dec. 78.5709, -40.0751 degrees (J2000) with a 90% confidence level (C.L.) radius of 5.8 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the source. SVOM/MXT began observing the field at 2025-09-06T21:21:09 UTC, 159 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 78.5386, -40.0520 degrees: R.A. (J2000) = 5h14m09.26s Dec. (J2000) = -40d03m07.30s with a 90% C.L. radius of 50 arcseconds (including systematic error). This location is 2 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. The MXT position is consistent with the position of LMXB 4U 0513-40, located at 44 arcseconds. VT began observing the field after the slew. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Maria Grazia Bernardini: maria.bernardini(a)inaf.it. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41743. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39808] EP250905a: Liverpool Telescope i-band upper limits
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41742 SUBJECT: EP250905a: Liverpool Telescope i-band upper limits DATE: 25/09/06 21:23:03 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250905a (Liu et al., GCN 41574) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS i’ filter starting at 2025-09-05 22:06:03 UT, approximately 10.9 hours after the trigger. We performed image subtraction of the stacked images against Pan-STARRS using PSF matching with the help of PSFEx. We do not detect the reported optical counterpart (He et al., GCN 41732, as well as GCN 41734) nor any new objects within the EP/FXT error region of the transient (Cheng et al., GCN 41725; Wang et al., GCN 41737). The 3-sigma limiting magnitude on the stacked images is i > 22.6 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/41742. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39807] LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41741 SUBJECT: LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates DATE: 25/09/06 17:01:35 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh(a)andrew.cmu.edu> Xander J. Hall (CMU), Lei Hu (CMU), Tomás Cabrera (CMU), James Freeburn (UNC), Antonella Palmese (CMU), Brendan O’Connor (CMU), Igor Andreoni (UNC), Keerthi Kunnumkai (CMU), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team report: DECam observed the high probability area of the LVK gravitational wave candidate S250830bp (GCN 41606) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-09-05T04:12:03 UTC (Prop ID: 2025B-485252; PI Soares-Santos) and covered the highest 90% probability region of the event (GCN 41607). We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and then visually inspect the remaining transients. We report on TNS 13 newly identified transients within the LVK 99% CI area. We report the new transient AT 2025xab as a likely supernova and note that none of our nuclear transients show any compelling evolution. A crossmatch with Gaia reveals AT 2025wzv and AT 2025wzw (McMahon et al. GCN 41739) as galactic sources, thus we conclude these are not associated with S250830bp (GCN 41607). We also provide updates on previously announced candidates: We report that AT 2025wpk has shown little to no color evolution or brightness change since its last observation and that AT 2025wpv has shown a slow decline in brightness, dropping ~0.1 mag/day. Finally, we report on AT 2025wpq (GCN 41643), which was observed by SOAR at 2025-09-04T05:32:07 UTC (PI Andreoni). We clearly see broad Halpha and Hbeta securing its classification as a quasar at a z ~ 0.4, thus, we therefore conclude this candidate is far too distant to be associated with S250830bp (GCN 41607). Further analysis is underway. We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41741. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39806] EP250905b: EP-FXT follow-up observation
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41740 SUBJECT: EP250905b: EP-FXT follow-up observation DATE: 25/09/06 15:00:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO,CAS), Q. C. Liu (THU), Y. H. Cheng (SWIFAR,YNU), G. J. Yang, Y. Liu (NAO,CAS) on behalf of the Einstein Probe team: EP-FXT performed a follow-up observation of EP250905b (GCN 41735) at 2025-09-06T05:05:21 (UTC), about 10 hours after the WXT detection, with an exposure time of 3.2 ks. FXT detected a weak uncatalogued source within the WXT error circle at R.A. = 90.7297, DEC = -54.1582 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). Assuming a powerlaw spectrum with the absorption fixed at the Galactic value of 7.64x10^20 cm^-2 and the photon index of 2, the flux in 0.5-10 keV is derived to be approximately 2x10^-14 erg/s/cm2 from the FXT count rate. Further follow-up observations are encouraged to identify the nature of this source. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/41740. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39805] LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41739 SUBJECT: LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates DATE: 25/09/06 13:37:14 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> Isaac McMahon, Sean MacBride, Marcelle Soares-Santos (UZH), Lillian Joseph (Benedictine U.), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team: At 2025-09-06 04:12:03 UTC, the Dark Energy Camera (DECam) conducted the second epoch of observations in response to the LVK alert issued for the candidate gravitational-wave event S250830bp (GCN 41606). We observed the same fields as epoch 1 (GCN 41640) and employed the same analysis. The average limiting magnitudes achieved for epoch 2 were 20.7 in g, 21.4 in r, and 21.3 in i, and 21.1 in z. We report the following seven candidates which have multiple good detections on both days of observation. The candidate reported previously, AT2025wpk, is confirmed to be variable and dimming with good detections in all four bands. The other six candidates are all nuclear-type transients at the centers of previously detected objects. | ID | ATNAME | RA | DEC | MAG_G | MAG_G_ERR | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | |--------- |-------- |------------ |----------- |------- |----------- |------- |----------- |------- |----------- |------- |----------- | | DESGW_3336579 | AT2025wpk | 329.476163 | -77.412560 | 22.43 | 0.24 | 21.58 | 0.19 | 21.30 | 0.13 | 21.05 | 0.09 | | DESGW_3336526 | AT2025wzu | 325.368195 | -77.603585 | N/A | N/A | 21.16 | 0.09 | N/A | N/A | 21.76 | 0.17 | | DESGW_3336621 | AT2025wzw | 323.031060 | -77.708095 | 23.21 | 0.49 | 21.74 | 0.23 | 21.52 | 0.10 | 20.68 | 0.07 | | DESGW_3336660 | AT2025wzv | 328.307211 | -78.281736 | 15.94 | 0.01 | N/A | N/A | N/A | N/A | N/A | N/A | | DESGW_3336681 | AT2025wpr | 321.643320 | -77.755092 | N/A | N/A | 21.07 | 0.08 | 21.72 | 0.14 | 20.98 | 0.10 | | DESGW_3336921 | AT2025wpo | 323.141341 | -78.204743 | 20.22 | 0.06 | 20.27 | 0.06 | 20.32 | 0.06 | 20.38 | 0.06 | | DESGW_3337296 | AT2025wzx | 321.552602 | -78.046756 | N/A | N/A | 21.77 | 0.16 | 20.95 | 0.07 | 21.65 | 0.19 | In particular, AT2025wzv seems to be very luminous and actively brightening in g-band but shows little to no transient activity in other bands. This behavior makes it an interesting transient but unlikely to be associated with S250830bp. We also recover the transient AT2025wpq reported in Hall et al (GCN 41643), although we note that the redshift reported for the host AGN by the Quaia catalog (Storey-Fisher et al 2024) is z = 0.43 +- 0.06, outside of the confidence volume for S250830bp. We do not recover the transient AT2025wpv. Further observations are ongoing and we encourage followup of the event region and the above candidates. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41739. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39804] EP250905a: Liverpool Telescope observations
by GCN Circulars 06 Sep '25

06 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41738 SUBJECT: EP250905a: Liverpool Telescope observations DATE: 25/09/06 13:20:01 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. Habeeb (U of Leicester) report on behalf of a larger collaboration: We observed the field of EP250905a with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS r’ and SDSS g’ filters starting at 2025-09-05 22:20:05 UT, approximately 11.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. We detect no new sources in either the subtractions or stacked images. At the position of the optical source proposed as the counterpart by He et al. (GCN 41732) and GCN 41734, we use forced photometry to measure r = 22.6 +/- 0.4. We therefore identify no significant variability. We derive 3-sigma upper limits of r’ > 22.5 and g’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41738. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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