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

[vsnet-grb-info 39280] EP250802a: Liverpool Telescope optical upper limits
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41224 SUBJECT: EP250802a: Liverpool Telescope optical upper limits DATE: 25/08/04 01:27:27 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 EP250802a (Yin et al., GCN 41221) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x120s exposures in the SDSS r’ and i’ filters starting at 2025-08-03 21:42:37 UT, approximately 35 hours after the trigger. The images were stacked, and their background was subtracted relative to Pan-STARRS-1 using PSF matching with the help of PSFEx. We do not detect any new object at the EP/WXT error region of the transient: the 3-sigma limiting magnitudes on the stacked images are r > 22.67 mag and i > 22.33 mag, in line with Mohan et al. (GCN 41222) and Lipunov et al. (GCN 41223). However, we note that there are a few bright, saturated stars inside the error region on our images, impacting the image subtraction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39279] EP250802a: Global MASTER-Net observations report
by GCN Circulars 04 Aug '25

04 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41223 SUBJECT: EP250802a: Global MASTER-Net observations report DATE: 25/08/04 00:09:32 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO), 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP250802a ( EP Team et al., GCN 41221) errorbox 39315 sec after notice time and 1 days 47045 sec after trigger time at 2025-08-03 23:41:13 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 62 deg. The sun altitude is -70.6 deg. The galactic latitude b = -6 deg., longitude l = 65 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2958029 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 11m 03.23s , +24d 50m 38.4s) | C | 60 | 18.0 | 133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 12m 56.78s , +24d 35m 32.1s) | C | 60 | 17.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39278] EP250802a: GROWTH-India Telescope optical upper limit
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41222 SUBJECT: EP250802a: GROWTH-India Telescope optical upper limit DATE: 25/08/03 19:17:03 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), D. Eappachen, G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of EP transient EP250802a (Yin et al., GCN 41221), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-08-03 16:11:32 UT, i.e., ~29.5 hours after the EP trigger and obtained an exposure in r' filter. We do not detect any afterglow candidates within the uncertainty region of WXT localization. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (day) | Exposure Time (sec) | Upper limit (AB) | | ------------ | ------ | ------------- | ------------------- | ---------------- | | 60890.67467 | r' | 1.23 | 300 | 20.8 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39277] EP250802a: Einstein Probe detection of an X-ray transient
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41221 SUBJECT: EP250802a: Einstein Probe detection of an X-ray transient DATE: 25/08/03 12:45:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.-H. I. Yin (NJU), X. Mao, T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by EP-WXT through ground data analysis, designated EP250802a (ObsID:06800000790). The transient was detected at 2025-08-02 10:37:08 (UTC). The WXT position of the source is R.A. = 303.321 deg, DEC = 24.814 deg (J2000) with an uncertainty of 3.1 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 650 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with absorption fixed at the Galactic value of 3.5 x 10^21 cm^-2 and a photon index of 2.81 (+/-0.47). The unabsorbed average 0.5-4 keV flux is estimated to be 3.81 (-0.57, +0.67) x 10^-11 erg/s/cm2. The peak flux is about 1.16 (-0.20, +0.25) x 10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT observations are scheduled. 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/41221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39276] LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
by GCN Circulars 03 Aug '25

03 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41220 SUBJECT: LIGO/Virgo/KAGRA S250802dn: Updated Sky localization DATE: 25/08/03 05:18:45 GMT FROM: lucy.thomas(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250802dn (GCN Circular 41218). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250802dn For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3209 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3070 +/- 1219 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] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/41220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39275] The EP-WXT trigger 01709198251 is likely a flaring star
by GCN Circulars 02 Aug '25

02 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41219 SUBJECT: The EP-WXT trigger 01709198251 is likely a flaring star DATE: 25/08/02 22:16:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO, CAS), Y.-H. I. Yin (NJU), T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709198251 at the time of 2025-08-02T20:32:45, is likely a stellar flare associated with V5663 Sgr. The estimated flux of the flare is around 1.8 x 10^-10 erg/s/cm^2 in 0.5-4.0 keV. The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) detected a source at R.A. = 301.4836, DEC = -32.2848 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic) within the WXT error circle, whose position is around 7.5 arcsec away from the high proper motion star V5663 Sgr. 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/41219. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39274] LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
by GCN Circulars 02 Aug '25

02 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41218 SUBJECT: LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate DATE: 25/08/02 21:13:36 GMT FROM: nzhang352(a)gatech.edu The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250802dn during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-08-02 20:25:12.022 UTC (GPS time: 1438201530.022). The candidate was found by the cWB BBH [1], GstLAL [2], and MBTA [3] analysis pipelines. S250802dn is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.5e-08 Hz, or about one in 6 months. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250802dn The classification of the GW signal, in order of descending probability, is BBH (93%), Terrestrial (7%), BNS (<1%), or NSBH (<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%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] 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 1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Three 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 [5], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 41 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 4470 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2957 +/- 1075 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] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [2] 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 [3] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41218. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39273] The EP-WXT trigger 01709198202 is likely a flaring star
by GCN Circulars 02 Aug '25

02 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41217 SUBJECT: The EP-WXT trigger 01709198202 is likely a flaring star DATE: 25/08/02 13:43:18 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Zhao (NAO, CAS), Q. C. Liu (THU), B. B. Zhang , Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709198202 at the time of 2025-08-02T12:44:54, is likely a stellar flare associated with BD-08 6022. The estimated flux of the flare is around 8.0 x 10^-11 erg/s/cm^2 in 0.5-4.0 keV. The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) detected a source at R.A. = 346.4735, DEC = -7.7644 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic) within the WXT error circle, whose position is 10.2 arcsec away from the Eclipsing Binary BD-08 6022. 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/41217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39272] LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
by GCN Circulars 01 Aug '25

01 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41216 SUBJECT: LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm DATE: 25/08/01 22:47:59 GMT FROM: Nelio Sasaki at NEPA-UEA <nsasaki(a)uea.edu.br> Wagner Corradi (LNA), Nélio Sasaki (UEA-Parintins), Leandro de Almeida (LNA), Felipe Navarete (LNA), S. Antier (OCA/IJCLAB), Yodgor Rajabov (UBAI), Yusufjion Tillayev (UBAI), Eslam Elhosseiny (NRIAG), C. Andrade (UMN), D. Turpin (CEA), I. Tosta e Melo (IFN), M. Coughlin (UMN), P. Hello (IJCLAB), P-A. Duverne (APC), S. Karpov (FZU) and T. Pradier (IPHC) on behalf of Observatório do Pico dos Dias (OPD/LNA/Brazil) and the GRANDMA collaboration, we inspected the optical candidate AT2025smm (GCNs 41179) of the gravitational-wave event  S250727dc (GCNs 41179, 41487), reported by Swift/UVOT (GCN 41179,GCN 41187, GCN 41188, GCN 41196, GCN 41197, GCN 41201, GCN 41202, GCN 41205, GCN 41211 and GCN 41214). Observations were conducted with the 0.6 m telescope at OPD, obtaining six frames of 300s exposures in the Bessel-R band between 2025-07-31T08:18:35.268  and 2025-07-31T08:48:35.268 UTC. No source is detected at the reported position in the stacked image. The final stacked frame covers a field of view of 11.6′ × 11.6′ with a pixel scale of 0.34″ arcsecond per pixel. Here we report the following limiting magnitudes, uncorrected for Galactic extinction: Filter | Mag (AB) r | > 22.53 This result is in agreement with the analysis of DECam GW-MMADS (GCN 41197). We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (http://grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). View this GCN Circular online at https://gcn.nasa.gov/circulars/41216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39271] GRB 250702B: SMA observations
by GCN Circulars 01 Aug '25

01 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41215 SUBJECT: GRB 250702B: SMA observations DATE: 25/08/01 22:24:26 GMT FROM: lauren.rhodes(a)mcgill.ca We observed the position of GRB 250702B (GCN #40883, #40886, #40890) with the Submillimeter Array (SMA) at a central frequency 225.5GHz for 4.5hours beginning at 06:51UT on 31 July 2025. Vesta and MWC349A were used as the flux calibrator, while 3C84 was used to calibrate the bandpass response. 1743-038 and 1911-201 were used as interleaved complex gain calibrators. The data was processed using the COMPASS pipeline (Keating et al, in prep). We do not detect any emission at the position of GRB 250702B (GCN #40924) with a 3sigma upper limit of 0.84mJy/beam. We thank the staff at the SMA for carrying out these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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