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

[vsnet-grb-info 39130] EP250711a: Global MASTER-Net observations report
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41077 SUBJECT: EP250711a: Global MASTER-Net observations report DATE: 25/07/12 22:18:20 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-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) was pointed to the EP250711a ( EP Team et al., GCN 41070) errorbox 51485 sec after notice time and 1 days 18055 sec after trigger time at 2025-07-12 22:11:51 UT, with upper limit up to 16.4 mag. The observations began at zenith distance = 40 deg. The sun altitude is -23.9 deg. The galactic latitude b = -7 deg., longitude l = 42 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2933283 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 104485 | 2025-07-12 22:11:51 | MASTER-Kislovodsk | (19h 27m 47.40s , +04d 52m 25.4s) | C | 60 | 16.4 | 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/41077. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39129] GRB 250711A: DDOTI Optical Upper Limit
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41076 SUBJECT: GRB 250711A: DDOTI Optical Upper Limit DATE: 25/07/12 15:29:33 GMT FROM: sahil.atri(a)students.uniroma2.eu Sahil Atri (U Roma), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250711A detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 41064) and SVOM/GRM (SVOM/GRM Team GCN Circ. 41072) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-07-12 UTC. DDOTI observed the BALROG error region (Pries et al., GCN Circ. 41065) from 04:12 UTC to 11:28 UTC (from T+ 13.5 h to T+ 20.8 h after the trigger) and obtained a total exposure of 1.7 hours, alternating with other scientific programs. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 10-sigma limiting AB magnitude of: w > 20.1 This value is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41076. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39128] LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41075 SUBJECT: LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate DATE: 25/07/12 15:04:55 GMT FROM: Cassius Melo at Universidade Federal de Alfenas - UNIFAL-MG <cassiusanderson.melo(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250712cd during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-07-12 14:25:32.329 UTC (GPS time: 1436365550.329). The candidate was found by the cWB [1], cWB BBH [2], GstLAL [3], and MBTA [4] analysis pipelines. S250712cd is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.7e-11 Hz, or about one in 1e3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250712cd The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), 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%. [5] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [5] 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. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [6], distributed via GCN and SCiMMA notices about 28 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [6], 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 well fit by an ellipse with an area of 395 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(19h30m, +55d32m, 15.21d, 8.35d, 104.26d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2177 +/- 664 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] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [2] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [3] 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 [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [5] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [6] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41075. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39127] EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41074 SUBJECT: EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate DATE: 25/07/12 13:03:56 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Jean-Luc Atteia (IRAP), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We continued the follow-up campaign of EP250711a (Wang et al., GCN Circ. 41070) using the DDRAGO wide-field imager on the COLIBRÍ telescope. Observations were conducted on 2025-07-12 from 03:40 to 05:46 UTC (10.5 to 12.6 hours after the trigger), obtaining 96 minutes of exposure in the i band. Additional observations were carried out from 2025-07-12 09:46 to 11:21 UTC (16.6 to 18.2 hours after the trigger), with a total of 64 minutes of exposure in the r band. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Due to the significantly larger number of images in the stacks than in López et al. (GCN Circ. 41069), it is now possible to confirm the candidate reported by Fu et al. (GCN Circ. 41071). We measure preliminary magnitudes of: r = 22.02 +/- 0.17 i = 21.13 +/- 0.11 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41074. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39126] EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41073 SUBJECT: EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate DATE: 25/07/12 13:02:51 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Jean-Luc Atteia (IRAP), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We continued the follow-up campaign of EP250711a (Wang et al., GCN Circ. 41070) using the DDRAGO wide-field imager on the COLIBRÍ telescope. Observations were conducted on 2025-07-12 from 03:40 to 05:46 UTC (10.5 to 12.6 hours after the trigger), obtaining 96 minutes of exposure in the i band. Additional observations were carried out from 2025-07-12 09:46 to 11:21 UTC (16.6 to 18.2 hours after the trigger), with a total of 64 minutes of exposure in the r band. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Due to the significantly larger number of images in the stacks than in López et al. (GCN Circ. 41069), it is now possible to confirm the candidate reported by Fu et al. (GCN Circ. 41071). We measure preliminary magnitudes of: r = 22.02 +/- 0.17 i = 21.13 +/- 0.11 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39125] EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41073 SUBJECT: EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate DATE: 25/07/12 13:02:51 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Jean-Luc Atteia (IRAP), Kin Ocelotl López (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We continued the follow-up campaign of EP250711a (Wang et al., GCN Circ. 41070) using the DDRAGO wide-field imager on the COLIBRÍ telescope. Observations were conducted on 2025-07-12 from 03:40 to 05:46 UTC (10.5 to 12.6 hours after the trigger), obtaining 96 minutes of exposure in the i band. Additional observations were carried out from 2025-07-12 09:46 to 11:21 UTC (16.6 to 18.2 hours after the trigger), with a total of 64 minutes of exposure in the r band. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. Due to the significantly larger number of images in the stacks than in López et al. (GCN Circ. 41069), it is now possible to confirm the candidate reported by Fu et al. (GCN Circ. 41071). We measure preliminary magnitudes of: r = 22.02 +/- 0.17 i = 21.13 +/- 0.11 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39124] GRB 250711A: SVOM/GRM observation
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41072 SUBJECT: GRB 250711A: SVOM/GRM observation DATE: 25/07/12 09:36:26 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier Godet, Sébastien Guillot (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a bright burst GRB 250711A (SVOM trigger reference: sb25071104) at 2025-07-11T14:40:14.00 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41064). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of double pulses with a T90 of 38.5 +/-4.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250711A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 261.2, DEC= 44.9, GCN#41064), is located at about 48 degrees from the SVOM optical axis, which is just outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-10 to T0+70 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.20 +0.09/-0.10 and the cutoff energy, parameterized as Epeak, is 146 +23/-17 keV. The event fluence (10-1000 keV) in this time interval is (1.69 +0.12/-0.10)E-05 erg/cm^2. The localization of GRB 250620C in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/grb250711A_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41072. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39123] EP250711a: NOT optical counterpart candidate
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41071 SUBJECT: EP250711a: NOT optical counterpart candidate DATE: 25/07/12 08:45:33 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> S.Y. Fu (HUST), S.Q. Jiang, J. An, Z.P. Zhu, X. Liu, L.B. He, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), V. Vuolteenaho (NOT) report on behalf of a large collaboration: We observed the field of EP250711a detected by EP/WXT (Wang et al., GCN 41070), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 5 x 200 s exposures in the SDSS z-band, starting at 03:02:59 UT on 2025-07-12, i.e., 9.87 hrs after the EP trigger. An uncatalogued optical transient (OT) is detected within the EP/FXT error circle (Wang et al., GCN 41070) at coordinates R.A.(J2000) = 19:28:37.94 Dec.(J2000) = +4:42:06.80 with an uncertainty of ~ 0.5 arcsec. The source has z ~ 20.2 mag, calibrated with nearby PanSTARRS stars and not corrected for Galactic extinction. We think the source is likely the optical counterpart of EP250711a. We also note that there is a source north-west to the OT, being offset only by ~ 0.9 arcsec in the PanSTARRS, which has z ~ 21.5 mag and may be physically connected to EP250711a. View this GCN Circular online at https://gcn.nasa.gov/circulars/41071. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39122] EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41070 SUBJECT: EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient DATE: 25/07/12 07:53:13 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), D.Y. Li, W.X. Wang, W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient by EP-WXT, designated EP250711a (trigger ID: 08500000365). The source was detected on ground from the telemetry data, causing a significant delay from the occuring time of the event. The onboard alert system was not triggered due to the low Galactic lattitude of the source, and no automated follow-up was performed with EP-FXT due to the observation was an non-interruptible one.The WXT position of the source is R.A. = 292.153 deg, DEC = 4.707 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). The observation begun at 2025-07-11T17:10:56 (UTC), and as suggested from the EP-WXT light curve, the transient was already present at the start time of the observation. The light curve exihbits a double-peak profile, and lasted for about 1300 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with the absorption fixed at the Galactic value of 3.78 x 10^22 cm^-2, and a photon index of 2.5 (+/-0.5). The derived average unabsorbed 0.5-4 keV flux is 2.1 (+/-0.4) x 10^-10 erg/s/cm2. The peak flux is about 8 x 10^(-10) erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. We performed a follow-up target of opportunity observation with EP-FXT, starting at 2025-07-12T04:02:18Z, about 11 hours after the WXT detection. Within the WXT error circle, an uncataloggued X-ray source was detected at R.A. = 292.1614 , Dec.= 4.7035 with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further analysis will be updated after receiving the telemetry data. An i band upper limit of 21.3 magnitude was given by a COLIBRÍ observation performed about 10.5 hours after the EP-WXT trigger (GCN 41069). 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/41070. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39121] EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
by GCN Circulars 12 Jul '25

12 Jul '25

TITLE: GCN CIRCULAR NUMBER: 41069 SUBJECT: EP candidate (ID=08500000365): COLIBRÍ optical Upper limit DATE: 25/07/12 05:52:18 GMT FROM: Kin Océlotl Cuauhtli López Mendoza at Instituto de Astronoma, UNAM <koclopez(a)astro.unam.mx> Kin Ocelotl López (UNAM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP alert (ID=08500000365 and trigger time T= 2025-07-11 17:10:56.00) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-07-12 03:40 to 03:59 UTC (from 10.5 to 10.8 hours after the trigger and starting 1.3 hours after the arrival of the notice) and obtained 16 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction (which is considerably high due to the proximity to the Galactic plane). In our stacked image, and after performing image subtraction using Pan-STARRS as a reference, we do not detect any new source at the WXT position, down to the following 5-sigma limit: i > 21.3 Nevertheless, we noticed the presence inside the WXT error box of the eclipsing binary (Gaia DR3 4292676364775382144) and an RR Lyrae star (Gaia DR3 4292676394808888448), suggesting that the alert is likely associated with one of these objects. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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