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[vsnet-grb-info 43114] GRB 260610B / AT 2026owq: Liverpool Telescope confirmation of continuing optical rebrightening
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44959 SUBJECT: GRB 260610B / AT 2026owq: Liverpool Telescope confirmation of continuing optical rebrightening DATE: 26/06/16 20:04:25 GMT FROM: Dimple at University of Birmingham <dimplepanchal96(a)gmail.com> Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), A. Bochenek (LJMU), D. A. Perley (LJMU), D. O’Neill (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud) and A. Martin-Carrillo (UCD) report on behalf of a larger collaboration: We have conducted nightly griz observations of the optical afterglow (O’Neill et al., GCNs 44903, 44914; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCNs 44910, 44955; Akl et al., GCNs 44911, 44930; Moskvitin et al., GCNs 44918, 44929; Jackson-Horne et al., GCN 44919; Izzo et al., GCN 44920; Li et al., GCN 44921; Bochenek et al., GCNs 44927, 44932; Pankov et al., GCN 44946; Angulo et al., GCN 44958) of GRB 260610B (Fermi GBM Team, GCN 44901; Yu et al., GCN 44944) with the IO:O optical camera on the 2m robotic Liverpool Telescope. In our two most recent epochs we detect the optical rebrightening first suggested by Gillanders et al. between their t-t0 = 3.3 and 4.3 day epochs (GCN 44955) in all filters. The measured g- and r-band AB magnitudes are: | t-t0(d) | filter | mag | | 3.99 | g | 21.71 ± 0.07 | | 3.97 | r | 21.34 ± 0.07 | | 5.08 | g | 21.49 ± 0.08 | | 5.09 | r | 21.02 ± 0.07 | These observations indicate that GRB 260610B continues experiencing a rebrightening episode beyond 5 days after trigger. We detect no change in g-r colour when comparing our observations to the earliest Liverpool Telescope epoch (Bochenek & Perley, GCN 44927), suggesting an achromatic rebrightening, inconsistent with expectations for an emerging supernova. The above magnitudes are calibrated against nearby Pan-STARRS objects and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43113] GRB 260610B / AT 2026owq: COLIBRÍ further observations and confirmation of the rebrigthening
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44958 SUBJECT: GRB 260610B / AT 2026owq: COLIBRÍ further observations and confirmation of the rebrigthening DATE: 26/06/16 19:58:21 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Camila Angulo (UNAM), Marion Guelfand (CPPM), Rosa L. Becerra (UNAM), Nikos Mandarakas (LAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Jean-Luc Atteia (IRAP),Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Alan M. Watson (UNAM) report: We reimaged the field of AT 2026owq (O'Neill et al., GCN Circ. 44903, 44914; Watson et al., GCN Circ. 44905; Zhu et al., GCN Circ. 44909; Gillanders et al., GCN Circ. 44910; Akl et al., GCNs 44911, 44930; Moskvitin et al., GCNs 44918, 44929; Jackson-Horne et al., GCN Circ. 44919; Izzo et al., GCN Circ. 44920; Li et al., GCN Circ. 44921; Bochenek et al., GCNs 44927, 44932; Pankov et al., GCN Circ. 44946; Gillanders et al., GCN Circ. 44995), which is the optical counterpart of GRB 260610B (Fermi GBM team, GCN Circ. 44901), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. In our latest epoch, we observed from 2026-06-16 07:26 to 08:41 UTC (from 5.32 to 5.37 days after the GRB trigger) and obtained 6, 4, 5, and 14 minutes of exposure in the g, r, i, and z filters, respectively. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the source AT2026owq with preliminary magnitudes of: g = 21.52 +/- 0.13, r = 21.02 +/- 0.10, i = 20.69 +/- 0.09, z = 20.43 +/- 0.10. Compared with previous observations reported for this event, we also observe the rebrightening/flattening first reported by the Pan-STARRS team (Gillanders et al., GCN Circ. 44995), beginning approximately 80 hours after the trigger and visible in all of our filters. 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 México (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, México. View this GCN Circular online at https://gcn.nasa.gov/circulars/44958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43112] GRB GRB260614A: AstroSat CZTI detection
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44957 SUBJECT: GRB GRB260614A: AstroSat CZTI detection DATE: 26/06/16 19:06:22 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260614A which was also detected by Fermi (GBM team, GCN Circ. 44935), GECAM (Xing-Hao Luo et. al., GCN Circ. 44940). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-06-14 10:06:15.64. The measured peak count rate associated with the burst is 57 (+28, -14) counts/s above the background in the combined data of three quadrants (out of four), with a total of 391 (+196, -206) counts. The local mean background count rate was 221 (+3, -3) counts/s. We measure a T90 of 20 (+3, -12) s from the cumulative CZT light curve. CZTI data products like interactive and downloadable light curves for this GRB can be found at:https://astrosat.iucaa.in/cift/cift_products/ET20260614T100614/ET20260614T100614_details.html CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43111] EP260616a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44956 SUBJECT: EP260616a: EP-WXT detection of a fast X-ray transient DATE: 26/06/16 16:27:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li (NAO, CAS), J. H. Wu (GZHU), T. Y. Liu, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP260616a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2026-06-16T07:05:16 (UTC). The position of the source is R.A. = 256.059 deg, DEC = -32.305 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). No onboard alert or automated X-ray follow-up observation was triggered at this position due to the low Galactic latitude. The start time and the position of the transient is consistent with that of GRB 260616B detected by Fermi/GBM (GCN 44953). The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 1.8 (+0.3/-0.3). The column density is fixed at the Galactic value of 3.4 x 10^21 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 4.1 (+/-0.5) x 10^-10 erg/s/cm^2. The peak flux is around 3.4 x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT will be arranged. 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/44956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43110] GRB 260610B / AT 2026owq: Possible re-brightening identified from Pan-STARRS observations
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44955 SUBJECT: GRB 260610B / AT 2026owq: Possible re-brightening identified from Pan-STARRS observations DATE: 26/06/16 15:30:51 GMT FROM: James Gillanders at University of Oxford <jhgillanders.astro(a)gmail.com> J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young (QUB), T.-W. Chen (NCU, Taiwan), A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii). We have been observing AT 2026owq (O’Neill et al., GCNs 44903, 44914; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCNs 44911, 44930; Moskvitin et al., GCNs 44918, 44929; Jackson-Horne et al., GCN 44919; Izzo et al., GCN 44920; Li et al., GCN 44921; Bochenek et al., GCNs 44927, 44932; Pankov et al., GCN 44946), the optical counterpart to GRB 260610B (detected by Fermi/GBM; GCN 44901) with a nightly cadence in grizy using the Pan-STARRS telescope system (Chambers et al., 2016) since MJD 61202.4. The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy. Our observations consist of 200 second exposures, and have been processed with the standard Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target images (Magnier et al., 2020a; Magnier et al., 2020b; Waters et al., 2020). Our most recent photometry indicates that the lightcurve evolution of AT 2026owq is no longer fading; instead, the transient appears to be flattening, or re-brightening, across all of griz. Full photometry is presented below. Note that these photometric measurements have not been corrected for Galactic extinction. MJD | Filter | Mag (AB) 61205.271 | g | 21.7+/-0.2 61205.273 | r | 21.2+/-0.1 61205.276 | i | 20.9+/-0.1 61205.278 | z | 20.7+/-0.2 61206.276 | g | 21.8+/-0.3 61206.270 | r | 21.3+/-0.2 61206.268 | i | 20.7+/-0.2 61206.265 | z | 20.6+/-0.2 At the redshift of AT 2026owq (z=0.473; O’Neill et al., GCN 44914), observer-frame i approximately corresponds to rest-frame g. Thus, the absolute magnitude of AT 2026owq on MJD 61206.3, in rest-frame g, is approximately -21.4. Given that, at MJD 61206.3, the transient is only ~2.9 rest-frame days post-explosion, this excess is too bright to be powered by the emergence of a typical GRB-supernova signal. Further follow-up is scheduled with Pan-STARRS to determine its nature. View this GCN Circular online at https://gcn.nasa.gov/circulars/44955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43109] The EP-WXT trigger 01709270148 is likely a flaring star
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44954 SUBJECT: The EP-WXT trigger 01709270148 is likely a flaring star DATE: 26/06/16 14:44:19 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Y. Liu, D. Y. Li (NAO, CAS), J. H. Wu (GZHU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709270148 at the time of 2026-06-16T14:22:03, is likely a stellar flare associated with LP 820-19. The estimated flux of the flare is around 1.2 x 10 ^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 8.6 x 10^(30) erg/s. 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/44954. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43108] GRB 260616B: Fermi GBM Detection
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44953 SUBJECT: GRB 260616B: Fermi GBM Detection DATE: 26/06/16 14:20:47 GMT FROM: Christian Malacaria at INAF-OAR <cmalacaria.astro(a)gmail.com> C. Malacaria (INAF-OAR) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:05:16.39 UT on 16 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260616B (trigger 803286321/260616295). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 257.49, Dec = -32.62 (J2000 degrees, equivalent to J2000 17h 9m, -32d 37'), with a statistical uncertainty of 1.70 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error [Connaughton et al. 2015, ApJS, 216, 32]). The angle from the Fermi LAT boresight is 76 degrees. The GBM light curve consists of two main pulses with a duration (T90) of about 13.8 s (50-300 keV). The time-averaged spectrum from T0+0.002 to T0+14.464 s is best fit by a Band function with Epeak = 240 +/- 10 keV, alpha = -0.63 +/- 0.04, and beta = -2.09 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (2.03 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 21.3 +/- 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/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44953. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43107] GRB 260604C: GRANDMA late observations with CFHT/MegaCam
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44952 SUBJECT: GRB 260604C: GRANDMA late observations with CFHT/MegaCam DATE: 26/06/16 13:14:53 GMT FROM: antier(a)ijclab.in2p3.fr Q. Bais (KNC), A. Bruna (KNC), L. Laumain (KNC), A. Delaplace (KNC), S. Antier (IJCLAB), M. Pillas (IAP), P. Hello (IJCLAB), M. Coughlin (UMN), L. Desrivieres (KNC) on behalf of GRANDMA and CM2 classroom of St Remy Lès Chevreuse: We conducted further follow-up observations of GRB 260604C (Fermi Team, GCN Circ. 44822, Gotz et al., GCN Circ. 44823) with the Canada-France-Hawaii Telescope/MegaPrime/MegaCam on 2026-06-10. We further detected the source and confirmed that the rebrightening episode ended on 2026-06-10. We posted some of our data in the public site group of the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GCN-260604_202037. To access, one simply needs to create an account using your ORCID id. These measurements are aligned with all our previous GRANDMA measurements. We thanks the CFHT team for observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. We also acknowledge funding from the European Union’s Horizon Europe Research and Innovation Programme under Grant Agreement No 101131928 (ACME project). The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (kilonovacatcher.in2p3.fr). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet(a)ijclab.in2p3.fr, skyportal.io). View this GCN Circular online at https://gcn.nasa.gov/circulars/44952. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43106] GRB 260616B: BALROG localization (Fermi Trigger 803286321 / GRB 260616295)
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44951 SUBJECT: GRB 260616B: BALROG localization (Fermi Trigger 803286321 / GRB 260616295) DATE: 26/06/16 09:17:04 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 803286321 at 07:05:16 on 16 June 2026 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) = 255.8 deg Decl.(2000.0) = -32.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260616295/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260616295/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260616295/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44951. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43105] The EP-WXT trigger 01709269893 is likely a flaring star
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44950 SUBJECT: The EP-WXT trigger 01709269893 is likely a flaring star DATE: 26/06/16 04:16:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li, T. Y. Liu (NAO, CAS), J. H. Wu (GZHU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709269893 at the time of 2026-06-16T03:28:01, is likely a stellar flare associated with UCAC3 45-262017. The estimated flux of the flare is around 8.0 x 10^(-11) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.2 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 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/44950. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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