{
  "circularId": 45844,
  "submittedHow": "web",
  "createdOn": 1791409350636,
  "format": "text/plain",
  "body": "E. Ruiz-Laguna, S. Abad Gómez, K.N. Alvez Báez, G. de la Mata Núñez, J. Díaz-Miguel Font, A. Fernández-Roselló, L. García Rodríguez, S. M. Holtham, R. Jiménez Rioja, H. Morín-González, L. Ortega-Barcenilla, C. Pasamontes-Duarte, M. Ríos-Jiménez, S.J. Riquelme-Salinas, L. Rodríguez-Torres, A. Rosendo Pato, I. Ruiz-Pérez, D. Zazo-Callejas (all ULL), S. R. Berlanas (IAC and ULL),\nand I. Pérez-Fournon (IAC and ULL)\n\nWe report on observations of the optical counterpart of GRB 261007A detected by SVOM/ECLAIRs and SVOM/GRM (Goto et al., GCN 45824), Einstein Probe WXT and FXT (EP261007a, Wen et al., GCN 45828), and Fermi GBM (Malacaria, GCN 45830).\n\nWe observed the field of GRB 261007A / EP261007a with a Las Cumbres Observatory (LCO) 40-cm telescope  \nlocated at the LCO node at McDonald Observatory, Texas, with 180-sec exposures in each of the SDSS g´, r´, and i' filters. The first observation started on 2026-10-07 at 07:07:24 UT, about 1.4225 hr after the SVOM trigger. The optical counterpart first detected with KAIT by Zheng et al. (GCN 45825) is clearly detected in all bands. We measure the following AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction:\n\nDate (UT, mid-time)       | filter  |  mag   | error | mid t - t0 (hr)  \n-----------------------------------------------------------------------\n  2026-10-07T07:08:54     |   g'    |  18.59 | 0.06  | 1.4475\n  2026-10-07T07:12:04     |   r'    |  18.33 | 0.08  | 1.5003\n  2026-10-07T07:15:11     |   i'    |  18.10 | 0.16  | 1.5522\n  \nOur results are consistent with other optical and near-IR detections: Saccardi et al. (GCN 45829, spectroscopic redshift of 2.101), Mohan et al. (GCN 45832), Saccardi et al. (GCN 45837), Shi et al. (GCN 45838), An et al. (GCN 45840), Arya et al. (GCN 45841), Rehemtulla et al. (ZTF26abzxgsr, GCN 45843), and Fracile et al. (AT 2026aepi, TNS Astronomical Transient Report No. 327228).\n\nBased on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (LCO program IAC2026B-010). \n\nThese observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).\n\n\n\n\n",
  "eventId": "GRB 261007A",
  "submitter": "Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>",
  "eventType": [
    "GRB",
    "X-ray Transient",
    "Afterglow",
    "Optical Transient"
  ],
  "subject": " GRB 261007A / EP261007a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at McDonald Observatory "
}