{
  "submittedHow": "web",
  "circularId": 39027,
  "format": "text/plain",
  "subject": "EP250125a: Gemini-South optical afterglow discovery and redshift z = 2.89",
  "createdOn": 1737797170935,
  "submitter": "Andrew Levan at Radboud University <a.levan@astro.ru.nl>",
  "eventId": "EP250125a",
  "body": "A. J. Levan (Radboud Univ. and Warwick Univ.), J. A. Quirola-Vasquez (Radboud Univ.), F. E. Bauer (PUC), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud Univ.) report on behalf of a larger collaboration.\n\nWe observed the field of the EP transient 01709130802 (EP250125a, trigger time: 2025-01-25 02:37:31.749 UT) using the Gemini South telescope equipped with the GMOS-S camera and spectrograph. A set of images in the r and z bands were secured, starting on 2025 25.294 UT (4.43 hr after the trigger).\n\nA point-like object not present in the archival Pan-STARRS images of the field is detected in both filters at coordinates (J2000), well within the 3 arcmin-radius WXT error circle:\n\nRA = 11:41:27.39\nDec = -21:42:51.5\n\nFor this object, we measure an AB magnitude r = 21.60 +- 0.03, calibrated against nearby objects from the Pan-STARRS catalog.\n\nWe suggest this object is the optical counterpart of EP250125a.\n\nA spectrum of the source was taken with the B480 grism, starting at 08:39 UT. In the first 600 s exposure, the source is well detected across the spectral range from 4300 to 8200 AA (preliminary wavelength calibration). A strong absorption trough is visible at ~4730 AA, which we interpret as a DLA. From the detection of several narrow absorption features, including those from Si II, C II, Si IV, Al II, and Fe II we determine z = 2.89, which we suggest to be the redshift of EP250125a.\n\nWe thank the Gemini staff, in particular Karleyne Silva, for masterfully executing the requested observations\n",
  "bibcode": "2025GCN.39027....1L"
}