{
  "eventId": "GRB 231117A",
  "bibcode": "2023GCN.35105....1C",
  "submitter": "Ting-Wan Chen at MPE <janet.chen@astro.su.se>",
  "subject": "GRB 231117A: Kinder observations with Lulin observatory for AT 2023yba without fading in r band",
  "submittedHow": "email-legacy",
  "body": "T.-W. Chen (NCUIA), S. Yang (HNAS), C.-S. Lin (NCUIA), S. Smartt (Oxford/QUB), M. Fraser (UCD), A.J. Levan (Radboud), M.-H. Lee, C.-C. Ngeow, Y.-C. Pan, H.-Y. Hsiao, W.-J. Hou, J.-K. Guo (NCUIA), Z.-N. Wang (HNAS), J. Gillanders (Oxford), M. Fulton, S. Srivastav, T. Moore, C. Angus, A. Aamer (QUB), and N. Tanvir (Leicester) report:\n\nWe observed the field of GRB 231117A (Laha et al., GCN 35071; Navaneeth et al., GCN 35072; Beardmore et al., GCN 35074; Cattaneo et al., GCN 35075; Svinkin et al., GCN 35079; Cheung et al., GCN 35081; Dafcikova et al. GCN 35095).\n\nThe afterglow candidate was initially identified in our previous report (Yang et al., GCN 35083) . Since it is a real astrophysical transient, but not yet confirmed as the afterglow, we registered it as AT2023yba (Chen et al., TNS 194096).\n\nWe used the 40cm SLT at Lulin Observatory, Taiwan to obtain r-band images of the field of GRB 231117A, as part of the Kinder collaboration (Chen et al., AstroNote 2021-92). The first SLT epoch of observations started at 10:51 UT on 18 of November 2023 (MJD = 60266.452), 1.32 days after the Swift trigger. The r-band images were combined from 21 frames with a 300-second exposure time for the r band, taken under seeing conditions of an average of 1\".87 and at a median airmass of 1.16. Then we continuously conducted observations of i, g, and z-band images, commencing from MJD = 60266.552, under seeing conditions of an average of 1\".94 and at a median airmass of 1.83.\n\nWe used the Kinder pipeline (Yang et al. A&A 646, A22) to measure the PSF photometry of AT 2023yba after template subtraction using the SDSS images. We obtained the following magnitudes and a 3-sigma detection limit (in the AB system):\n\nr = 20.86 +/- 0.13 mag (exposure time of 300sec*21),\ni = 20.94 +/- 0.17 mag (300sec*6),\ng = 21.37 +/- 0.13 mag (300sec*6) and\nz > 20.02 mag (300sec*6).\n\nThe given magnitudes derived based on calibrating against SDSS field stars and is not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.06 mag in the direction of the burst (Schlafly & Finkbeiner 2011).\n\nSince the various GCNs on this source have heterogeneous methods, we focus on comparing our own nightly template subtracted measurements. By comparing these data with measurements on MJD = 60265.435 (at the epoch of 7.39 hours after the Swift trigger), we found AT 2023yba has faded by more than 0.4 mag in g and i bands in one day, but no fading in the r band. No fading in r band was also noticed in Kumar et al. (GCN 35089) at the epoch of 10.56 hours. The redshift of the host galaxy, SDSS J220933.34+133119.5, has been spectroscopically confirmed at z = 0.257 (Ahumada et al., GCN 35093; Gonzalez-Bañuelos et al., GCN 35098), placing this transient at absolute magnitude M_r = -19.6 mag.\n\n",
  "circularId": 35105,
  "createdOn": 1700335008916
}