TITLE:   GCN CIRCULAR
NUMBER:  35121
SUBJECT: GRB 231117A: Pan-STARRS1 follow-up confirms rapid fading
DATE:    23/11/19 11:22:19 GMT
FROM:    shubhamsrivastav@gmail.com

M. D. Fulton (QUB), S. Srivastav, S. J. Smartt (Oxford/QUB), J. H. Gillanders (Oxford), K. C. Chambers, M. E. Huber, A. S. B. Schultz (IfA, Hawaii), K. W. Smith, D. R. Young, M. Nicholl, M. McCollum, T. Moore, S. Sim, J. Weston, A. Aamer, C. R. Angus, X. Sheng (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), J. Sommer (LMU/QUB), H. Stevance, L. Rhodes, S. Ramaiya, A. Andersson (Oxford), T. de Boer, J. Herman, J. Fairlamb, H. Gao, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii), T.-W. Chen (NCU), A. Rest (STScI), C. Stubbs (Harvard) report:

We 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) with Pan-STARRS1 (Chambers et al., 2016) on two nights in the grizy filters, with the exposures beginning on MJDs 60266.255617 and 60267.271553.

We apply the Pan-STARRS1 reference frames for image subtraction and in all exposures, the afterglow candidate identified by Yang et al. (GCN 35083) as AT2023yba is well detected in griz and marginally in y. We confirm a clear and significant fading in all bands in a comparison between the two nights of:

delta-g = 1.5 +/- 0.2
delta-r = 1.3 +/- 0.2
delta-i = 1.2 +/- 0.2
delta-z = 1.1 +/- 0.2

The latest r-band magnitude at 60267.282458 is r = 22.0 +/- 0.2. This confirms the fast-fading nature of the optical transient AT2023yba, indicating this optical source, discovered by Yang et al. (GCN 35083), is very likely the afterglow of GRB 231117A.

Operation of the Pan-STARRS1 and Pan-STARRS2 telescopes is primarily supported by the National Aeronautics and Space Administration under Grant No. NNX12AR65G and Grant No. NNX14AM74G issued through the SSO Near-Earth Object Observations Program. Data are processed at Queen's University Belfast enabled through the STFC grants ST/P000312/1 and ST/T000198/1.