TITLE:   GCN CIRCULAR
NUMBER:  35080
SUBJECT: GRB 231117A: ATLAS non-detection of an optical counterpart
DATE:    23/11/17 14:22:29 GMT
FROM:    James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>

J. H. Gillanders (Oxford), S. J. Smartt, S. Srivastav (Oxford/QUB), M. D. Fulton, K. W. Smith, A. Aamer, C. R. Angus, M. McCollum, T. Moore, M. Nicholl, X. Sheng, J. Weston, D. R. Young (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), A. Andersson, S. Ramaiya, L. Rhodes, H. Stevance (Oxford), J. Sommer (LMU/QUB), L. Denneau, J. Tonry, H. Weiland, A. Lawrence, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Jordan, V. Suc (UAI, Obstech), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard).

Here we report optical observations in the field of the Swift-BAT discovered GRB 231117A (Laha et al. GCN Circ. 35071), obtained during normal survey operations with ATLAS.

ATLAS is a quadruple 0.5-m telescope system with two units in Hawaii, one in Chile and one in South Africa (see Tonry et al. 2018, PASP, 130:064505), routinely surveying the visible sky on a daily basis. We promptly process all data with our transient science server (Smith et al. 2020, PASP, 132:085002).

The ATLAS system observed the field of the GRB 231117A in normal survey mode 3.3-hr after the GRB trigger date of MJD 60265.127 (=2023-11-17 03:03:19 UT, hereafter T0). We obtained forced photometry at the enhanced Swift-XRT X-ray source coordinates of RA = 332.38988, Dec = +13.52255 (Beardmore et al. GCN Circ. 35074). We found no historical detections of any excess optical flux at this position, or at any location within the XRT and BAT error regions.

Forced photometry at those coordinates results in the following most recent non-detection in the ATLAS c-band. These measurements are not corrected for any Galactic dust extinction.

Exp. time (s) = 120 (4 x 30)
MJD = 60265.310 (T0 + 3.3-hr)
Flux (uJy) < 19 (3-sigma)
Mag (AB) > 20.7 (3-sigma)