TITLE:   GCN CIRCULAR
NUMBER:  36857
SUBJECT: GRB240713A: Optical upper limit with Kinder observations
DATE:    24/07/14 01:15:25 GMT
FROM:    Janet Chen at National Central University <janetstars@gmail.com>

A. Sankar. K, A. Aryan, Y. J. Yang, H.-Y. Hsiao, C.-S. Lin, T.-W. Chen (all NCU), S. Yang (HNAS), W.-J. Hou, C.-C. Ngeow, C.-H. Lai, M.-H. Lee, Y.-C. Pan, H.-C. Lin, J.-K. Guo (all NCUIA), S. J. Smartt (Oxford/QUB), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, J. Gillanders, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (IfA, University of Hawaii) report: 

We observed the field of the first probable GRB240713A Located On-Board SVOM by ECLAIRs (Schanne et al., GCN 36854) and followed by Hello et al. (GCN 36855) and Burns et al. (GCN 36856). We use the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2024arXiv240609270C). The first SLT epoch of observations started at 16:02 UT on the 13th of July 2024 (MJD = 60504.668), 14 hrs after the SVOM trigger. 

We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. 
We do not detect any evidence of a new uncatalogued source in our stacked frames having a Field of View (FoV) of around 13'.0 x 13'.0 centered at R.A. = 23:30:24.55 and Dec. = +01:52:50.9. Moreover, we utilized the python based package, AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform the PSF photometry on our stacked frame. The details of the observations and measured 3-sigma upper limit (in the AB system) are as follows:

Telescope | Filter | MJD (start) | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
SLT | r | 60504.668 | 15 hrs | 300 sec * 12 | > 20.5 | 2".27 | 1.69

The presented magnitudes are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.03 mag in the direction of the burst (Schlafly & Finkbeiner 2011).