GCN Circular 39709
Subject
EP250304a: Pan-STARRS r and i-band imaging and photometry
Date
2025-03-13T20:31:31Z (22 days ago)
From
James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>
Via
Web form
J. H. Gillanders (Oxford), M. Huber, K. C. Chambers (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, S. Srivastav (Oxford), M. Nicholl, D. Young, M. Fulton (QUB), T.-W. Chen (NCU, Taiwan) A. S. B. Schultz, T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii).
We observed the field of EP250304a (Chen et al., GCN 39580), using the Pan-STARRS telescope system (Chambers et al., 2016, arXiv e-prints, 1612.05560) on MJD 60745.55 (2025-03-11 13:12 UTC), approximately ~7.5 days after the EP-WXT detection (Chen et al., GCN 39580). The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters.
Our observation consisted of 2x300s exposures in both the r and i filters. The images were processed with the Pan-STARRS pipeline. After astrometric and photometric calibration, reference images were subtracted from the target stacked images in the i-band only (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). At this declination (Dec = -42), we possess a proprietary i-band reference stack with a total exposure time of 1170s. We also possess an r-band reference stack, but this has just 90s total exposure time.
From these difference images, we measure an i-band AB magnitude, i~21.4. Previously reported r/R-band magnitudes by Liu et al., (GCN 39583; R = 20.8 +/- 0.1 at 2.4 hours post-burst) and Saccardi et al., (GCN 39585; r = 20.97 +/- 0.03 at 5.7 hours post-burst) indicate that the optical transient has not faded substantially in the ~week since explosion. A faint source is visible in the r-band images, but with only a 90s reference stack we cannot determine if this corresponds to host or transient flux.