{
  "submittedHow": "web",
  "eventType": [
    "X-ray Transient",
    "Optical Transient"
  ],
  "createdOn": 1788481095714,
  "circularId": 45507,
  "format": "text/markdown",
  "submitter": "Michael Davis at University of Minnesota <davi4614@umn.edu>",
  "subject": "NuSTAR Transient 260828: SOAR Optical Upper Limits",
  "body": "Michael C. Davis (UMN), James Freeburn (UNC), Tomas Ahumada (NOIRLab), Michael Coughlin (UMN), Akash Anumarlapudi (UNC), Anirudh Salgundi (UNC) report:\n\nWe observed the field of the fast X-ray transient NuSTAR 260828 (Brightman, GCN 45478) with the 4.1-m Southern Astrophysical Research (SOAR) Telescope at Cerro Pachón, Chile, using the Goodman High-Throughput Spectrograph in imaging mode. Observations consisted of 3 × 300 s exposures in the SDSS r band, reduced using the Goodman Spectroscopic Pipeline (Torres-Robledo et al. 2020).\n\nWe performed image subtraction using SFFT (Hu et al. 2022) on the stacked image using an archival Pan-STARRS1 stacked image as a reference. We find no new source within the NuSTAR localization down to a 3-sigma limiting magnitude of r > 22.25 (midtime of 2026-09-01 09:57:29 UT, ~3.64 days after the NuSTAR detection).\n\nOur nondetection is consistent with the contemporaneous LCO observations reported by Eyles-Ferris et al. (GCN 45488), who obtained r > 22.22 approximately one hour earlier.\n\nThe upper limit is reported in the AB magnitude system and was calibrated using nearby stars from the Pan-STARRS1 catalog. The magnitude has not been corrected for Galactic extinction.\n"
}