GCN Circular 36251

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

We report observations of the skymap of the NSBH/BNS merger event S240422ed (The LIGO-Virgo-Kagra Collaboration, GCN 36236
Not found
 
 
) with the ATLAS survey (Tonry et al., 2018, PASP, 13, 164505). ATLAS is a quadruple 0.5m optical telescope survey system (Hawaii, South Africa, Chile) employing two filters, cyan and orange. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24 hrs to magnitude depths m ~ 19.5, weather and Moon permitting.

We targeted the accessible skymap of S240422ed with a sequence of quads (4 x 110 s images) obtained at each pointing position. Data acquisition began at MJD 60422.9653 or 2024-04-22 23:10:01.920 (UTC), 0.8 hrs after the LVC initial alert and 1.6 hrs after the merger event. The images were processed with the ATLAS pipeline, and reference images were subtracted. Transient candidates were identified and run through our standard filtering procedures (Smith et al., 2020, PASP, 132, 1). We covered 242 square degrees of the bilby.fits skymap 90% area, and covered a sky region totalling 77% of the event's full localisation likelihood. 

Observations lasted between ~1.6 hrs to 7.2 hrs after the NSBH/BNS merger. We found no plausible new transient sources that had not been previously detected by ATLAS before the merger event or reported to the IAU Transient name server. The 5-sigma depths of our images were typically 18.7 < m_o < 19.5 AB mag. We are reporting all discoveries to the TNS, where they can be tracked, classified, searched, and commented upon. We encourage further information to be reported on the TNS object pages.

The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.