Design and Operation of the ATLAS Transient Science Server
Rest, A.; Smartt, S. J.; Stalder, B.; Stubbs, C. W.; Chen, T. -W.; Smith, K. W.; Denneau, L.; Young, D. R.; Flewelling, H.; Wright, D. E.; Do, A.; Anderson, J. P.; Tonry, J. L.; Heinze, A. N.; Weiland, H. J.; McBrien, O. R.; Srivastav, S.; Förster, F.; Fulton, M.; O'Neill, D.; Clark, P.; Gillanders, J.
United Kingdom, United States, Chile, Sweden
Abstract
The Asteroid Terrestrial impact Last Alert System (ATLAS) system consists of two 0.5 m Schmidt telescopes with cameras covering 29 square degrees at plate scale of 1.86 arcsec per pixel. Working in tandem, the telescopes routinely survey the whole sky visible from Hawaii (above $\delta \gt -50^\circ $ ) every two nights, exposing four times per night, typically reaching $o\lt 19$ magnitude per exposure when the moon is illuminated and $c\lt 19.5$ magnitude per exposure in dark skies. Construction is underway of two further units to be sited in Chile and South Africa which will result in an all-sky daily cadence from 2021. Initially designed for detecting potentially hazardous near earth objects, the ATLAS data enable a range of astrophysical time domain science. To extract transients from the data stream requires a computing system to process the data, assimilate detections in time and space and associate them with known astrophysical sources. Here we describe the hardware and software infrastructure to produce a stream of clean, real, astrophysical transients in real time. This involves machine learning and boosted decision tree algorithms to identify extragalactic and Galactic transients. Typically we detect 10-15 supernova candidates per night which we immediately announce publicly. The ATLAS discoveries not only enable rapid follow-up of interesting sources but will provide complete statistical samples within the local volume of 100 Mpc. A simple comparison of the detected supernova rate within 100 Mpc, with no corrections for completeness, is already significantly higher (factor 1.5 to 2) than the current accepted rates.