The First Year of S-CUBED: The Swift Small Magellanic Cloud Survey

TL;DR

The S-CUBED survey is a high-cadence, shallow X-ray monitoring program of the Small Magellanic Cloud that discovers and characterizes X-ray outbursts from BeXRBs, including new sources and outburst types.

Contribution

This paper presents the first-year results of S-CUBED, including a new catalog of X-ray sources and detailed observations of BeXRB outbursts, demonstrating its effectiveness as a discovery tool.

Findings

Discovery of 265 X-ray sources, 160 previously uncataloged.

Detection of three Type II outbursts from BeXRBs.

Observation of Type I outbursts and orbital periods in 6 BeXRB systems.

Abstract

The Swift Small Magellanic Cloud Survey, S-CUBED, is a high cadence shallow X-ray survey of the SMC. The survey consists of 142 tiled pointings covering the optical extent of the SMC, which is performed weekly by NASA's Neil Gehrels Swift Observatory, with an exposure per tile of 60 seconds. The survey is focused on discovery and monitoring of X-ray outbursts from the large known and unknown population of BeXRBs in the SMC. Given the very low background of Swift's X-ray telescope, even with a short exposure per tile, S- CUBED is typically sensitive to outbursts in the SMC at > 1 - 2% Eddington Luminosity for a typical 1.4M neutron star compact object. This sensitivity, combined with the high cadence, and the fact that the survey can be performed all year round, make it a powerful discovery tool for outbursting accreting X-ray pulsars in the SMC. In this paper describe results from the first year of observations of S-CUBED, which includes the 1SCUBEDX catalog of 265 X-ray sources, 160 of which are not identified with any previously cataloged X-ray source. We report on bulk properties of sources in the 1SCUBEDX catalog. Finally we focus on results of S-CUBED observations of several interesting sources, which includes discovery of three Type II outbursts from BeXRBs, and the detection of Type I outbursts and orbital periods in 6 BeXRB systems.