INTEGRAL observations of the Small Magellanic Cloud

TL;DR

This paper reports initial INTEGRAL observations of the Small Magellanic Cloud, detecting two X-ray sources, including a known pulsar and a potential high mass X-ray binary with unique optical and X-ray characteristics.

Contribution

First INTEGRAL observations of the SMC revealing two sources, including a pulsar with long-term spin-up and a candidate high mass X-ray binary with potential Roche lobe overflow.

Findings

Detection of SMC X-1 with a hard X-ray eclipse and long-term spin-up.

Identification of a potential high mass X-ray binary with 6.8s periodicity.

Possible classification of a new Roche lobe overflow system.

Abstract

The first INTEGRAL observations of the Small Magellanic Cloud (carried out in 2003) are reported in which two sources are clearly detected. The first source, SMC X-1, shows a hard X-ray eclipse and measurements of its pulse period indicate a continuation of the long-term spin-up now covering ~30 years. The second source is likely to be a high mass X-ray binary, and shows a potential periodicity of 6.8s in the IBIS lightcurve. An exact X-ray or optical counterpart cannot be designated, but a number of proposed counterparts are discussed. One of these possible counterparts shows a strong coherent optical modulation at ~2.7d, which, together with the measured hard X-ray pulse period, would lead to this INTEGRAL source being classified as the fourth known high mass Roche lobe overflow system.