An unexpected outburst from A0535+262

TL;DR

This paper reports the detection of an unexpected outburst from the Be/X-ray binary system A0535+262 in 2003, revealing ongoing activity and variability during its quiescent phase through timing and spectral analysis.

Contribution

It provides new observational data on A0535+262's activity during quiescence, including pulsation detection and spin-down analysis, highlighting the presence of an accretion disk.

Findings

Detected pulsations with P=103.7 seconds during quiescence

Observed continued spin-down indicating an accretion disk

System remains active and variable without recent outbursts

Abstract

A0535+262 is a transient Be/X-ray binary system which was in a quiescent phase from 1994-2005. In this paper we report on the timing and spectral properties of the INTEGRAL detection of the source in October 2003. The source is detected for ~6000 seconds in the 18-100 keV energy band at a luminosity of ~3.8 x 10^{35} erg s^{-1}; this is compatible with the high end of the range of luminosities expected for quiescent emission. The system is observed to be outside of the centrifugal inhibition regime and pulsations are detected with periodicity, P=103.7 +/- 0.1 seconds. An examination of the pulse history of the source shows that it had been in a constant state of spin-down since it entered the quiescent phase in 1994. The rate of spin-down implies the consistent presence of an accretion disk supplying torques to the pulsar. The observations show that the system is still active and highly variable even in the absence of recent Type I or Type II X-ray outbursts.