Precursors and Outbursts of A 0535+26 in 2009-2011 observed by the MAXI/GSC and the Swift/BAT

Abstract

Over the 3-year active period from 2008 September to 2011 November, the outburst behavior of the Be/X-ray binary A 0535+26 was continuously monitored with the MAXI/GSC and the Swift/BAT. The source exhibited nine outbursts, every binary revolution of 111.1 days, of which two are categorized into the giant (type-II) outbursts. The recurrence period of these outbursts is found to be $\sim 115$ days, significantly longer than the orbital period of 111.1 days. With the MAXI/GSC, a low-level active period, or a "precursor", was detected prior to at least four giant outbursts. The precursor recurrence period agrees with that of the giant outbursts. The period difference of the giant outbursts from the orbital period is possibly related with some structures in the circumstellar disc formed around the Be companion. Two scenarios, one based on a one-armed disc structure and the other a Be-disc precession, are discussed.

15 pages, 7 figures, 1 table. Accepted for publication in PASJ

References in corpus (4)

• Precessing Warped Be Disk Triggering the Giant Outbursts in 2009 and 2011 in A 0535+262/V725 Tau
• The pre-outburst flare of the A 0535+26 August/September 2005 outburst
• A double-peaked outburst of A 0535+26 observed with INTEGRAL, RXTE, and Suzaku
• The appearance of magnetospheric instability in flaring activity at the onset of X-ray outbursts in A0535+26

Cited by in corpus (1)

• Possible regular phenomena in EXO 2030+375