Outburst Characteristics of Transient Low Mass X-ray Binary 4U 1608-52

TL;DR

This study analyzes the long-term X-ray behavior of 4U 1608-52, classifying outbursts into three types based on duration and intensity, and finds that longer quiescent periods lead to more energetic outbursts.

Contribution

It introduces a detailed classification scheme for outbursts of 4U 1608-52 and links quiescent duration to outburst energy, providing new insights into outburst dynamics.

Findings

Three classes of FRED outbursts identified: long-high, short-medium, short-low.

Longer quiescent periods correlate with more energetic outbursts.

Outburst peak and total counts are related to pre-outburst quiescent duration.

Abstract

We present a deep study of the long-term X-ray light curve of 4U 1608-52 by investigating the fast rising exponential decay (FRED) outbursts, low intensity state (LIS) and quiescent intervals. By calibrating the onset times of the outbursts, we identify three distinct classes for the FRED-type events: (i) the long-high outbursts, exceeding ~50 d in duration with peak count rates above ~40 cnt/s; (ii) the short-medium outbursts, with durations of ~20 d and peak count rates of ~30-50 cnt/s; and (iii) the short-low outbursts, also lasting ~20 d but reaching only ~20-30 cnt/s at peak. We, furthermore, examine the relation between pre-outburst duration and the peak & integrated count rates of the upcoming outburst. We show that outbursts following longer quiescent periods tend to be more energetic.