A Swift BAT Look at Super-Orbital X-ray Binaries

TL;DR

This study uses Swift BAT data to analyze long-term variability in five low mass X-ray binaries, finding some known super-orbital periods and suggesting jet precession as a possible cause for observed modulations.

Contribution

First long-term high-energy variability analysis of these binaries, revealing new insights into super-orbital periods and their possible origins.

Findings

Detected 170-day period in 4U 1820-303 up to 24 keV.

Detected 46-day period in 4U 1636-536 up to 100 keV.

No significant periodicity found in 4U 1916-053, Cyg X-2, Sco X-1.

Abstract

We present the results of a study with the Swift Burst Alert Telescope in the 14 - 195 keV range of the long-term variability of 5 low mass X-ray binaries with reported or suspected super-orbital periods -- 4U 1636-536, 4U 1820-303, 4U 1916-053, Cyg X-2 and Sco X-1. No significant periodic modulation was detected around the previously reported values in the 4U 1916-053, Cyg X-2 or Sco X-1 light curves. The $\sim$170 d period of 4U 1820-303 was detected up to 24 keV, consistent with the proposed triple system model. The $\sim$46 d period in 4U 1636-536 was detected up to 100 keV, clearly inconsistent with variable photoelectric absorption via a warped precessing disc. We speculate that the appearance of this modulation after 4U 1636-536 entered the low/hard state indicates that this variability could be linked to jet precession such as observed in SS 433.