The 54 days orbital period of AX J1820.5-1434 unveiled by Swift

TL;DR

This study used Swift-BAT data to discover a 54-day orbital period in the high mass X-ray binary AX J1820.5-1434, providing new insights into its timing and spectral properties.

Contribution

The paper unveils the 54-day orbital period of AX J1820.5-1434 through extensive analysis of BAT survey data, enhancing understanding of its orbital and spectral characteristics.

Findings

Detected a 54-day orbital period in AX J1820.5-1434

The light curve shows an asymmetric profile with a near-zero minimum

Spectral analysis reveals an absorbed power-law without cutoff

Abstract

The hard X-ray survey that Swift-BAT has been performing since late 2004 has provided a considerable database for a large number of sources whose hard X-ray emission was poorly known. We are exploiting the BAT survey archive to improve the temporal and spectral characterization of the Galactic hard-X-ray sources. In this letter we focus on the study of the high mass X-ray binary AX J1820.5-1434. All the data relevant to AX J1820.5-1434 have been extracted from the BAT survey archive and analyzed using a folding technique to search for periodical modulations. A broad-band spectral analysis was also performed complementing the BAT spectrum with the available Swift-XRT and XMM-Newton pointed observations. A timing analysis has revealed the detection of a coherent signal at P_0=54.0 +/- 0.4 days, that we interpret as the orbital period of the binary system. When folded with a period of P_0, the light curve shows an asymmetric profile, with a minimum roughly consistent with zero intensity. The broad band spectral analysis performed coupling Swift-XRT, XMM-Newton and Swift-BAT spectra is well modeled with an absorbed power law with no evidence for an exponential cutoff.