Suzaku X-Ray Study of an Anomalous Source XSS J12270-4859

TL;DR

This Suzaku X-ray study of XSS J12270-4859 reveals it is likely a low-mass X-ray binary with exotic phenomena, challenging its previous classification as an intermediate polar based on spectral and timing analysis.

Contribution

The paper provides new Suzaku observations that refute the prior IP classification and suggest XSS J12270-4859 is a rare low-mass X-ray binary with unique X-ray variability features.

Findings

Lack of Fe Ka emission features in the spectrum.

Failure to confirm the ~860 s X-ray period.

Presence of repetitive flares and dips with spectral hardening.

Abstract

We report the results of the Suzaku X-ray observation of XSS J12270-4859, one of the hard X-ray sources in the INTEGRAL catalogue. The object has been classified as an intermediate polar (IP) by optical spectra and a putative X-ray period of ~860 s. With a 30 ks exposure of Suzaku, we obtained a well-exposed spectrum in the 0.2-70 keV band. We conclude against the previous IP classification based on the lack of Fe Ka emission features in the spectrum and the failure to confirm the previously reported X-ray period. Instead, the X-ray light curve is filled with exotic phenomena, including repetitive flares lasting ~100 s, occasional dips with no apparent periodicities, spectral hardening after some flares, and bimodal changes pivoting between quiet and active phases. The rapid flux changes, the dips, and the power-law spectrum point toward the interpretation that this is a low-mass X-ray binary. Some temporal characteristics are similar to those in the Rapid Burster and GRO J1744-28, making XSS J12270-4859 a very rare object.