Swift/XRT orbital monitoring of the candidate supergiant fast X-ray transient IGR J17354-3255

TL;DR

This study presents the first sensitive soft X-ray monitoring of the candidate supergiant fast X-ray transient IGR J17354-3255, revealing orbital modulation, a dip in the light curve, and insights into the accretion processes and possible eclipse or gating mechanisms.

Contribution

It provides the first detailed soft X-ray timing analysis of IGR J17354-3255, identifying variability features and proposing explanations for observed dips beyond simple orbital effects.

Findings

Detected moderate orbital modulation in X-ray light curve

Observed a dip in the X-ray emission not explained by orbital modulation

Suggested eclipse or gated accretion as likely causes for the dip

Abstract

We report on the Swift/X-ray Telescope (XRT) monitoring of the field of view around the candidate supergiant fast X-ray transient (SFXT) IGR J17354-3255, which is positionally associated with the AGILE/GRID gamma-ray transient AGL J1734-3310. Our observations, which cover 11 days for a total on-source exposure of about 24 ks, span 1.2 orbital periods (P_orb=8.4474 d) and are the first sensitive monitoring of this source in the soft X-rays. These new data allow us to exploit the timing variability properties of the sources in the field to unambiguously identify the soft X-ray counterpart of IGR J17354-3255. The soft X-ray light curve shows a moderate orbital modulation and a dip. We investigated the nature of the dip by comparing the X-ray light curve with the prediction of the Bondi-Hoyle-Lyttleton accretion theory, assuming both spherical and nonspherical symmetry of the outflow from the donor star. We found that the dip cannot be explained with the X-ray orbital modulation. We propose that an eclipse or the onset of a gated mechanism is the most likely explanation for the observed light curve.