IGR J17354-3255 as a candidate intermediate SFXT possibly associated with the transient MeV AGL J1734-3310

TL;DR

This study characterizes IGR J17354-3255 as an intermediate SFXT with unique X-ray variability and potential association with the MeV source AGL J1734-3310, indicating a possible physical link between the two objects.

Contribution

It provides the first detailed spectral and temporal analysis of IGR J17354-3255, proposing its classification as an intermediate SFXT and suggesting a connection with the MeV source AGL J1734-3310.

Findings

Confirmed 8.4-day orbital period with smooth profile

Observed high dynamic range in X-ray flux (>300)

Detected fast X-ray flares similar to SFXTs

Abstract

We present spectral and temporal results from INTEGRAL long-term monitoring of the unidentified X-ray source IGR J17354-3255. We show that it is a weak persistent hard X-ray source spending a major fraction of the time in an out-of-outburst state with average 18-60 keV X-ray flux of about 1.1 mCrab, occasionally interspersed with fast X-ray flares (duration from a few hours to a few days) with a dynamic range as high as 200. From archival Swift/XRT observations, we also show that the dynamic range from non-detection to highest level of measured X-ray activity is >300. Our IBIS timing analysis strongly confirms the 8.4 days orbital period previously detected with Swift/BAT, in addition we show that the shape of the orbital profile is rather smooth and appears to be dominated by low level X-ray emission rather than by bright outbursts, the measured degree of outburst recurrence is about 25 per cent. The spectral and temporal characteristics of IGR J17354-3255 are highly indicative of a Supergiant High Mass X-ray Binary nature (SGXB). However, our inferred dynamic ranges both at soft and hard X-rays are significantly greater than those of classical SGXB systems, but instead are typical of intermediate Supergiant Fast X-ray Transient (SFXTs). Finally, we note for the first time that the observed fast flaring X-ray behaviour of IGR J17354-3255 is very similar to that detected with AGILE from the spatially associated MeV source AGL J1734-3310, suggesting a possible physical link between the two objects.