The nature of the X-ray binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift observations

TL;DR

This study characterizes the X-ray binary IGR J19294+1816 using multi-instrument observations, revealing pulsations, potential orbital period, and complex behavior suggesting it may be a Be-HMXB or an SFXT.

Contribution

It provides refined localization, spectral analysis, and evidence of pulsations and absorption, offering new insights into the nature of IGR J19294+1816.

Findings

Detected 12.44 s pulsations indicating a pulsar

Identified potential 117-day orbital period

Observed short, intense X-ray flares

Abstract

We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+1816. The Swift/XRT data allow us to refine the position of the source to RA= 19h 29m 55.9s Dec=+18deg 18' 38.4" (+- 3.5"), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma ~ 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic absorption in this source. We detected a strong (P=40%) pulsation at 12.43781 (+-0.00003) s that we interpret as the spin period of a pulsar. All these results, coupled with the possible 117 day orbital period, point to IGR J19294+1816 being an HMXB with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI 18--40 keV light curve shows that the source spends most of its time in an undetectable state, we detect occurrences of short (~2000-3000 s) and intense flares that are more typical of supergiant fast X-ray transients. We therefore cannot make firm conclusions on the type of system, and we discuss the possible implications of IGR J19294+1816 being an SFXT.