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arXiv · 2510.06920

Recasting the nature of INTEGRAL hard X-ray transients previously classified as active galactic nuclei

V. Sguera·L. Sidoli
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Abstract

We present new broad-band X-ray results aimed at the identification and characterization of four poorly studied hard X-ray transients discovered by INTEGRAL: IGR J16426+6536, IGR J09446-2636, IGR J21268+6203, and IGR J02447+7046. The key properties and X-ray behavior of these sources have remained largely unknown until now. We investigated the temporal, spectral, and energetic characteristics of their hard X-ray outbursts detected above 20 keV by INTEGRAL. In addition, we performed a systematic analysis of unpublished archival soft X-ray observations below 10 keV, enabling a full exploration of their large INTEGRAL error circles in search of the most likely soft X-ray counterparts. Within their arcsecond-sized X-ray error circles, we identified single optical/near-infrared counterparts for each source. We analyzed their photometric properties to constrain the nature of the systems. Our results show that the X-ray properties of these four transients are inconsistent with the previously proposed extragalactic AGN origin, and instead support a Galactic nature for all of them. Specifically, we propose a very faint X-ray transient classification for IGR J16426+6536, a nearby flaring star for IGR J09446-2636 and IGR J21268+6203, finally a gamma-ray binary nature for IGR J02447+7046.

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V. Sguera, L. Sidoli. 2025-10-08. Recasting the nature of INTEGRAL hard X-ray transients previously classified as active galactic nuclei. https://arxiv.org/abs/2510.06920

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