SAXJ1712.6-3739: a persistent hard X-ray source as monitored with INTEGRAL

TL;DR

This study uses INTEGRAL data to characterize SAXJ1712.6-3739 as a persistent, low-luminosity, hard state X-ray burster with spectral features consistent with ultra-compact binary systems.

Contribution

It provides the first detailed long-term hard X-ray monitoring of SAXJ1712.6-3739, establishing it as a persistent source with properties aligning with ultra-compact X-ray binaries.

Findings

SAXJ1712.6-3739 is a weak persistent hard X-ray source.

The broad-band spectrum is modeled with a Comptonized model.

Features suggest it belongs to the ultra-compact binary class.

Abstract

The X-ray source SAXJ1712.6-3739 is a very weak Low Mass X-ray Binary discovered in 1999 with BeppoSAX and located in the Galactic Center. This region has been deeply investigated by the INTEGRAL satellite with an unprecedented exposure time, giving us an unique opportunity to study the hard X-ray behavior also for weak objects. The spectral results are based on the systematic analysis of all INTEGRAL observations covering the source position performed between February 2003 and October 2006. SAXJ1712.6-3739 did not shows any flux variation along this period as well as compared to previous BeppoSAX observation. Hence, to better constrain the physical parameters we combined both instrument data. Long INTEGRAL monitoring reveals, for the first time, that this X-ray burster is a weak persistent source, displaying a X-ray spectrum extended to high energy and spending most of the time in a low luminosity hard state. The broad-band spectrum is well modeled with a simple Comptonized model with a seed photons temperature of ~0.5keV and an electron temperature of ~24keV. The low mass accretion rate (~2x10^{-10} Msun/yr), the long bursts recurrence time, the small sizes of the region emitting the seed photons consisting with the inner disk radius and the high luminosity ratio in the 40-100keV and 20-40keV band, are all features common to the Ultra Compact source class.