A study of the low-mass X-ray binary dip sources XB 1916-053, XB 1323-619, X 1624-490 and 4U 1746-371 observed with INTEGRAL

TL;DR

This study analyzes four low-mass X-ray binary dip sources using INTEGRAL data, revealing spectral characteristics, dipping activity, and ionized absorption features across different energy ranges, contributing to understanding their coronal structures and plasma properties.

Contribution

It provides the first detailed spectral analysis of these sources with INTEGRAL, highlighting plasma temperatures, absorption differences, and ionized absorber properties in the 4-200 keV range.

Findings

Detection of dipping activity in 3-10 keV and 20-40 keV ranges.

Spectral parameters indicate hot coronal plasma with temperatures up to 224.9 keV.

Absorption differences observed in some sources between dipping and non-dipping intervals.

Abstract

We detect dipping activity/modulations in the light curve of the four LMXBs in the 3--10 keV and 20--40 keV energy ranges. The spectral parameters derived from the fits to the INTEGRAL data are consistent with hot coronal structures in these systems where we find a range of plasma temperatures 3.0--224.9 keV. The unabsorbed X-ray to soft Gamma-ray flux between 4--200 keV are 5.9$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for XB 1916-053, 3.3$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for XB 1323-619, 21.6$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for X 1624-490 and 11.0$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for 4U 1746-371. The optical depth to Compton scattering, $\tau$, varies in a range 4.4--0.002 consistent with electron densities $n_e$ $<$ 1.4$\times 10^{15}$ cm$^{-3}$. In general, we find no significant difference in the dip and non-dip spectra in the ISGRI energy range (above 20 keV) for all the four sources. We only detect absorption differences between dipping and non-dipping intervals for XB 1916-053 and X 1624-490 in the JEM-X energy range. Fits in the 4--200 keV range including an additional photo-ionized absorber model for the two sources show that XB 1916-053 has the highest ionized absorber amoung the two.