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

Abstract

We detect dipping activity/modulations in the light curve of the four low-mass X-ray binaries in the 3-10 keV and 20-40 keV energy ranges. The spectral parameters derived from the fits to the International Gamma-Ray Astrophysics Laboratory 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 fluxes between 4 keV and 200 keV are 5.9 × 10^-10 erg s^-1 cm^-2 for XB 1916 - 053, 3.3 × 10^-10 erg s^-1 cm^-2 for XB 1323 - 619, 21.6 × 10^-10 erg s^-1 cm^-2 for X 1624 - 490, and 11.0 × 10^-10 erg s^-1 cm^-2 for 4U 1746 - 371. The optical depth to Compton scattering, τ, varies in a range 4.4-0.002 consistent with electron densities n _e < 1.4 × 10¹⁵ 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 photoionized absorber model for the two sources show that XB 1916 - 053 has the highest ionized absorber among the two.