A study of the low-mass X-ray binary dip sources XB1916 - 053, XB1323 - 619, X1624 - 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 XB1916 - 053, 3.3 × 10-10 erg s-1 cm-2 for XB1323 - 619, 21.6 × 10-10 erg s-1 cm-2 for X1624 - 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 XB1916 - 053 and X1624 - 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 XB1916 - 053 has the highest ionized absorber among the two. © 2009. The American Astronomical Society. All rights reserved.