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 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.