Paper detail

Is 4U 0114+65 an eclipsing HMXB?

We present the pulsation and spectral characteristics of the HMXB 4U 0114+65 during a \emph{Suzaku} observation covering the part of the orbit that included the previously known low intensity emission of the source (dip) and the egress from this state. This dip has been interpreted in previous works as an X-ray eclipse. Notably, in this Suzaku observation, the count rate during and outside the dip vary by a factor of only 2-4 at odds with the eclipses of other HMXBs, where the intensity drops upto two orders of magnitude. The orbital intensity profile of 4U 0114+65 is characterized by a narrow dip in the RXTE-ASM (2-12 \rm{keV}) light curve and a shallower one in the Swift-BAT (15-50 \rm{keV}), which is different from eclipse ingress/egress behaviour of other HMXBs. The time-resolved spectral analysis reveal moderate absorption column density (N$_{H}$ - 2-20 $\times$ $10^{22}$ atoms $cm^{-2}$) and a relatively low equivalent width ($\sim$ 30 \rm{eV} \& 12 \rm{eV} of the iron K$_α$ and K$_β$ lines respectively) as opposed to the typical X-ray spectra of HMXBs during eclipse where the equivalent width is $\sim$ 1 \rm{keV}. Both XIS and PIN data show clear pulsations during the dip, which we have further confirmed using the entire archival data of the IBIS/ISGRI and JEM-X instruments onboard \emph{INTEGRAL}. The results we presented question the previous interpretation of the dip in the light curve of 4U 0114+65 as an X-ray eclipse. We thus discuss alternative interpretations of the periodic dip in the light curve of 4U 0114+65.