Discovery of a peculiar dip from GX 301-2

Official URL: http://dx.doi.org/10.1051/0004-6361/201015905

We present temporal and spectral properties of a unique X-ray dip in GX 301-2 as seen with Rossi X-ray Timing Explorer in May 2010. The X-ray pulsation from the source gradually declined prior to the dip, disappears for one spin cycle during the dip, and is abruptly restored in the spin cycle immediately after the dip. Moreover, the phase-integrated spectrum of the source becomes softer before and during the dip, and it quickly hardens again following the dip. Our findings indicate that the mechanism for pulsations gradually turned off briefly, and the underlying dim and softer emission likely from the accretion column became observable in the brief absence of high-level emission due to wind accretion.