Letters to the Editor

Discovery of a peculiar dip from GX 301–2 

¹ Sabancı University, Faculty of Engineering and Natural Sciences, Orhanlı- Tuzla, 34956 İstanbul, Turkey
e-mail: ersing@sabanciuniv.edu
² Dr. Karl Remeis-Sternwarte & ECAP, Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
³ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy

Received: 11 October 2010
Accepted: 16 November 2010

Abstract

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.