Study of the many fluorescent lines and the absorption variability in GX 301−2 withXMM-Newton

Abstract

We present an in-depth study of the high mass X-ray binary (HMXB) GX 301−2 during its pre-periastron flare using data from the XMM-Newton satellite. The energy spectrum shows a power law continuum absorbed by a large equivalent hydrogen column on the order of 10 24 cm −2 and a prominent Fe Kα fluorescent emission line. Besides the Fe Kα line, evidence for Fe Kβ, Ni Kα, Ni Kβ, S Kα, Ar Kα, Ca Kα, and Cr Kα fluorescent lines is found. The observed line strengths are consistent with fluorescence in a cold absorber. This is the first time that Cr Kα is seen in emission in the X-ray spectrum of a HMXB. In addition to the modulation by the strong pulse period of ∼685 s the source is highly variable and shows different states of activity. We perform time-resolved as well as pulse-to-pulse resolved spectroscopy to investigate differences between these states of activity. We find that fluorescent line fluxes are strongly variable and generally follow the overall flux. The N H value is variable by a factor of 2, but not correlated to continuum normalization. We find an interval of low flux in the light curve in which the pulsations cease almost completely, without any indication of an increasing absorption column. We investigate this dip in detail and argue that it is most likely that during the dip the accretion ceased and the afterglow of the fluorescent iron accounted for the main portion of the X-ray flux. A similar dip was found earlier in RXTE data, and we compare our findings to these results.

Staring at 4U 1909+07 withSuzaku

“…Within these winds, dense structures with column densities on the order of 10 24 cm −2 can be reached, as seen in many other sources (e.g., GX 301−2 or IGR J16318−4848; Fürst et al 2011b;Barragán et al 2009). The absorption column of the partial coverer in 4U 1909+07 is measured to be also of that order, with values between (0.5-1) × 10 24 cm −2 , as seen in Tables 1-3.…”

“…A partial coverer can be used as an approximation to a complex structured stellar wind ("clumpy" wind), as seen in many HMXBs as well as isolated O and B stars (see, e.g., Oskinova et al 2007;Fürst et al 2011b, among many others). Within these winds, dense structures with column densities on the order of 10 24 cm −2 can be reached, as seen in many other sources (e.g., GX 301−2 or IGR J16318−4848; Fürst et al 2011b;Barragán et al 2009).…”

High-mass X-ray binaries in the Milky Way

“…The absence of eclipse constrains the inclination angle in the range (44 • − 78 • ). A deep and variable 60 R. Walter et al cyclotron resonance feature is observed at hard X-rays Filippova et al, 2005;Fürst et al, 2011b). Spin up episodes have been observed and explained by the formation of transient accretion disks .…”

A 78 Day X-Ray Period Detected From NGC 5907 Ulx1 by Swift

“…However, it may be possible for an elliptical orbit to result in more moderate accretion rate variations via changes in the degree of Roche-lobe overflow as the distance between the compact object and its stellar companion varies (e.g., Church et al 2009). Alternatively, if NGC 5907 ULX1 is a wind-fed X-ray binary, the accretor could enter a higher-density region of the stellar wind, resulting in an enhanced accretion rate, similar to the case of GX 301−2 (Fürst et al 2011). However, sustaining the extreme luminosities observed from NGC 5907 ULX1 would be a major challenge for a wind-fed scenario.…”