1,192 research outputs found
X-ray Scattered Halo around IGR J17544-2619
X-ray photons coming from an X-ray point source not only arrive at the
detector directly, but also can be strongly forward-scattered by the
interstellar dust along the line of sight (LOS), leading to a detectable
diffuse halo around the X-ray point source. The geometry of small angle X-ray
scattering is straightforward, namely, the scattered photons travel longer
paths and thus arrive later than the unscattered ones; thus the delay time of
X-ray scattered halo photons can reveal information of the distances of the
interstellar dust and the point source. Here we present a study of the X-ray
scattered around IGR J17544-2619, which is one of the so-called supergiant fast
X-ray transients. IGR J17544-2619 underwent a striking outburst when observed
with Chandra on 2004 July 3, providing a near delta-function lightcurve. We
find that the X-ray scattered halo around IGR J17544-2619 is produced by two
interstellar dust clouds along the LOS. The one which is closer to the observer
gives the X-ray scattered at larger observational angles; whereas the farther
one, which is in the vicinity of the point source, explains the halo with a
smaller angular size. By comparing the observational angle of the scattered
halo photons with that predicted by different dust grain models, we are able to
determine the normalized dust distance. With the delay times of the scattered
halo photons, we can determine the point source distance, given a dust grain
model. Alternatively we can discriminate between the dust grain models, given
the point source distance.Comment: Accepted for publication in ApJ. 25 pages, 9 figures, 6 table
Relativistic effects on the observed AGN luminosity distribution
Recently Zhang (2005) has proposed a model to account for the well
established effect that the fraction of type-II AGNs is anti-correlated with
the observed X-ray luminosity; the model consists of an X-ray emitting
accretion disk coaligned to the dusty torus within the standard AGN unification
model. In this paper the model is refined by including relativistic effects of
the observed X-ray radiations from the vicinity of the supermassive black hole
in an AGN. The relativistic corrections improve the combined fitting results of
the observed luminosity distribution and the type-II AGN fraction, though the
improvement is not significant. The type-II AGN fraction prefers non- or mildly
spinning black hole cases and rules out the extremely spinning case.Comment: 9 pages, 4 figures, accepted for publication in PAS
GRO J1655-40: from ASCA and XMM-Newton Observations
We have analysed four ASCA observations (1994--1995, 1996--1997) and three
XMM-Newton observations (2005) of this source, in all of which the source is in
high/soft state. We modeled the continuum spectra with relativistic disk model
kerrbb, estimated the spin of the central black hole, and constrained the
spectral hardening factor f_col and the distance. If kerrbb model applies, for
normally used value of f_col, the distance cannot be very small, and f_col
changes with observations.Comment: 2 pages, 1 figure, Conference proceedings to appear in "The Central
Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San
Francisco: ASP
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