1,168 research outputs found
The XMM-Newton long look of NGC 1365: uncovering of the obscured X-ray source
We present an analysis of the extreme obscuration variability observed during an XMM–Newton 5-d continuous monitoring of the active galactic nuclei (AGN) in NGC 1365. The source was in a reflection-dominated state in the first ∼1.5 d, then a strong increase in the 7–10 keV emission was observed in ∼10 h, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation, we estimate a size of the X-ray source DS < 1013 cm, a distance of the obscuring clouds R∼ 1016 cm and a density n∼ 1011 cm−3. These values suggest that the X-ray absorption/reflection originates from the broad-line region clouds. This is also supported by the resolved width of the iron narrow Kα emission line, consistent with the width of the broad Hβ line
X-ray absorption by Broad Line Region Clouds in Mrk 766
We present a new analysis of a 9-day long XMM-Newton monitoring of the Narrow
Line Seyfert 1 galaxy Mrk 766. We show that the strong changes in spectral
shape which occurred during this observation can be interpreted as due to Broad
Line Region clouds crossing the line of sight to the X-ray source. Within the
occultation scenario, the spectral and temporal analysis of the eclipses
provides precise estimates of the geometrical structure, location and physical
properties of the absorbing clouds. In particular, we show that these clouds
have cores with column densities of at least a few 10^23 cm^-2 and velocities
in the plane of the sky of the order of thousands km/s. The three different
eclipses monitored by XMM-Newton suggest a broad range in cloud velocities (by
a factor ~4-5). Moreover, two iron absorption lines clearly associated with
each eclipse suggest the presence of highly ionized gas around the obscuring
clouds, and an outflow component of the velocity spanning from 3,000 to 15,000
km/sComment: 10 pages, 7 figures. Accepted for publication in MNRA
Chandra monitoring of UGC 4203: the structure of the X-ray absorber
We present a Chandra monitoring campaign of the highly variable Seyfert
galaxy UGC 4203 (the "Phoenix Galaxy") which revealed variations in the X-ray
absorbing column density on time scales of two weeks. This is the third, clear
case, after NGC 1365 and NGC 7582, of dramatic N_H variability on short time
scales observed in a "changing look" source, i.e. an AGN observed in the past
in both a reflection-dominated and a Compton-thin state. The inferred limits on
the distance of the X-ray absorber from the center suggest that the X-ray
"torus" could be one and the same with the broad emission line region. This
scenario, first proposed for an "ad-hoc" picture for NGC 1365, may be the
common structure of the circumnuclear medium in AGN.Comment: 5 Pages, 4 figures. Accepted for publication in MNRAS. Missing
references added and typos correcte
Variable partial covering and a relativistic iron line in NGC 1365
We present a complete analysis of the hard X-ray (2-10 keV) properties of the
Seyfert galaxy NGC 1365, based on a 60 ks XMM-Newton observation performed in
January 2004. The two main results are: 1) We detect an obscuring cloud with
N_H~3.5x10^23 cm^(-2) crossing the line of sight in ~25 ks. This implies a
dimension of the X-ray source not larger than a few 10^13 cm and a distance of
the obscuring cloud of the order of 10^16 cm. Adopting the black hole mass
M(BH) estimated from the M(BH)-velocity dispersion relation, the source size is
D_S<20 R_G and the distance and density of the obscuring clouds are
R~3000-10000 R_G and n~10^(10) cm^(-3), i.e. typical values for broad line
region clouds. 2) An iron emission line with a relativistic profile is detected
with high statistical significance. A time integrated fit of the line+continuum
reflection components suggests a high iron abundance (~3 times solar) and an
origin of these components in the inner part (~10 R_G) of the accretion disk,
in agreement with the small source size inferred from the analysis of the
absorption variability.Comment: 31 pages, 8 figs. Accepted for publication in the Astrophysical
Journa
"Comets" orbiting a black hole
We use a long (300 ksec), continuous Suzaku X-ray observation of the active
nucleus in NGC1365 to investigate the structure of the circumnuclear BLR clouds
through their occultation of the X-ray source. The variations of the absorbing
column density and of the covering factor indicate that the clouds surrounding
the black hole are far from having a spherical geometry (as sometimes assumed),
instead they have a strongly elongated and cometary shape, with a dense head
(n=10^11 cm^-3) and an expanding, dissolving tail. We infer that the cometary
tails must be longer than a few times 10^13 cm and their opening angle must be
smaller than a few degrees. We suggest that the cometary shape may be a common
feature of BLR clouds in general, but which has been difficult to recognize
observationally so far. The cometary shape may originate from shocks and
hydrodynamical instabilities generated by the supersonic motion of the BLR
clouds into the intracloud medium. As a consequence of the mass loss into their
tail, we infer that the BLR clouds probably have a lifetime of only a few
months, implying that they must be continuously replenished. We also find a
large, puzzling discrepancy (two orders of magnitude) between the mass of the
BLR inferred from the properties of the absorbing clouds and the mass of the
BLR inferred from photoionization models; we discuss the possible solutions to
this discrepancy.Comment: Accepted for publication in A&A. 11 pages, 9 figure
A strong excess in the 20-100 keV emission of NGC 1365
We present a new Suzaku observation of the obscured AGN in NGC 1365,
revealing an unexpected excess of X-rays above 20 keV of at least a factor ~2
with respect to the extrapolation of the best-fitting 3-10 keV model.
Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is
concentrated within ~1.5 arcmin from the center of the galaxy, and is not
significantly variable on time scales from days to years. A comparison of this
component with the 3-10 keV emission, which is characterized by a rapidly
variable absorption, suggests a complex structure of the circumnuclear medium,
consisting of at least two distinct components with rather different physical
properties, one of which covering >80% of the source with a column density
NH~3-4x10^24 cm^(-2). An alternative explanation is the presence of a double
active nucleus in the center of NGC 1365.Comment: 13 pages, 3 figures. Accepted for publication in ApJ Letter
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