2,570 research outputs found
IRAS 13197-1627 has them all: Compton-thin absorption, photo-ionized gas, thermal plasmas, and a broad Fe line
We report results from the XMM-Newton observation of IRAS 13197-1627, a
luminous IR galaxy with a Seyfert 1.8 nucleus. The hard X-ray spectrum is steep
and is absorbed by Compton-thin neutral gas. We detect an Fe emission line at
6.4 keV, consistent with transmission through the absorber. The most striking
result of our spectral analysis is the detection of a dominant X-ray reflection
component and broad Fe line from the inner accretion disc. The
reflection-dominated hard X-ray spectrum is confirmed by the strong Compton
hump seen in a previous BeppoSAX observation and could be the sign that most of
the primary X-rays are radiated from a compact corona (or e.g. base of the jet)
within a few gravitational radii from the black hole. We also detect a
relatively strong absorption line at 6.81 keV which, if interpreted as Fe xxv
resonant absorption intrinsic to the source, implies an outflow with velocity
of about 5000 km/s. In the soft energy band, the high-resolution RGS and the
CCD-resolution data show the presence of both photo-ionized gas and thermal
plasma emission, the latter being most likely associated with a recent
starburst of 15-20 solar masses per year.Comment: accepted for publication in MNRA
XMM-Newton unveils the type 2 nature of the BLRG 3C 445
We present an observation of XMM-Newton that unambiguously reveals the
``Seyfert 2'' nature of the Broad Line Radio Galaxy 3C 445. For the first time
the soft excess of this source has been resolved. It consists of unobscured
scattered continuum flux and emission lines, likely produced in a warm
photoionized gas near the pole of an obscuring torus. The presence of
circumnuclear (likely stratified) matter is supported by the complex
obscuration of the nuclear region. Seventy percent of the nuclear radiation
(first component) is indeed obscured by a column density ~4*10^{23} cm^{-2},
and 30 % (second component) is filtered by ~7* 10^{22} cm^{-2}. The first
component is nuclear radiation directly observed by transmission through the
thicker regions. The second one is of more uncertain nature. If the observer
has a deep view into the nucleus but near the edge of the torus, it could be
light scattered by the inner wall of the torus and/or by photoionized gas
within the Broad Line Region observed through the thinner rim of the
circumnuclear matter.Comment: MNRAS Letters, in pres
A connection between accretion state and in an accreting neutron star: black hole-like soft state winds?
High resolution X-ray spectra of accreting stellar mass Black Holes reveal
the presence of accretion disc winds, traced by high ionisation Fe K lines.
These winds appear to have an equatorial geometry and to be observed only
during disc dominated states in which the radio jet is absent. Accreting
neutron star systems also show equatorial high ionisation absorbers. However,
the presence of any correlation with the accretion state has not been
previously tested. We have studied EXO 0748-676, a transient neutron star
system, for which we can reliably determine the accretion state, in order to
investigate the Fe K absorption/accretion state/jet connection. Not one of
twenty X-ray spectra obtained in the hard state revealed any significant Fe K
absorption line. However, intense Fe and Fe
(as well as a rarely observed Fe line plus S ; a blend of S and Ar ; Ca and Ca
, possibly produced by the same high ionisation
material) absorption lines ( eV, eV) are clearly detected during the only soft state
observation. This suggests that the connection between Fe K absorption and
states (and anticorrelation between the presence of Fe K absorption and jets)
is also valid for EXO 0748-676 and therefore it is not a unique property of
black hole systems but a more general characteristic of accreting sources.Comment: Accepted for publication in MNRAS Letter
Constraints on a strong X-ray flare in the Seyfert galaxy MCG-6-30-15
We discuss implications of a strong flare event observed in the Seyfert
galaxy MCG-6-30-15 assuming that the emission is due to localized magnetic
reconnection. We conduct detailed radiative transfer modeling of the
reprocessed radiation for a primary source that is elevated above the disk. The
model includes relativistic effects and Keplerian motion around the black hole.
We show that for such a model setup the observed time-modulation must be
intrinsic to the primary source. Using a simple analytical model we then
investigate time delays between hard and soft X-rays during the flare. The
model considers an intrinsic delay between primary and reprocessed radiation,
which measures the geometrical distance of the flare source to the reprocessing
sites. The observed time delays are well reproduced if one assumes that the
reprocessing happens in magnetically confined, cold clouds.Comment: 4 pages, 2 figures, proceedings of a talk given at the symposium 238
at the IAU General Assembly 200
Polarization and long-term variability of Sgr A* X-ray echo
We use a model of the molecular gas distribution within ~100 pc from the
center of the Milky Way (Kruijssen, Dale & Longmore) to simulate time evolution
and polarization properties of the reflected X-ray emission, associated with
the past outbursts from Sgr A*. While this model is too simple to describe the
complexity of the true gas distribution, it illustrates the importance and
power of long-term observations of the reflected emission. We show that the
variable part of X-ray emission observed by Chandra and XMM from prominent
molecular clouds is well described by a pure reflection model, providing strong
support of the reflection scenario. While the identification of Sgr A* as a
primary source for this reflected emission is already a very appealing
hypothesis, a decisive test of this model can be provided by future X-ray
polarimetric observations, that will allow placing constraints on the location
of the primary source. In addition, X-ray polarimeters (like, e.g., XIPE) have
sufficient sensitivity to constrain the line-of-sight positions of molecular
complexes, removing major uncertainty in the model.Comment: 17 pages, 10 figures, accepted for publication in MNRA
Can Sgr A* flares reveal the molecular gas density PDF?
Illumination of dense gas in the Central Molecular Zone (CMZ) by powerful
X-ray flares from Sgr A* leads to prominent structures in the reflected
emission that can be observed long after the end of the flare. By studying this
emission we learn about past activity of the supermassive black hole in our
Galactic Center and, at the same time, we obtain unique information on the
structure of molecular clouds that is essentially impossible to get by other
means. Here we discuss how X-ray data can improve our knowledge of both sides
of the problem. Existing data already provide: i) an estimate of the flare age,
ii) a model-independent lower limit on the luminosity of Sgr A* during the
flare and iii) an estimate of the total emitted energy during Sgr A* flare. On
the molecular clouds side, the data clearly show a voids-and-walls structure of
the clouds and can provide an almost unbiased probe of the mass/density
distribution of the molecular gas with the hydrogen column densities lower than
few . For instance, the probability distribution
function of the gas density can be measured this way. Future high
energy resolution X-ray missions will provide the information on the gas
velocities, allowing, for example a reconstruction of the velocity field
structure functions and cross-matching the X-ray and molecular data based on
positions and velocities.Comment: 13 pages, 7 figures; Accepted for publication in MNRA
Not that long time ago in the nearest galaxy: 3D slice of molecular gas revealed by a 110 years old flare of Sgr A*
A powerful outburst of X-ray radiation from the supermassive black hole Sgr
A* at the center of the Milky Way is believed to be responsible for the
illumination of molecular clouds in the central ~100 pc of the Galaxy (Sunyaev
et al., 1993, Koyama et al., 1996). The reflected/reprocessed radiation comes
to us with a delay corresponding to the light propagation time that depends on
the 3D position of molecular clouds with respect to Sgr A*. We suggest a novel
way of determining the age of the outburst and positions of the clouds by
studying characteristic imprints left by the outburst in the spatial and time
variations of the reflected emission. We estimated the age of the outburst that
illuminates the Sgr A molecular complex to be ~110 yr. This estimate implies
that we see the gas located ~10 pc further away from us than Sgr A*. If the Sgr
B2 complex is also illuminated by the same outburst, then it is located ~130 pc
closer than our Galactic Center. The outburst was short (less than a few years)
and the total amount of emitted energy in X-rays is erg, where is the mean hydrogen density of the
cloud complex in units of . Energetically, such fluence can
be provided by a partial tidal disruption event or even by a capture of a
planet. Further progress in more accurate positioning and timing of the
outburst should be possible with future X-ray polarimetric observations and
long-term systematic observations with Chandra and XMM-Newton. A few
hundred-years long X-ray observations would provide a detailed 3D map of the
gas density distribution in the central pc region.Comment: 10 pages, 7 figures, accepted for publication in MNRA
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