420 research outputs found
Absorption spectra of Fe L-lines in Seyfert 1 galaxies
Absorption L-lines of iron ions are observed, in absorption, in spectra of
Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA)
and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved.
Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden
transitions of the Fe16+ to Fe6+ ions were previously observed, for the same
objects, in the visible and infra-red regions, showing that the plasma had a
low density. To interpret X-ray, visible and infra-red data, astrophysical
models assume an extended absorbing medium of very low density surrounding an
intense X-ray source. We have calculated atomic data (wavelengths, radiative
and autoionization rates) for n=2 to n'=3-4 transitions and used them to
construct refined synthetic spectra of the unresolved part of the L-line
spectra.Comment: 17 pages, 5 figures, Journal of Quantitative Spectroscopy and
Radiative Transfer, in pres
A prominent relativistic iron line in the Seyfert 1 MCG-02-14-009
I report the discovery of a prominent broad and asymmetrical feature near 6.4
keV in the Seyfert 1 MCG-02-14-009 (z=0.028) with XMM-Newton/EPIC. The present
short X-ray observation (PN net exposure time ~5 ks) is the first one above 2
keV for MCG-02-14-009. The feature can be explained by either a relativistic
iron line around either a Schwarzschild (non-rotating) or a Kerr (rotating)
black hole. If the feature is a relativistic iron line around a Schwarzschild
black hole, the line energy is 6.51 (+0.21,-0.12) keV with an equivalent width
of 631 (+259,-243) eV and that the inclination angle of the accretion disc
should be less than 43 degrees. A relativistically blurred photoionized disc
model gives a very good spectral fit over the broad band 0.2-12keV energy
range. The spectrum is reflection dominated and this would indicate that the
primary source in MCG-02-14-009 is located very close to the black hole, where
gravitational light bending effect is important (about 3-4 Rg), and that the
black hole may rapidly rotate.Comment: Accepted for publication, A&A Letters, 5 pages, 3 figures, and 1
tabl
Discovery of X-ray eclipses from the transient source CXOGC J174540.0-290031 with XMM-Newton
We present the XMM-Newton observations obtained during four revolutions in
Spring and Summer 2004 of CXOGC J174540.0-290031, a moderately bright transient
X-ray source, located at only 2.9" from SgrA*. We report the discovery of sharp
and deep X-ray eclipses, with a period of 27,961+/-5 s and a duration of about
1,100+/-100 s, observed during the two consecutive XMM revolutions from August
31 to September 2. No deep eclipses were present during the two consecutive XMM
revolutions from March 28 to April 1, 2004. The spectra during all four
observations are well described with an absorbed power law continuum. While our
fits on the power law index over the four observations yield values that are
consistent with Gamma=1.6-2.0, there appears to be a significant increase in
the column density during the Summer 2004 observations, i.e. the period during
which the eclipses are detected. The intrinsic luminosity in the 2-10 keV
energy range is almost constant with 1.8-2.3 x 10^34 (d_8kpc)^2 erg/s over the
four observations. In the framework of eclipsing semidetached binary systems,
we show that the eclipse period constrains the mass of the assumed
main-sequence secondary star to less than 1.0 M_odot. Therefore, we deduce that
CXOGC J174540.0-290031 is a low-mass X-ray binary (LMXB). Moreover the eclipse
duration constrains the mass of the compact object to less than about 60
M_odot, which is consistent with a stellar mass black hole or a neutron star.
The absence of deep X-ray eclipses during the Spring 2004 observations could be
explained if the centroid of the X-ray emitting region moves from a position on
the orbital plane to a point above the compact object, possibly coincident with
the base of the jet which was detected in radio at this epoch. [Abstract
truncated].Comment: A&A, accepted for publication (10 pages, 8 figures, 2 Tables
Multi-Wavelength Study of Sgr A*: The Short Time Scale Variability
To understand the correlation and the radiation mechanism of flare emission
in different wavelength bands, we have coordinated a number of telescopes to
observe SgrA* simultaneously. We focus only on one aspect of the preliminary
results of our multi-wavelength observing campaigns, namely, the short time
scale variability of emission from SgrA* in near-IR, X-ray and radio
wavelengths. The structure function analysis indicate most of the power
spectral density is detected on hourly time scales in all wavelength bands. We
also report minute time scale variability at 7 and 13mm placing a strong
constraint on the nature of the variable emission. The hourly time scale
variability can be explained in the context of a model in which the peak
frequency of emission shifts toward lower frequencies as a self-absorbed
synchrotron source expands adiabatically near the acceleration site. The short
time scale variability, on the other hand, places a strong constraint on the
size of the emitting region. Assuming that rapid minute time scale fluctuations
of the emission is optically thick in radio wavelength, light travel arguments
requires relativistic particle energy, thus suggesting the presence of outflow
from SgrA*.Comment: 9 pages, 4 figures, The Galactic Center: A Window on the Nuclear
Environment of Disk Galaxies ASP Conference Series, 2010 eds: M. Morris, D.
Q. Wang and F. Yua
Evidence for a Truncated Accretion Disc in the Low Luminosity Seyfert Galaxy, NGC 7213?
We present the broad-band 0.6-150 keV Suzaku and Swift BAT spectra of the low
luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is
well fitted by a single powerlaw of photon index Gamma = 1.75 and from
consideration of the Fermi flux limit we constrain the high energy cutoff to be
350 keV < E < 25 MeV. Line emission from both near-neutral iron K_alpha at 6.39
keV and highly ionised iron, from Fe_(xxv) and Fe_(xxvi), is strongly detected
in the Suzaku spectrum, further confirming the results of previous observations
with Chandra and XMM-Newton. We find the centroid energies for the Fe_(xxv) and
Fe_(xxvi) emission to be 6.60 keV and 6.95 keV respectively, with the latter
appearing to be resolved in the Suzaku spectrum. We show that the Fe_(xxv) and
Fe_(xxvi) emission can result from a highly photo-ionised plasma of column
density N_(H) ~ 3 x 10^(23) cm^(-2). A Compton reflection component, e.g.,
originating from an optically-thick accretion disc or a Compton-thick torus,
appears either very weak or absent in this AGN, subtending < 1 sr to the X-ray
source, consistent with previous findings. Indeed the absence of either neutral
or ionised Compton reflection coupled with the lack of any relativistic Fe K
signatures in the spectrum suggests that an inner, optically-thick accretion
disc is absent in this source. Instead, the accretion disc could be truncated
with the inner regions perhaps replaced by a Compton-thin Radiatively
Inefficient Accretion Flow. Thus, the Fe_(xxv) and Fe_(xxvi) emission could
both originate in ionised material perhaps at the transition region between the
hot, inner flow and the cold, truncated accretion disc on the order of 10^(3) -
10^(4) gravitational radii from the black hole. The origin for the unresolved
neutral Fe K_alpha emission is then likely to be further out, perhaps
originating in the optical BLR or a Compton-thin pc-scale torus.Comment: 15 pages, 11 figures, accepted for publication by MNRA
An extreme, blueshifted iron line profile in the Narrow Line Seyfert 1 PG 1402+261; an edge-on accretion disk or highly ionized absorption?
We report on a short XMM-Newton observation of the radio-quiet Narrow Line
Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong
excess of counts between 6-9 keV in the rest frame. This feature can be modeled
by an unusually strong (equivalent width 2 keV) and very broad (FWHM velocity
of 110000 km/s) iron K-shell emission line. The line centroid energy at 7.3 keV
appears blue-shifted with respect to the iron Kalpha emission band between
6.4-6.97 keV, while the blue-wing of the line extends to 9 keV in the quasar
rest frame. The line profile can be fitted by reflection from the inner
accretion disk, but an inclination angle of >60 deg is required to model the
extreme blue-wing of the line. Furthermore the extreme strength of the line
requires a geometry whereby the hard X-ray emission from PG 1402+261 above 2
keV is dominated by the pure-reflection component from the disk, while little
or none of the direct hard power-law is observed. Alternatively the spectrum
above 2 keV may instead be explained by an ionized absorber, if the column
density is sufficiently high (N_H > 3 x 10^23 cm^-2) and if the matter is
ionized enough to produce a deep (tau~1) iron K-shell absorption edge at 9 keV.
This absorber could originate in a large column density, high velocity outflow,
perhaps similar to those which appear to be observed in several other high
accretion rate AGN. Further observations, especially at higher spectral
resolution, are required to distinguish between the accretion disk reflection
or outflow scenarios.Comment: Accepted for publication in ApJ (18 pages, 5 figures, 1 table
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