259 research outputs found
Variable line profiles due to non-axisymmetric patterns in an accretion disc around a rotating black hole
We have explored spectral line profiles due to spiral patterns in accretion
discs around black holes. A parametrization was employed for the shape and
emissivity of spiral waves, which can be produced by non-axisymmetric
perturbations affecting the disc density and ionization structure. The effects
of the light-travel time, energy shift, and gravitational focusing near to a
rotating black hole were taken into account. A high-resolution ray-tracing code
was used to follow the time variations of the synthetic line profile. A variety
of expected spectral features were examined and the scheme applied to a broad
iron line observed in MCG-6-30-15.Comment: 11 pages (LaTeX), 7 figures (EPS); PASJ accepte
On the origin of the broad, relativistic iron line of MCG-6-30-15 observed by XMM-Newton
The relativistic iron line profile recently observed by XMM-Newton in the spectrum of the Seyfert 1 galaxy MCG--6-30-15 (Wilms et al., 2001) is discussed in the framework of the lamp-post model. It is shown that the steep disc emissivity, the large line equivalent width and the amount of Compton reflection can be self- consistently reproduced in this scenario
Effects of Kerr Spacetime on Spectral Features from X-Ray Illuminated Accretion Discs
We performed detailed calculations of the relativistic effects acting on both
the reflection continuum and the iron line from accretion discs around rotating
black holes. Fully relativistic transfer of both illuminating and reprocessed
photons has been considered in Kerr spacetime. We calculated overall spectra,
line profiles and integral quantities, and present their dependences on the
black hole angular momentum.
We show that the observed EW of the lines is substantially enlarged when the
black hole rotates rapidly and/or the source of illumination is near above the
hole. Therefore, such calculations provide a way to distinguish among different
models of the central source.Comment: 9 pages, latex, 13 figures, 3 Tables; accepted for publication in
MNRA
The XMM-Newton view of the relativistic spectral features in AXJ0447-0627
The XMM-Newton observation of the optically Type 1 AGN AXJ0447-0627 (z=0.214)
unambiguously reveals a complex, bright and prominent set of lines in the 4-8
keV rest frame energy range. Although, from a phenomenological point of view,
the observed properties can be described by a simple power law model plus 5
narrow Gaussian lines (at rest frame energies of nearly 4.49, 5.55, 6.39, 7.02
and 7.85 keV), we find that a model comprising a power law (Gamma of the order
of 2.2), a reflected relativistic continuum, a narrow Fe I Kalpha line from
neutral material as well as a broad Fe Kalpha relativistic line from a ionized
accretion disk represents a good physical description of the data. The ''double
horned'' profile of the relativistic line implies an inclination of the
accretion disk of the order of 45 degree, and an origin in a narrow region of
the disk, from R_in of the order of 19 GM/c^2 to R_out of the order of 30
GM/c^2. The narrow Fe I Kalpha line from neutral material is probably produced
far from the central black hole, most likely in the putative molecular torus.
Although some of these properties have been already found in other Type 1 AGN
and discussed in the literature, at odd with the objects reported so far we
measure high equivalent widths (EWs) of the observed lines: nearly 1.4 keV for
the ``double horned'' relativistic line and nearly 0.4 keV for the narrow line.Comment: 16 pages, 3 figures, Latex manuscript; accepted for publication in
Ap
The WISSH Quasars Project III. X-ray properties of hyper-luminous quasars
We perform a survey of the X-ray properties of 41 objects from the WISE/SDSS
selected Hyper-luminous (WISSH) quasars sample, composed by 86 broad-line
quasars (QSOs) with bolometric luminosity , at z~2-4. All but 3 QSOs show unabsorbed 2-10 keV luminosities
. Thanks to their extreme radiative output
across the Mid-IR-to-X-ray range, WISSH QSOs offer the opportunity to
significantly extend and validate the existing relations involving .
We study as a function of (i) X-ray-to-Optical (X/O) flux ratio,
(ii) mid-IR luminosity (), (iii) as well as (iv)
vs. the 2500 luminosity. We find that WISSH QSOs
show very low X/O(<0.1) compared to typical AGN values;
ratios significantly smaller than those derived for AGN with lower luminosity;
large X-ray bolometric corrections 100-1000; and steep
. These results lead to a scenario where the X-ray
emission of hyper-luminous quasars is relatively weaker compared to
lower-luminosity AGN. Models predict that such an X-ray weakness can be
relevant for the acceleration of powerful high-ionization emission line-driven
winds, commonly detected in the UV spectra of WISSH QSOs, which can in turn
perturb the X-ray corona and weaken its emission. Accordingly, hyper-luminous
QSOs represent the ideal laboratory to study the link between the AGN energy
output and wind acceleration. Additionally, WISSH QSOs show very large BH
masses (>9.5). This enables a more robust modeling
of the relation by increasing the statistics at high masses. We
derive a flatter dependence than previously found over the broad range
5 < < 11.Comment: 20 pages, 14 Figures. Accepted for publication on A&
Evidence for a relativistic iron line in GRS 1915+105
We report on the discovery of a relativistic iron K\alpha fluorescent
emission line in the BeppoSAX spectrum of the microquasar GRS 1915+105, taken
on April 19, 1998, when the line was unusually intense. The feature is broad
and skewed, clearly indicating emission from the innermost regions of the
accretion disc. The inner emitting orbit is larger than the innermost stable
orbit, even in Schwarzschild metric: thus, a non-zero BH spin is not required
by these data.Comment: 7 pages, accepted for publication on A&
Iron K-alpha Fluorescent Line Profiles from Spiral Accretion Flows in AGNs
We present 6.4 keV iron K-alpha fluorescent line profiles predicted for a
relativistic black hole accretion disk in the presence of a spiral motion in
Kerr geometry, the work extended from an earlier literature motivated by recent
magnetohydrodynamic (MHD) simulations. The velocity field of the spiral motion,
superposed on the background Keplerian flow, results in a complicated redshift
distribution in the accretion disk. An X-ray source attributed to a localized
flaring region on the black hole symmetry axis illuminates the iron in the
disk. The emissivity form becomes very steep because of the light bending
effect from the primary X-ray source to the disk. The predicted line profile is
calculated for various spiral waves, and we found, regardless of the source
height, that: (i) a multiple-peak along with a classical double-peak structure
generally appears, (ii) such a multiple-peak can be categorized into two types,
sharp sub-peaks and periodic spiky peaks, (iii) a tightly-packed spiral wave
tends to produce more spiky multiple peaks, whereas (iv) a spiral wave with a
larger amplitude seems to generate more sharp sub-peaks, (v) the effect seems
to be less significant when the spiral wave is centrally concentrated, (vi) the
line shape may show a drastic change (forming a double-peak, triple-peak or
multiple-peak feature) as the spiral wave rotates with the disk. Our results
emphasize that around a rapidly-rotating black hole an extremely redshifted
iron line profile with a noticeable spike-like feature can be realized in the
presence of the spiral wave. Future X-ray observations, from {\it Astro-E2} for
example, will have sufficient spectral resolution for testing our spiral wave
model which exhibits unique spike-like features.Comment: 30 pages, 10 figures, submitted to ApJ, will be presented at 204th
Meeting of AAS in Denve
Broad-band X-ray measurements of the black hole candidate XTE J1908+094
XTE J1908+094 is an X-ray transient that went into outburst in February 2002.
After two months it reached a 2-250 keV peak flux of 1 to 2 X 10-8 erg/s/cm2.
Circumstantial evidence points to an accreting galactic black hole as the
origin of the the X-radiation: pulsations nor thermonuclear flashes were
detected that would identify a neutron star and the spectrum was unusually hard
for a neutron star at the outburst onset. We report on BeppoSAX and RXTE All
Sky Monitor observations of the broad-band spectrum of XTE J1908+094. The
spectrum is consistent with a model consisting of a Comptonization component by
a ~40 keV plasma (between 2 and 60 keV this component can be approximated by a
power law with a photon index of 1.9 to 2.1), a multicolor accretion disk
blackbody component with a temperature just below 1 keV and a broad emission
line at about 6 keV. The spectrum is heavily absorbed by cold interstellar
matter with an equivalent hydrogen column density of 2.5 X 10+22 cm-2, which
makes it difficult to study the black body component in detail. The black body
component exhibits strong evolution about 6 weeks into the outburst. Two weeks
later this is followed by a swift decay of the power law component. The
broadness of the 6 keV feature may be due to relativistic broadening or Compton
scattering of a narrow Fe-K line.Comment: Accepted for publication in Astronomy & Astrophysic
Expanding the Time Domain of Multiple Populations: Evidence of Nitrogen Variations in the ~1.5 Gyr Old Star Cluster NGC 1783
We present the result of a detailed analysis of Hubble Space Telescope UV and optical deep images of the massive and young (~1.5 Gyr) stellar cluster NGC 1783 in the Large Magellanic Cloud. This system does not show evidence of multiple populations (MPs) along the red giant branch (RGB) stars. However, we find that the cluster main sequence (MS) shows evidence of a significant broadening (50% larger than what is expected from photometric errors) along with hints of possible bimodality in the MP sensitive (m F343N - m F438W, m F438W) color-magnitude diagram (CMD). Such an effect is observed in all color combinations including the m F343N filter, while it is not found in the optical CMDs. This observational evidence suggests we might have found light-element chemical abundance variations along the MS of NGC 1783, which represents the first detection of MPs in a system younger than 2 Gyr. A comparison with isochrones including MP-like abundances shows that the observed broadening is compatible with a N abundance enhancement of ?([N/Fe]) ~ 0.3. Our analysis also confirms previous results about the lack of MPs along the cluster RGB. However, we find that the apparent disagreement between the results found on the MS and the RGB is compatible with the mixing effects linked to the first dredge up. This study provides new key information about the MP phenomenon and suggests that star clusters form in a similar way at any cosmic age
- …