1,902 research outputs found
XMM-Newton study of the ULIRG NGC 6240
A recently performed XMM-Newton observation of the ULIRG NGC 6240 clearly
indicates the presence of an AGN contribution to its X-ray spectrum. In the 5.0
- 7.0 keV energy range there is a clear signature of the fluorescent Fe K lines
at 6.4, 6.7 and 6.9 keV, respectively.
The line strength of the 6.4 keV line cannot be produced by a thermal
component. The 0.3 - 10.0 keV spectral energy distribution is characterized by
the following components: (I) two hot thermal components (the starburst), (II)
one direct component (heavily absorbed; AGN is hidden), (III) one reflection
component (the AGN), (IV) three narrow Fe lines. The model parameters for the
broad-band spectral energy distribution are consistent with the results of
previously works.Comment: 2 pages incl. 2 figures, to appear in the proceedings of the "New
Century of X-ray Astronomy" symposium held in Yokohama, Japan (March 6-8,
2001), eds. H. Kunieda and H. Inoue, ASP pres
Does AFLP Diversity Reflect Consanguinity Within Meadow Fescue Breeding Material?
Cultivars of perennial grass species are usually synthetics with a limited number of constituent parental clones, prone to inbreeding depression. Plant breeders aim at a balance between intensity of selection and maintenance of genetic diversity when making their choice of parent clones in an intuitive way, aided by fragmentary pedigree information. Molecular markers offer new opportunities for assessing genetic diversity among selected plants. The objective of the investigation presented here is to check if the genetic distance as measured by AFLP polymorphisms reflects consanguinity among Festuca pratensis individuals from our breeding programme
Search for X-ray Afterglows from Gamma-Ray Bursts in the RASS
We report on a search for X-ray afterglows from gamma-ray bursts using the
ROSAT all-sky survey (RASS) data. If the emission in the soft X-ray band is
significantly less beamed than in the gamma-ray band, we expect to detect many
afterglows in the RASS. Our search procedure generated 23 afterglow candidates,
where about 4 detections are predicted. Follow-up spectroscopy of several
counterpart candidates strongly suggests a flare star origin of the RASS events
in many, if not all, cases. Given the small number of events we conclude that
the data are consistent with comparable beaming angles in the X-ray and
gamma-ray bands. Models predicting a large amount of energy emerging as a
nearly isotropic X-ray component, and a so far undetected class of ``dirty
fireballs'' and re-bursts are constrained.Comment: 5 pages, LATEX with aipproc.sty, incl. 1 ps-Fig., Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AIP; also
available at http://www.aip.de/~jcg/publis.htm
HST STIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow-line Seyfert 1 Galaxies: II. Modeling and Interpretation
We present modeling to explore the conditions of the broad-line emitting gas
in two extreme Narrow-line Seyfert 1 galaxies, using the observational results
described in the first paper of this series. Photoionization modeling using
Cloudy was conducted for the broad, blueshifted wind lines and the narrow,
symmetric, rest-wavelength-centered disk lines separately. A broad range of
physical conditions were explored for the wind component, and a figure of merit
was used to quantitatively evaluate the simulation results. Of the three minima
in the figure-of-merit parameter space, we favor the solution characterized by
an X-ray weak continuum, elevated abundances, a small column density
(log(N_H)\approx 21.4), relatively high ionization parameter (log(U)\approx
-1.2 - -0.2), a wide range of densities (log(n)\approx 7 - 11), and a covering
fraction of ~0.15. The presence of low-ionization emission lines implies the
disk component is optically thick to the continuum, and the SiIII]/CIII] ratio
implies a density of 10^10 - 10^10.25 cm^-3. A low ionization parameter
(log(U)=-3) is inferred for the intermediate-ionization lines, unless the
continuum is ``filtered'' through the wind before illuminating the
intermediate-line emitting gas, in which case log(U)=-2.1. The location of the
emission regions was inferred from the photoionization modeling and a simple
``toy'' dynamical model. A large black hole mass (1.3 x 10^8 M_\odot) radiating
at 11% of the Eddington luminosity is consistent with the kinematics of both
the disk and wind lines, and an emission radius of ~10^4 R_S is inferred for
both. We compare these results with previous work and discuss implications.Comment: 45 pages, 15 figures (4 color), accepted for publication in ApJ,
abstract shortene
XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the complex Fe K line emission
We report on an XMM-Newton observation of the ultraluminous infrared galaxy
NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three
collisionally ionized plasma components with temperatures of about 0.7, 1.4,
and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a
neutral Fe K_alpha and K_beta line. We detect a significant neutral column
density gradient which is correlated with the temperature of the three plasma
components. Combining the XMM-Newton spectral model with the high spatial
resolution Chandra image we find that the temperatures and the column densities
increase towards the center.
With high significance, the Fe K line complex is resolved into three distinct
narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line
at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe
XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due
to reflection from optically thick material, the Fe XXV and Fe XXVI emission
arises from the highest temperature ionized plasma component.
We have compared the plasma parameters of the ultraluminous infrared galaxy
NGC 6240 with those found in the local starburst galaxy NGC 253. We find a
striking similarity in the plasma temperatures and column density gradients,
suggesting a similar underlying physical process at work in both galaxies.Comment: 8 pages including 9 figures. Accepted for publication in A&
XMM-Newton observations of the BL Lac MS 0737+7441
We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441
during the performance verification phase. A simple power-law fit provides an
adequate description of the integrated spectrum in the 0.2-10 keV energy band.
The photon index is slightly steeper in the EPIC pn data with 2.38+-0.01
compared to the EPIC MOS data (2.28+-0.01). The difference is most probably due
to the present uncertainties in the calibration of the EPIC MOS and EPIC pn
data sets. We report evidence for intrinsic absorption in the distant BL Lac
above the Galactic column N_H,Gal=3.2*10^20 cm^-2 which is N_H,fit(z=0.315)=
(2.70+-0.20)*10^20cm^-2 in the EPIC pn data and N_H,fit(z=0.315)=
(3.25+-0.25)*10^20cm^-2 in the EPIC MOS data assuming neutral gas and solar
abundances. The flux variations are found to be of the order of 10 %.Comment: 4 pages, 4 Figures, accepted for publication in the special A&A
Letters issue for XMM-Newto
HST STIS Ultraviolet Spectral Evidence for Outflow in Extreme Narrow-line Seyfert 1 Galaxies: I. Data and Analysis
We present HST STIS observations of two extreme NLS1s, IRAS 13224-3809 and 1H
0707-495. The spectra are characterized by very blue continua, broad, strongly
blueshifted high-ionization lines (including \ion{C}{4} and \ion{N}{5}), and
narrow, symmetric intermediate- (including \ion{C}{3}], \ion{Si}{3}],
\ion{Al}{3}) and low-ionization (e.g., \ion{Mg}{2}) lines centered at their
rest wavelengths. The emission-line profiles suggest that the high-ionization
lines are produced in a wind, and the intermediate- and low-ionization lines
are produced in low-velocity gas associated with the accretion disk or base of
the wind. In this paper, we present the analysis of the spectra from these two
objects; in a companion paper we present photoionization analysis and a toy
dynamical model for the wind. The highly asymmetric profile of \ion{C}{4}
suggests that it is dominated by emission from the wind, so we develop a
template for the wind from the \ion{C}{4} line. We model the bright emission
lines in the spectra using a combination of this template, and a narrow,
symmetric line centered at the rest wavelength. We also analyzed a comparison
sample of HST spectra from 14 additional NLS1s, and construct a correlation
matrix of emission line and continuum properties. A number of strong
correlations were observed, including several involving the asymmetry of the
\ion{C}{4} line.Comment: 26 pages, 10 figures, accepted for publication in ApJ with no change
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