33,218 research outputs found
The XMM-Newton Iron Line Profile of NGC 3783
We report on observations of the iron K line in the nearby Seyfert 1 galaxy,
NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line
profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV,
with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV
emission is the K-alpha line from near neutral Fe, whilst the 7.0 keV feature
probably originates from a blend of the neutral Fe K-beta line and the H-like
line of Fe at 6.97 keV. The relatively narrow velocity width of the K-alpha
line (<5000 km/s), its lack of response to the continuum emission on short
timescales and the detection of a neutral Compton reflection component are all
consistent with a distant origin in Compton-thick matter such as the putative
molecular torus. A strong absorption line from highly ionized iron (at 6.67
keV) is detected in the time-averaged iron line profile, whilst the depth of
the feature appears to vary with time, being strongest when the continuum flux
is higher. The iron absorption line probably arises from the highest ionization
component of the known warm absorber in NGC 3783, with an ionization of logxi=3
and column density of 5x10^{22}cm{-2} and may originate from within 0.1pc of
the nucleus. A weak red-wing to the iron K line profile is also detected below
6.4 keV. However when the effect of the highly ionized warm absorber on the
underlying continuum is taken into account, the requirement for a relativistic
iron line component from the inner disk is reduced.Comment: 34 pages, including 11 figures. Accepted for publication in Ap
ASCA observations of type-2 Seyfert galaxies: II. The Importance of X-ray Scattering and Reflection
We discuss the importance of X-ray scattering and Compton reflection in
type-2 Seyfert galaxies, based upon the analysis of ASCA observations of 25
such sources. Consideration of the iron Kalpha, [O III] line and X-ray
variability suggest that NGC 1068, NGC 4945, NGC 2992, Mrk 3, Mrk 463E and Mrk
273 are dominated by reprocessed X-rays. We examine the properties of these
sources in more detail.
We find that the iron Kalpha complex contains significant contributions from
neutral and high-ionization species of iron. Compton reflection, hot gas and
starburst emission all appear to make significant contributions to the observed
X-ray spectra.
Mrk 3 is the only source in this subsample which does not have a significant
starburst contamination. The ASCA spectrum below 3 keV is dominated by hot
scattering gas with U_X ~ 5, N_H ~ 4 x 10^23 cm^-2. This material is more
highly ionized than the zone of material comprising the warm absorber seen in
Seyfert~1 galaxies, but may contain a contribution from shock-heated gas
associated with the jet. Estimates of the X-ray scattering fraction cover 0.25
- 5%. The spectrum above 3 keV appears to be dominated by a Compton reflection
component although there is evidence that the primary continuum component
becomes visible close to 10 keV.Comment: 27 pages, 6 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journal. Also available via
http://lheawww.gsfc.nasa.gov/~george/papers/gnt_s2p2/abstract.htm
Correlation of electrical conductivity and radiation-induced free radical concentration in poly/ethylene terephthalate/ and related compounds
Gamma and ultraviolet radiation effects on electronic properties of polyethylene terephthalate and related compound
The topological glass in ring polymers
We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward Tg. Here we are interested in temperatures well above Tg where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics
SHEEP: The Search for the High Energy Extragalactic Population
We present the SHEEP survey for serendipitously-detected hard X-ray sources
in ASCA GIS images. In a survey area of deg, 69 sources were
detected in the 5-10 keV band to a limiting flux of erg
cm s. The number counts agree with those obtained by the similar
BeppoSAX HELLAS survey, and both are in close agreement with ASCA and BeppoSAX
2-10 keV surveys. Spectral analysis of the SHEEP sample reveals that the 2-10
and 5-10 keV surveys do not sample the same populations, however, as we find
considerably harder spectra, with an average assuming no
absorption. The implication is that the agreement in the number counts is
coincidental, with the 5-10 keV surveys gaining approximately as many hard
sources as they lose soft ones, when compared to the 2-10 keV surveys. This is
hard to reconcile with standard AGN ``population synthesis'' models for the
X-ray background, which posit the existence of a large population of absorbed
sources. We find no evidence of the population hardening at faint fluxes, with
the exception that the few very brightest objects are anomalously soft. 53 of
the SHEEP sources have been covered by ROSAT in the pointed phase. Of these 32
were detected. An additional 3 were detected in the RASS. As expected the
sources detected with ROSAT are systematically softer than those detected with
ASCA alone, and of the sample as a whole (truncated).Comment: 36 pages, 7 figs, to appear in Ap
A Highly Doppler Blueshifted Fe-K Emission Line in the High-Redshift QSO PKS 2149-306
We report the results from an \asca observation of the QSO PKS 2149-306
(z=2.345). We detect an emission line centered at keV in the quasar
frame. Line emission at this energy has not been observed in any other active
galaxy or quasar to date. We present evidence rejecting the possibility that
this line is the result of instrumental artifacts, or a serendipitous source.
The most likely explanation is blueshifted Fe-K emission (the EW is 300+/-200
eV, QSO frame). Bulk velocities of the order of 0.75c are implied by the data.
We show that Fe-K line photons originating in an accretion disk and
Compton-scattering off a leptonic can account for the emission line. Curiously,
if the emission-line feature recently discovered in another quasar PKS
0637752, , is blueshifted Ovii, the Doppler factor is the same
(~2.7) for both.Comment: 15 pages plus 3 figures. Latex with separate .ps files (Accepted by
Astrophysical Journal Letters
The use of satellites in non-goestationary orbits for unloading geostationary communication satellite traffic peaks. Volume 2: Technical report
The part of the geostationary (GEO) orbital arc used for United States domestic fixed, communications service is rapidly becoming filled with satellites. One of the factors currently limiting its utilization is that communications satellites must be designed to have sufficient capacity to handle peak traffic leads, and thus are under utilized most of the time. A solution is to use satellites in suitable non-geostationary orbits to unload the traffic peaks. Three different designs for a non-geostationary orbit communications satellite system are presented for the 1995 time frame. The economic performance is analyzed and compared with geostationary satellites for two classes of service, trunking and customer premise service. The result is that the larger payload of the non-geostationary satellite offsets the burdens of increased complexity and worse radiation environment to give improved economic performance. Depending on ground terminal configuration, the improved economic performance of the space segment may be offset by increased ground terminal expenses
X-ray Observations of the Seyfert galaxy LB 1727 (1H 0419-577)
We discuss the properties of the Seyfert 1.5 galaxy LB 1727, also known as 1H
0419-577, from X-ray observations obtained by ASCA and ROSAT along with optical
observations from earlier epochs. ASCA shows only modest (< 20%) variations in
X-ray flux within or between the observations. In contrast, a daily monitoring
campaign over 1996 Jun - Sept by the ROSAT HRI instrument reveals the soft
X-ray (0.1-2 keV) flux to have increased by a factor ~3.
The 2 - 10 keV continuum can be parameterized as a power-law with a photon
index Gamma ~ 1.45-1.68 across ~0.7 - 11 keV in the rest-frame. We also report
the first detection of iron Kalpha line emission in this source. Simultaneous
ASCA and ROSAT data show the X-ray spectrum to steepen sharply at a rest-energy
\~0.75 keV, the spectrum below this energy can be parameterized as a power-law
of slope Gamma ~3.6. We show that LB 1727 is one of the few Seyferts for which
we can rule out the possibility that the presence of a warm absorber is solely
responsible for the spectral steepening in the soft X-ray regime. Consideration
of the overall spectral-energy-distribution for this source indicates the
presence of a pronounced XUV-bump visible in optical, ultraviolet and soft
X-ray data.Comment: 27 pages, 7 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journa
Hypothesis of path integral duality: Applications to QED
We use the modified propagator for quantum field based on a ``principle of
path integral duality" proposed earlier in a paper by Padmanabhan to
investigate several results in QED. This procedure modifies the Feynman
propagator by the introduction of a fundamental length scale. We use this
modified propagator for the Dirac particles to evaluate the first order
radiative corrections in QED. We find that the extra factor of the modified
propagator acts like a regulator at the Planck scales thereby removing the
divergences that otherwise appear in the conventional radiative correction
calculations of QED. We find that:(i) all the three renormalisation factors
, , and pick up finite corrections and (ii) the modified
propagator breaks the gauge invariance at a very small level of
. The implications of this result to generation of the
primordial seed magnetic fields are discussed.Comment: 15 pages, LaTeX2e (uses ijmpd.sty); To appear in IJMP-D; References
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