865 research outputs found
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
Old and Young X-ray Point Source Populations in Nearby Galaxies
We analyzed 1441 Chandra X-ray point sources in 32 nearby galaxies. The total
point-source X-ray luminosity L_XP is well correlated with B, K, and FIR+UV
luminosities of spiral host galaxies, and with the B and K luminosities for
ellipticals. This suggests an intimate connection between L_XP and both the old
and young stellar populations, for which K and FIR+UV luminosities are proxies
for the galaxy mass M and star-formation rate SFR. We derive proportionality
constants 1.3E29 erg/s/Msol and 0.7E39 erg/s/(Msol/yr), which can be used to
estimate the old and young components from M and SFR, respectively. The
cumulative X-ray luminosity functions for the point sources have quite
different slopes for the spirals (gamma ~= 0.5-0.8) and ellipticals (gamma ~=
1.4), implying *the most luminous point sources dominate L_XP* for the spirals.
Most of the point sources have X-ray colors that are consistent with either
LMXBs or Ultraluminous X-ray sources (ULXs a.k.a. IXOs) and we rule out
classical HMXBs (e.g. neutron-star X-ray pulsars) as contributing much to L_XP.
Thus, for spirals, the ULXs dominate L_XP. We estimate that >~20% of all ULXs
found in spirals originate from the older (pop II) stellar populations,
indicating that many of the ULXs that have been found in spiral galaxies are in
fact pop II ULXs, like those in elliptical galaxies. The linear dependence of
L_XP on the SFR argues for either a steepening in the X-ray luminosity function
of the young (pop I) X-ray source population at L_X >~10^(38.5-39) erg/s, or a
decreasing efficiency for producing all types of young X-ray point sources as
the galaxy SFR increases.Comment: 33 pages AASTEX, ApJ accepted. Please download full version with
figures from http://www.pha.jhu.edu/~colbert/chps_accepted.p
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
Modeling the Redshift Evolution of the Normal Galaxy X-ray Luminosity Function
Emission from X-ray binaries (XRBs) is a major component of the total X-ray
luminosity of normal galaxies, so X-ray studies of high redshift galaxies allow
us to probe the formation and evolution of X-ray binaries on very long
timescales. In this paper, we present results from large-scale population
synthesis models of binary populations in galaxies from z = 0 to 20. We use as
input into our modeling the Millennium II Cosmological Simulation and the
updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently
account for the star formation history (SFH) and metallicity evolution of each
galaxy. We run a grid of 192 models, varying all the parameters known from
previous studies to affect the evolution of XRBs. We use our models and
observationally derived prescriptions for hot gas emission to create
theoretical galaxy X-ray luminosity functions (XLFs) for several redshift bins.
Models with low CE efficiencies, a 50% twins mass ratio distribution, a steeper
IMF exponent, and high stellar wind mass loss rates best match observational
results from Tzanavaris & Georgantopoulos (2008), though they significantly
underproduce bright early-type and very bright (Lx > 10d41) late-type galaxies.
These discrepancies are likely caused by uncertainties in hot gas emission and
SFHs, AGN contamination, and a lack of dynamically formed Low-mass XRBs. In our
highest likelihood models, we find that hot gas emission dominates the emission
for most bright galaxies. We also find that the evolution of the normal galaxy
X-ray luminosity density out to z = 4 is driven largely by XRBs in galaxies
with X-ray luminosities between 10d40 and 10d41 erg/s.Comment: Accepted into ApJ, 17 pages, 3 tables, 7 figures. Text updated to
address referee's comment
The X-ray Emission from the Nucleus of the Dwarf Elliptical Galaxy NGC 3226
We present the first high resolution X-ray image of the dwarf elliptical
galaxy NGC 3226. The data were obtained during an observation of the nearby
Seyfert Galaxy NGC 3227 using the Chandra X-ray Observatory. We detect a point
X-ray source spatially consistent with the optical nucleus of NGC 3226 and a
recently-detected, compact, flat-spectrum, radio source. The X-ray spectrum can
be measured up to ~10 keV and is consistent with a power law with a photon
index 1.7 <~ Gamma <~ 2.2, or thermal bremmstrahlung emission with 4 <~ kT <~
10 keV. In both cases the luminosity in the 2--10 keV band ~10^{40} h_{75}^{-1}
erg/s. We find marginal evidence that the nucleus varies within the
observation. These characteristics support evidence from other wavebands that
NGC 3226 harbors a low-luminosity, active nucleus. We also comment on two
previously-unknown, fainter X-ray sources <~ 15 arcsec from the nucleus of NGC
3226. Their proximity to the nucleus (with projected distances <~ 1.3/h_{75}
kpc) suggests both are within NGC 3226, and thus have luminosities (~few x
10^{38} -- few x 10^{39} erg/s) consistent with black-hole binary systems.Comment: Accepted for publication in ApJ. Figures in colo
Experimental verification of semiconductor diode aging based on thermal analyzes and numerical methods
Many electronic systems, such as computers and telephones, have a short service life, typically between two and five years. However, there are applications such as cars or airplanes that can have service life of 15 years or more. While product maintenance is usually practiced for mechanical components, it is difficult to find information in the technical literature as to whether the maintenance of electronic circuits can be justified in the case of very long-term use and whether it is possible at all. The approach to the behavior of components during failure is the closest to describing the "life time of electronic products." The described product life models are useful in cases where this life is limited by predictable physical mechanisms. These models perform well, for example, for solder joint fatigue caused by thermal cycling. This article describes an experimental verification of the aging of semiconductor diodes in order to determine their technical condition and current characteristics after 15 years of use. The obtained results of experimental research were compared with those from numerical simulations. On the basis of the obtained data, it was determined whether the aging process of the analyzed components takes place and how it affects their operation. Numerical models were created on the basis of the Coffin-Manson and Arrhenius equations.Web of Science139552051
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