384 research outputs found
Competition in National And Appalachian Coal Markets
Paper examines concentration ratios for Appalachian coal production and the output behavior of coal-oil merged firms in Appalachia
Nucleon Superfluidity vs Observations of Cooling Neutron Stars
Cooling simulations of neutron stars (NSs) are performed assuming that
stellar cores consist of neutrons, protons and electrons and using realistic
density profiles of superfluid critical temperatures and
of neutrons and protons. Taking a suitable profile of
with maximum K one can obtain smooth
transition from slow to rapid cooling with increasing stellar mass. Adopting
the same profile one can explain the majority of observations of thermal
emission from isolated middle--aged NSs by cooling of NSs with different masses
either with no neutron superfluidity in the cores or with a weak superfluidity,
K. The required masses range from for (young
and hot) RX J0822-43 and (old and warm) PSR 1055-52 and RX J1856-3754 to
for the (colder) Geminga and Vela pulsars. Observations
constrain the and profiles with respect to the
threshold density of direct Urca process and maximum central density of NSs.Comment: 4 pages, 2 figures, AA Letters, accepte
2003--2005 INTEGRAL and XMM-Newton observations of 3C 273
The aim of this paper is to study the evolution of the broadband spectrum of
one of the brightest and nearest quasars 3C 273.
We analyze the data obtained during quasi-simultaneous INTEGRAL and XMM
monitoring of the blazar 3C 273 in 2003--2005 in the UV, X-ray and soft
gamma-ray bands and study the results in the context of the long-term evolution
of the source.
The 0.2-100 keV spectrum of the source is well fitted by a combination of a
soft cut-off power law and a hard power law. No improvement of the fit is
achieved if one replaces the soft cut-off power law by either a blackbody, or a
disk reflection model. During the observation period the source has reached the
historically softest state in the hard X-ray domain with a photon index
. Comparing our data with available archived X-ray data
from previous years, we find a secular evolution of the source toward softer
X-ray emission (the photon index has increased by
over the last thirty years). We argue that existing theoretical models have to
be significantly modified to account for the observed spectral evolution of the
source.Comment: 11 pages, accepted to A&
Pan-chromatic observations of the remarkable nova LMC 2012
We present the results of an intensive multiwavelength campaign on nova LMC
2012. This nova evolved very rapidly in all observed wavelengths. The time to
fall two magnitudes in the V band was only 2 days. In X-rays the super soft
phase began 135 days after discovery and ended around day 50 after
discovery. During the super soft phase, the \Swift/XRT and \Chandra\ spectra
were consistent with the underlying white dwarf being very hot, 1 MK,
and luminous, 10 erg s. The UV, optical, and near-IR
photometry showed a periodic variation after the initial and rapid fading had
ended. Timing analysis revealed a consistent 19.240.03 hr period in all
UV, optical, and near-IR bands with amplitudes of 0.3 magnitudes which
we associate with the orbital period of the central binary. No periods were
detected in the corresponding X-ray data sets. A moderately high inclination
system, = 6010^{\arcdeg}, was inferred from the early optical
emission lines. The {\it HST}/STIS UV spectra were highly unusual with only the
\ion{N}{5} (1240\AA) line present and superposed on a blue continuum. The lack
of emission lines and the observed UV and optical continua from four epochs can
be fit with a low mass ejection event, 10 M, from a hot
and massive white dwarf near the Chandrasekhar limit. The white dwarf, in turn,
significantly illuminated its subgiant companion which provided the bulk of the
observed UV/optical continuum emission at the later dates. The inferred extreme
white dwarf characteristics and low mass ejection event favor nova LMC 2012
being a recurrent nova of the U Sco subclass.Comment: 18 figures, 6 tables (one online only containing all the photometry
Swift detection of the super-swift switch-on of the super-soft phase in nova V745 Sco (2014)
V745 Sco is a recurrent nova, with the most recent eruption occurring in
February 2014. V745 Sco was first observed by Swift a mere 3.7 hr after the
announcement of the optical discovery, with the super-soft X-ray emission being
detected around four days later and lasting for only ~two days, making it both
the fastest follow-up of a nova by Swift and the earliest switch-on of
super-soft emission yet detected. Such an early switch-on time suggests a
combination of a very high velocity outflow and low ejected mass and, together
with the high effective temperature reached by the super-soft emission, a high
mass white dwarf (>1.3 M_sun). The X-ray spectral evolution was followed from
an early epoch where shocked emission was evident, through the entirety of the
super-soft phase, showing evolving column density, emission lines, absorption
edges and thermal continuum temperature. UV grism data were also obtained
throughout the super-soft interval, with the spectra showing mainly emission
lines from lower ionization transitions and the Balmer continuum in emission.
V745 Sco is compared with both V2491 Cyg (another nova with a very short
super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet
discovered). The longer recurrence time compared to M31N 2008-12a could be due
to a lower mass accretion rate, although inclination of the system may also
play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft
source phase yet discovered, providing a detailed and informative dataset for
study.Comment: 14 pages, 11 figures (4 in colour), accepted for publication in MNRA
XMM-Newton observations of seven soft X-ray excess QSOs
XMM-Newton observations of seven QSOs are presented and the EPIC spectra
analysed. Five of the AGN show evidence for Fe K-alpha emission, with three
being slightly better fitted by lines of finite width; at the 99 per cent level
they are consistent with being intrinsically narrow, though. The broad-band
spectra can be well modelled by a combination of different temperature
blackbodies with a power-law, with temperatures between kT ~ 100-300 eV. On the
whole, these temperatures are too high to be direct thermal emission from the
accretion disc, so a Comptonization model was used as a more physical
parametrization. The Comptonizing electron population forms the soft excess
emission, with an electron temperature of ~ 120-680 eV. Power-law, thermal
plasma and disc blackbody models were also fitted to the soft X-ray excess. Of
the sample, four of the AGN are radio-quiet and three radio-loud. The
radio-quiet QSOs may have slightly stronger soft excesses, although the
electron temperatures cover the same range for both groups.Comment: 13 pages, 7 figures, accepted for publication in MNRA
Detection of an X-ray periodicity in the Narrow-line Seyfert 1 Galaxy Mrk 766 with XMM-Newton
We have analyzed the timing properties of the Narrow-line Seyfert 1 galaxy
Mrk 766 observed with XMM-Newton during the PV phase. The source intensity
changes by a factor of 1.3 over the 29,000 second observation. If the soft
excess is modeled by a black body component, as indicated by the EPIC pn data,
the luminosity of the black body component scales with its temperature
according to L ~ T^4. This requires a lower limit 'black body size` of about
1.3*10^25 cm^2. In addition, we report the detection of a strong periodic
signal with 2.4*10^-4 Hz. Simulations of light curves with the observed time
sequence and phase randomized for a red noise spectrum clearly indicate that
the periodicity peak is intrinsic to the distant AGN. Furthermore, its
existence is confirmed by the EPIC MOS and RGS data. The spectral fitting
results show that the black body temperature and the absorption by neutral
hydrogen remain constant during the periodic oscillations. This observational
fact tends to rule out models in which the intensity changes are due to hot
spots orbiting the central black hole. Precession according to the
Bardeen-Petterson effect or instabilities in the inner accretion disk may
provide explanations for the periodic signal.Comment: 6 pages, 8 Figures, accepted for publication in the special A&A
Letters issue for XMM-Newton; corrections in Section 2.2 require
Simultaneous observations of the quasar 3C 273 with INTEGRAL, XMM-Newton and RXTE
INTEGRAL has observed the bright quasar 3C 273 on 3 epochs in January 2003 as
one of the first observations of the open programme. The observation on January
5 was simultaneous with RXTE and XMM-Newton observations. We present here a
first analysis of the continuum emission as observed by these 3 satellites in
the band from 3 keV to 500 keV. The continuum spectral energy distribution of
3C 273 was observed to be weak and steep in the high energies during this
campaign. We present the actual status of the cross calibrations between the
instruments on the three platforms using the calibrations available in June
2003.Comment: 4 figures, accepted for publication in A+A letter
Unveiling the broad band X-ray continuum and iron line complex in Mkr 841
Mkr 841 is a bright Seyfert 1 galaxy known to harbor a strong soft excess and
a variable K iron line. It has been observed during 3 different periods
by XMM for a total cumulated exposure time of 108 ks. We present in this
paper a broad band spectral analysis of the complete EPIC-pn data sets. We were
able to test two different models for the soft excess, a relativistically
blurred photoionized reflection (\r model) and a relativistically smeared
ionized absorption (\a model). The continuum is modeled by a simple cut-off
power law and we also add a neutral reflection. These observations reveal the
extreme and puzzling spectral and temporal behaviors of the soft excess and
iron line. The 0.5-3 keV soft X-ray flux decreases by a factor 3 between 2001
and 2005 and the line shape appears to be a mixture of broad and narrow
components. We succeed in describing this complex broad-band 0.5-10 keV
spectral variability using either \r or \a to fit the soft excess. Both models
give statistically equivalent results even including simultaneous BeppoSAX data
up to 200 keV. Both models are consistent with the presence of remote
reflection characterized by a constant narrow component in the data. However
they differ in the presence of a broad line component present in \r but not
needed in \a. This study also reveals the sporadic presence of relativistically
redshifted narrow iron lines.Comment: Accepted in A&A. 17 pages and 21 figure
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