9,446 research outputs found
Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
We report the X-ray detection of the Type II-plateau supernova SN 2004et in
the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position
of the X-ray source was found to agree with the optical position within ~0.4
arcsec. Chandra also surveyed the region before the 2004 event, finding no
X-ray emission at the location of the progenitor. For the post-explosion
observations, a total of 202, 151, and 158 photons were detected in three
pointings, each ~29 ks in length, on 2004 October 22, November 6, and December
3, respectively. The spectrum of the first observation is best fit by a thermal
model with a temperature of kT=1.3 keV and a line-of-sight absorption of
N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is
~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and
soft counts on the first and third epochs indicates a softening over this time,
although there is an insufficient number of photons to constrain the variation
of temperature and absorption by spectral fitting. We model the emission as
arising from the reverse shock region in the interaction between the supernova
ejecta and the progenitor wind. For a Type IIP supernova with an extended
progenitor, the cool shell formed at the time of shock wave breakout from the
star can affect the initial evolution of the interaction shell and the
absorption of radiation from the reverse shock. The observed spectral softening
might be due to decreasing shell absorption. We find a pre-supernova mass loss
rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is
in line with expectations for a Type IIP supernova.Comment: total 19 pages including 7 figures. ApJ, in press. See
http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper
including full resolution image
An adjustable law of motion for relativistic spherical shells
A classical and a relativistic law of motion for an advancing shell are
deduced applying the thin layer approximation. A new parameter connected with
the quantity of absorbed matter in the expansion is introduced; this allows of
matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal
of Physics 201
Influence of the r-mode instability on hypercritically accreting neutron stars
We have investigated an influence of the r-mode instability on
hypercritically accreting () neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.Comment: 6 pages, 3 figure
X-Ray Observations of Type Ia Supernovae with Swift: Evidence for Circumstellar Interaction for SN 2005ke
We present a study of the early (days to weeks) X-ray and UV properties of
eight Type Ia supernovae (SNe Ia) which have been extensively observed with the
X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) onboard Swift, ranging
from 5-132 days after the outburst. SN 2005ke is tentatively detected (at a
3-3.6 sigma level of significance) in X-rays based on deep monitoring with the
XRT ranging from 8 to 120 days after the outburst. The inferred X-ray
luminosity [(2+/-1) x 10^{38} ergs/s; 0.3-2 keV band] is likely caused by
interaction of the SN shock with circumstellar material (CSM), deposited by a
stellar wind from the progenitor's companion star with a mass-loss rate of ~ 3
x 10^{-6} M_sun/yr (v_w/10 km/s). Evidence of CSM interaction in X-rays is
independently confirmed by an excess of UV emission as observed with the UVOT
onboard Swift, starting around 35 days after the explosion. The non-detection
of SN 2005ke with Chandra 105 days after the outburst implies a rate of decline
steeper than L_x \propto t^{-0.75}, consistent with the decline expected from
the interaction of the SN shock with a spherically symmetric CSM (t^{-1}). None
of the other seven SNe Ia is detected in X-rays or shows a UV excess, which
allows us to put tight constraints on the mass-loss rates of the progenitor
systems.Comment: 12 pages, 3 figures, accpeted for publication in ApJ
Markup cyclicality, competition and liquidity constraints: Evidence from a panel VAR analysis
© 2020 The Author. This is an open access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.The main scope of this study is to investigate the effects of competition and liquidity constraints on the cyclical behaviour of the markup ratio. In particular, 79 2-digit NACE Rev.2 sectors across the UK manufacturing and services industry over 2008-2017 are taken into account in order to observe markup cyclicality and whether pricing decisions are significantly influenced by the degree of competition and liquidity restrictions. A panel VAR framework is used to take into account the presence of cross-section dependence and heterogeneity amongst the constituent regressors of the model. The empirical results provide the following significant insights: (i) the markup ratio across the UK sectors follows a countercyclical pattern, (ii) concentrated sectors tend to charge countercyclical price-cost margins as they attempt to increase their market share in normal periods, and (iii) sectors with liquidity constrained firms charge countercyclical markups in order to substitute lack of funding with additional revenue. Complementary findings also suggest that more profitable firms charge procyclical markup ratios, thus validating the predatory pricing strategy in more concentrated sectors.Peer reviewe
Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S
We study a possibility of detection of circumstellar absorption lines of Na I
D and Ca II H,K in spectra of type IIP supernovae at the photospheric
epoch. The modelling shows that the circumstellar lines of Na I doublet will
not be seen in type IIP supernovae for moderate wind density, e.g.,
characteristic of SN 1999em, whereas rather pronounced Ca II lines with P Cygni
profile should be detectable. A similar model is used to describe Na I and Ca
II circumstellar lines seen in SN 1998S, type IIL with a dense wind. We show
that line intensities in this supernova are reproduced, if one assumes an
ultraviolet excess, which is caused primarily by the comptonization of
supernova radiation in the shock wave.Comment: To be published in Astronomy Letter
Observations of the Crab Nebula and its pulsar in the far-ultraviolet and in the optical
We present HST/STIS far-UV observations of the Crab nebula and its pulsar.
Broad, blueshifted absorption arising in the nebula is seen in C IV 1550,
reaching about 2500 km/s. This can be interpreted as evidence for a fast outer
shell, and we adopt a spherically symmetric model to constrain the properties
of this. We find that the density appears to decrease outward in the shell. A
lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy
of 1.5EE{49} ergs. A massive 10^{51} erg shell cannot be excluded, but is less
likely if the density profile is much steeper than R^{-4} and the velocity is
<6000 km/s. The observations cover the region 1140-1720 A. With the time-tag
mode of the spectrograph we obtain the pulse profile. It is similar to that in
the near-UV, although the primary peak is marginally narrower. Together with
the near-UV data, and new optical data from NOT, our spectrum of the pulsar
covers the entire region from 1140-9250 A. Dereddening the spectrum gives a
flat spectrum for E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab
pulsar can be fitted by a power law with spectral index alpha_{\nu} = 0.11 +/-
0.04. The main uncertainty is the amount and characteristics of the interstel-
lar reddening, and we have investigated the dependence of \alpha_{\nu} on
E(B-V) and R. In the extended emission covered by our 25" x 0.5" slit in the
far-UV, we detect C IV 1550 and He II 1640 emission lines from the Crab nebula.
Several interstellar absorption lines are detected toward the pulsar. The Ly
alpha absorption indicates a column density of 3.0+/-0.5\EE{21} cm^{-2} of
neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other
lines show no evidence of severe depletion of metals in atomic gas.Comment: 18 pages emulateapj style, including 10 figures. ApJ, accepte
A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction
We present initial results of a 750 ks Chandra observation of the remnant of
Kepler's supernova of AD 1604. The strength and prominence of iron emission,
together with the absence of O-rich ejecta, demonstrate that Kepler resulted
from a thermonuclear supernova, even though evidence for circumstellar
interaction is also strong. We have analyzed spectra of over 100 small regions,
and find that they fall into three classes. (1) The vast majority show Fe L
emission between 0.7 and 1 keV and Si and S K alpha emission; we associate
these with shocked ejecta. A few of these are found at or beyond the mean blast
wave radius. (2) A very few regions show solar O/Fe abundance rations; these we
associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A
few regions are dominated by continuum, probably synchrotron radiation.
Finally, we find no central point source, with a limit about 100 times fainter
than the central object in Cas A. The evidence that the blast wave is
interacting with CSM may indicate a Ia explosion in a more massive progenitor.Comment: Accepted by ApJ Letter
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