30,068 research outputs found
An asymmetric arcsecond radio jet from Circinus X-1
In observations with the Australia Telescope Compact Array we have resolved
the radio counterpart of the unusual X-ray binary Cir X-1 into an asymmetric
extended structure on arcsecond scales. In order to quantify the asymmetry we
have redetermined as accurately as possible both the optical and radio
coordinates of the source. The extended emission can be understood as a
compact, absorbed core at the location of the X-ray binary, and extended
emission up to 2 arcsec to the southeast of the core. The arcsec-scale extended
emission aligns with the larger, more symmetric arcmin-scale collimated
structures in the surrounding synchrotron nebula. This suggests that the
transport of mass and/or energy from the X-ray binary to the synchroton nebula
is occurring via the arcsec-scale structures. The ratio of extended flux from
the southeast to that from the northwest of the core is at least 2:1.
Interpreted as relativistic aberration of an intrinsically symmetric jet from
the source, this implies a minimum outflow velocity of 0.1 c. Alternatively,
the emission may be intrinsically asymmetric, perhaps as a result of the high
space velocity of the system.Comment: Accepted for publication in ApJ Letters. Three figure
Optical Spectroscopy of Galactic Cirrus Clouds: Extended Red Emission in the Diffuse Interstellar Medium
We present initial results from the first optical spectroscopic survey of
high latitude Galactic cirrus clouds. The observed shape of the cirrus spectrum
does not agree with that of scattered ambient Galactic starlight. This mismatch
can be explained by the presence of Extended Red Emission (ERE) in the diffuse
interstellar medium, as found in many other astronomical objects, probably
caused by photoluminescence of hydrocarbons. The integrated ERE intensity,
I_ERE \approx 1.2 x 10^{-5} erg s^{-1} cm^{-2} sr^{-1}, is roughly a third of
the scattered light intensity, consistent with recent color measurements of
diffuse Galactic light. The peak of the cirrus ERE (lambda_{0} \sim 6000 AA) is
shifted towards short (bluer) wavelengths compared to the ERE in sources
excited by intense ultraviolet radiation, such as HII regions (lambda_{0} sim
8000 AA); such a trend is seen in laboratory experiments on hydrogenated
amorphous carbon films.Comment: 7 pages, 2 figures. Accepted for publication in ApJ Letter
A stochastic volatility Libor model and its robust calibration
In this paper we propose a Libor model with a high-dimensional specially structured system of driving CIR volatility processes. A stable calibration procedure which takes into account a given local correlation structure is presented. The calibration algorithm is FFT based, so fast and easy to implement.Libor modelling, stochastic volatility, CIR processes, calibration
Credit Derivatives Pricing with a Smile-Extended Jump Stochastic Intensity Model
We present a two-factor stochastic default intensity and interest rate model for pricing single-name default swaptions. The specific positive square root processes considered fall in the relatively tractable class of affine jump diffusions while allowing for inclusion of stochastic volatility and jumps in default swap spreads. The parameters of the short rate dynamics are first calibrated to the interest rates markets, before calibrating separately the default intensity model to credit derivatives market data. A few variants of the model are calibrated in turn to market data, and different calibration procedures are compared. Numerical experiments show that the calibrated model can generate plausible volatility smiles. Hence, the model can be calibrated to a default swap term structure and few default swaptions, and the calibrated parameters can be used to value consistently other default swaptions (different strikes and maturities, or more complex structures) on the same credit reference name.Credit derivatives, credit default, swap, credit default swaption, jump-diffusion, stochastic intensity, doubly stochastic poisson process, cox process
SPIRE-FTS observations of RCW 120
The expansion of Galactic HII regions can trigger the formation of a new
generation of stars. However, little is know about the physical conditions that
prevail in these regions. We study the physical conditions that prevail in
specific zones towards expanding HII regions that trace representative media
such as the photodissociation region, the ionized region, and condensations
with and without ongoing star formation. We use the SPIRE Fourier Transform
Spectrometer (FTS) on board to observe the HII region RCW 120.
Continuum and lines are observed in the m range. Line intensities
and line ratios are obtained and used as physical diagnostics of the gas. We
used the Meudon PDR code and the RADEX code to derive the gas density and the
radiation field at nine distinct positions including the PDR surface and
regions with and without star-formation activity. For the different regions we
detect the atomic lines [NII] at m and [CI] at and m,
the ladder between the and levels and the
ladder between the and levels, as well as CH in absorption. We find gas temperatures in the range K for
densities of , and a high column density on the order
of that is in agreement with dust
analysis. The ubiquitousness of the atomic and CH emission suggests the
presence of a low-density PDR throughout RCW 120. High-excitation lines of CO
indicate the presence of irradiated dense structures or small dense clumps
containing young stellar objects, while we also find a less dense medium
() with high temperatures (K).Comment: 11 pages, 11 figures, accepted by A&
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