5,609 research outputs found
Summary of Discussion Question 4: Energy Expandability of a Linear Collider
We report on Discussion Question 4, in Sub-group 1 (`TeV-class') of the
Snowmass Working Group E3: `Experimental Approaches: Linear Colliders', which
addresses the energy expandability of a linear collider. We first synthesize
discussions of the energy reach of the hardware of the 500 GeV designs for
TESLA and NLC/JLC. Next, we review plans for increasing the energy to 800-1000
GeV. We then look at options for expanding the energies to 1500 GeV and sketch
the two-beam accelerator approach to achieving multi-TeV energies.Comment: Presented at Snowmass 2001 (6 pages, 2 figures
Axions and SN1987A
The effect of free-streaming axion emission on numerical models for the cooling of the newly born neutron star associated with SN1987A is considered. It is found that for an axion mass of greater than approximately 10 to the -3 eV, axion emission shortens the duration of the expected neutrino burst so significantly that it would be inconsistent with the neutrino observations made by the Kamiokande II and Irvine-Michigan-Brookhaven detectors. However, the possibility has not been investigated that axion trapping (which should occur for masses greater than or equal to 0.02 eV) sufficiently reduces axion emission so that axion masses greater than approximately 2 eV would be consistent with the neutrino observations
z'-band Ground-Based Detection of the Secondary Eclipse of WASP-19b
We present the ground-based detection of the secondary eclipse of the
transiting exoplanet WASP-19b. The observations were made in the Sloan z'-band
using the ULTRACAM triple-beam CCD camera mounted on the NTT. The measurement
shows a 0.088\pm0.019% eclipse depth, matching previous predictions based on H-
and K-band measurements. We discuss in detail our approach to the removal of
errors arising due to systematics in the data set, in addition to fitting a
model transit to our data. This fit returns an eclipse centre, T0, of
2455578.7676 HJD, consistent with a circular orbit. Our measurement of the
secondary eclipse depth is also compared to model atmospheres of WASP-19b, and
is found to be consistent with previous measurements at longer wavelengths for
the model atmospheres we investigated.Comment: 20 pages, 10 figures. Published in the ApJ Supplement serie
Mu and Tau Neutrino Thermalization and Production in Supernovae: Processes and Timescales
We investigate the rates of production and thermalization of and
neutrinos at temperatures and densities relevant to core-collapse
supernovae and protoneutron stars. Included are contributions from electron
scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and
nucleon scattering. For the scattering processes, in order to incorporate the
full scattering kinematics at arbitrary degeneracy, the structure function
formalism developed by Reddy et al. (1998) and Burrows and Sawyer (1998) is
employed. Furthermore, we derive formulae for the total and differential rates
of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in
asymmetric matter. We find that electron scattering dominates nucleon
scattering as a thermalization process at low neutrino energies
( MeV), but that nucleon scattering is always faster
than or comparable to electron scattering above MeV. In
addition, for g cm, MeV, and
neutrino energies MeV, nucleon-nucleon bremsstrahlung always
dominates electron-positron annihilation as a production mechanism for
and neutrinos.Comment: 29 pages, LaTeX (RevTeX), 13 figures, submitted to Phys. Rev. C. Also
to be found at anonymous ftp site http://www.astrophysics.arizona.edu; cd to
pub/thompso
Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry
Here we describe an autonomous way of producing more accurate prompt XRT
positions for Swift-detected GRBs and their afterglows, based on UVOT
astrometry and a detailed mapping between the XRT and UVOT detectors. The
latter significantly reduces the dominant systematic error -- the star-tracker
solution to the World Coordinate System. This technique, which is limited to
times when there is significant overlap between UVOT and XRT PC-mode data,
provides a factor of 2 improvement in the localisation of XRT refined positions
on timescales of less than a few hours. Furthermore, the accuracy achieved is
superior to astrometrically corrected XRT PC mode images at early times (for up
to 24 hours), for the majority of bursts, and is comparable to the accuracy
achieved by astrometrically corrected X-ray positions based on deep XRT PC-mode
imaging at later times (abridged).Comment: 12 pages, 8 figures, 1 table, submitted to Astronomy and
Astrophysics, August 7th 200
The first Swift X-ray Flash: The faint afterglow of XRF 050215B
We present the discovery of XRF 050215B and its afterglow. The burst was
detected by the Swift BAT during the check-out phase and observations with the
X-ray telescope began approximately 30 minutes after the burst. These
observations found a faint, slowly fading X-ray afterglow near the centre of
the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10
hours also revealed a very faint K-band afterglow. The afterglow appear unusual
since it is very faint, especially in the infrared with K>20 only 9 hours post
burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with
alpha=0.8 and no evidence for steepening associated with the jet break to 10
days post burst. We discuss possible explanations for the faintness and slow
decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap
A Half-Megasecond Chandra Observation of the Oxygen-Rich Supernova Remnant G292.0+1.8
We report on our initial analysis of a deep 510 ks observation of the
Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8 with the {\it Chandra
X-ray Observatory}. Our new {\it Chandra} ACIS-I observation has a larger field
of view and an order of magnitude deeper exposure than the previous {\it
Chandra} observation, which allows us to cover the entire SNR and to detect new
metal-rich ejecta features. We find a highly non-uniform distribution of
thermodynamic conditions of the X-ray emitting hot gas that correlates well
with the optical [O {\small III}] emission, suggesting the possibility that the
originating supernova explosion of G292.0+1.8 was itself asymmetric. We also
reveal spectacular substructures of a torus, a jet, and an extended central
compact nebula all associated with the embedded pulsar J11245916.Comment: 10 pages including 1 table and 2 figures (both figures are color),
accepted by ApJ Letter
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
The Radial Structure of SNR N103B
We report on the results from a Chandra ACIS observation of the young,
compact, supernova remnant N103B. The unprecedented spatial resolution of
Chandra reveals sub-arcsecond structure, both in the brightness and in spectral
variations. Underlying these small-scale variations is a surprisingly simple
radial structure in the equivalent widths of the strong Si and S emission
lines. We investigate these radial variations through spatially resolved
spectroscopy using a plane-parallel, non-equilibrium ionization model with
multiple components. The majority of the emission arises from components with a
temperature of 1 keV: a fully ionized hydrogen component; a high ionization
timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe;
and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg
component. To reproduce the strong Fe Kalpha line, it is necessary to include
additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3)
component. This hot Fe may be in the form of hot Fe bubbles, formed in the
radioactive decay of clumps of 56Ni. We find no radial variation in the
ionization timescales or temperatures of the various components. Rather, the Si
and S equivalent widths increase at large radii because these lines, as well as
those of Ar and Ca, are formed in a shell occupying the outer half of the
remnant. A shell of hot Fe is located interior to this, but there is a large
region of overlap between these two shells. In the inner 30% of the remnant,
there is a core of cooler, 1 keV Fe. We find that the distribution of the
ejecta and the yields of the intermediate mass species are consistent with
model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap
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