787 research outputs found
Neutrino cross-section measurement with neutrinos from muon decay
In this paper we stress the idea that new, more precise neutrino
cross-sections measurements at low energies will be necessary to improve the
results of future big neutrino detectors, which will be dominated by the
contribution of the systematic errors. The use of a muon beam instead of the
traditional pion beams is proposed. This choice allows the simultaneous
measurement of both, numu and nue interactions and the two helicities, in a
clean environment and with a precise knowledge of the beam flux. We show that
with approx 10^{15} mu's/year and a moderate mass detector (approx 100 tons)
placed close to the muon storage ring, precisions of the order of 10% in
sigma(nu) (E_nu bin size of 100 MeV) can be reached for neutrino energies below
2 GeV.Comment: 4 pages, proceeding to NUFACT0
A Possible Origin of Dark Energy
We discuss the possibility that the existence of dark energy may be due to
the presence of a spin zero field , either elementary or composite. In
the presence of other matter field, the transformation
constant can generate a negative pressure, like the cosmological constant. In
this picture, our universe can be thought as a very large bag, similar to the
much smaller MIT bag model for a single nucleon.Comment: 4 pages, no figure, typos correcte
Time Domain Explorations With Digital Sky Surveys
One of the new frontiers of astronomical research is the exploration of time
variability on the sky at different wavelengths and flux levels. We have
carried out a pilot project using DPOSS data to study strong variables and
transients, and are now extending it to the new Palomar-QUEST synoptic sky
survey. We report on our early findings and outline the methodology to be
implemented in preparation for a real-time transient detection pipeline. In
addition to large numbers of known types of highly variable sources (e.g., SNe,
CVs, OVV QSOs, etc.), we expect to find numerous transients whose nature may be
established by a rapid follow-up. Whereas we will make all detected variables
publicly available through the web, we anticipate that email alerts would be
issued in the real time for a subset of events deemed to be the most
interesting. This real-time process entails many challenges, in an effort to
maintain a high completeness while keeping the contamination low. We will
utilize distributed Grid services developed by the GRIST project, and implement
a variety of advanced statistical and machine learning techniques.Comment: 5 pages, 2 postscript figures, uses adassconf.sty. To be published
in: "ADASS XIV (2004)", Eds. Patrick Shopbell, Matthew Britton and Rick
Ebert, ASP Conference Serie
The Rising Light Curves of Type Ia Supernovae
We present an analysis of the early, rising light curves of 18 Type Ia
supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the
La Silla-QUEST variability survey (LSQ). We fit these early data flux using a
simple power-law to determine the time of first
light , and hence the rise-time from first light to
peak luminosity, and the exponent of the power-law rise (). We find a mean
uncorrected rise time of days, with individual SN rise-times
ranging from to days. The exponent n shows significant
departures from the simple 'fireball model' of (or ) usually assumed in the literature. With a mean value of , our data also show significant diversity from event to event. This
deviation has implications for the distribution of 56Ni throughout the SN
ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The
range of n found also confirms that the 56Ni distribution is not standard
throughout the population of SNe Ia, in agreement with earlier work measuring
such abundances through spectral modelling. We also show that the duration of
the very early light curve, before the luminosity has reached half of its
maximal value, does not correlate with the light curve shape or stretch used to
standardise SNe Ia in cosmological applications. This has implications for the
cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA
The QUEST large area CCD camera
We have designed, constructed, and put into operation a very large area CCD camera that covers the field of view of the 1.2 m Samuel Oschin Schmidt Telescope at the Palomar Observatory. The camera consists of 112 CCDs arranged in a mosaic of four rows with 28 CCDs each. The CCDs are 600 x 2400 pixel Sarnoff thinned, back-illuminated devices with 13 µm x 13 µm pixels. The camera covers an area of 4.6° x 3.6° on the sky with an active area of 9.6 deg_2. This camera has been installed at the prime focus of the telescope and commissioned, and scientific-quality observations on the Palomar-QUEST Variability Sky Survey were started in 2003 September. The design considerations, construction features, and performance parameters of this camera are described in this paper
A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw
We report on our findings based on the analysis of observations of the Type
II-L supernova LSQ13cuw within the framework of currently accepted physical
predictions of core-collapse supernova explosions. LSQ13cuw was discovered
within a day of explosion, hitherto unprecedented for Type II-L supernovae.
This motivated a comparative study of Type II-P and II-L supernovae with
relatively well-constrained explosion epochs and rise times to maximum
(optical) light. From our sample of twenty such events, we find evidence of a
positive correlation between the duration of the rise and the peak brightness.
On average, SNe II-L tend to have brighter peak magnitudes and longer rise
times than SNe II-P. However, this difference is clearest only at the extreme
ends of the rise time versus peak brightness relation. Using two different
analytical models, we performed a parameter study to investigate the physical
parameters that control the rise time behaviour. In general, the models
qualitatively reproduce aspects of the observed trends. We find that the
brightness of the optical peak increases for larger progenitor radii and
explosion energies, and decreases for larger masses. The dependence of the rise
time on mass and explosion energy is smaller than the dependence on the
progenitor radius. We find no evidence that the progenitors of SNe II-L have
significantly smaller radii than those of SNe II-P.Comment: 19 pages, 10 figures, accepted by A&
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
Massive stars exploding in a He-rich circumstellar medium. VI. Observations of two distant Type Ibn supernova candidates discovered by La Silla-QUEST
We present optical observations of the peculiar stripped-envelope supernovae
(SNe) LSQ12btw and LSQ13ccw discovered by the La Silla-QUEST survey. LSQ12btw
reaches an absolute peak magnitude of M(g) = -19.3 +- 0.2, and shows an
asymmetric light curve. Stringent prediscovery limits constrain its rise time
to maximum light to less than 4 days, with a slower post-peak luminosity
decline, similar to that experienced by the prototypical SN~Ibn 2006jc.
LSQ13ccw is somewhat different: while it also exhibits a very fast rise to
maximum, it reaches a fainter absolute peak magnitude (M(g) = -18.4 +- 0.2),
and experiences an extremely rapid post-peak decline similar to that observed
in the peculiar SN~Ib 2002bj. A stringent prediscovery limit and an early
marginal detection of LSQ13ccw allow us to determine the explosion time with an
uncertainty of 1 day. The spectra of LSQ12btw show the typical narrow He~I
emission lines characterising Type Ibn SNe, suggesting that the SN ejecta are
interacting with He-rich circumstellar material. The He I lines in the spectra
of LSQ13ccw exhibit weak narrow emissions superposed on broad components. An
unresolved Halpha line is also detected, suggesting a tentative Type Ibn/IIn
classification. As for other SNe~Ibn, we argue that LSQ12btw and LSQ13ccw
likely result from the explosions of Wolf-Rayet stars that experienced
instability phases prior to core collapse. We inspect the host galaxies of SNe
Ibn, and we show that all of them but one are hosted in spiral galaxies, likely
in environments spanning a wide metallicity range.Comment: 15 pages, 9 figures, 4 tables. Accepted by MNRA
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