2,651 research outputs found
ArgoNeuT: A Liquid Argon Time Projection Chamber Test in the NuMI Beamline
Liquid Argon Time Projection Chamber detectors are ideally suited for
studying neutrino interactions and probing the parameters that characterize
neutrino oscillations. The ability to drift ionization particles over long
distances in purified argon and to trigger on abundant scintillation light
allows for excellent particle identification and triggering capability. In
these proceedings the details of the ArgoNeuT test-beam project will be
presented after a brief introduction to the detector technique. ArgoNeuT is a
175 liter detector exposed to Fermilab's NuMI neutrino beamline. The first
neutrino interactions observed in ArgoNeuT will be presented, along with
discussion of the various physics analyses to be performed on this data sample.Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July
2009, eConf C09072
Radio and X-ray Observations of the Type Ic SN 2007gr Reveal an Ordinary, Non-relativistic Explosion
We present extensive radio and X-ray observations of the nearby Type Ic SN
2007gr in NGC 1058 obtained with the Very Large Array and the Chandra X-ray
Observatory and spanning 5 to 150 days after explosion. Through our detailed
modeling of these data, we estimate the properties of the blastwave and the
circumstellar environment. We find evidence for a freely-expanding and
non-relativistic explosion with an average blastwave velocity, v~0.2c, and a
total internal energy for the radio emitting material of E ~ 2 x 10^46 erg
assuming equipartition of energy between electrons and magnetic fields
(epsilon_e=epsilon_B=0.1). The temporal and spectral evolution of the radio
emission points to a stellar wind-blown environment shaped by a steady
progenitor mass loss rate of Mdot ~ 6 x 10^-7 solar masses per year (wind
velocity, v_w=10^3 km/s). These parameters are fully consistent with those
inferred for other SNe Ibc and are in line with the expectations for an
ordinary, homologous SN explosion. Our results are at odds with those of Paragi
et al. (2010) who recently reported evidence for a relativistic blastwave in SN
2007gr based on their claim that the radio emission was resolved away in a low
signal-to-noise Very Long Baseline Interferometry (VLBI) observation. Here we
show that the exotic physical scenarios required to explain the claimed
relativistic velocity -- extreme departures from equipartition and/or a highly
collimated outflow -- are excluded by our detailed Very Large Array radio
observations. Moreover, we present an independent analysis of the VLBI data and
propose that a modest loss of phase coherence provides a more natural
explanation for the apparent flux density loss which is evident on both short
and long baselines. We conclude that SN 2007gr is an ordinary Type Ibc
supernova.Comment: 14 pages, 6 figures, submitted to Ap
The Unique Signature of Shell Curvature in Gamma-Ray Bursts
As a result of spherical kinematics, temporal evolution of received gamma-ray
emission should demonstrate signatures of curvature from the emitting shell.
Specifically, the shape of the pulse decay must bear a strict dependence on the
degree of curvature of the gamma-ray emitting surface. We compare the spectral
evolution of the decay of individual GRB pulses to the evolution as expected
from curvature. In particular, we examine the relationship between photon flux
intensity (I) and the peak of the \nu F\nu distribution (E_{peak}) as predicted
by colliding shells. Kinematics necessitate that E_{peak} demonstrate a
power-law relationship with I described roughly as: I=E_{peak}^{(1-\zeta)}
where \zeta represents a weighted average of the low and high energy spectral
indices. Data analyses of 24 BATSE gamma-ray burst pulses provide evidence that
there exists a robust relationship between E_{peak} and I in the decay phase.
Simulation results, however, show that a sizable fraction of observed pulses
evolve faster than kinematics allow. Regardless of kinematic parameters, we
found that the existence of curvature demands that the I - E_{peak} function
decay be defined by \sim (1-\zeta). Efforts were employed to break this
curvature dependency within simulations through a number of scenarios such as
anisotropic emission (jets) with angular dependencies, thickness values for the
colliding shells, and various cooling mechanisms. Of these, the only method
successful in dominating curvature effects was a slow cooling model. As a
result, GRB models must confront the fact that observed pulses do not evolve in
the manner which curvature demands.Comment: 3 pages, To appear in Proc. from the 2nd Workshop on Gamma-Ray Bursts
in the Afterglow Er
Constraints on the Bulk Lorentz Factor of GRB 990123
GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely
bright optical flash. We present the collective constraints on the bulk Lorentz
factor for this burst based on estimates from burst kinematics, synchrotron
spectral decay, prompt radio flash observations, and prompt emission pulse
width. Combination of these constraints leads to an average bulk Lorentz factor
for GRB 990123 of Gamma_0=1000 +/- 100 which implies a baryon loading of
M_jet=8 (+17/-2) x 10^-8 Msolar. We find these constraints to be consistent
with the speculation that the optical light is emission from the reverse shock
component of the external shock. In addition, we find the implied value of
M_jet to be in accordance with theoretical estimates: the baryonic loading is
sufficiently small to allow acceleration of the outflow to Gamma > 100.Comment: 4 pages, 2 postscript figures, to appear in "Gamma-Ray Burst and
Afterglow Astronomy 2001", Woods Hole; 5-9 Nov, 200
The Yale Lar TPC
In this paper we give a concise description of a liquid argon time projection
chamber (LAr TPC) developed at Yale, and present results from its first
calibration run with cosmic rays.Comment: 4 pages, 3 figures, NuInt07 Conference Proceeding
The Radio Properties of Type Ibc Supernovae
Over the past few years, long-duration gamma-ray bursts (GRBs), including the
subclass of X-ray flashes (XRFs), have been revealed to be a rare variety of
Type Ibc supernova (SN Ibc). While all these events result from the death of
massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those
of ordinary Type Ibc SNe by many orders of magnitude. The observed diversity of
stellar death corresponds to large variations in the energy, velocity, and
geometry of the explosion ejecta. Using multi-wavelength (radio, optical,
X-ray) observations of the nearest GRBs, XRFs, and SNe Ibc, I show that while
GRBs and XRFs couple at least 10^48 erg to relativistic material, SNe Ibc
typically couple less than 10^48 erg to their fastest (albeit non-relativistic)
outflows. Specifically, I find that less than 3% of local SNe Ibc show any
evidence for association with a GRB or XRF. Recently, a new class of GRBs and
XRFs has been revealed which are under-luminous in comparison with the
statistical sample of GRBs. Owing to their faint high-energy emission, these
sub-energetic bursts are only detectable nearby (z < 0.1) and are likely 10
times more common than cosmological GRBs. In comparison with local SNe Ibc and
typical GRBs/XRFs, these explosions are intermediate in terms of both
volumetric rate and energetics. Yet the essential physical process that causes
a dying star to produce a GRB, XRF, or sub-energetic burst, and not just a SN,
remains a crucial open question. Progress requires a detailed understanding of
ordinary SNe Ibc which will be facilitated with the launch of wide-field
optical surveys in the near future.Comment: 8 pages, Proceedings for "Supernova 1987A: 20 Years After: Supernovae
and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R.
McCra
Metallicity in the GRB 100316D/SN 2010bh Host Complex
The recent long-duration GRB 100316D, associated with supernova SN 2010bh and
detected by Swift, is one of the nearest GRB-SNe ever observed (z = 0.059).
This provides us with a unique opportunity to study the explosion environment
on ~kpc scale in relation to the host galaxy complex. Here we present
spatially-resolved spectrophotometry of the host galaxy, focusing on both the
explosion site and the brightest star-forming regions. Using these data, we
extract the spatial profiles of the relevant emission features (Halpha, Hbeta,
[OIII] 5007A, and [NII] 6584A), and use these profiles to examine variations in
metallicity and star formation rate as a function of position in the host
galaxy. We conclude that GRB 100316D/SN2010bh occurred in a low-metallicity
host galaxy, and that the GRB-SN explosion site corresponds to the region with
the lowest metallicity and highest star formation rate sampled by our
observations.Comment: 7 pages, 3 figures, accepted for publication in The Astrophysical
Journa
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