823 research outputs found
Optical Bumps in Cosmological GRBs as Supernovae
From both photometric and broadband spectral monitoring of gamma-ray burst
(GRB) lightcurve ``bumps,'' particularly in GRB 011121, a strong case grew for
a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a
reasonable doubt with the discovery that the bump in GRB 030329 was
spectroscopically similar to a bright Type Ic SN. In light of this result, I
redress the previous SN bump claims and conclude that 1) the distribution of
GRB-SN bump peak magnitudes is consistent with the local Type Ibc SNe peak
distribution and suggest that 2) the late-time bumps in all long-duration GRBs
are likely supernovae.Comment: 5 pages, 2 figures. To be published in Proc. IAU Colloquium #192
``Supernovae (10 years of SN1993J),'' held 22-26 April 2003, Valencia, Spain.
Editors: J.M. Marcaide and K.W. Weiler. Uses svmult.cl
Optical and near-IR observations of SN 1998bw
SN 1998bw, especially after the discovery of GRB 030329/SN 2003dh, seems to
be the equivalent of the Rosetta stone for the SN/GRB connection. In this paper
I review optical and near IR observations that have been carried out for this
uncanny object, which has probably confirmed suspicions and ideas originally
formulated in the early seventies of last century.Comment: 9 pages, 7 figures. Invited review to the IAU Colloquium n. 192,
SUPERNOVAE: ten years of SN 1993J, Valencia (Spain
Higher twists in the pion structure function
We calculate the QCD moments of the pion structure function using Drell-Yan
data on the quark distributions in the pion and a phenomenological model for
the resonance region. The extracted higher twist corrections are found to be
larger than those for the nucleon, contributing around 50% of the lowest moment
at Q^2=1 GeV^2.Comment: 8 pages, 3 figures, to appear in Phys. Rev.
The Supernova Gamma-Ray Burst Connection
The chief distinction between ordinary supernovae and long-soft gamma-ray
bursts (GRBs) is the degree of differential rotation in the inner several solar
masses when a massive star dies, and GRBs are rare mainly because of the
difficulty achieving the necessary high rotation rate. Models that do provide
the necessary angular momentum are discussed, with emphasis on a new single
star model whose rapid rotation leads to complete mixing on the main sequence
and avoids red giant formation. This channel of progenitor evolution also gives
a broader range of masses than previous models, and allows the copious
production of bursts outside of binaries and at high redshifts. However, even
the production of a bare helium core rotating nearly at break up is not, by
itself, a sufficient condition to make a gamma-ray burst. Wolf-Rayet mass loss
must be low, and will be low in regions of low metallicity. This suggests that
bursts at high redshift (low metallicity) will, on the average, be more
energetic, have more time structure, and last longer than bursts nearby. Every
burst consists of three components: a polar jet (~0.1 radian), high energy,
subrelativistic mass ejection (~1 radian), and low velocity equatorial mass
that can fall back after the initial explosion. The relative proportions of
these three components can give a diverse assortment of supernovae and high
energy transients whose properties may vary with redshift.Comment: 10 pages, to appear in AIP Conf. Proc. "Gamma Ray Bursts in the Swift
Era", Eds. S. S. Holt, N. Gehrels, J. Nouse
On the Truncated Pareto Distribution with applications
The Pareto probability distribution is widely applied in different fields
such us finance, physics, hydrology, geology and astronomy. This note deals
with an application of the Pareto distribution to astrophysics and more
precisely to the statistical analysis of mass of stars and of diameters of
asteroids. In particular a comparison between the usual Pareto distribution and
its truncated version is presented. Finally a possible physical mechanism that
produces Pareto tails for the distribution of the masses of stars is suggested.Comment: 10 pages 6 figure
GRB 081028 and its late-time afterglow re-brightening
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical SocietySwift captured for the first time a smoothly rising X-ray re-brightening of clear non-flaring origin after the steep decay in a long gamma-ray burst (GRB): GRB 081028. A rising phase is likely present in all GRBs but is usually hidden by the prompt tail emission and constitutes the first manifestation of what is later to give rise to the shallow decay phase. Contemporaneous optical observations reveal a rapid evolution of the injection frequency of a fast cooling synchrotron spectrum through the optical band, which disfavours the afterglow onset (start of the forward shock emission along our line of sight when the outflow is decelerated) as the origin of the observed re-brightening. We investigate alternative scenarios and find that the observations are consistent with the predictions for a narrow jet viewed off-axis. The high on-axis energy budget implied by this interpretation suggests different physical origins of the prompt and (late) afterglow emission. Strong spectral softening takes place from the prompt to the steep decay phase: we track the evolution of the spectral peak energy from the γ-rays to the X-rays and highlight the problems of the high latitude and adiabatic cooling interpretations. Notably, a softening of both the high and low spectral slopes with time is also observed. We discuss the low on-axis radiative efficiency of GRB 081028 comparing its properties against a sample of Swift long GRBs with secure Eγ,iso measurements.Peer reviewe
Putting theory oriented evaluation into practice
Evaluations of gaming simulations and business games as teaching devices are typically end-state driven. This emphasis fails to detect how the simulation being evaluated does or does not bring about its desired consequences. This paper advances the use of a logic model approach which possesses a holistic perspective that aims at including all elements associated with the situation created by a game. The use of the logic model approach is illustrated as applied to Simgame, a board game created for secondary school level business education in six European Union countries
Relativistic Mass Ejecta from Phase-transition-induced Collapse of Neutron Stars
We study the dynamical evolution of a phase-transition-induced collapse
neutron star to a hybrid star, which consists of a mixture of hadronic matter
and strange quark matter. The collapse is triggered by a sudden change of
equation of state, which result in a large amplitude stellar oscillation. The
evolution of the system is simulated by using a 3D Newtonian hydrodynamic code
with a high resolution shock capture scheme. We find that both the temperature
and the density at the neutrinosphere are oscillating with acoustic frequency.
However, they are nearly 180 out of phase. Consequently, extremely
intense, pulsating neutrino/antineutrino fluxes will be emitted periodically.
Since the energy and density of neutrinos at the peaks of the pulsating fluxes
are much higher than the non-oscillating case, the electron/positron pair
creation rate can be enhanced dramatically. Some mass layers on the stellar
surface can be ejected by absorbing energy of neutrinos and pairs. These mass
ejecta can be further accelerated to relativistic speeds by absorbing
electron/positron pairs, created by the neutrino and antineutrino annihilation
outside the stellar surface. The possible connection between this process and
the cosmological Gamma-ray Bursts is discussed.Comment: 40 pages, 11 figures, accepted for publication in JCA
Attrition among families of divorce: Patterns in an outpatient psychiatric population
The accelerated divorce rate has greatly increased the number of children of divorce. In addition, the children and families of divorce are proportionately overrepresented in populations seeking child guidance and psychiatric services. However, the patterns in the use of such services by these families has been unexamined. In our study we find no differences in the use of outpatient psychiatric services between families where both biological parents are present and families of divorce. A closer look at the divorced families reveals that recently divorced mother-headed families more frequently interrupt both the evaluation and treatment phases of clinic contact. Several clinical patterns are described which help explain the finding and it is suggested that the traditional child guidance model may not be the most suitable intervention modality in working with these families.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44293/1/10591_2004_Article_BF00927093.pd
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