72 research outputs found
Gamma-ray Bursts: Light on the distant Universe
Observations of a long-lasting Gamma-ray burst, one that has the brightest
optical counterpart yet discovered, challenge theoretical understanding of
these bursts but may enhance their usefulness as cosmic probes.Comment: News and Views article for Nature (Sept. 11, 2008
Flavor conversion of cosmic neutrinos from hidden jets
High energy cosmic neutrino fluxes can be produced inside relativistic jets
under the envelopes of collapsing stars. In the energy range E ~ (0.3 - 1e5)
GeV, flavor conversion of these neutrinos is modified by various matter effects
inside the star and the Earth. We present a comprehensive (both analytic and
numerical) description of the flavor conversion of these neutrinos which
includes: (i) oscillations inside jets, (ii) flavor-to-mass state transitions
in an envelope, (iii) loss of coherence on the way to observer, and (iv)
oscillations of the mass states inside the Earth. We show that conversion has
several new features which are not realized in other objects, in particular
interference effects ("L- and H- wiggles") induced by the adiabaticity
violation. The neutrino-neutrino scattering inside jet and inelastic neutrino
interactions in the envelope may produce some additional features at E > 1e4
GeV. We study dependence of the probabilities and flavor ratios in the
matter-affected region on angles theta13 and theta23, on the CP-phase delta, as
well as on the initial flavor content and density profile of the star. We show
that measurements of the energy dependence of the flavor ratios will, in
principle, allow to determine independently the neutrino and astrophysical
parameters.Comment: 56 pages, 19 figures. Minor changes. Accepted by JHEP
Hypernova Nucleosynthesis and Galactic Chemical Evolution
We study nucleosynthesis in 'hypernovae', i.e., supernovae with very large
explosion energies ( \gsim 10^{52} ergs) for both spherical and aspherical
explosions. The hypernova yields compared to those of ordinary core-collapse
supernovae show the following characteristics: 1) Complete Si-burning takes
place in more extended region, so that the mass ratio between the complete and
incomplete Si burning regions is generally larger in hypernovae than normal
supernovae. As a result, higher energy explosions tend to produce larger [(Zn,
Co)/Fe], small [(Mn, Cr)/Fe], and larger [Fe/O], which could explain the trend
observed in very metal-poor stars. 2) Si-burning takes place in lower density
regions, so that the effects of -rich freezeout is enhanced. Thus
Ca, Ti, and Zn are produced more abundantly than in normal
supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars
strongly suggest a significant contribution of hypernovae. 3) Oxygen burning
also takes place in more extended regions for the larger explosion energy. Then
a larger amount of Si, S, Ar, and Ca ("Si") are synthesized, which makes the
"Si"/O ratio larger. The abundance pattern of the starburst galaxy M82 may be
attributed to hypernova explosions. Asphericity in the explosions strengthens
the nucleosynthesis properties of hypernovae except for "Si"/O. We thus suggest
that hypernovae make important contribution to the early Galactic (and cosmic)
chemical evolution.Comment: To be published in "The Influence of Binaries on Stellar Population
Studies", ed. D. Vanbeveren (Kluwer), 200
A low energy core-collapse supernova without a hydrogen envelope
The final fate of massive stars depends on many factors, including mass,
rotation rate, magnetic fields and metallicity. Theory suggests that some
massive stars (initially greater than 25-30 solar masses) end up as Wolf-Rayet
stars which are deficient in hydrogen because of mass loss through strong
stellar winds. The most massive of these stars have cores which may form a
black hole and theory predicts that the resulting explosion produces ejecta of
low kinetic energy, a faint optical display and a small mass fraction of
radioactive nickel(1,2,3). An alternative origin for low energy supernovae is
the collapse of the oxygen-neon core of a relatively lowmass star (7-9 solar
masses) through electron capture(4,5). However no weak, hydrogen deficient,
core-collapse supernovae are known. Here we report that such faint, low energy
core-collapse supernovae do exist, and show that SN2008ha is the faintest
hydrogen poor supernova ever observed. We propose that other similar events
have been observed but they have been misclassified as peculiar thermonuclear
supernovae (sometimes labelled SN2002cx-like events(6)). This discovery could
link these faint supernovae to some long duration gamma-ray bursts. Extremely
faint, hydrogen-stripped core-collapse supernovae have been proposed to produce
those long gamma-ray bursts whose afterglows do not show evidence of
association with supernovae (7,8,9).Comment: Submitted 12 January 2009 - Accepted 24 March 200
Hypernovae and Other Black-Hole-Forming Supernovae
During the last few years, a number of exceptional core-collapse supernovae
(SNe) have been discovered. Their kinetic energy of the explosions are larger
by more than an order of magnitude than the typical values for this type of
SNe, so that these SNe have been called `Hypernovae'. We first describe how the
basic properties of hypernovae can be derived from observations and modeling.
These hypernovae seem to come from rather massive stars, thus forming black
holes. On the other hand, there are some examples of massive SNe with only a
small kinetic energy. We suggest that stars with non-rotating black holes are
likely to collapse "quietly" ejecting a small amount of heavy elements (Faint
supernovae). In contrast, stars with rotating black holes are likely to give
rise to very energetic supernovae (Hypernovae). We present distinct
nucleosynthesis features of these two types of "black-hole-forming" supernovae.
Hypernova nucleosynthesis is characterized by larger abundance ratios
(Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe. Nucleosynthesis in Faint supernovae is
characterized by a large amount of fall-back. We show that the abundance
pattern of the most Fe deficient star, HE0107-5240, and other extremely
metal-poor carbon-rich stars are in good accord with those of
black-hole-forming supernovae, but not pair-instability supernovae. This
suggests that black-hole-forming supernovae made important contributions to the
early Galactic (and cosmic) chemical evolution.Comment: 49 pages, to be published in "Stellar Collapse" (Astrophysics and
Space Science; Kluwer) ed. C. L. Fryer (2003
A Relativistic Type Ibc Supernova Without a Detected Gamma-ray Burst
Long duration gamma-ray bursts (GRBs) mark the explosive death of some
massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They
are distinguished by the production of an energetic and collimated relativistic
outflow powered by a central engine (an accreting black hole or neutron star).
Observationally, this outflow is manifested in the pulse of gamma-rays and a
long-lived radio afterglow. To date, central engine-driven SNe have been
discovered exclusively through their gamma-ray emission, yet it is expected
that a larger population goes undetected due to limited satellite sensitivity
or beaming of the collimated emission away from our line-of-sight. In this
framework, the recovery of undetected GRBs may be possible through radio
searches for SNe Ibc with relativistic outflows. Here we report the discovery
of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb,
which requires a substantial relativistic outflow powered by a central engine.
The lack of a coincident GRB makes SN 2009bb the first engine-driven SN
discovered without a detected gamma-ray signal. A comparison with our extensive
radio survey of SNe Ibc reveals that the fraction harboring central engines is
low, ~1 percent, measured independently from, but consistent with, the inferred
rate of nearby GRBs. Our study demonstrates that upcoming optical and radio
surveys will soon rival gamma-ray satellites in pinpointing the nearest
engine-driven SNe. A similar result for a different supernova is reported
independently.Comment: To appear in Nature on Jan 28 2010. Embargoed for discussion in the
press until 13:00 US Eastern Time on Jan 27 (Accepted version, 27 pages,
Manuscript and Suppl. Info.
An apparently normal gamma-ray burst with an unusually low luminosity
Much of progress in gamma-ray bursts has come from the studies of distant
events (redshift z~1). The brightest GRBs are the most collimated events and
seen across the Universe due to their brilliance. It has long been suspected
that nearest (and most common) events have been missed because they are not so
collimated or under-energetic or both. Here we report soft gamma-ray
observations of GRB 031203, the nearest event to date (z=0.106). This event
with a duration of 40 s and peak energy of >190 keV appears to be a typical
long duration GRB. However, the isotropic gamma-ray energy <~10^50 erg, about
three orders of magnitude smaller than the cosmological population. This event
as well as the other nearby but somewhat controversial event GRB 980425 are
clear outliers for the much discussed isotropic-energy peak-energy relation and
luminosity spectral-lag relations. Radio calorimetry shows that both these
events are under-energetic explosions. We conclude that there does indeed exist
a large population of under-energetic events.Comment: 11 pages, 3 figure
Long gamma-ray bursts and core-collapse supernovae have different environments
When massive stars exhaust their fuel they collapse and often produce the
extraordinarily bright explosions known as core-collapse supernovae. On
occasion, this stellar collapse also powers an even more brilliant relativistic
explosion known as a long-duration gamma-ray burst. One would then expect that
long gamma-ray bursts and core-collapse supernovae should be found in similar
galactic environments. Here we show that this expectation is wrong. We find
that the long gamma-ray bursts are far more concentrated on the very brightest
regions of their host galaxies than are the core-collapse supernovae.
Furthermore, the host galaxies of the long gamma-ray bursts are significantly
fainter and more irregular than the hosts of the core-collapse supernovae.
Together these results suggest that long-duration gamma-ray bursts are
associated with the most massive stars and may be restricted to galaxies of
limited chemical evolution. Our results directly imply that long gamma-ray
bursts are relatively rare in galaxies such as our own Milky Way.Comment: 27 pages, 4 figures, submitted to Nature on 22 August 2005, revised 9
February 2006, online publication 10 May 2006. Supplementary material
referred to in the text can be found at
http://www.stsci.edu/~fruchter/GRB/locations/supplement.pdf . This new
version contains minor changes to match the final published versio
A Common Origin for Cosmic Explosions Inferred from Fireball Calorimetry
Past studies suggest that long-duration gamma-ray bursts (GRBs) have a
standard energy of E_gamma ~ 10^51 erg in ultra-relativistic ejecta when
corrected for asymmetry ("jets"). However, recently a group of sub-energetic
bursts, including the peculiar GRB 980425 associated with SN 1998bw (E_gamma ~
10^48 erg), has been identified. Here we report radio observations of GRB
030329, the nearest burst to date, which allow us to undertake calorimetry of
the explosion. Our observations require a two-component explosion: a narrow (5
degrees) ultra-relativistic component responsible for the gamma-rays and early
afterglow, and a wide, mildly relativistic component responsible for the radio
and optical afterglow beyond 1.5 days. While the gamma-rays are energetically
minor, the total energy release, dominated by the wide component, is similar to
that of other GRBs. Given the firm link of GRB 030329 with SN 2003dh our result
suggests a common origin for cosmic explosions in which, for reasons not
understood, the energy in the highest velocity ejecta is highly variableComment: Accepted to Natur
The gamma-ray burst GRB060614 requires a novel explosive process
Over the past decade our physical understanding of gamma-ray bursts (GRBs)
has progressed rapidly thanks to the discovery and observation of their
long-lived afterglow emission. Long-duration (T < 2 s) GRBs are associated with
the explosive deaths of massive stars (``collapsars''), which produce
accompanying supernovae, while the short-duration (T > 2 s) GRBs arise from a
different origin, which has been argued to be the merger of two compact
objects, either neutron stars or black holes. Here we present observations of
GRB060614, a 100-s long burst discovered by the Swift satellite, which require
the invocation of a new explosive process: either a massive ``collapsar'' that
powers a GRB without any associated supernova, or a new type of engine, as
long-lived as the collapsar but without any such massive stellar host. We also
discuss the properties of this burst's redshift z=0.125 host galaxy, which
distinguish it from other long-duration GRBs and suggest that an entirely new
type of GRB progenitor may be required
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