23 research outputs found
The Detectability of Pair-Production Supernovae at z < 6
Nonrotating, zero metallicity stars with initial masses 140 < M < 260 solar
masses are expected to end their lives as pair-production supernovae (PPSNe),
in which an electron-positron pair-production instability triggers explosive
nuclear burning. Interest in such stars has been rekindled by recent
theoretical studies that suggest primordial molecular clouds preferentially
form stars with these masses. Since metal enrichment is a local process, the
resulting PPSNe could occur over a broad range of redshifts, in pockets of
metal-free gas. Using the implicit hydrodynamics code KEPLER, we have
calculated a set of PPSN light curves that addresses the theoretical
uncertainties and allows us to assess observational strategies for finding
these objects at intermediate redshifts. The peak luminosities of typical PPSNe
are only slightly greater than those of Type Ia, but they remain bright much
longer (~ 1 year) and have hydrogen lines. Ongoing supernova searches may soon
be able to limit the contribution of these very massive stars to < 1% of the
total star formation rate density out to z=2 which already provides useful
constraints for theoretical models. The planned Joint Dark Energy Mission
satellite will be able to extend these limits out to z=6.Comment: 12 pages, 6 figures, ApJ in press; slightly revised version, a few
typos correcte
Evolution of progenitor stars of Type Ibc supernovae and long gamma-ray bursts
We discuss how rotation and binary interactions may be related to the
diversity of type Ibc supernovae and long gamma-ray bursts. After presenting
recent evolutionary models of massive single and binary stars including
rotation, the Tayler-Spruit dynamo and binary interactions, we argue that the
nature of SNe Ibc progenitors from binary systems may not significantly differ
from that of single star progenitors in terms of rotation, and that most long
GRB progenitors may be produced via the quasi-chemically homogeneous evolution
at sub-solar metallicity. We also briefly discuss the possible role of magnetic
fields generated in the convective core of a massive star for the transport of
angular momentum, which is potentially important for future stellar evolution
models of supernova and GRB progenitors.Comment: 6 pages, 4 figures, to appear in IAU Symp. 250, Massive Stars as
Cosmic Engines, Kauai (HI), 12/2007, ed. F. Bresolin, P. Crowther, & J. Pul
Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae
We present a detailed spectral analysis of the prompt and afterglow emission
of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and
060218) that were spectroscopically found to be associated with type Ic
supernovae, and compare them to the general GRB population. For each event, we
investigate the spectral and luminosity evolution, and estimate the total
energy budget based upon broadband observations. The observational inventory
for these events has become rich enough to allow estimates of their energy
content in relativistic and sub-relativistic form. The result is a global
portrait of the effects of the physical processes responsible for producing
long-soft GRBs. In particular, we find that the values of the energy released
in mildly relativistic outflows appears to have a significantly smaller scatter
than those found in highly relativistic ejecta. This is consistent with a
picture in which the energy released inside the progenitor star is roughly
standard, while the fraction of that energy that ends up in highly relativistic
ejecta outside the star can vary dramatically between different events.Comment: 55 pages including 23 figures and 8 tables. Accepted for publication
in ApJ. Replaced with the accepted versio
The Physics of Core-Collapse Supernovae
Supernovae are nature's grandest explosions and an astrophysical laboratory
in which unique conditions exist that are not achievable on Earth. They are
also the furnaces in which most of the elements heavier than carbon have been
forged. Scientists have argued for decades about the physical mechanism
responsible for these explosions. It is clear that the ultimate energy source
is gravity, but the relative roles of neutrinos, fluid instabilities, rotation
and magnetic fields continue to be debated.Comment: Review article; 17 pages, 5 figure
A very energetic supernova associated with the gamma-ray burst of 29 March 2003
Over the past five years evidence has mounted that long-duration (> 2 s)
gamma-ray bursts (GRBs)--the most brilliant of all astronomical
explosions--signal the collapse of massive stars in our Universe. This evidence
was originally based on the probable association of one unusual GRB with a
supernova, but now includes the association of GRBs with regions of massive
star formation in distant galaxies, the appearance of supernova-like 'bumps' in
the optical afterglow light curves of several bursts and lines of freshly
synthesized elements in the spectra of a few X-ray afterglows. These
observations support, but do not yet conclusively demonstrate, the idea that
long-duration GRBs are associated with the deaths of massive stars, presumably
arising from core collapse. Here we report evidence that a very energetic
supernova (a hypernova) was temporally and spatially coincident with a GRB at
redshift z = 0.1685. The timing of the supernova indicates that it exploded
within a few days of the GRB, strongly suggesting that core-collapse events can
give rise to GRBs, thereby favouring the 'collapsar' model.Comment: 19 pages, 3 figure
GRB 020410: A Gamma-Ray Burst Afterglow Discovered by its Supernova Light
We present the discovery and monitoring of the optical transient (OT)
associated with GRB 020410. The fading OT was found by Hubble Space Telescope
(HST) observations taken 28 and 65 days after burst at a position consistent
with the X-ray afterglow. Subsequent re-examination of early ground based
observations revealed that a faint OT was present 6 hours after burst,
confirming the source association with GRB 020410. A deep non-detection after
one week requires that the OT re-brightened between day 7 and day 28, and
further late time HST data taken approximately 100 days after burst imply that
it is very red.We compare both the flux and color of the excess with supernova
models and show that the data are best explained by the presence of a Type Ib/c
supernova at a redshift z ~ 0.5, which occured roughly coincident with the day
of GRB.Comment: 23 Pages, 9 figures, submitted to Ap