765 research outputs found
SN2008am: A Super-Luminous Type IIn Supernova
We present observations and interpretation of the Type IIn supernova SN
2008am discovered by the ROTSE Supernova Verification Project (RSVP). SN 2008am
peaked at approximately -22.3 mag at a redshift of z=0.2338, giving it a peak
luminosity of 3 x 10^{44}erg/s and making it one of the most luminous
supernovae ever observed. The total radiated energy is ~ 2 x 10^{51} erg.
Photometric observations in the ultraviolet, optical and infrared bands
(J,H,Ks) constrain the SED evolution. We obtained six optical spectra of the
supernova, five on the early decline from maximum light and a sixth nearly a
year later plus a very late-time spectrum (~2 yr) of the host galaxy. The
spectra of SN 2008am show strong Balmer-line and He I lambda 5876A emission
with intermediate widths (~25A) in the first ~40 days after optical maximum. We
examine a variety of models for the line wings and conclude that multiple
scattering is most likely, implying that our spectra contain no specific
information on the bulk flow velocity. We examine a variety of models for the
ROTSE light curve subject to the rise time and the nature of the spectra,
including radioactive decay, shocks in optically-thick and optically-thin
circumstellar media (CSM) and a magnetar. The most successful model is one for
which the CSM is optically-thick and in which diffusion of forward
shock-deposited luminosity gives rise to the observed light curve. Diffusion of
the shock-deposited energy from the forward shock is found to be important to
account for the rising part of the light curve. Although there are differences
in detail, SN 2008am appears to be closely related to other super-luminous Type
IIn supernovae, SN 2006gy, SN 2006tf and perhaps SN 2008iy, that may represent
the deaths of very massive LBV-type progenitors and for which the luminosity is
powered by the interaction of the ejecta with a dense circumstellar medium.Comment: 58 pages, 14 figure
SN 2010jl in UGC 5189: Yet another luminous type IIn supernova in a metal-poor galaxy
We present ASAS data starting 25 days before the discovery of the recent type
IIn SN 2010jl, and we compare its light curve to other luminous IIn SNe,
showing that it is a luminous (M_I ~ -20.5) event. Its host galaxy, UGC 5189,
has a low gas-phase oxygen abundance (12 + log(O/H) = 8.2), which reinforces
the emerging trend that over-luminous core-collapse supernovae are found in the
low-metallicity tail of the galaxy distribution, similar to the known trend for
the hosts of long GRBs. We compile oxygen abundances from the literature and
from our own observations of UGC 5189, and we present an unpublished spectrum
of the luminous type Ic SN 2010gx that we use to estimate its host metallicity.
We discuss these in the context of host metallicity trends for different
classes of core-collapse objects. The earliest generations of stars are known
to be enhanced in [O/Fe] relative to the Solar mixture; it is therefore likely
that the stellar progenitors of these overluminous supernovae are even more
iron-poor than they are oxygen-poor. A number of mechanisms and massive star
progenitor systems have been proposed to explain the most luminous
core-collapse supernovae; any successful theory will need to include the
emerging trend that points towards low-metallicity for the massive progenitor
stars. This trend for very luminous supernovae to strongly prefer
low-metallicity galaxies should be taken into account when considering various
aspects of the evolution of the metal-poor early universe. (abridged)Comment: 27 pages, 7 figures, 2 tables. Accepted for publication in Ap
Discovery of the Ultra-Bright Type II-L Supernova 2008es
We report the discovery by the Robotic Optical Transient Experiment
(ROTSE-IIIb) telescope of SN 2008es, an overluminous supernova (SN) at z=0.205
with a peak visual magnitude of -22.2. We present multiwavelength follow-up
observations with the Swift satellite and several ground-based optical
telescopes. The ROTSE-IIIb observations constrain the time of explosion to be
23+/-1 rest-frame days before maximum. The linear decay of the optical light
curve, and the combination of a symmetric, broad H\alpha emission line profile
with broad P Cygni H\beta and Na I \lambda5892 profiles, are properties
reminiscent of the bright Type II-L SNe 1979C and 1980K, although SN 2008es is
greater than 10 times more luminous. The host galaxy is undetected in
pre-supernova Sloan Digital Sky Survey images, and similar to Type II-L SN
2005ap (the most luminous SN ever observed), the host is most likely a dwarf
galaxy with M_r > -17. Swift Ultraviolet/Optical Telescope observations in
combination with Palomar photometry measure the SED of the SN from 200 to 800
nm to be a blackbody that cools from a temperature of 14,000 K at the time of
the optical peak to 6400 K 65 days later. The inferred blackbody radius is in
good agreement with the radius expected for the expansion speed measured from
the broad lines (10,000 km/s). The bolometric luminosity at the optical peak is
2.8 x 10^44 erg/s, with a total energy radiated over the next 65 days of 5.6 x
10^50 erg. We favor a model in which the exceptional peak luminosity is a
consequence of the core-collapse explosion of a progenitor star with a low-mass
extended hydrogen envelope and a stellar wind with a density close to the upper
limit on the mass-loss rate measured from the lack of an X-ray detection by the
Swift X-Ray Telescope. (Abridged).Comment: Accepted to ApJ, 14 pages, 7 figures, 3 tables, emulateapj,
corrections from proofs adde
Hydrogen-poor superluminous stellar explosions
Supernovae (SNe) are stellar explosions driven by gravitational or
thermonuclear energy, observed as electromagnetic radiation emitted over weeks
or more. In all known SNe, this radiation comes from internal energy deposited
in the outflowing ejecta by either radioactive decay of freshly-synthesized
elements (typically 56Ni), stored heat deposited by the explosion shock in the
envelope of a supergiant star, or interaction between the SN debris and
slowly-moving, hydrogen-rich circumstellar material. Here we report on a new
class of luminous SNe whose observed properties cannot be explained by any of
these known processes. These include four new SNe we have discovered, and two
previously unexplained events (SN 2005ap; SCP 06F6) that we can now identify as
members. These SNe are all ~10 times brighter than SNe Ia, do not show any
trace of hydrogen, emit significant ultra-violet (UV) flux for extended periods
of time, and have late-time decay rates which are inconsistent with
radioactivity. Our data require that the observed radiation is emitted by
hydrogen-free material distributed over a large radius (~10^15 cm) and
expanding at high velocities (>10^4 km s^-1). These long-lived, UV-luminous
events can be observed out to redshifts z>4 and offer an excellent opportunity
to study star formation in, and the interstellar medium of, primitive distant
galaxies.Comment: Accepted to Nature. Press embargoed until 2011 June 8, 18:00 U
SN 2006oz: rise of a super-luminous supernova observed by the SDSS-II SN Survey
We study SN 2006oz, a newly-recognized member of the class of H-poor,
super-luminous supernovae. We present multi-color light curves from the SDSS-II
SN Survey, that cover the rise time, as well as an optical spectrum that shows
that the explosion occurred at z~0.376. We fitted black body functions to
estimate the temperature and radius evolution of the photosphere and used the
parametrized code SYNOW to model the spectrum. We constructed a bolometric
light curve and compared it with explosion models. The very early light curves
show a dip in the g- and r-bands and a possible initial cooling phase in the
u-band before rising to maximum light. The bolometric light curve shows a
precursor plateau with a duration of 6-10 days in the rest-frame. A lower limit
of M_u < -21.5 can be placed on the absolute peak luminosity of the SN, while
the rise time is constrained to be at least 29 days. During our observations,
the emitting sphere doubled its radius to 2x10^15 cm, while the temperature
remained hot at 15000 K. As for other similar SNe, the spectrum is best modeled
with elements including O II and Mg II, while we tentatively suggest that Fe
III might be present. We suggest that the precursor plateau might be related to
a recombination wave in a circumstellar medium (CSM) and discuss whether this
is a common property of all similar explosions. The subsequent rise can be
equally well described by input from a magnetar or by ejecta-CSM interaction,
but the models are not well constrained owing to the lack of post-maximum
observations, and CSM interaction has difficulties accounting for the precursor
plateau self-consistently. Radioactive decay is less likely to be the mechanism
that powers the luminosity. The host galaxy, detected in deep imaging with the
10 m GTC, is a moderately young and star-forming, but not a starburst, galaxy.
It has an absolute magnitude of M_g = -16.9.Comment: Contains minor changes (of editorial nature) with respect to v1 in
order to match the published version. The abstract has been modified to fit
the arXiv space requirements. 11 pages, 8 figures, 3 table
Interaction-powered supernovae: Rise-time vs. peak-luminosity correlation and the shock-breakout velocity
Interaction of supernova (SN) ejecta with the optically thick circumstellar
medium (CSM) of a progenitor star can result in a bright, long-lived shock
breakout event. Candidates for such SNe include Type IIn and superluminous SNe.
If some of these SNe are powered by interaction, then there should be a
relation between their peak luminosity, bolometric light-curve rise time, and
shock-breakout velocity. Given that the shock velocity during shock breakout is
not measured, we expect a correlation, with a significant spread, between the
rise time and the peak luminosity of these SNe. Here, we present a sample of 15
SNe IIn for which we have good constraints on their rise time and peak
luminosity from observations obtained using the Palomar Transient Factory. We
report on a possible correlation between the R-band rise time and peak
luminosity of these SNe, with a false-alarm probability of 3%. Assuming that
these SNe are powered by interaction, combining these observables and theory
allows us to deduce lower limits on the shock-breakout velocity. The lower
limits on the shock velocity we find are consistent with what is expected for
SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light
curves of SNe IIn are caused by shock breakout in a dense CSM. We note that
such a correlation can arise from other physical mechanisms. Performing such a
test on other classes of SNe (e.g., superluminous SNe) can be used to rule out
the interaction model for a class of events.Comment: Accepted to ApJ, 6 page
Evidence for a Compact Wolf-Rayet Progenitor for the Type Ic Supernova PTF 10vgv
We present the discovery of PTF 10vgv, a Type Ic supernova (SN) detected by the Palomar Transient Factory, using the Palomar 48 inch telescope (P48). R-band observations of the PTF 10vgv field with P48 probe the SN emission from its very early phases (about two weeks before R-band maximum) and set limits on its flux in the week prior to the discovery. Our sensitive upper limits and early detections constrain the post-shock-breakout luminosity of this event. Via comparison to numerical (analytical) models, we derive an upper-limit of R ≾ 4.5 R_☉ (R ≾ 1 R_☉) on the radius of the progenitor star, a direct indication in favor of a compact Wolf-Rayet star. Applying a similar analysis to the historical observations of SN 1994I yields R ≾ 1/4 R_☉ for the progenitor radius of this SN
Social support for and through exercise and sport in a sample of men with serious mental illness.
Social support is important for people experiencing serious mental illness and is also important during the initiation and maintenance of exercise. In this article we draw on interpretive research into the experiences of 11 men with serious mental illness to explore four dimensions of social support both for and through exercise. Our findings suggest that informational, tangible, esteem, and emotional support were both provided for and given by participants through exercise. We conclude that experiences of both receiving and giving diverse forms of support in this way are significant for some people living with and recovering from serious mental illness
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