640 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
SN 2003du: Signatures of the Circumstellar Environment in a Normal Type Ia Supernova?
We present observations of the Type Ia supernova 2003du and report the
detectionof an unusual, high-velocity component in the Ca II infrared triplet,
similar tofeatures previously observed in SN 2000cx and SN 2001el. This feature
exhibits a large expansion velocity (~18,000 km/s) which is nearly constant
between -7 and +2 days relative to maximum light, and disappears shortly
thereafter. Otherthan this feature, the spectral evolution and light curve
resemble those of a normal SN Ia.
We find that the Ca II feature can plausibly be caused by a dense shell
formed when circumstellar material of solar abundance is overrun by the rapidly
expanding outermost layers of the SN ejecta. Model calculations show that the
optical and infrared spectra are remarkably unaffected by the circumstellar
interaction. In particular, no hydrogen lines are detectable in either
absorption or emission. The only qualitatively different features are the
strong, high-velocity feature in the Ca II IR-triplet, and a somewhat weaker O
I feature near 7,300 AA. The morphology and time evolution of these features
provide an estimate for the amount of accumulated matter and an indication of
the mixing in the dense shell. We apply these diagnostic tools to SN 2003du and
infer that about 2 x 10^{-2} M_sun of solar abundance material may have
accumulated in a circumstellar shell prior to the observations. Furthermore,
the early light curve data imply that the circumstellar material was originally
very close to the progenitor system, perhaps from an accretion disk, Roche lobe
or common envelope.Comment: 35 Pages, 11 Figures, to appear in ApJ. Resubmission includes
expanded discussion & new figures to match with accepted journal versio
SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material
We present photometry, spectra, and spectropolarimetry of supernova (SN)
2012ab, mostly obtained over the course of days after discovery. SN
2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral
galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN
1998S, its spectral evolution does not. We see indications of CSM interaction
in the strong intermediate-width emission features, the high luminosity (peak
at absolute magnitude ), and the lack of broad absorption features in
the spectrum. The H emission undergoes a peculiar transition. At early
times it shows a broad blue emission wing out to km
and a truncated red wing. Then at late times (
100days) it shows a truncated blue wing and a very broad red emission wing
out to roughly km . This late-time broad red wing
probably arises in the reverse shock. Spectra also show an asymmetric
intermediate-width H component with stronger emission on the red side
at late times. The evolution of the asymmetric profiles requires a density
structure in the distant CSM that is highly aspherical. Our spectropolarimetric
data also suggest asphericity with a strong continuum polarization of % and depolarization in the H line, indicating asphericity in the
CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss
rate of for km extending back at least 75yr prior to the
SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest
that the progenitor was an eccentric binary system undergoing eruptive mass
loss.Comment: 18 pages, 12 figure
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
The Palomar Transient Factory photometric catalog 1.0
We construct a photometrically calibrated catalog of non-variable sources
from the Palomar Transient Factory (PTF) observations. The first version of
this catalog presented here, the PTF photometric catalog 1.0, contains
calibrated R_PTF-filter magnitudes for about 21 million sources brighter than
magnitude 19, over an area of about 11233 deg^2. The magnitudes are provided in
the PTF photometric system, and the color of a source is required in order to
convert these magnitudes into other magnitude systems. We estimate that the
magnitudes in this catalog have typical accuracy of about 0.02 mag with respect
to magnitudes from the Sloan Digital Sky Survey. The median repeatability of
our catalog's magnitudes for stars between 15 and 16 mag, is about 0.01 mag,
and it is better than 0.03 mag for 95% of the sources in this magnitude range.
The main goal of this catalog is to provide reference magnitudes for
photometric calibration of visible light observations. Subsequent versions of
this catalog, which will be published incrementally online, will be extended to
a larger sky area and will also include g_PTF-filter magnitudes, as well as
variability and proper motion information.Comment: 6 pages, 6 figures, PASP in pres
Optical and Near-Infrared Observations of the Highly Reddened, Rapidly Expanding Type Ia Supernova 2006X in M100
We present extensive optical (UBVRI), near-infrared (JK) light curves and
optical spectroscopy of the Type Ia supernova (SN) 2006X in the nearby galaxy
NGC 4321 (M100). Our observations suggest that either SN 2006X has an
intrinsically peculiar color evolution, or it is highly reddened [E(B -
V)_{host} = 1.42+/-0.04 mag] with R_V = 1.48+/-0.06, much lower than the
canonical value of 3.1 for the average Galactic dust. SN 2006X also has one of
the highest expansion velocities ever published for a SN Ia. Compared with the
other SNe Ia we analyzed, SN 2006X has a broader light curve in the U band, a
more prominent bump/shoulder feature in the V and R bands, a more pronounced
secondary maximum in the I and near-infrared bands, and a remarkably smaller
late-time decline rate in the B band. The B - V color evolution shows an
obvious deviation from the Lira-Phillips relation at 1 to 3 months after
maximum brightness. At early times, optical spectra of SN 2006X displayed
strong, high-velocity features of both intermediate-mass elements (Si, Ca, and
S) and iron-peak elements, while at late times they showed a relatively blue
continuum, consistent with the blue U-B and B-V colors at similar epochs. A
light echo and/or the interaction of the SN ejecta and its circumstellar
material may provide a plausible explanation for its late-time photometric and
spectroscopic behavior. Using the Cepheid distance of M100, we derive a Hubble
constant of 72.7+/-8.2 km s^{-1} Mpc^{-1}(statistical) from the normalized
dereddened luminosity of SN 2006X. We briefly discuss whether abnormal dust is
a universal signature for all SNe Ia, and whether the most rapidly expanding
objects form a subclass with distinct photometric and spectroscopic properties.Comment: 48 pages, 20 figures and 11 tables. Accepted Version (ApJ, 2008,
March issue
GRB021004: a Massive Progenitor Star Surrounded by Shells
We present spectra of the optical transient of GRB021004 obtained with the Hobby-Eberly telescope starting 15.48, 20.31 hours, and 4.84 days after the burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting 14.31 hours after the burst. GRB021004 is the first afterglow whose spectrum is dominated by absorption lines from high ionization species with multiple velocity components separated by up to 3000 km/s. We argue that these lines are likely to come from shells around a massive progenitor star. The high velocities and high ionizations arise from a combination of acceleration and flash-ionization by the burst photons and the wind velocity and steady ionization by the progenitor. We also analyze the broad-band spectrum and the light curve. We distinguish six components along the line of sight: (1) The z~2.293 absorption lines arise from the wind of a massive star. For a mass loss rate of ~6 x 10^{-5} solar masses per year, this component also provides the external medium to create the afterglow light. (2) A second shell produces absorption lines with a relative velocity of 560 km/s, and this is associated with the shell created by the fast massive star wind blowing a bubble in the preceding slow wind at a radial distance of order 10 pc. (3) More distant clouds within the host galaxy lie between 30-2500 pc, where they have been ionized by the burst. (4-6) The massive star wind has clumps with radii and over-densities of 0.022, 0.063, and 0.12 parsecs and 50%, 10%, and 10% respectively. The immediate progenitor of the burster could either be a WC-type Wolf-Rayet star or a highly evolved star whose original mass was just too small for it to become a WN-type Wolf-Rayet star
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