1,154 research outputs found
WISeREP - An Interactive Supernova Data Repository
We have entered an era of massive data sets in astronomy. In particular, the
number of supernova (SN) discoveries and classifications has substantially
increased over the years from few tens to thousands per year. It is no longer
the case that observations of a few prototypical events encapsulate most
spectroscopic information about SNe, motivating the development of modern tools
to collect, archive, organize and distribute spectra in general, and SN spectra
in particular. For this reason we have developed the Weizmann Interactive
Supernova data REPository - WISeREP - an SQL-based database (DB) with an
interactive web-based graphical interface. The system serves as an archive of
high quality SN spectra, including both historical (legacy) data as well as
data that is accumulated by ongoing modern programs. The archive provides
information about objects, their spectra, and related meta-data. Utilizing
interactive plots, we provide a graphical interface to visualize data, perform
line identification of the major relevant species, determine object redshifts,
classify SNe and measure expansion velocities. Guest users may view and
download spectra or other data that have been placed in the public domain.
Registered users may also view and download data that are proprietary to
specific programs with which they are associated. The DB currently holds >8000
spectra, of which >5000 are public; the latter include published spectra from
the Palomar Transient Factory, all of the SUSPECT archive, the
Caltech-Core-Collapse Program, the CfA SN spectra archive and published spectra
from the UC Berkeley SNDB repository. It offers an efficient and convenient way
to archive data and share it with colleagues, and we expect that data stored in
this way will be easy to access, increasing its visibility, usefulness and
scientific impact.Comment: To be published in PASP. WISeREP:
http://www.weizmann.ac.il/astrophysics/wiserep
Caltech Core-Collapse Project (CCCP) observations of type IIn supernovae: typical properties and implications for their progenitor stars
Type IIn Supernovae (SNe IIn) are rare events, constituting only a few
percent of all core-collapse SNe, and the current sample of well observed SNe
IIn is small. Here, we study the four SNe IIn observed by the Caltech
Core-Collapse Project (CCCP). The CCCP SN sample is unbiased to the extent that
object selection was not influenced by target SN properties. Therefore, these
events are representative of the observed population of SNe IIn. We find that a
narrow P-Cygni profile in the hydrogen Balmer lines appears to be a ubiquitous
feature of SNe IIn. Our light curves show a relatively long rise time (>20
days) followed by a slow decline stage (0.01 to 0.15 mag/day), and a typical
V-band peak magnitude of M_V=-18.4 +/- 1.0 mag. We measure the progenitor star
wind velocities (600 - 1400 km/s) for the SNe in our sample and derive
pre-explosion mass loss rates (0.026 - 0.12 solar masses per year). We compile
similar data for SNe IIn from the literature, and discuss our results in the
context of this larger sample. Our results indicate that typical SNe IIn arise
from progenitor stars that undergo LBV-like mass-loss shortly before they
explode.Comment: ApJ, submitte
Real-time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey
The Palomar Transient Factory (PTF) is an optical wide-field variability survey carried out using a camera with a 7.8 deg^2 field of view mounted on the 48 inch Oschin Schmidt telescope at Palomar Observatory. One of the key goals of this survey is to conduct high-cadence monitoring of the sky in order to detect optical transient sources shortly after they occur. Here, we describe the real-time capabilities of the PTF and our related rapid multiwavelength follow-up programs, extending from the radio to the γ-ray bands. We present as a case study observations of the optical transient PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P) supernova having a remarkably low luminosity. Our results demonstrate that the PTF now provides for optical transients the real-time discovery and rapid-response follow-up capabilities previously reserved only for high-energy transients like gamma-ray bursts
SN2007ax : An Extremely Faint Type Ia Supernova
We present multi-band photometric and optical spectroscopic observations of
SN2007ax, the faintest and reddest Type Ia supernova (SNIa) yet observed. With
M_B = -15.9 and (B-V)max = 1.2, this SN is over half a magnitude fainter at
maximum light than any other SNIa. Similar to subluminous SN2005ke, SN2007ax
also appears to show excess in UV emission at late time. Traditionally,
Delta-m_15(B) has been used to parameterize the decline rate for SNeIa.
However, the B-band transition from fast to slow decline occurs sooner than 15
days for faint SNeIa. Therefore we suggest that a more physically motivated
parameter, the time of intersection of the two slopes, be used instead. Only by
explaining the faintest (and the brightest) supernovae, we can thoroughly
understand the physics of thermonuclear explosions. We suggest that future
surveys should carefully design their cadence, depth, pointings and follow-up
to find an unbiased sample of extremely faint members of this subclass of faint
SNeIa.Comment: Accepted for publication in ApJ
A Very Large Array Search for 5 GHz Radio Transients and Variables at Low Galactic Latitudes
We present the results of a 5 GHz survey with the Very Large Array (VLA) and the expanded VLA, designed to search for short-lived (≾1 day) transients and to characterize the variability of radio sources at milli-Jansky levels. A total sky area of 2.66 deg^2, spread over 141 fields at low Galactic latitudes (b≅6-8 deg), was observed 16 times with a cadence that was chosen to sample timescales of days, months, and years. Most of the data were reduced, analyzed, and searched for transients in near real-time. Interesting candidates were followed up using visible light telescopes (typical delays of 1-2 hr) and the X-ray Telescope on board the Swift satellite. The final processing of the data revealed a single possible transient with a peak flux density of f_ν≅2.4 mJy. This implies a transient's sky surface density of κ(f_ν > 1.8 mJy) = 0.039^(+0.13 +0.18)_(–0.032,–0.038) deg^(–2) (1σ, 2σ confidence errors). This areal density is roughly consistent with the sky surface density of transients from the Bower et al. survey extrapolated to 1.8 mJy. Our observed transient areal density is consistent with a neutron star's origin for these events. Furthermore, we use the data to measure the source variability on timescales of days to years, and we present the variability structure function of 5 GHz sources. The mean structure function shows a fast increase on ≈1 day timescale, followed by a slower increase on timescales of up to 10 days. On timescales between 10 and 60 days, the structure function is roughly constant. We find that ≳30% of the unresolved sources brighter than 1.8 mJy are variables at the >4σ confidence level, presumably mainly due to refractive scintillation
Preliminary Results from the Caltech Core-Collapse Project (CCCP)
We present preliminary results from the Caltech Core-Collapse Project (CCCP),
a large observational program focused on the study of core-collapse SNe.
Uniform, high-quality NIR and optical photometry and multi-epoch optical
spectroscopy have been obtained using the 200'' Hale and robotic 60''
telescopes at Palomar, for a sample of 50 nearby core-collapse SNe. The
combination of both well-sampled optical light curves and multi-epoch
spectroscopy will enable spectroscopically and photometrically based subtype
definitions to be disentangled from each other. Multi-epoch spectroscopy is
crucial to identify transition events that evolve among subtypes with time. The
CCCP SN sample includes every core-collapse SN discovered between July 2004 and
September 2005 that was visible from Palomar, found shortly (< 30 days) after
explosion (based on available pre-explosion photometry), and closer than ~120
Mpc. This complete sample allows, for the first time, a study of core-collapse
SNe as a population, rather than as individual events. Here, we present the
full CCCP SN sample and show exemplary data collected. We analyze available
data for the first ~1/3 of the sample and determine the subtypes of 13 SNe II
based on both light curve shapes and spectroscopy. We discuss the relative SN
II subtype fractions in the context of associating SN subtypes with specific
progenitor stars.Comment: To appear in the proceedings of the meeting "The Multicoloured
Landscape of Compact Objects and their Explosive Origins", Cefalu, Italy,
June 2006, to be published by AIP, Eds. L. Burderi et a
The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters
Supernova (SN) rates are potentially powerful diagnostics of metal enrichment
and SN physics, particularly in galaxy clusters with their deep,
metal-retaining potentials and relatively simple star-formation histories. We
have carried out a survey for supernovae (SNe) in galaxy clusters, at a
redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the
Hubble Space Telescope. We reimaged a sample of 15 clusters that were
previously imaged by ACS, thus obtaining two to three epochs per cluster, in
which we discovered five likely cluster SNe, six possible cluster SNe Ia, two
hostless SN candidates, and several background and foreground events. Keck
spectra of the host galaxies were obtained to establish cluster membership. We
conducted detailed efficiency simulations, and measured the stellar
luminosities of the clusters using Subaru images. We derive a cluster SN rate
of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01
(systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM
+0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic)
[where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of
cluster SN rates, the uncertainties are dominated by small-number statistics.
The SN rate in this redshift bin is consistent with the SN rate in clusters at
lower redshifts (to within the uncertainties), and shows that there is, at
most, only a slight increase of cluster SN rate with increasing redshift. The
low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron
mass in clusters was already in place by z~1. The recently observed doubling of
iron abundances in the intracluster medium between z=1 and 0, if real, is
likely the result of redistribution of existing iron, rather than new
production of iron.Comment: Accepted to ApJ. Full resolution version available at
http://kicp.uchicago.edu/~kerens/HSTclusterSNe
The supernova rate in local galaxy clusters
We report a measurement of the supernova (SN) rates (Ia and core-collapse) in
galaxy clusters based on the 136 SNe of the sample described in Cappellaro et
al. (1999) and Mannucci et al. (2005).
Early-type cluster galaxies show a type Ia SN rate (0.066 SNuM) similar to
that obtained by Sharon et al. (2007) and more than 3 times larger than that in
field early-type galaxies (0.019 SNuM). This difference has a 98% statistical
confidence level. We examine many possible observational biases which could
affect the rate determination, and conclude that none of them is likely to
significantly alter the results. We investigate how the rate is related to
several properties of the parent galaxies, and find that cluster membership,
morphology and radio power all affect the SN rate, while galaxy mass has no
measurable effect. The increased rate may be due to galaxy interactions in
clusters, inducing either the formation of young stars or a different evolution
of the progenitor binary systems.
We present the first measurement of the core-collapse SN rate in cluster
late-type galaxies, which turns out to be comparable to the rate in field
galaxies. This suggests that no large systematic difference in the initial mass
function exists between the two environments.Comment: MNRAS, revised version after referee's comment
Supernova PTF 09uj: A possible shock breakout from a dense circumstellar wind
Type-IIn supernovae (SNe), which are characterized by strong interaction of
their ejecta with the surrounding circumstellar matter (CSM), provide a unique
opportunity to study the mass-loss history of massive stars shortly before
their explosive death. We present the discovery and follow-up observations of a
Type IIn SN, PTF 09uj, detected by the Palomar Transient Factory (PTF).
Serendipitous observations by GALEX at ultraviolet (UV) wavelengths detected
the rise of the SN light curve prior to the PTF discovery. The UV light curve
of the SN rose fast, with a time scale of a few days, to a UV absolute AB
magnitude of about -19.5. Modeling our observations, we suggest that the fast
rise of the UV light curve is due to the breakout of the SN shock through the
dense CSM (n~10^10 cm^-3). Furthermore, we find that prior to the explosion the
progenitor went through a phase of high mass-loss rate (~0.1 solar mass per
year) that lasted for a few years. The decay rate of this SN was fast relative
to that of other SNe IIn.Comment: Accepted to Apj, 6 pages, 4 figure
A survey for large image-separation lensed quasars
The statistics of gravitationally lensed quasars with multiple images in the
0.1''-7'' range have been measured in various surveys. Little is known,
however, about lensed-quasar statistics at larger image separations, which
probe masses on the scale of galaxy clusters. We extend the results of the HST
Snapshot Survey for Lensed Quasars to the 7''-50'' range for a sub-sample of 76
quasars that is free of known selection effects. Using a combination of
multicolor photometry and spectroscopy, we show that none of the point sources
in the entire field of view of the HST observations of these quasars are lensed
images. Large-separation quasar lensing is therefore not common. We carry out a
detailed calculation of the expected statistics of large-separation lensing for
this quasar sample, incorporating realistic input for the mass profiles and
mass function of galaxy clusters. We find that the observational null results
are consistent with the expected effect of galaxy clusters, even if these have
existed in their present form and number since z of about 2. The rarity of
large-separation lensed quasars can rule out some extreme scenarios, e.g. that
the mass-function of clusters has been severely underestimated, or that large
mass concentrations that are not associated with galaxies (i.e. ``failed''
clusters) are common. The rareness of wide lensing also sets limits on the
cosmological constant that are independent of limits derived from galaxy
lensing. The lensing statistics of larger quasar samples can probe the
structure, number, and evolution of clusters, as well as the geometry of space.Comment: LaTex, ApJ, submitte
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