241 research outputs found
The macroeconomic effects of oil price shocks : why are the 2000s so different from the 1970s
August 17, 2007, revised: March 25, 200
The macroeconomic effects of oil price shocks : why are the 2000s so different from the 1970s
August 17, 2007, revised: March 25, 200
Caltech Core-Collapse Project (CCCP) Observations of Type II Supernovae: Evidence for Three Distinct Photometric Subtypes
We present R-Band light curves of Type II supernovae (SNe) from the Caltech
Core Collapse Project (CCCP). With the exception of interacting (Type IIn) SNe
and rare events with long rise times, we find that most light curve shapes
belong to one of three distinct classes: plateau, slowly declining and rapidly
declining events. The last class is composed solely of Type IIb SNe which
present similar light curve shapes to those of SNe Ib, suggesting, perhaps,
similar progenitor channels. We do not find any intermediate light curves,
implying that these subclasses are unlikely to reflect variance of continuous
parameters, but rather might result from physically distinct progenitor
systems, strengthening the suggestion of a binary origin for at least some
stripped SNe. We find a large plateau luminosity range for SNe IIP, while the
plateau lengths seem rather uniform at approximately 100 days. As analysis of
additional CCCP data goes on and larger samples are collected, demographic
studies of core collapse SNe will likely continue to provide new constraints on
progenitor scenarios.Comment: Submitted to ApJ
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
The Effects of Government Spending on Real Exchange Rates: Evidence from Military Spending Panel Data
PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterisation of PTF10iya, a short-lived (dt
~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21
mag) transient source found by the Palomar Transient Factory. The
ultraviolet/optical spectral energy distribution is reasonably well fit by a
blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x
10^44 erg per s (depending on the details of the extinction correction). A
comparable amount of energy is radiated in the X-ray band that appears to
result from a distinct physical process. The location of PTF10iya is consistent
with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within
350 mas (99.7 per cent confidence radius), or a projected distance of less than
1.2 kpc. At first glance, these properties appear reminiscent of the
characteristic "big blue bump" seen in the near-ultraviolet spectra of many
active galactic nuclei (AGNs). However, emission-line diagnostics of the host
galaxy, along with a historical light curve extending back to 2007, show no
evidence for AGN-like activity. We therefore consider whether the tidal
disruption of a star by an otherwise quiescent supermassive black hole may
account for our observations. Though with limited temporal information,
PTF10iya appears broadly consistent with the predictions for the early
"super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black
hole. Regardless of the precise physical origin of the accreting material, the
large luminosity and short duration suggest that otherwise quiescent galaxies
can transition extremely rapidly to radiate near the Eddington limit; many such
outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment
H-NS binds with high affinity to the Tn10 transpososome and promotes transpososome stabilization
H-NS is a bacterial DNA-binding protein that regulates gene expression and DNA transposition. In the case of Tn10, H-NS binds directly to the transposition machinery (i.e. the transpososome) to influence the outcome of the reaction. In the current work we evaluated the binding affinity of H-NS for two forms of the Tn10 transpososome, including the initial folded form and a pre-unfolded form. These two forms differ in that IHF is bound to the former but not the latter. IHF binding induces a bend (or fold) in the transposon end that facilitates transpososome formation. However, the continued presence of IHF in the transpososome inhibits intermolecular transposition events. We show that H-NS binds particularly strongly to the pre-unfolded transpososome with an apparent Kd of ∼0.3 nM. This represents the highest affinity interaction between H-NS and a binding partner documented to date. We also show that binding of H-NS to the transpososome stabilizes this structure and propose that both high-affinity binding and stabilization result from the combined interaction between H-NS and DNA and H-NS and transposase within the transpososome. Mechanistic implications for tight binding of H-NS to the transpososome and transpososome stabilization are considered
- …