273 research outputs found
Case Notes
For decades, optical time-domain searches have been tuned to find ordinary supernovae, which rise and fall in brightness over a period of weeks. Recently, supernova searches have improved their cadences and a handful of fast-evolving luminous transients have been identified(1-5). These have peak luminosities comparable to type Ia supernovae, but rise to maximum in less than ten days and fade from view in less than one month. Here we present the most extreme example of this class of object thus far: KSN 2015K, with a rise time of only 2.2 days and a time above half-maximum of only 6.8 days. We show that, unlike type Ia supernovae, the light curve of KSN 2015K was not powered by the decay of radioactive elements. We further argue that it is unlikely that it was powered by continuing energy deposition from a central remnant (a magnetar or black hole). Using numerical radiation hydrodynamical models, we show that the light curve of KSN 2015K is well fitted by a model where the supernova runs into external material presumably expelled in a pre-supernova mass-loss episode. The rapid rise of KSN 2015K therefore probes the venting of photons when a hypersonic shock wave breaks out of a dense extended medium.NASA
NNH15ZDA001N
NNX17AI64G
Australian Research Council Centre of Excellence for All-sky Astrophysics
CE11000102
Weak lensing analysis of RXC J2248.7-4431
We present a weak lensing analysis of the cluster of galaxies RXC
J2248.7-4431, a massive system at z=0.3475 with prominent strong lensing
features covered by the HST/CLASH survey (Postman et al. 2012). Based on UBVRIZ
imaging from the WFI camera at the MPG/ESO-2.2m telescope, we measure
photometric redshifts and shapes of background galaxies. The cluster is
detected as a mass peak at 5sigma significance. Its density can be parametrised
as an NFW profile (Navarro et al. 1996) with two free parameters, the mass
M_200m=(33.1+9.6-6.8)x10^14Msol and concentration c_200m=2.6+1.5-1.0. We
discover a second cluster inside the field of view at a photometric redshift of
z~0.6, with an NFW mass of M_200m=(4.0+3.7-2.6)x10^14Msol.Comment: 15 pages, 17 figures; matching published versio
Baryon Content of Massive Galaxy Clusters (0.57 < z < 1.33)
We study the stellar, Brightest Cluster Galaxy (BCG) and intracluster medium
(ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with
median redshift and median mass . We
estimate stellar masses for each cluster and BCG using six photometric bands
spanning the range from the ultraviolet to the near-infrared observed with the
VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton
X-ray observations, and the virial masses are derived from the SPT
Sunyaev-Zel'dovich Effect signature.
At the BCG mass constitutes %
of the halo mass for a cluster, and this fraction
falls as . The cluster stellar mass function has a
characteristic mass , and the number of
galaxies per unit mass in clusters is larger than in the field by a factor
. Both results are consistent with measurements on group scales and
at lower redshift. We combine our SPT sample with previously published samples
at low redshift that we correct to a common initial mass function and for
systematic differences in virial masses. We then explore mass and redshift
trends in the stellar fraction (fstar), the ICM fraction (fICM), the cold
baryon fraction (fc) and the baryon fraction (fb). At a pivot mass of
and redshift , the characteristic values are
fstar=%, fICM=%, fc=% and fb=%.
These fractions all vary with cluster mass at high significance, indicating
that higher mass clusters have lower fstar and fc and higher fICM and fb. When
accounting for a 15% systematic virial mass uncertainty, there is no
statistically significant redshift trend at fixed mass in these baryon
fractions.
(abridged)Comment: Accepted for publication in MNRA
Searching for a Hypervelocity White Dwarf Companion: A Proper Motion Survey of SN 1006
Type Ia Supernovae (SNe Ia) are securely understood to come from the
thermonuclear explosion of a white dwarf as a result of binary interaction, but
the nature of that binary interaction and the secondary object is uncertain.
Recently, a double white dwarf model known as the dynamically driven
double-degenerate double-detonation (D6) model has become a promising
explanation for these events. One realization of this scenario predicts that
the companion may survive the explosion and reside within the remnant as a fast
moving ( km s), overluminous ()
white dwarf. Recently, three objects which appear to have these unusual
properties have been discovered in the Gaia survey. We obtained photometric
observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four
years to attempt to discover a similar star. We present a deep, high precision
astrometric proper motion survey of the interior stellar population of the
remnant. We rule out the existence of a high proper motion object consistent
with our tested realization of the D6 scenario ( km
s with ). We conclude that such a star does not exist within the
remnant, or is hidden from detection by either strong localized dust or the
unlikely possibility of ejection from the binary system near parallel to the
line of sight.Comment: 15 pages, 10 figure
Detection of Enhancement in Number Densities of Background Galaxies due to Magnification by Massive Galaxy Clusters
We present a detection of the enhancement in the number densities of
background galaxies induced from lensing magnification and use it to test the
Sunyaev-Zel'dovich effect (SZE) inferred masses in a sample of 19 galaxy
clusters with median redshift selected from the South Pole
Telescope SPT-SZ survey. Two background galaxy populations are selected for
this study through their photometric colours; they have median redshifts
(low- background) and
(high- background). Stacking these
populations, we detect the magnification bias effect at and
for the low- and high- backgrounds, respectively. We fit NFW
models simultaneously to all observed magnification bias profiles to estimate
the multiplicative factor that describes the ratio of the weak lensing
mass to the mass inferred from the SZE observable-mass relation. We further
quantify systematic uncertainties in resulting from the photometric
noise and bias, the cluster galaxy contamination and the estimations of the
background properties. The resulting for the combined background
populations with uncertainties is
, indicating good consistency
between the lensing and the SZE-inferred masses. We use our best-fit to
predict the weak lensing shear profiles and compare these predictions with
observations, showing agreement between the magnification and shear mass
constraints. This work demonstrates the promise of using the magnification as a
complementary method to estimate cluster masses in large surveys.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Constraining Cosmic Evolution of Type Ia Supernovae
We present the first large-scale effort of creating composite spectra of
high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift
counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88
high-redshift SNe Ia with excellent light-curve information. In addition, we
have obtained 397 spectra of low-redshift SNe through a multiple-decade effort
at Lick and Keck Observatories, and we have used 45 UV spectra obtained by
HST/IUE. The low-redshift spectra act as a control sample when comparing to the
ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra
appear very similar. The addition of galaxy light to the Lick composite spectra
allows a nearly perfect match of the overall spectral-energy distribution with
the ESSENCE composite spectra, indicating that the high-redshift SNe are more
contaminated with host-galaxy light than their low-redshift counterparts. This
is caused by observing objects at all redshifts with the same slit width, which
corresponds to different projected distances. After correcting for the
galaxy-light contamination, subtle differences in the spectra remain. We have
estimated the systematic errors when using current spectral templates for
K-corrections to be ~0.02 mag. The variance in the composite spectra give an
estimate of the intrinsic variance in low-redshift maximum-light SN spectra of
~3% in the optical and growing toward the UV. The difference between the
maximum light low and high-redshift spectra constrain SN evolution between our
samples to be < 10% in the rest-frame optical.Comment: 22 pages, 22 figures, submitted to ApJ. Composite spectra can be
downloaded from http://astro.berkeley.edu/~rfoley/composite
The ESSENCE Supernova Survey: Survey Optimization, Observations, and Supernova Photometry
We describe the implementation and optimization of the ESSENCE supernova
survey, which we have undertaken to measure the equation of state parameter of
the dark energy. We present a method for optimizing the survey exposure times
and cadence to maximize our sensitivity to the dark energy equation of state
parameter w=P/rho c^2 for a given fixed amount of telescope time. For our
survey on the CTIO 4m telescope, measuring the luminosity distances and
redshifts for supernovae at modest redshifts (z~0.5 +- 0.2) is optimal for
determining w. We describe the data analysis pipeline based on using reliable
and robust image subtraction to find supernovae automatically and in near
real-time. Since making cosmological inferences with supernovae relies
crucially on accurate measurement of their brightnesses, we describe our
efforts to establish a thorough calibration of the CTIO 4m natural photometric
system. In its first four years, ESSENCE has discovered and spectroscopically
confirmed 102 type Ia SNe, at redshifts from 0.10 to 0.78, identified through
an impartial, effective methodology for spectroscopic classification and
redshift determination. We present the resulting light curves for the all type
Ia supernovae found by ESSENCE and used in our measurement of w, presented in
Wood-Vasey et al, 2007.Comment: Submitted to ApJ. Companion paper to Wood-Vasey et al (2007).
Electronic tables available at http://www.ctio.noao.edu/essence/wresult
Nut production in Bertholletia excelsa across a logged forest mosaic: implications for multiple forest use
Although many examples of multiple-use forest management may be found in tropical smallholder systems, few studies provide empirical support for the integration of selective timber harvesting with non-timber forest product (NTFP) extraction. Brazil nut (Bertholletia excelsa, Lecythidaceae) is one of the worldâs most economically-important NTFP species extracted almost entirely from natural forests across the Amazon Basin. An obligate out-crosser, Brazil nut flowers are pollinated by large-bodied bees, a process resulting in a hard round fruit that takes up to 14 months to mature. As many smallholders turn to the financial security provided by timber, Brazil nut fruits are increasingly being harvested in logged forests. We tested the influence of tree and stand-level covariates (distance to nearest cut stump and local logging intensity) on total nut production at the individual tree level in five recently logged Brazil nut concessions covering about 4000 ha of forest in Madre de Dios, Peru. Our field team accompanied Brazil nut harvesters during the traditional harvest period (January-April 2012 and January-April 2013) in order to collect data on fruit production. Three hundred and ninety-nine (approximately 80%) of the 499 trees included in this study were at least 100 m from the nearest cut stump, suggesting that concessionaires avoid logging near adult Brazil nut trees. Yet even for those trees on the edge of logging gaps, distance to nearest cut stump and local logging intensity did not have a statistically significant influence on Brazil nut production at the applied logging intensities (typically 1â2 timber trees removed per ha). In one concession where at least 4 trees ha-1 were removed, however, the logging intensity covariate resulted in a marginally significant (0.09) P value, highlighting a potential risk for a drop in nut production at higher intensities. While we do not suggest that logging activities should be completely avoided in Brazil nut rich forests, when a buffer zone cannot be observed, low logging intensities should be implemented. The sustainability of this integrated management system will ultimately depend on a complex series of socioeconomic and ecological interactions. Yet we submit that our study provides an important initial step in understanding the compatibility of timber harvesting with a high value NTFP, potentially allowing for diversification of forest use strategies in Amazonian PerĂč
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