252 research outputs found
Three Gravitationally Lensed Supernovae behind CLASH Galaxy Clusters
We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and A383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was ~1.0 ± 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is ~0.2 ± 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak-lensing maps of the clusters (in magnitude units, 2.5 log_(10)μ): 0.83 ± 0.16 mag for SN CLO12Car, 0.28 ± 0.08 mag for SN CLN12Did, and 0.43 ± 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications
Optimizing the Resolution of Hydrodynamic Simulations for MCRaT Radiative Transfer Calculations
Despite their discovery about half a century ago, the Gamma-ray burst (GRB)
prompt emission mechanism is still not well understood. Theoretical modeling of
the prompt emission has advanced considerably due to new computational tools
and techniques. One such tool is the PLUTO hydrodynamics code, which is used to
numerically simulate GRB outflows. PLUTO uses Adaptive Mesh Refinement to focus
computational efforts on the portion of the grid that contains the simulated
jet. Another tool is the Monte Carlo Radiation Transfer (MCRaT) code, which
predicts electromagnetic signatures of GRBs by conducting photon scatterings
within a jet using PLUTO. The effects of the underlying resolution of a PLUTO
simulation with respect to MCRaT post-processing radiative transfer results
have not yet been quantified. We analyze an analytic spherical outflow and a
hydrodynamically simulated GRB jet with MCRaT at varying spatial and temporal
resolutions and quantify how decreasing both resolutions affect the resulting
mock observations. We find that changing the spatial resolution changes the
hydrodynamic properties of the jet, which directly affect the MCRaT mock
observable peak energies. We also find that decreasing the temporal resolution
artificially decreases the high energy slope of the mock observed spectrum,
which increases both the spectral peak energy and the luminosity. We show that
the effects are additive when both spatial and temporal resolutions are
modified. Our results allow us to understand how decreased hydrodynamic
temporal and spatial resolutions affect the results of post-processing
radiative transfer calculations, allowing for the optimization of hydrodynamic
simulations for radiative transfer codes.Comment: 12 pages, 10 figures, submitted to ApJ, for calculations, see:
https://github.com/jaritaes99/MCRaT-resolutio
Evidence for High-Frequency QPOs with a 3:2 Frequency Ratio from a 5000 Solar Mass Black Hole
Following the discovery of 3:2 resonance quasi-periodic oscillations (QPOs)
in M82X-1 (Pasham et al. 2014), we have constructed power density spectra (PDS)
of all 15 (sufficiently long) {\it XMM-Newton} observations of the
ultraluminous X-ray source NGC1313X-1 ( 210
erg/sec). We detect a strong QPO at a frequency of 0.290.01 Hz in data
obtained on 2012 December 16. Subsequent searching of all the remaining
observations for a 3:2/2:3 frequency pair revealed a feature at 0.460.02
Hz on 2003 Dec 13 (frequency ratio of 1.590.09). The global significance
of the 0.29 Hz feature considering all frequencies between 0.1 and 4 Hz is
3.5 . The significance of the 0.460.02 Hz QPO is 3.5
for a search at 2/3 and 3/2 of 0.29 Hz. We also detect lower frequency QPOs
(32.92.6 and 79.71.2 mHz). All the QPOs are super-imposed on a
continuum consisting of flat-topped, band-limited noise, breaking into a
power-law at a frequency of 163 mHz and white noise at 0.1 Hz.
NGC1313X-1's PDS is analogous to stellar-mass black holes' (StMBHs) PDS in the
so-called steep power-law state, but with the respective frequencies (both QPOs
and break frequencies) scaled down by a factor of 1000. Using the
inverse mass-to-high-frequency QPO scaling of StMBHs, we estimate NGC1313X-1's
black hole mass to be 50001300 , consistent with an inference
from the scaling of the break frequency. However, the implied Eddington ratio,
L 0.030.01, is significantly lower compared to StMBHs in the
steep power-law state (L 0.2).Comment: Published in ApJ Letter
Photometry of Some Recent Gamma-ray Bursts
We present the results of the optical, X-ray and gamma-ray analysis of some
recent GRBs. The data were obtained by the automated P60 telescope and the
Swift telescope (UVOT, XRT and BAT). We present some example fits for the
lightcurves. The data reduction and the investigations were made by the Konkoly
Observatory HEART group (http://www.konkoly.hu/HEART/index.html).Comment: 4 pages, 1 figure, appeared in GAMMA RAY BURSTS 2010, AIP Conference
Proceedings, Volume 1358, pp. 134-137 (2011
Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li
We carried out the first multi-wavelength (optical/UV and X-ray) photometric
reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find
that its X-ray variations are correlated with and lag the optical/UV
fluctuations by 324 days. Based on the direction and the magnitude of the
X-ray time lag, we rule out X-ray reprocessing and direct emission from a
standard circular thin disk as the dominant source of its optical/UV emission.
The lag magnitude also rules out an AGN disk-driven instability as the origin
of ASASSN-14li and thus strongly supports the tidal disruption picture for this
event and similar objects. We suggest that the majority of the optical/UV
emission likely originates from debris stream self-interactions. Perturbations
at the self-interaction sites produce optical/UV variability and travel down to
the black hole where they modulate the X-rays. The time lag between the
optical/UV and the X-rays variations thus correspond to the time taken by these
fluctuations to travel from the self-interaction site to close to the black
hole. We further discuss these time lags within the context of the three
variants of the self-interaction model. High-cadence monitoring observations of
future TDFs will be sensitive enough to detect these echoes and would allow us
to establish the origin of optical/UV emission in TDFs in general.Comment: Publish in ApJ Letter
BatAnalysis -- A Comprehensive Python Pipeline for Swift BAT Survey Analysis
The Swift Burst Alert Telescope (BAT) is a coded aperture gamma-ray
instrument with a large field of view that primarily operates in survey mode
when it is not triggering on transient events. The survey data consists of
eighty-channel detector plane histograms that accumulate photon counts over
time periods of at least 5 minutes. These histograms are processed on the
ground and are used to produce the survey dataset between and keV.
Survey data comprises of all BAT data by volume and allows for the
tracking of long term light curves and spectral properties of cataloged and
uncataloged hard X-ray sources. Until now, the survey dataset has not been used
to its full potential due to the complexity associated with its analysis and
the lack of easily usable pipelines. Here, we introduce the BatAnalysis python
package which provides a modern, open-source pipeline to process and analyze
BAT survey data. BatAnalysis allows members of the community to use BAT survey
data in more advanced analyses of astrophysical sources including pulsars,
pulsar wind nebula, active galactic nuclei, and other known/unknown transient
events that may be detected in the hard X-ray band. We outline the steps taken
by the python code and exemplify its usefulness and accuracy by analyzing
survey data from the Crab Pulsar, NGC 2992, and a previously uncataloged MAXI
Transient. The BatAnalysis package allows for 18 years of BAT survey to
be used in a systematic way to study a large variety of astrophysical sources.Comment: 13 pages, 6 figures; Submitted to ApJ; BatAnalysis github link is:
https://github.com/parsotat/BatAnalysis, comments/suggestions are welcome
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