334 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
Late-Time Circumstellar Interaction in a Spitzer Selected Sample of Type IIn Supernovae
Type IIn supernovae (SNe IIn) are a rare (< 10%) subclass of core-collapse
SNe that exhibit relatively narrow emission lines from a dense, pre-existing
circumstellar medium (CSM). In 2009, a warm Spitzer survey observed 30 SNe IIn
discovered in 2003 - 2008 and detected 10 SNe at distances out to 175 Mpc with
unreported late-time infrared emission, in some cases more than 5 years
post-discovery. For this single epoch of data, the warm-dust parameters suggest
the presence of a radiative heating source consisting of optical/X-ray emission
continuously generated by ongoing CSM interaction. Here we present
multi-wavelength follow-up observations of this sample of 10 SNe IIn and the
well-studied Type IIn SN 2010jl. A recent epoch of Spitzer observations reveals
ongoing mid-infrared emission from nine of the SNe in this sample. We also
detect three of the SNe in archival WISE data, in addition to SNe 1987A,
2004dj, and 2008iy. For at least five of the SNe in the sample, optical and/or
X-ray emission confirms the presence of radiative emission from ongoing CSM
interaction. The two Spitzer nondetections are consistent with the forward
shock overrunning and destroying the dust shell, a result that places upper
limits on the dust-shell size. The optical and infrared observations confirm
the radiative heating model and constrain a number of model parameters,
including progenitor mass-loss characteristics. All of the SNe in this sample
experienced an outburst on the order of tens to hundreds of years prior to the
SN explosion followed by periods of less intense mass loss. Although all
evidence points to massive progenitors, the variation in the data highlights
the diversity in SN IIn progenitor evolution. While these observations do not
identify a particular progenitor system, they demonstrate that future,
coordinated, multi-wavelength campaigns can constrain theoretical mass-loss
models.Comment: 10 pages, 6 figures, accepted to AJ (with comments
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
A Search for High-Energy Counterparts to Fast Radio Bursts
We report on a search for high-energy counterparts to fast radio bursts
(FRBs) with the Fermi Gamma-ray Burst Monitor (GBM), Fermi Large Area Telescope
(LAT), and the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT). We
find no significant associations for any of the 23 FRBs in our sample, but
report upper limits to the high-energy fluence for each on timescales of 0.1,
1, 10, and 100 s. We report lower limits on the ratio of the radio to
high-energy fluence, , for timescales of 0.1 and 100
s. We discuss the implications of our non-detections on various proposed
progenitor models for FRBs, including analogs of giant pulses from the Crab
pulsar and hyperflares from magnetars. This work demonstrates the utility of
analyses of high-energy data for FRBs in tracking down the nature of these
elusive sources
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