5,694 research outputs found
Gamma-ray lines from SN2014J
On 21 January 2014, SN2014J was discovered in M82 and found to be the closest
type Ia supernova (SN Ia) in the last four decades. INTEGRAL observed SN2014J
from the end of January until late June for a total exposure time of about 7
Ms. SNe Ia light curves are understood to be powered by the radioactive decay
of iron peak elements of which Ni is dominantly synthesized during the
thermonuclear disruption of a CO white dwarf (WD). The measurement of
-ray lines from the decay chain
NiCoFe provides unique
information about the explosion in supernovae. Canonical models assume
Ni buried deeply in the supernova cloud, absorbing most of the early
-rays, and only the consecutive decay of Co should become
directly observable through the overlaying material several weeks after the
explosion when the supernova envelope dilutes as it expands. Surprisingly, with
the spectrometer on INTEGRAL, SPI, we detected Ni -ray lines at
158 and 812 keV at early times with flux levels corresponding to roughly 10% of
the total expected amount of Ni, and at relatively small velocities.
This implies some mechanism to create a major amout of Ni at the
outskirts, and at the same time to break the spherical symmetry of the
supernova. One plausible explanation would be a belt accreted from a He
companion star, exploding, and triggering the explosion of the white dwarf. The
full set of observations of SN2014J show Co -ray lines at 847
and 1238 keV, and we determine for the first time a SN Ia -ray light
curve. The irregular appearance of these -ray lines allows deeper
insights about the explosion morphology from its temporal evolution and
provides additional evidence for an asymmetric explosion, from our
high-resolution spectroscopy and comparisons with recent models.Comment: 12 pages, 15 figures, 10th INTEGRAL Workshop: "A Synergistic View of
the High Energy Sky" - Integral2014, 15-19 September 2014, Annapolis, MD, US
Adaptive Binning of X-ray data with Weighted Voronoi Tesselations
We present a technique to adaptively bin sparse X-ray data using weighted
Voronoi tesselations (WVTs). WVT binning is a generalisation of Cappellari &
Copin's (2001) Voronoi binning algorithm, developed for integral field
spectroscopy. WVT binning is applicable to many types of data and creates
unbiased binning structures with compact bins that do not lead the eye. We
apply the algorithm to simulated data, as well as several X-ray data sets, to
create adaptively binned intensity images, hardness ratio maps and temperature
maps with constant signal-to-noise ratio per bin. We also illustrate the
separation of diffuse gas emission from contributions of unresolved point
sources in elliptical galaxies. We compare the performance of WVT binning with
other adaptive binning and adaptive smoothing techniques. We find that the CIAO
tool csmooth creates serious artefacts and advise against its use to interpret
diffuse X-ray emission.Comment: 14 pages; submitted to MNRAS; code freely available at
http://www.phy.ohiou.edu/~diehl/WVT/index.html with user manual, examples and
high-resolution version of this pape
The Hot Interstellar Medium in Normal Elliptical Galaxies III: The Thermal Structure of the Gas
This is the third paper in a series analyzing X-ray emission from the hot
interstellar medium in a sample of 54 normal elliptical galaxies observed by
Chandra, focusing on 36 galaxies with sufficient signal to compute radial
temperature profiles. We distinguish four qualitatively different types of
profile: positive gradient (outwardly rising), negative gradients (falling),
quasi-isothermal (flat) and hybrid (falling at small radii, then rising). We
measure the mean logarithmic temperature gradients in two radial regions: from
0--2 -band effective radii (excluding the central point source), and
from 2--. We find the outer gradient to be uncorrelated with intrinsic
host galaxy properties, but strongly influenced by the environment: galaxies in
low-density environments tend to show negative outer gradients, while those in
high-density environments show positive outer gradients, suggesting influence
of circumgalactic hot gas. The inner temperature gradient is unaffected by the
environment but strongly correlated with intrinsic host galaxy characteristics:
negative inner gradients are more common for smaller, optically faint, low
radio-luminosity galaxies, whereas positive gradients are found in bright
galaxies with stronger radio sources. There is no evidence for bimodality in
the distribution of inner or outer gradients. We propose three scenarios to
explain the inner temperature gradients: (1) Weak AGN heat the ISM locally,
higher-luminosity AGN heat the system globally through jets inflating cavities
at larger radii; (2) The onset of negative inner gradients indicates a
declining importance of AGN heating relative to other sources, such as
compressional heating or supernovae; (3) The variety of temperature profiles
are snapshots of different stages of a time-dependent flow.Comment: 18 pages, emulateapj, 55 figures (36 online-only figures included in
astro-ph version), submitted to Ap
Achieving sub-electron readout noise in Skipper CCDs
The readout noise for Charge-Coupled Devices (CCDs) has been the main
limitation when using these detectors for measuring small amplitude signals. A
readout system for a new scientific, low noise CCD is presented in this paper.
The Skipper CCD architecture, and its advantages for low noise applications are
discussed. A technique for obtaining sub-electron readout noise levels is
presented, and its noise and signal characteristics are derived. We demonstrate
a very low readout noise of RMS. Also, we show the results using the
detector in a low-energy X-ray detection experiment.Comment: 16 pages, 11 figure
Generalized Parton Distributions and Transversity in Nucleons and Nuclei
We present an exploratory study using generalized parton distributions of
several observables related to transverse degrees of freedom in hadronic
structure -- the nucleon transverse momentum, the transverse radius, or impact
parameter, and the momentum transfer, , dependence of the longitudinal
variable -- in both nucleons and nuclei.Comment: 6 pages, 3 figures, Talk presented at "Baryons 04", October
25th-30th, 2004, Palaiseau, Franc
Comparing simulated Al maps to gamma-ray measurements
© ESO 2019.Context. The diffuse gamma-ray emission of at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. Interstellar-medium morphology and dynamics are investigated in astrophysics through 3D hydrodynamic simulations in fine detail, as only few suitable astronomical probes are available. Aims. We compare a galactic-scale hydrodynamic simulation of the Galaxy's interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on emission in the Milky Way extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we perform maximum likelihood fits of simulated sky maps as well as observation-based maximum entropy maps to measurements with INTEGRAL/SPI. To study general morphological properties, we compare the scale heights of emission produced by the simulation to INTEGRAL/SPI measurements.} Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, but differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small scale height features and a mismatch at larger scale heights. We attribute this to the prominent foreground emission sites that are not captured by the simulation.Peer reviewedFinal Accepted Versio
Initial Calibration of CCD Images for the Dark Energy Survey
Astronomical images taken from a telescope must go through “astronomical image processing” to remove instrumental signatures. The Dark Energy Survey (DES), which will start operations in 2012, will use a 570 megapixel Dark Energy Camera (DECam) to study the mystery of the acceleration of the expanding universe. The DECam will use DES filters and 74 of a new type of astronomical Charge Coupled Device (CCD) that is particularly efficient in detecting near-infrared light. Together, the DES filters and DECam CCDs are optimized for the measurement of redshifts of distant galaxies. In preparation for the DES, data were collected from the 1 meter telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile, using a DES filter set and a DECam CCD as a test set for the initial analysis of data. Here, these CTIO-1m data were used to determine the relationship between the apparent measured brightness of stars of known brightness (standard stars) and the amount of atmosphere the telescope looks through (angular distance from the zenith or “airmass”). This relationship was tested against the results from another telescope using similar filters. Finally, this relationship was used to calibrate the brightness of stars of unknown brightness that were also observed in the CTIO 1m data set
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