81 research outputs found
NuSTAR Observations of Abell 2163: Constraints on Non-thermal Emission
Since the first non-thermal reports of inverse Compton (IC) emission from the
intracluster medium (ICM) of galaxy clusters at hard X-ray energies, we have
yet to unambiguously confirm IC emission in observations with newer facilities.
RXTE detected IC emission in one of the hottest known clusters, Abell 2163
(A2163), a massive merging cluster with a giant radio halo--the presumed source
of relativistic electrons IC scattering CMB photons to X-ray energies. The
cluster's redshift (z~0.2) allows its thermal and non-thermal radio emission to
fit NuSTARS's FOV, permitting a deep observation capable of confirming or
ruling out the RXTE report. The IC flux provides constraints on the average
magnetic field strength in a cluster. To determine the global diffuse IC
emission in A2163, we fit its global NuSTAR spectrum with four models: single
(1T) and two-temperature (2T), 1T+power law component (T+IC), and
multi-temperature+power law (9T+IC). Each represent different characterizations
of the thermal ICM emission, with power law components added to represent IC
emission. We find the 3-30 keV spectrum can be described by purely thermal
emission, with a global average temperature of kT = (11.8 0.2) keV. The
IC flux is constrained to
using the 1T+IC model and
with the more physical 9T+IC model, both to 90% confidence
levels. Combining these limits with 1.4 GHz diffuse radio data from the VLA, we
find the average magnetic field strength to be and
, respectively, providing the strongest constraints on these
values in A2163 to date.Comment: 16 pages, 17 figure
Breadboard model of the LISA phasemeter
An elegant breadboard model of the LISA phasemeter is currently under
development by a Danish-German consortium. The breadboard is build in the frame
of an ESA technology development activity to demonstrate the feasibility and
readiness of the LISA metrology baseline architecture. This article gives an
overview about the breadboard design and its components, including the
distribution of key functionalities.Comment: 5 pages, 3 figures, published in ASP Conference Series, Vol. 467, 9th
LISA Symposium (2012), pp 271-27
The<i> Nustar </i>Extragalactic Surveys: The Number Counts of Active Galactic Nuclei and the Resolved Fraction of the Cosmic X-Ray Background
We present the 3–8 keV and 8–24 keV number counts of active galactic nuclei (AGNs) identified in the NuclearSpectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now resolved 33%–39% of the X-raybackground in the 8–24 keV band, directly identifying AGNs with obscuring columns up to ~1025 cm-2. In the softer 3–8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5 x 10-15 ≤ S(3–8 keV)/erg s-1 cm-2 ≤10-12 probed by NuSTAR. In the hard 8–24 keV band NuSTAR probes fluxes over the range 2 x 10-14 ≤ S(8–24 keV)/erg s-1 cm-2 ≤ 10-12, a factor ∼100 fainter than previous measurements. The 8–24 keV number counts match predictions from AGN populationsynthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferredfrom the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly abovesimple extrapolation with a Euclidian slope to low flux of the Swift/BAT 15–55 keV number counts measured at higher fluxes (S(15–55 keV) ≤ 10−11 erg s-1 cm-2), reflecting the evolution of the AGN population between the Swift/BAT local (z < 0.1) sample and NuSTAR’s z ~ 1 sample. CXB synthesis models, which account for AGNevolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured AGNs at low redshifts
The Nuclear Spectroscopic Telescope Array (NuSTAR)
The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer
mission that will carry the first focusing hard X-ray (5 -- 80 keV) telescope
to orbit. NuSTAR will offer a factor 50 -- 100 sensitivity improvement compared
to previous collimated or coded mask imagers that have operated in this energy
band. In addition, NuSTAR provides sub-arcminute imaging with good spectral
resolution over a 12-arcminute field of view. After launch, NuSTAR will carry
out a two-year primary science mission that focuses on four key programs:
studying the evolution of massive black holes through surveys carried out in
fields with excellent multiwavelength coverage, understanding the population of
compact objects and the nature of the massive black hole in the center of the
Milky Way, constraining explosion dynamics and nucleosynthesis in supernovae,
and probing the nature of particle acceleration in relativistic jets in active
galactic nuclei. A number of additional observations will be included in the
primary mission, and a guest observer program will be proposed for an extended
mission to expand the range of scientific targets. The payload consists of two
co-aligned depth-graded multilayer coated grazing incidence optics focused onto
solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus
rocket into a low-inclination Earth orbit. Data will be publicly available at
GSFC's High Energy Astrophysics Science Archive Research Center (HEASARC)
following validation at the science operations center located at Caltech.Comment: 9 pages, 5 figures, to appear in Proceedings of the SPIE, Space
Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ra
INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane
The center of our Galaxy is a known strong source of electron-positron
511-keV annihilation radiation. Thus far, however, there have been no reliable
detections of annihilation radiation outside of the central radian of our
Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy
Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study
of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution
coded-aperture gamma-ray telescope with an unprecedented combination of
sensitivity, angular resolution and energy resolution. We report results from
the first 10 months of observation. During this period a significant fraction
of the observing time was spent in or near the Galactic Plane. No positive
annihilation flux was detected outside of the central region (|l| > 40 deg) of
our Galaxy. In this paper we describe the observations and data analysis
methods and give limits on the 511-keV flux.Comment: Accepted for publication in the Astrophysical Journal. 13 pages, 3
figure
I. Flux and color variations of the quadruply imaged quasar HE 0435-1223
aims: We present VRi photometric observations of the quadruply imaged quasar
HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla
Observatory. Our aim was to monitor and study the magnitudes and colors of each
lensed component as a function of time. methods: We monitored the object during
two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data
with two independent techniques: difference imaging and PSF (Point Spread
Function) fitting.results: Between these two seasons, our results show an
evident decrease in flux by ~0.2-0.4 magnitudes of the four lensed components
in the three filters. We also found a significant increase (~0.05-0.015) in
their V-R and R-i color indices. conclusions: These flux and color variations
are very likely caused by intrinsic variations of the quasar between the
observed epochs. Microlensing effects probably also affect the brightest "A"
lensed component.Comment: 10 pages, 8 figure
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