14,285 research outputs found
POLARIX: a pathfinder mission of X-ray polarimetry
Since the birth of X-ray astronomy, spectral, spatial and timing observation
improved dramatically, procuring a wealth of information on the majority of the
classes of the celestial sources. Polarimetry, instead, remained basically
unprobed. X-ray polarimetry promises to provide additional information
procuring two new observable quantities, the degree and the angle of
polarization. POLARIX is a mission dedicated to X-ray polarimetry. It exploits
the polarimetric response of a Gas Pixel Detector, combined with position
sensitivity, that, at the focus of a telescope, results in a huge increase of
sensitivity. Three Gas Pixel Detectors are coupled with three X-ray optics
which are the heritage of JET-X mission. POLARIX will measure time resolved
X-ray polarization with an angular resolution of about 20 arcsec in a field of
view of 15 arcmin 15 arcmin and with an energy resolution of 20 % at 6
keV. The Minimum Detectable Polarization is 12 % for a source having a flux of
1 mCrab and 10^5 s of observing time. The satellite will be placed in an
equatorial orbit of 505 km of altitude by a Vega launcher.The telemetry
down-link station will be Malindi. The pointing of POLARIX satellite will be
gyroless and it will perform a double pointing during the earth occultation of
one source, so maximizing the scientific return. POLARIX data are for 75 % open
to the community while 25 % + SVP (Science Verification Phase, 1 month of
operation) is dedicated to a core program activity open to the contribution of
associated scientists. The planned duration of the mission is one year plus
three months of commissioning and SVP, suitable to perform most of the basic
science within the reach of this instrument.Comment: 42 pages, 28 figure
X-ray investigation of the diffuse emission around plausible gamma-ray emitting pulsar wind nebulae in Kookaburra region
We report on the results from {\it Suzaku} X-ray observations of the radio
complex region called Kookaburra, which includes two adjacent TeV -ray
sources HESS J1418-609 and HESS J1420-607. The {\it Suzaku} observation
revealed X-ray diffuse emission around a middle-aged pulsar PSR J1420-6048 and
a plausible PWN Rabbit with elongated sizes of
and , respectively. The peaks of the diffuse
X-ray emission are located within the -ray excess maps obtained by
H.E.S.S. and the offsets from the -ray peaks are for PSR
J1420-6048 and for Rabbit. The X-ray spectra of the two sources
were well reproduced by absorbed power-law models with . The
spectral shapes tend to become softer according to the distance from the X-ray
peaks. Assuming the one zone electron emission model as the first order
approximation, the ambient magnetic field strengths of HESS J1420-607 and HESS
J1418-609 can be estimated as 3 G, and G, respectively. The X-ray
spectral and spatial properties strongly support that both TeV sources are
pulsar wind nebulae, in which electrons and positrons accelerated at
termination shocks of the pulsar winds are losing their energies via the
synchrotron radiation and inverse Compton scattering as they are transported
outward.Comment: To appear in Ap
The Active Nucleus of IC4970: A Nearby Example of Merger-Induced Cold-Gas Accretion
We present results from Chandra X-ray and Spitzer mid-infrared observations
of the interacting galaxy pair NGC6872/IC4970 in the Pavo galaxy group and show
that the smaller companion galaxy IC4970 hosts a highly obscured active
galactic nucleus (AGN). The 0.5-10 keV X-ray luminosity of the nucleus is
variable, increasing by a factor 2.9 to 1.7 x 10^{42} erg/s (bright state) on
~100 ks timescales. The X-ray spectrum of the is heavily absorbed (N_H = 3 x
10^{23} cm^{-2}) for power law models with Gamma = 1.5-2.0 and shows a clear
6.4 keV Fe Kalpha line with equivalent width of 144-195 eV. Limits on the
diffuse emission in IC4970 from Chandra X-ray data suggest that the available
power from Bondi accretion of hot interstellar gas may be an order of magnitude
too small to power the AGN. Spitzer images show that 8 micron nonstellar
emission is concentrated in the central 1 kpc of IC4970, consistent with high
obscuration in this region. The mid-infrared colors of the nucleus are
consistent with those expected for a highly obscured AGN. Taken together these
data suggest that the nucleus of IC4970 is a Seyfert 2, triggered and fueled by
cold material supplied to the central supermassive black hole as a result of
the off-axis collision of IC4970 with the cold-gas rich spiral galaxy NGC6872.Comment: 10 pages, 9 figures, submitted to ApJ, MIR flux conversion error
corrected in Table 4, MIR colors and paper text unchange
Cavity Induced Interfacing of Atoms and Light
This chapter introduces cavity-based light-matter quantum interfaces, with a
single atom or ion in strong coupling to a high-finesse optical cavity. We
discuss the deterministic generation of indistinguishable single photons from
these systems; the atom-photon entanglement intractably linked to this process;
and the information encoding using spatio-temporal modes within these photons.
Furthermore, we show how to establish a time-reversal of the aforementioned
emission process to use a coupled atom-cavity system as a quantum memory. Along
the line, we also discuss the performance and characterisation of cavity
photons in elementary linear-optics arrangements with single beam splitters for
quantum-homodyne measurements.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Extended X-ray emission in the vicinity of the microquasar LS 5039: pulsar wind nebula?
LS 5039 is a high-mass binary with a period of 4 days, containing a compact
object and an O star, one of the few high-mass binaries detected in gamma-rays.
Our Chandra ACIS observation of LS 5039 provided a high-significance (~10sigma)
detection of extended emission clearly visible for up to 1' from the point
source. The spectrum of this emission can be described by an absorbed power-law
model with photon index Gamma=1.9pm0.3, somewhat softer than the point source
spectrum Gamma=1.44pm0.07, with the same absorption, N_H=(6.4pm0.6)e21 /cm2.
The observed 0.5-8 keV flux of the extended emission is 8.8e-14 erg/s/cm2, or
5% of the point source flux; the latter is a factor of ~2 lower than the lowest
flux detected so far. Fainter extended emission with comparable flux and a
softer (Gamma~3) spectrum is detected at even greater radii (up to 2'). Two
possible interpretations of the extended emission are a dust scattering halo
and a synchrotron nebula powered by energetic particles escaping the binary. We
discuss both of these scenarios and favor the nebula interpretation, although
some dust contribution is possible. We have also found transient sources
located within a narrow stripe south of LS 5039. We discuss the likelihood of
these sources to be related to LS 5039.Comment: 28 pages. Accepted for publication in Ap
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