593 research outputs found
Point and Interval Estimation on the Degree and the Angle of Polarization. A Bayesian approach
Linear polarization measurements provide access to two quantities, the degree
(DOP) and the angle of polarization (AOP). The aim of this work is to give a
complete and concise overview of how to analyze polarimetric measurements. We
review interval estimations for the DOP with a frequentist and a Bayesian
approach. Point estimations for the DOP and interval estimations for the AOP
are further investigated with a Bayesian approach to match observational needs.
Point and interval estimations are calculated numerically for frequentist and
Bayesian statistics. Monte Carlo simulations are performed to clarify the
meaning of the calculations.
Under observational conditions, the true DOP and AOP are unknown, so that
classical statistical considerations - based on true values - are not directly
usable. In contrast, Bayesian statistics handles unknown true values very well
and produces point and interval estimations for DOP and AOP, directly. Using a
Bayesian approach, we show how to choose DOP point estimations based on the
measured signal-to-noise ratio. Interval estimations for the DOP show great
differences in the limit of low signal-to-noise ratios between the classical
and Bayesian approach. AOP interval estimations that are based on observational
data are presented for the first time. All results are directly usable via
plots and parametric fits.Comment: 11 pages, 14 figures, 3 table
Orbit and intrinsic spin-up of the newly discovered transient X-ray pulsar Swift J0243.6+6124
We present the orbital solution for the newly discovered transient Be X-ray
binary Swift J0243.6+6124 based on the data from gamma-ray burst monitor
onboard Fermi obtained during the Oct 2017 outburst. We model the Doppler
induced and intrinsic spin variations of the neutron star assuming that the
later is driven by accretion torque and discuss the implications of the
observed spin variations for the parameters of the neutron star and the binary.
In particular we conclude that the neutron star must be strongly magnetized,
and estimate the distance to the source at 5 kpc.Comment: accepted in A&
A new solution for mirror coating in -ray Cherenkov Astronomy
In the -ray Cherenkov Astronomy framework mirror coating plays a
crucial role in defining the light response of the telescope. We carried out a
study for new mirror coating solutions with both a numerical simulation
software and a vacuum chamber for small sample production. In this article, we
present a new mirror coating solution consisting of a 28-layer interferometric
SiO-TiO-HfO design deposited on a glass substrate, whose
average reflectance is above for normally incident light in the
wavelength range between 300 and 550 nm.Comment: 6 pages, 5 figures. Article submitted to Experimental Astronomy, the
final publication is available at link.springer.co
Luminosity-dependent spectral and timing properties of the accreting pulsar GX 304-1 measured with INTEGRAL
Context: Be/X-ray binaries show outbursts with peak luminosities up to a few
times erg/s, during which they can be observed and studied in
detail. Most (if not all) Be/X-ray binaries harbour accreting pulsars, whose
X-ray spectra in many cases contain cyclotron resonant scattering features
related to the magnetic field of the sources. Spectral variations as a function
of luminosity and of the rotational phase of the neutron star are observed in
many accreting pulsars. Aims: We explore X-ray spectral and timing properties
of the Be/X-ray binary GX 304-1 during an outburst episode. Specifically, we
investigate the behavior of the cyclotron resonant scattering feature, the
continuum spectral parameters, the pulse period, and the energy- and
luminosity-resolved pulse profiles. We combine the luminosity-resolved spectral
and timing analysis to probe the accretion geometry and the beaming patterns of
the rotating neutron star. Methods: We analyze the INTEGRAL data from the two
JEM-X modules, ISGRI and SPI, covering the January-February 2012 outburst,
divided in six observations. We obtain pulse profiles in two energy bands,
phase-averaged and phase-resolved spectra for each observation. Results: We
confirm the positive luminosity-dependence of the cyclotron line energy in GX
304-1, and report a dependence of the photon index on luminosity. Using a
pulse-phase connection technique, we find a pulse period solution valid for the
entire outburst. Our pulse-phase resolved analysis shows, that the centroid
energy of the cyclotron line is varying only slightly with pulse phase, while
other spectral parameters show more pronounced variations. Our results are
consistent with a scenario in which, as the pulsar rotates, we are exploring
only a small portion of its beam pattern.Comment: 12 pages, 12 figures, Accepted for publication in A&
The Mirror Alignment and Control System for CT5 of the H.E.S.S. experiment
The High Energy Stereoscopic System (H.E.S.S.) experiment is one of the
largest observatories for gamma-ray astronomy. It consists of four telescopes
with a reflecting dish diameter of 12m (CT1 to CT4) and a newer large telescope
(CT5) with a reflecting dish diameter of 28m. On CT5 876 mirror facets are
mounted, all of them equipped with a computerised system for their alignment.
The design of the mirror alignment and control system and the performance of
the hardware installed to the telescope are presented. Furthermore the achieved
point spread function of the telescope over the full operational elevation
range as well as the stability of the alignment over an extended period of time
are shown
XMM-Newton observations of 1A 0535+262 in quiescence
Accretion onto magnetized neutron stars is expected to be centrifugally
inhibited at low accretion rates. Several sources, however, are known to
pulsate in quiescence at luminosities below the theoretical limit predicted for
the onset of the centrifugal barrier. The source 1A 0535+262 is one of them.
Here we present the results of an analysis of a ~50 ks long XMM-Newton
observation of 1A 0535+262 in quiescence. At the time of the observation, the
neutron star was close to apastron, and the source had remained quiet for two
orbital cycles. In spite of this, we detected a pulsed X-ray flux of ~3e-11
erg/cm2/s . Several observed properties, including the power spectrum, remained
similar to those observed in the outbursts. Particularly, we have found that
the frequency of the break detected in the quiescent noise power spectrum
follows the same correlation with flux observed when the source is in outburst.
This correlation has been associated with the truncation of the accretion disk
at the magnetosphere boundary. We argue that our result, along with other
arguments previously reported in the literature, suggests that the accretion in
quiescence also proceeds from an accretion disk around the neutron star. The
proposed scenario consistently explains the energy of the cyclotron line
observed in 1A 0535+262, and the timing properties of the source including the
spin frequency evolution within and between the outbursts, and the frequency of
the break in power spectrum.Comment: 7 pages, 5 figures, accepted for publication in A&
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