138 research outputs found
The continued spectral and temporal evolution of RX J0720.4-3125
RX J0720.4-3125 is the most peculiar object among a group of seven isolated
X-ray pulsars (the so-called "Magnificent Seven"), since it shows long-term
variations of its spectral and temporal properties on time scales of years.
This behaviour was explained by different authors either by free precession
(with a seven or fourteen years period) or possibly a glitch that occurred
around .
We analysed our most recent XMM-Newton and Chandra observations in order to
further monitor the behaviour of this neutron star. With the new data sets, the
timing behaviour of RX J0720.4-3125 suggests a single (sudden) event (e.g. a
glitch) rather than a cyclic pattern as expected by free precession. The
spectral parameters changed significantly around the proposed glitch time, but
more gradual variations occurred already before the (putative) event. Since
the spectra indicate a very slow cooling by
2 eV over 7 years.Comment: seven pages, three figures, three tables; accepted by MNRA
On the compactness of the isolated neutron star RX J0720.4-3125
The data from all observations of RX J0720.4-3125 conducted by XMM-Newton
EPIC-pn with the same instrumental setup in 2000-2012 were reprocessed to form
a homogenous data set of solar barycenter corrected photon arrival times
registered from RX J0720.4-3125. A Bayesian method for the search, detection,
and estimation of the parameters of an unknown-shaped periodic signal was
employed as developed by Gregory & Loredo (1992).
A number of complex models (single and double peaked) of light curves from
pulsating neutron stars were statistically analyzed. The distribution of phases
for the registered photons was calculated by folding the arrival times with the
derived spin-period and the resulting distribution of phases approximated with
a mixed von Mises distribution, and its parameters were estimated by using the
Expected Maximization method. Spin phase-resolved spectra were extracted, and a
number of highly magnetized atmosphere models of an INS were used to fit
simultaneously, the results were verified via an MCMC approach. The
phase-folded light curves in different energy bands with high S/N ratio show a
high complexity and variations depending on time and energy.
They can be parameterized with a mixed von Mises distribution, i.e. with
double-peaked light curve profile showing a dependence of the estimated
parameters (mean directions, concentrations, and proportion) upon the energy
band, indicating that radiation emerges from at least two emitting areas.
The genuine spin-period of the isolated neutron star RX J0720-3125 derived as
more likely is twice of that reported in the literature (16.78s instead of
8.39s).
The gravitational redshift of RX J0720.4-3125 was determined to
and the compactness was estimated to
.Comment: Comments: 19 pages, 15 figures and 5 tables, Astronomy and
Astrophysics accepted. arXiv admin note: text overlap with arXiv:1108.389
On identifying the neutron star that was born in the supernova that placed 60Fe onto the Earth
Recently, 60Fe was found in the Earth crust formed in a nearby recent
supernova (SN). If the distance to the SN and mass of the progenitor of that SN
was known, then one could constrain SN models. Knowing the positions, proper
motions, and distances of dozens of young nearby neutron stars, we can
determine their past flight paths and possible kinematic origin. Once the birth
place of a neutron star in a SN is found, we would have determined the distance
of the SN and the mass of the SN progenitor star.Comment: refereed NPA5 conference proceedings, in pres
Spectral monitoring of RX J1856.5-3754 with XMM-Newton. Analysis of EPIC-pn data
Using a large set of XMM-Newton observations we searched for long term
spectral and flux variability of the isolated neutron star RX J1856.5-3754 in
the time interval from April 2002 to October 2011. This is the brightest and
most extensively observed source of a small group of nearby, thermally emitting
isolated neutron stars, of which at least one member (RX J0720.4-3125, Hohle et
al., 2010) has shown long term variability. A detailed analysis of the data
obtained with the EPIC-pn camera in the 0.15-1.2 keV energy range reveals small
variations in the temperature derived with a single blackbody fit (of the order
of 1% around kT^inf \sim 61 eV). Such variations are correlated with the
position of the source on the detector and can be ascribed to an instrumental
effect, most likely a spatial dependence of the channel to energy relation. For
the sampled instrumental coordinates, we quantify this effect as variations of
\sim 4% and \sim 15 eV in the gain slope and offset, respectively. Selecting
only a homogeneous subset of observations, with the source imaged at the same
detector position, we find no evidence for spectral or flux variations of RX
J1856.5-3754 from March 2005 to present-day, with limits of Delta kT^inf < 0.5%
and Delta f_X < 3% (0.15-1.2 keV), with 3sigma confidence. A slightly higher
temperature (kT^inf \sim 61.5 eV, compared to kT^\inf \sim 61 eV) was instead
measured in April 2002. If this difference is not of instrumental origin, it
implies a rate of variation \sim -0.15 eV yr^-1 between April 2002 and March
2005. The high-statistics spectrum from the selected observations is best
fitted with the sum of two blackbody models, with temperatures kT_h^inf =
62.4_{-0.4}^{+0.6} eV and kT_s^\inf = 38.9_{-2.9}^{+4.9} eV, which account for
the flux seen in the optical band. No significant spectral features are
detected, with upper limits of 6 eV on their equivalent width.Comment: 11 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
Transit observations at the observatory in Grossschwabhausen: XO-1b and TrES-1
We report on observations of transit events of the transiting planets XO-1b
and TrES-1 with the AIU Jena telescope in Grossschwabhausen. Based on our IR
photometry (in March 2007) and available transit timings (SuperWASP, XO and
TLC-project-data) we improved the orbital period of XO-1b (P =
3.9414970.000006) and TrES-1 (P = 3.03007370.000006), respectively.
The new ephemeris for the both systems are presented.Comment: 4 pages, 2 figure
Neutron stars from young nearby associations the origin of RXJ1605.3+3249
Many neutron stars (NSs) and runaway stars apparently come from the same
regions on the sky. This suggests that they share the same birth places, namely
associations and clusters of young massive stars. To identify NS birth places,
we attempt to and NS-runaway pairs that could be former companions that were
disrupted in a supernova (SN). The remains of recent (<few Myr) nearby (< 150
pc) SNe should still be identifiable by observing the emission of rare
radioisotopes such as 26Al and 60Fe that can also be used as additional
indicators to confirm a possible SN event. We investigated the origin of the
isolated NS RXJ1605.3+3249 and found that it was probably born ~100 pc far from
Earth 0.45 Myr ago in the extended Corona-Australis or Octans associations, or
in Sco OB4 ~1 kpc 3.5 Myr ago. A SN in Octans is supported by the
identification of one to two possible former companions the runaway stars HIP
68228 and HIP 89394, as well as the appearance of a feature in the gamma ray
emission from 26Al decay at the predicted SN place. Both, the progenitor masses
estimated by comparison with theoretical 26Al yields as well as derived from
the life time of the progenitor star, are found to be ~11MSun.Comment: accepted for publication in PASA, special volume Astronomy with
Radioactivities; 10 pages, 4 figures, 5 table
Constraints on the Equation-of-State of neutron stars from nearby neutron star observations
We try to constrain the Equation-of-State (EoS) of supra-nuclear-density
matter in neutron stars (NSs) by observations of nearby NSs. There are seven
thermally emitting NSs known from X-ray and optical observations, the so-called
Magnificent Seven (M7), which are young (up to few Myrs), nearby (within a few
hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that we can
observe their surfaces. As bright X-ray sources, we can determine their
rotational (pulse) period and their period derivative from X-ray timing. From
XMM and/or Chandra X-ray spectra, we can determine their temperature. With
precise astrometric observations using the Hubble Space Telescope, we can
determine their parallax (i.e. distance) and optical flux. From flux, distance,
and temperature, one can derive the emitting area - with assumptions about the
atmosphere and/or temperature distribution on the surface. This was recently
done by us for the two brightest M7 NSs RXJ1856 and RXJ0720. Then, from
identifying absorption lines in X-ray spectra, one can also try to determine
gravitational redshift. Also, from rotational phase-resolved spectroscopy, we
have for the first time determined the compactness (mass/radius) of the M7 NS
RBS1223. If also applied to RXJ1856, radius (from luminosity and temperature)
and compactness (from X-ray data) will yield the mass and radius - for the
first time for an isolated single neutron star. We will present our
observations and recent results.Comment: refereed NPA5 conference proceedings, in pres
Analytic Detection Thresholds for Measurements of Linearly Polarized Intensity Using Rotation Measure Synthesis
A fully analytic statistical formalism does not yet exist to describe
radio-wavelength measurements of linearly polarized intensity that are produced
using rotation measure synthesis. In this work we extend the analytic formalism
for standard linear polarization, namely that describing measurements of the
quadrature sum of Stokes Q and U intensities, to the rotation measure synthesis
environment. We derive the probability density function and expectation value
for Faraday-space polarization measurements for both the case where true
underlying polarized emission is present within unresolved Faraday components,
and for the limiting case where no such emission is present. We then derive
relationships to quantify the statistical significance of linear polarization
measurements in terms of standard Gaussian statistics. The formalism developed
in this work will be useful for setting signal-to-noise ratio detection
thresholds for measurements of linear polarization, for the analysis of
polarized sources potentially exhibiting multiple Faraday components, and for
the development of polarization debiasing schemes.Comment: 14 pages, 6 figures, accepted for publication in MNRA
The origin of the Guitar pulsar
Among a sample of 140 OB associations and clusters, we want to identify
probable parent associations for the Guitar pulsar (PSR B2224+65) which would
then also constrain its age. For this purpose, we are using an Euler-Cauchy
technique treating the vertical component of the galactic potential to
calculate the trajectories of the pulsar and each association into the past. To
include errors we use Monte-Carlo simulations varying the initial parameters
within their error intervals. The whole range of possible pulsar radial
velocities is taken into account during the simulations. We find that the
Guitar pulsar most probably originated from the Cygnus OB3 association ~0.8 Myr
ago inferring a current radial velocity of v_r~-30 km/s, consistent with the
inclination of its bow shock.Comment: 4 pages, 1 figure, 3 table
Transit Timing Analysis in the HAT-P-32 system
We present the results of 45 transit observations obtained for the transiting
exoplanet HAT-P-32b. The transits have been observed using several telescopes
mainly throughout the YETI network. In 25 cases, complete transit light curves
with a timing precision better than min have been obtained. These light
curves have been used to refine the system properties, namely inclination ,
planet-to-star radius ratio , and the ratio between
the semimajor axis and the stellar radius . First analyses by
Hartman et al. (2011) suggest the existence of a second planet in the system,
thus we tried to find an additional body using the transit timing variation
(TTV) technique. Taking also literature data points into account, we can
explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we
can exclude TTV amplitudes of more than min.Comment: MNRAS accepted; 13 pages, 10 figure
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