208 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
XMM-Newton reveals a candidate period for the spin of the "Magnificent Seven" neutron star RX J1605.3+3249
The group of thermally emitting isolated neutron stars (INSs) known as the
"Magnificent Seven" (M7) is unique among the various neutron star populations.
Crustal heating by means of magnetic field decay and an evolutionary link with
magnetars may explain why these objects rotate more slowly and have higher
thermal luminosities and magnetic field intensities than standard pulsars of
similar age. The third brightest INS, RX J1605.3+3249, is the only object
amidst the seven still lacking a detected periodicity. We observed the source
with the XMM-Newton Observatory for 60 ks aiming at unveiling the neutron star
rotation rate and investigating its spectrum in detail. A periodic signal at
P=3.387864(16) s, most likely the neutron star spin period, is detected at the
4-sigma confidence level. The coherent combination of the new data with a past
XMM-Newton EPIC-pn observation of the source constrains the pulsar spin-down
rate at the 2-sigma confidence level, implying a dipolar magnetic field of
B~7.4e13 G. If confirmed, RX J1605.3+3249 would be the neutron star with the
highest dipolar field amongst the M7. The spectrum of the source shows evidence
of a cool blackbody component, as well as for the presence of two broad
absorption features. Furthermore, high-resolution spectroscopy with the RGS
cameras confirms the presence of a narrow absorption feature at energy 0.57 keV
in the co-added spectrum of the source, also seen in other thermally emitting
isolated neutron stars. Phase-resolved spectroscopy, as well as a dedicated
observing campaign aimed at determining a timing solution, will give invaluable
constraints on the neutron star geometry and will allow one to confirm the high
value of spin down, which would place the source closer to a magnetar than any
other M7 INS.Comment: 12 pages, 6 figures; accepted for publication in A&A (revised version
after language editing; results unchanged
Narrow absorption features in the co-added XMM-Newton RGS spectra of isolated Neutron Stars
We co-added the available XMM-Newton RGS spectra for each of the isolated
X-ray pulsars RX\,J0720.43125, RX\,J1308.6+2127 (RBS\,1223),
RX\,J1605.3+3249 and RX\,J1856.43754 (four members of the "Magnificent
Seven") and the "Three Musketeers" Geminga, PSR\,B0656+14 and PSR\,B1055-52. We
confirm the detection of a narrow absorption feature at 0.57 keV in the
co-added RGS spectra of RX\,J0720.43125 and RX\,J1605.3+3249 (including most
recent observations). In addition we found similar absorption features in the
spectra of RX\,J1308.6+2127 (at 0.53 keV) and maybe PSR\,B1055-52 (at 0.56
keV). The absorption feature in the spectra of RX\,J1308.6+2127 is broader than
the feature e.g. in RX\,J0720.43125. The narrow absorption features are
detected with 2 to 5.6 significance. Although very bright and
frequently observed, there are no absorption features visible in the spectra of
RX\,J1856.43754 and PSR\,B0656+14, while the co-added XMM-Newton RGS
spectrum of Geminga has not enough counts to detect such a feature. We discuss
a possible origin of these absorption features as lines caused by the presence
of highly ionised oxygen (in particular OVII and/or OVI at 0.57 keV) in the
interstellar medium and absorption in the neutron star atmosphere, namely the
absorption features at 0.57 keV as gravitational redshifted (=1.17)
OVIII.Comment: 14 pages, 10 figures and 10 tables. Accepted for publication by MNRAS
(Sep 12th, 2011
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
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
Variability of young stars: Determination of rotational periods of weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region
We report on observation and determination of rotational periods of ten
weak-line T Tauri stars in the Cepheus-Cassiopeia star-forming region.
Observations were carried out with the Cassegrain-Teleskop-Kamera (CTK) at
University Observatory Jena between 2007 June and 2008 May. The periods
obtained range between 0.49 d and 5.7 d, typical for weak-line and post T Tauri
stars.Comment: 11 pages, 26 figures, accepted to be published in A
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
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