5,408 research outputs found
Some comments on the ''the composition of the Martian surface'' by R. A. Van Tassel and J. W. Salisbury
Feasibility of Martian surface layer composed of silicates coated with limonit
Upper limits on liquid water in the Venus atmosphere
Upper limits on liquid water in Venus atmosphere due to presence of hydrogen chlorid
The Influence of Topography on the Formation of Temporary Bright Patches on Mars
Influence of topography on formation of bright patches on Mar
Spin frequency distributions of binary millisecond pulsars
Rotation-powered millisecond radio pulsars have been spun up to their present
spin period by a - yr long X-ray-bright phase of accretion of
matter and angular momentum in a low-to-intermediate mass binary system.
Recently, the discovery of transitional pulsars that alternate cyclically
between accretion and rotation-powered states on time scales of a few years or
shorter, has demonstrated this evolutionary scenario. Here, we present a
thorough statistical analysis of the spin distributions of the various classes
of millisecond pulsars to assess the evolution of their spin period between the
different stages. Accreting sources that showed oscillations exclusively during
thermonuclear type I X-ray bursts (nuclear-powered millisecond pulsars) are
found to be significantly faster than rotation-powered sources, while accreting
sources that possess a magnetosphere and show coherent pulsations (accreting
millisecond pulsars) are not. On the other hand, if accreting millisecond
pulsars and eclipsing rotation-powered millisecond pulsars form a common class
of transitional pulsars, these are shown to have a spin distribution
intermediate between the faster nuclear-powered millisecond pulsars and the
slower non-eclipsing rotation-powered millisecond pulsars. We interpret these
findings in terms of a spin-down due to the decreasing mass-accretion rate
during the latest stages of the accretion phase, and in terms of the different
orbital evolutionary channels mapped by the various classes of pulsars. We
summarize possible instrumental selection effects, showing that even if an
unbiased sample of pulsars is still lacking, their influence on the results of
the presented analysis is reduced by recent improvements in instrumentation and
searching techniques.Comment: Accepted for publication in A&A (6 pages, 4 figures
Comparing supernova remnants around strongly magnetized and canonical pulsars
The origin of the strong magnetic fields measured in magnetars is one of the
main uncertainties in the neutron star field. On the other hand, the recent
discovery of a large number of such strongly magnetized neutron stars, is
calling for more investigation on their formation. The first proposed model for
the formation of such strong magnetic fields in magnetars was through
alpha-dynamo effects on the rapidly rotating core of a massive star. Other
scenarios involve highly magnetic massive progenitors that conserve their
strong magnetic moment into the core after the explosion, or a common envelope
phase of a massive binary system. In this work, we do a complete re-analysis of
the archival X-ray emission of the Supernova Remnants (SNR) surrounding
magnetars, and compare our results with all other bright X-ray emitting SNRs,
which are associated with Compact Central Objects (CCOs; which are proposed to
have magnetar-like B-fields buried in the crust by strong accretion soon after
their formation), high-B pulsars and normal pulsars. We find that emission
lines in SNRs hosting highly magnetic neutron stars do not differ significantly
in elements or ionization state from those observed in other SNRs, neither
averaging on the whole remnants, nor studying different parts of their total
spatial extent. Furthermore, we find no significant evidence that the total
X-ray luminosities of SNRs hosting magnetars, are on average larger than that
of typical young X-ray SNRs. Although biased by a small number of objects, we
found that for a similar age, there is the same percentage of magnetars showing
a detectable SNR than for the normal pulsar population.Comment: 16 pages, 5 figures, Accepted for publication in MNRA
Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910
Previous studies of the X-ray flux and spectral properties of 1RXS
J170849-400910 showed hints of a possible correlation with the spin glitches
that occurred in 1999 and 2001. However, due to the sparseness of spectral
measurements and the paucity of detected glitches no firm conclusion could be
drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910
covering the time interval between January 2003 and June 2006 and carried out a
detailed timing analysis by means of phase fitting techniques. We detected two
relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in
January and June 2005. Interestingly, the occurrence times of these glitches
are in agreement with the predictions made in our previous studies. This
finding strongly suggests a connection between the flux, spectral and timing
properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The
Neutron Star Crust and Surface: Observations and Models" on June 27; referee
comments adde
The Spectral Evolution of Transient Anomalous X-ray Pulsar XTE J1810--197
(Abridged) We present a multi-epoch spectral study of the Transient Anomalous
X-ray Pulsar XTE J1810-197 obtained with the XMM X-ray telescope. Four
observations taken over the course of a year reveal strong spectral evolution
as the source fades from outburst. The origin of this is traced to the
individual decay rates of the pulsar's spectral components. A 2-T fit at each
epoch requires nearly constant temperatures of kT=0.25 & 0.67 keV while the
component luminosities decrease exponentially with tau=900 & 300d,
respectively. One possible interpretation is that the slowly decaying cooler
component is the radiation from a deep heating event that affected a large
fraction of the crust, while the hotter component is powered by external
surface heating at the foot-points of twisted magnetic field lines, by
magnetospheric currents that are decaying more rapidly. The energy-dependent
pulse profile of XTE J1810-197 is well modeled at all epochs by the sum of a
sine and triangle function. These profiles peak at the same phase, suggesting a
concentric surface emission geometry. The spectral and pulse evolution together
argue against the presence of a significant ``power-law'' contribution to the
X-ray spectrum below 8 keV. The extrapolated flux is projected to return to the
historic quiescent level, characterized by an even cooler blackbody spectrum,
by the year 2007.Comment: 12 pages, 6 Figures, Latex, emulateapj. To appear in the
Astrophysical Journa
Long term hard X-ray variability of the anomalous X-ray pulsar 1RXS J170849.0-400910 discovered with INTEGRAL
We report on a multi-band high-energy observing campaign aimed at studying
the long term spectral variability of the Anomalous X-ray Pulsar (AXP) 1RXS
J170849.0-400910, one of the magnetar candidates. We observed 1RXS
J170849.0-400910 in Fall 2006 and Spring 2007 simultaneously with Swift/XRT, in
the 0.1-10 keV energy range, and with INTEGRAL/IBIS, in the 20-200 keV energy
range. Furthermore, we also reanalyzed, using the latest calibration and
software, all the publicly available INTEGRAL data since 2002, and the soft
X-ray data starting from 1999 taken using BeppoSAX, Chandra, XMM, and
Swift/XRT, in order to study the soft and hard X-ray spectral variability of
1RXS J170849.0-400910. We find a long-term variability of the hard X-ray flux,
extending the hardness-intensity correlation proposed for this source over 2
orders of magnitude in energy.Comment: 5 pages, 2 figures, accepted for publication in Astronomy &
Astrophysics main journa
Magnetars' Giant Flares: the case of SGR 1806-20
We first review on the peculiar characteristics of the bursting and flaring
activity of the Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We then
report on the properties of the SGR 1806-20's Giant Flare occurred on 2004
December 27th, with particular interest on the pre and post flare
intensity/hardness correlated variability. We show that these findings are
consistent with the picture of a twisted internal magnetic field which stresses
the star solid crust that finally cracks causing the giant flare (and the
observed torsional oscillations). This crustal fracturing is accompanied by a
simplification of the external magnetic field with a (partial) untwisting of
the magnetosphere.Comment: 6 pages, 2 figures; accepted for publication in the Chinese Journal
for Astronomy and Astrophysics (Vulcano conference - 2005
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