819 research outputs found
High Magnetic Field Rotation-powered Pulsars
Anomalous X-ray pulsars and soft gamma repeaters have recently emerged as a
unified class of neutron stars, identified by dramatic X-ray and gamma-ray
outbursts and via luminous X-ray pulsations, both thought to be powered by the
decay of an enormous internal magnetic field. This "magnetar" hypothesis has
raised the question of these objects' physical relationship with conventional
rotation-powered pulsars (RPPs). The highest magnetic-field RPPs might
therefore be expected to be transition objects between the two populations. The
recently reported magnetar-like outburst of PSR J1846-0258, previously thought
to be purely rotation-powered, clearly supports this suggestion. Here we review
the observational properties of the highest magnetic-field RPPs known, and show
some common characteristics that are notable among RPPs, which are plausibly
related to their high fields. Using these objects, we consider the evidence for
proposed "magneto-thermal evolution" in neutron stars, and argue that while
some exists, it is not yet conclusive.Comment: 6 pages, 4 figures, Conference proceeding of "ASTROphysics of Neutron
Stars 2010 -- a conference in honor of M. Ali Alpar", 2-6 August 2010, Cesme,
Izmir, Turke
Constraining Jupiter's internal flows using Juno magnetic and gravity measurements
Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth-dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence: an upper region in which the flow affects mostly the gravity field and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields
The Effects of Gravity on the Climate and Circulation of a Terrestrial Planet
The climate and circulation of a terrestrial planet are governed by, among
other things, the distance to its host star, its size, rotation rate,
obliquity, atmospheric composition and gravity. Here we explore the effects of
the last of these, the Newtonian gravitational acceleration, on its atmosphere
and climate. We first demonstrate that if the atmosphere obeys the hydrostatic
primitive equations, which are a very good approximation for most terrestrial
atmospheres, and if the radiative forcing is unaltered, changes in gravity have
no effect at all on the circulation except for a vertical rescaling. That is to
say, the effects of gravity may be completely scaled away and the circulation
is unaltered. However, if the atmosphere contains a dilute condensible that is
radiatively active, such as water or methane, then an increase in gravity will
generally lead to a cooling of the planet because the total path length of the
condensible will be reduced as gravity increases, leading to a reduction in the
greenhouse effect. Furthermore, the specific humidity will decrease, leading to
changes in the moist adiabatic lapse rate, in the equator-to-pole heat
transport, and in the surface energy balance because of changes in the sensible
and latent fluxes. These effects are all demonstrated both by theoretical
arguments and by numerical simulations with moist and dry general circulation
models.Comment: 17 pages, 9 figures. Submitted to QJRMS on 23/01/1
Permanent Superhumps in V1974 Cyg
We present results of 32 nights of CCD photometry of V1974 Cygni, from the
years 1994 and 1995. We verify the presence of two distinct periodicities in
the light curve: 0.0812585 day~1.95 hours and 0.0849767 d~2.04 hr. We establish
that the shorter periodicity is the orbital period of the underlying binary
system. The longer period oscillates with an average value of |dot(P)| ~
3x10^(7)--typical to permanent superhumps. The two periods obey the linear
relation between the orbital and superhump periods that holds among members of
the SU Ursae Majoris class of dwarf novae. A third periodicity of 0.083204
d~2.00 hr appeared in 1994 but not in 1995. It may be related to the recently
discovered anti-superhump phenomenon. These results suggest a linkage between
the classical nova V1974 Cyg and the SU UMa stars, and indicate the existence
of an accretion disk and permanent superhumps in the system no later than 30
months after the nova outburst. From the precessing disk model of the superhump
phenomenon we estimate that the mass ratio in the binary system is between 2.2
and 3.6. Combined with previous results this implies a white dwarf mass of
0.75-1.07 M sun.Comment: 11 pages, 10 eps. figures, Latex, accepted for publication in MNRA
Theory of cooling neutron stars versus observations
We review current state of neutron star cooling theory and discuss the
prospects to constrain the equation of state, neutrino emission and superfluid
properties of neutron star cores by comparing the cooling theory with
observations of thermal radiation from isolated neutron stars.Comment: 9 pages, 4 figures, 3 tables, to appear in the proceedings of "40
Years of Pulsars" held in Montreal, Canada, August 12-17, 2007, eds. C.
Bassa, Z. Wang, A. Cumming, V. Kaspi, AIP, in press (v.2 - minor bibliography
corrections
On the X-ray variability of magnetar 1RXS J170849.0-400910
We present a long-term X-ray flux and spectral analysis for 1RXS
J170849.0-400910 using Swift/XRT spanning over 8 years from 2005-2013. We also
analyze two observations from Chandra and XMM in the period from 2003-2004. In
this 10-yr period, 1RXS J170849.0-400910 displayed several rotational glitches.
Previous studies have claimed variations in the X-ray emission associated with
some of the glitches. From our analysis we find no evidence for significant
X-ray flux variations and evidence for only low-level spectral variations. We
also present an updated timing solution for 1RXS J170849.0-400910, from RXTE
and Swift observations, which includes a previously unreported glitch at MJD
56019. We discuss the frequency and implications of radiatively quiet glitches
in magnetars.Comment: 9 pages, 2 figures, accepted for publication in Ap
Accretion Properties of A Sample of Hard X-ray (<60keV) Selected Seyfert 1 Galaxies
We examine the accretion properties in a sample of 42 hard (3-60keV) X-ray
selected nearby broad-line AGNs. The energy range in the sample is harder than
that usually used in the similar previous studies. These AGNs are mainly
complied from the RXTE All Sky Survey (XSS), and complemented by the released
INTEGRAL AGN catalog. The black hole masses, bolometric luminosities of AGN,
and Eddington ratios are derived from their optical spectra in terms of the
broad H emission line. The tight correlation between the hard X-ray
(3-20keV) and bolometric/line luminosity is well identified in our sample. Also
identified is a strong inverse Baldwin relationship of the H emission
line. In addition, all these hard X-ray AGNs are biased toward luminous objects
with high Eddington ratio (mostly between 0.01 to 0.1) and low column density
(), which is most likely due to the selection effect
of the surveys. The hard X-ray luminosity is consequently found to be strongly
correlated with the black hole mass. We believe the sample completeness will be
improved in the next few years by the ongoing Swift and INTEGRAL missions, and
by the next advanced missions, such as NuSTAR, Simbol-X, and NeXT. Finally, the
correlation between RFe (=optical FeII/H) and disk temperature as
assessed by leads us to
suggest that the strength of the FeII emission is mainly determined by the
shape of the ionizing spectrum.Comment: 28 pages, 7 figures, 2 tables, accepted by A
Chandra and RXTE Observations of 1E 1547.0-5408: Comparing the 2008 and 2009 Outbursts
We present results from observations of the magnetar 1E 1547.0-5408 (SGR
J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing
Explorer (RXTE) following the source's outbursts in 2008 October and 2009
January. During the time span of the Chandra observations, which covers days 4
through 23 and days 2 through 16 after the 2008 and 2009 events, respectively,
the source spectral shape remained stable, while the pulsar's spin-down rate in
the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The
lack of spectral variation suggests decoupling between magnetar spin-down and
radiative changes, hence between the spin-down-inferred magnetic field strength
and that inferred spectrally. We also found a strong anti-correlation between
the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra
data, but not in the pre-2008 measurements. We discuss these results in the
context of the magnetar model.Comment: 4 figures, accepted for publication in Ap
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