133 research outputs found
Faraday Rotation in Pulsar Magnetosphere
The magnetosphere of a pulsar is composed of relativistic plasmas streaming
along the magnetic field lines and corotating with the pulsar. We study the
intrinsic Faraday rotation in the pulsar magnetosphere by critically examining
the wave modes and the variations of polarization properties for the circularly
polarized natural modes under various assumptions about the magnetosphere
plasma properties. Since it is difficult to describe analytically the Faraday
rotation effect in such a plasma, we use numerical integrations to study the
wave propagation effects in the corotating magnetosphere. Faraday rotation
effect is identified among other propagation effects, such as wave mode
coupling and the cyclotron absorption. In a highly symmetrical
electron-positron pair plasma, the Faraday rotation effect is found to be
negligible. Only for asymmetrical plasmas, such as the electron-ion streaming
plasma, can the Faraday rotation effect become significant, and the Faraday
rotation angle is found to be approximately proportional to
instead of the usual -law. For such electrons-ion plasma of pulsar
magnetosphere, the induced rotation measure becomes larger at higher
frequencies, and should have opposite signs for the emissions from opposite
magnetic poles.Comment: 15 pages, 4 figure, submitted to MNRA
Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop
Upper limits on the shock speeds in supernova remnants can be combined with
post-shock temperatures to obtain upper limits on the ratio of cosmic ray to
gas pressure (P_CR / P_G) behind the shocks. We constrain shock speeds from
proper motions and distance estimates, and we derive temperatures from X-ray
spectra. The shock waves are observed as faint H-alpha filaments stretching
around the Cygnus Loop supernova remnant in two epochs of the Palomar
Observatory Sky Survey (POSS) separated by 39.1 years. We measured proper
motions of 18 non-radiative filaments and derived shock velocity limits based
on a limit to the Cygnus Loop distance of 576 +/- 61 pc given by Blair et al.
for a background star. The PSPC instrument on-board ROSAT observed the X-ray
emission of the post-shock gas along the perimeter of the Cygnus Loop, and we
measure post-shock electron temperature from spectral fits. Proper motions
range from 2.7 arcseconds to 5.4 arcseconds over the POSS epochs and post-shock
temperatures range from kT ~ 100-200 eV. Our analysis suggests a cosmic ray to
post-shock gas pressure consistent with zero, and in some positions P_CR is
formally smaller than zero. We conclude that the distance to the Cygnus Loop is
close to the upper limit given by the distance to the background star and that
either the electron temperatures are lower than those measured from ROSAT PSPC
X-ray spectral fits or an additional heat input for the electrons, possibly due
to thermal conduction, is required.Comment: Submitted to ApJ, 7 color figure
Nonideal strongly magnetized plasmas of neutron stars and their electromagnetic radiation
We study the equation of state, polarization and radiation properties for
nonideal, strongly magnetized plasmas which compose outer envelopes of magnetic
neutron stars. Detailed calculations are performed for partially ionized
hydrogen atmospheres and for condensed hydrogen or iron surfaces of these
stars. This is a companion paper to astro-ph/0511803Comment: 7 pages, 3 figures. Invited topical talk at Strongly Coupled Coulomb
Systems (Moscow, June 20-25, 2005); to appear in Journal of Physics
Surface structure of Quark stars with magnetic fields
We investigate the impact of magnetic fields on the electron distribution in
the electrosphere of quark stars. For moderately strong magnetic fields G, quantization effects are generally weak due to the large number
density of electrons at surface, but can nevertheless affect the spectral
features of quark stars. We outline the main observational characteristics of
quark stars as determined by their surface emission, and briefly discuss their
formation in explosive events termed Quark-Novae, which may be connected to the
-process.Comment: 9 pages, 3 figures. Contribution to the proceedings of the IXth
Workshop on High Energy Physics Phenomenology (WHEPP-9), Bhubaneswar, India,
3-14 Jan. 200
The kinematics and chemical stratification of the Type Ia supernova remnant 0519-69.0
We present an analysis of the XMM-Newton and Chandra X-ray data of the young
Type Ia supernova remnant 0519-69.0 in the Large Magellanic Cloud. We used data
from both the Chandra ACIS and XMM-Newton EPIC-MOS instruments, and high
resolution X-ray spectra obtained with the XMM-Newton Reflection Grating
Spectrometer. The Chandra data show that there is a radial stratification of
oxygen, intermediate mass elements and iron, with the emission from more
massive elements more toward the center. Using a deprojection technique we
measure a forward shock radius of 4.0(3) pc and a reverse shock radius of
2.7(4) pc. We took the observed stratification of the shocked ejecta into
account in the modeling of the X-ray spectra with multi-component NEI models,
with the components corresponding to layers dominated by one or two elements.
An additional component was added in order to represent the ISM, which mostly
contributed to the continuum emission. This model fits the data well, and was
also employed to characterize the spectra of distinct regions extracted from
the Chandra data. From our spectral analysis we find that the fractional masses
of shocked ejecta for the most abundant elements are: M(O)=32%, M(Si/S)=7%/5%,
M(Ar+Ca)=1%, and M(Fe) = 55%. From the continuum component we derive a
circumstellar density of nH= 2.4(2)/cm^3. This density, together with the
measurements of the forward and reverse shock radii suggest an age of 450+/-200
yr,somewhat lower than, but consistent with the estimate based on the optical
light echo (600+/-200 yr). From the RGS spectra we measured a Doppler
broadening of sigma=1873+/-50 km/s, from implying a forward shock velocity of
vS = 2770+/-500 km/s. We discuss the results in the context of single
degenerate explosion models, using semi-analytical and numerical modeling, and
compare the characteristics of 0519-69.0 with those of other Type Ia supernova
remnants.Comment: Astronomy and Astrophysics in press. This version is the A&A accepted
version, which contains improved figures and an extended discussion sectio
HST-COS Observations of Hydrogen, Helium, Carbon and Nitrogen Emission from the SN 1987A Reverse Shock
We present the most sensitive ultraviolet observations of Supernova 1987A to
date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins
Spectrograph shows many narrow (dv \sim 300 km/s) emission lines from the
circumstellar ring, broad (dv \sim 10 -- 20 x 10^3 km/s) emission lines from
the reverse shock, and ultraviolet continuum emission. The high signal-to-noise
(> 40 per resolution element) broad LyA emission is excited by soft X-ray and
EUV heating of mostly neutral gas in the circumstellar ring and outer supernova
debris. The ultraviolet continuum at \lambda > 1350A can be explained by HI
2-photon emission from the same region. We confirm our earlier, tentative
detection of NV \lambda 1240 emission from the reverse shock and we present the
first detections of broad HeII \lambda1640, CIV \lambda1550, and NIV]
\lambda1486 emission lines from the reverse shock. The helium abundance in the
high-velocity material is He/H = 0.14 +/- 0.06. The NV/H-alpha line ratio
requires partial ion-electron equilibration (T_{e}/T_{p} \approx 0.14 - 0.35).
We find that the N/C abundance ratio in the gas crossing the reverse shock is
significantly higher than that in the circumstellar ring, a result that may be
attributed to chemical stratification in the outer envelope of the supernova
progenitor. The N/C abundance ratio may have been stratified prior to the ring
expulsion, or this result may indicate continued CNO processing in the
progenitor subsequent to the expulsion of the circumstellar ring.Comment: 12 pages, 8 figures. ApJ - accepte
RCW 86: A Type Ia Supernova in a Wind-Blown Bubble
We report results from a multi-wavelength analysis of the Galactic SNR RCW
86, the proposed remnant of the supernova of 185 A.D. We report new infrared
observations from {\it Spitzer} and {\it WISE}, where the entire shell is
detected at 24 and 22 m. We fit the infrared flux ratios with models of
collisionally heated ambient dust, finding post-shock gas densities in the
non-radiative shocks of 2.4 and 2.0 cm in the SW and NW portions of the
remnant, respectively. The Balmer-dominated shocks around the periphery of the
shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact
remnant support a Type Ia origin for this remnant. From hydrodynamic
simulations, the observed characteristics of RCW 86 are successfully reproduced
by an off-center explosion in a low-density cavity carved by the progenitor
system. This would make RCW 86 the first known case of a Type Ia supernova in a
wind-blown bubble. The fast shocks ( km s) observed in the NE
are propagating in the low-density bubble, where the shock is just beginning to
encounter the shell, while the slower shocks elsewhere have already encountered
the bubble wall. The diffuse nature of the synchrotron emission in the SW and
NW is due to electrons that were accelerated early in the lifetime of the
remnant, when the shock was still in the bubble. Electrons in a bubble could
produce gamma-rays by inverse-Compton scattering. The wind-blown bubble
scenario requires a single-degenerate progenitor, which should leave behind a
companion star.Comment: Accepted for publication in ApJ. 50 pages, 9 figure
3D Models of Radiatively Driven Colliding Winds In Massive O+O Star Binaries: I. Hydrodynamics
The dynamics of the wind-wind collision in massive stellar binaries is
investigated using three-dimensional hydrodynamical models which incorporate
gravity, the driving of the winds, the orbital motion of the stars, and
radiative cooling of the shocked plasma. In this first paper we restrict our
study to main-sequence O+O binaries. The nature of the wind-wind collision
region is highly dependent on the degree of cooling of the shocked plasma, and
the ratio of the flow timescale of the shocked plasma to the orbital timescale.
The pre-shock wind speeds are lower in close systems as the winds collide prior
to their acceleration to terminal speeds. Radiative inhibition may also reduce
the pre-shock wind speeds. Together, these effects can lead to rapid cooling of
the post-shock gas. Radiative inhibition is less important in wider systems,
where the winds are accelerated to higher speeds before they collide, and the
resulting collision region can be largely adiabatic. In systems with eccentric
orbits, cold gas formed during periastron passage can persist even at apastron,
before being ablated and mixed into its surroundings and/or accelerated out of
the system.Comment: 21 pages, 15 figures, accepted for publication in MNRA
Turning Points in the Evolution of Isolated Neutron Stars' Magnetic Fields
During the life of isolated neutron stars (NSs) their magnetic field passes
through a variety of evolutionary phases. Depending on its strength and
structure and on the physical state of the NS (e.g. cooling, rotation), the
field looks qualitatively and quantitatively different after each of these
phases. Three of them, the phase of MHD instabilities immediately after NS's
birth, the phase of fallback which may take place hours to months after NS's
birth, and the phase when strong temperature gradients may drive thermoelectric
instabilities, are concentrated in a period lasting from the end of the
proto--NS phase until 100, perhaps 1000 years, when the NS has become almost
isothermal. The further evolution of the magnetic field proceeds in general
inconspicuous since the star is in isolation. However, as soon as the product
of Larmor frequency and electron relaxation time, the so-called magnetization
parameter, locally and/or temporally considerably exceeds unity, phases, also
unstable ones, of dramatic changes of the field structure and magnitude can
appear. An overview is given about that field evolution phases, the outcome of
which makes a qualitative decision regarding the further evolution of the
magnetic field and its host NS.Comment: References updated, typos correcte
Magnetic field dissipation in neutron star crusts: from magnetars to isolated neutron stars
We study the non--linear evolution of magnetic fields in neutron star crusts
with special attention to the influence of the Hall drift. Our goal is to
understand the conditions for fast dissipation due to the Hall term in the
induction equation. We study the interplay of Ohmic dissipation and Hall drift
in order to find a timescale for the overall crustal field decay. We solve
numerically the Hall induction equation by means of a hybrid method (spectral
in angles but finite differences in the radial coordinate). The microphysical
input consists of the most modern available crustal equation of state,
composition and electrical conductivities. We present the first long term
simulations of the non--linear magnetic field evolution in realistic neutron
star crusts with a stratified electron number density and temperature dependent
conductivity. We show that Hall drift influenced Ohmic dissipation takes place
in neutron star crusts on a timescale of 1 Myr. When the initial magnetic field
has magnetar strength, the fast Hall drift results in an initial rapid
dissipation stage that lasts 10-50 kyr. The interplay of the Hall drift with
the temporal variation and spatial gradient of conductivity tends to favor the
displacement of toroidal fields toward the inner crust, where stable
configurations can last for 1 Myr. We show that the thermally emitting isolated
neutron stars, as the Magnificent Seven, are very likely descendants of neutron
stars born as magnetars.Comment: 14 pages, 10 figure
- …