1,948 research outputs found
Coaligned dual-channel STED nanoscopy and molecular diffusion analysis at 20 nm resolution.
We report on a fiber laser-based stimulated emission-depletion microscope providing down to ~20 nm resolution in raw data images as well as 15â19 nm diameter probing areas in fluorescence correlation spectroscopy. Stimulated emission depletion pulses of nanosecond duration and 775 nm wavelength are used to silence two fluorophores simultaneously, ensuring offset-free colocalization analysis. The versatility of this superresolution method is exemplified by revealing the octameric arrangement of Xenopus nuclear pore complexes and by quantifying the diffusion of labeled lipid molecules in artificial and living cell membranes
PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV Gamma-ray Source HESS J1857+026
We present the discovery of the Vela-like radio pulsar J1856+0245 in the
Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81ms, a
characteristic age of 21kyr, and a spin-down luminosity Edot = 4.6 x 10^36
ergs/s. It is positionally coincident with the TeV gamma-ray source HESS
J1857+026, which has no other known counterparts. Young, energetic pulsars
create wind nebulae, and more than a dozen pulsar wind nebulae have been
associated with very-high-energy (100GeV-100TeV) gamma-ray sources discovered
with the HESS telescope. The gamma-ray emission seen from HESS J1857+026 is
potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint
X-ray emission detected by ASCA at the pulsar's position supports this
hypothesis. The inferred gamma-ray efficiency is epsilon_gamma = L_gamma/Edot =
3.1% (1-10TeV, for a distance of 9kpc), comparable to that observed in similar
associations.Comment: 13 pages, 1 figure, accepted for publication in The Astrophysical
Journal Letter
100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06
We have invented a novel technique to measure the radio image of a pulsar
scattered by the interstellar plasma with 0.1 mas resolution. We extend the
"secondary spectrum" analysis of parabolic arcs by Stinebring et al. (2001) to
very long baseline interferometry and, when the scattering is anisotropic, we
are able to map the scattered brightness astrometrically with much higher
resolution than the diffractive limit of the interferometer. We employ this
technique to measure an extremely anisotropic scattered image of the pulsar
B0834+06 at 327 MHz. We find that the scattering occurs in a compact region
about 420 pc from the Earth. This image has two components, both essentially
linear and nearly parallel. The primary feature, which is about 16 AU long and
less than 0.5 AU in width, is highly inhomogeneous on spatial scales as small
as 0.05 AU. The second feature is much fainter and is displaced from the axis
of the primary feature by about 9 AU. We find that the velocity of the
scattering plasma is 16+-10 km/s approximately parallel to the axis of the
linear feature. The origin of the observed anisotropy is unclear and we discuss
two very different models. It could be, as has been assumed in earlier work,
that the turbulence on spatial scales of ~1000 km is homogeneous but
anisotropic. However it may be that the turbulence on these scales is
homogeneous and isotropic but the anisotropy is produced by highly elongated
(filamentary) inhomogeneities of scale 0.05-16 AU.Comment: 18 pages, 7 figures, accepted for publication in Astrophysical
Journa
Arecibo timing and single-pulse observations of 17 pulsars
We report on timing and single-pulse observations of 17 pulsars discovered at
the Arecibo observatory. The highlights of our sample are the recycled pulsars
J1829+2456, J1944+0907 and the drifting subpulses observed in PSR J0815+0939.
For the double neutron star binary J1829+2456, in addition to improving upon
our existing measurement of relativistic periastron advance, we have now
measured the pulsar's spin period derivative. This new result sets an upper
limit on the transverse speed of 120 km/s and a lower limit on the
characteristic age of 12.4 Gyr. From our measurement of proper motion of the
isolated 5.2-ms pulsar J1944+0907, we infer a transverse speed of 188 +/- 65
km/s. This is higher than that of any other isolated millisecond pulsar. An
estimate of the speed, using interstellar scintillation, of 235 +/- 45 km/s
indicates that the scattering medium along the line of sight is non-uniform. We
discuss the drifting subpulses detected from three pulsars in the sample, in
particular the remarkable drifting subpulse properties of the 645-ms pulsar
J0815+0939. Drifting is observed in all four components of the pulse profile,
with the sense of drift varying among the different components. This unusual
`bi-drifting'' behaviour challenges standard explanations of the drifting
subpulse phenomenon.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
How strange are compact star interiors ?
We discuss a Nambu--Jona-Lasinio (NJL) type quantum field theoretical
approach to the quark matter equation of state with color superconductivity and
construct hybrid star models on this basis. It has recently been demonstrated
that with increasing baryon density, the different quark flavors may occur
sequentially, starting with down-quarks only, before the second light quark
flavor and at highest densities also the strange quark flavor appears. We find
that color superconducting phases are favorable over non-superconducting ones
which entails consequences for thermodynamic and transport properties of hybrid
star matter. In particular, for NJL-type models no strange quark matter phases
can occur in compact star interiors due to mechanical instability against
gravitational collapse, unless a sufficiently strong flavor mixing as provided
by the Kobayashi-Maskawa-'t Hooft determinant interaction is present in the
model. We discuss observational data on mass-radius relationships of compact
stars which can put constraints on the properties of dense matter equation of
state.Comment: 7 pages, 2 figures, to appear in the Proceedings of the International
Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200
The repeating Fast Radio Burst FRB 121102: Multi-wavelength observations and additional bursts
We report on radio and X-ray observations of the only known repeating Fast
Radio Burst (FRB) source, FRB 121102. We have detected six additional radio
bursts from this source: five with the Green Bank Telescope at 2 GHz, and one
at 1.4 GHz at the Arecibo Observatory for a total of 17 bursts from this
source. All have dispersion measures consistent with a single value (
pc cm) that is three times the predicted maximum Galactic value. The
2-GHz bursts have highly variable spectra like those at 1.4 GHz, indicating
that the frequency structure seen across the individual 1.4 and 2-GHz
bandpasses is part of a wideband process. X-ray observations of the FRB 121102
field with the Swift and Chandra observatories show at least one possible
counterpart; however, the probability of chance superposition is high. A radio
imaging observation of the field with the Jansky Very Large Array at 1.6 GHz
yields a 5 upper limit of 0.3 mJy on any point-source continuum
emission. This upper limit, combined with archival WISE 22-m and IPHAS
H surveys, rules out the presence of an intervening Galactic HII
region. We update our estimate of the FRB detection rate in the PALFA survey to
be 1.1 FRBs sky day (95% confidence)
for peak flux density at 1.4 GHz above 300 mJy. We find that the intrinsic
widths of the 12 FRB 121102 bursts from Arecibo are, on average, significantly
longer than the intrinsic widths of the 13 single-component FRBs detected with
the Parkes telescope.Comment: 18 pages, 5 figures. Accepted for publication in Ap
Out of the frying pan: a young pulsar with a long radio trail emerging from SNR G315.9-0.0
The faint radio supernova remnant SNR G315.9-0.0 is notable for a long and
thin trail that extends outward perpendicular from the edge of its
approximately circular shell. In a search with the Parkes telescope we have
found a young and energetic pulsar that is located at the tip of this
collimated linear structure. PSR J1437-5959 has period P = 61 ms,
characteristic age tau_c = 114 kyr, and spin-down luminosity dE/dt = 1.4e36
erg/s. It is very faint, with a flux density at 1.4 GHz of about 75 uJy. From
its dispersion measure of 549 pc/cc, we infer d ~ 8 kpc. At this distance and
for an age comparable to tau_c, the implied pulsar velocity in the plane of the
sky is V_t = 300 km/s for a birth at the center of the SNR, although it is
possible that the SNR/pulsar system is younger than tau_c and that V_t > 300
km/s. The highly collimated linear feature is evidently the pulsar wind trail
left from the supersonic passage of PSR J1437-5959 through the interstellar
medium surrounding SNR G315.9-0.0.Comment: accepted for publication in ApJ Letter
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