564 research outputs found
The Proper Motion of PSR J0205+6449 in 3C 58
We report on sensitive phase-referenced and gated 1.4-GHz VLBI radio
observations of the pulsar PSR J0205+6449 in the young pulsar-wind nebula 3C
58, made in 2007 and 2010. We employed a novel technique where the ~105-m Green
Bank telescope is used simultaneously to obtain single-dish data used to
determine the pulsar's period as well as to obtain the VLBI data, allowing the
VLBI correlation to be gated synchronously with the pulse to increase the
signal-to-noise. The high timing noise of this young pulsar precludes the
determination of the proper motion from the pulsar timing. We derive the
position of the pulsar accurate at the milliarcsecond level, which is
consistent with a re-determined position from the Chandra X-ray observations.
We reject the original tentative optical identification of the pulsar by
Shearer and Neustroev (2008), but rather identify a different optical
counterpart on their images, with R-band magnitude ~24. We also determine an
accurate proper motion for PSR J0205+6449 of (2.3 +- 0.3) mas/yr, corresponding
to a projected velocity of only (35 +- 6) km/s for a distance of 3.2 kpc, at
p.a. -38 deg. This projected velocity is quite low compared to the velocity
dispersion of known pulsars of ~200 km/s. Our measured proper motion does not
suggest any particular kinematic age for the pulsar.Comment: 10 pages, 7 figures; accepted for publication in MNRA
High Resolution X-ray Observations of the Pulsar Wind Nebula Associated with the Gamma-ray Source HESSJ1640-465
We present a Chandra X-ray observation of the very high energy -ray
source HESSJ1640-465. We identify a point source surrounded by a diffuse
emission that fills the extended object previously detected by XMM Newton at
the centroid of the HESS source, within the shell of the radio supernova
remnant (SNR) G338.3-0.0. The morphology of the diffuse emission strongly
resembles that of a pulsar wind nebula (PWN) and extends asymmetrically to the
South-West of a point-source presented as a potential pulsar. The spectrum of
the putative pulsar and compact nebula are well-characterized by an absorbed
power-law model which, for a reasonable value of , exhibit an index of 1.1 and 2.5 respectively, typical of
Vela-like PWNe. We demonstrate that, given the HI absorption features
observed along the line of sight, the SNR and the HII surrounding region are
probably connected and lie between 8 kpc and 13 kpc. The resulting age of the
system is between 10 and 30 kyr. For a 10 kpc distance (also consistent with
the X-ray absorption) the 2-10 keV X-ray luminosities of the putative pulsar
and nebula are and
(). Both the flux ratio of and the total luminosity of this system predict a pulsar spin-down
power around . We finally
consider several reasons for the asymmetries observed in the PWN morphology and
discuss the potential association with the HESS source in term of a
time-dependent one-zone leptonic model.Comment: 35 pages, 9 figure
An ASCA Study of the High Luminosity SNR G349.7+0.2
We present ASCA observations of supernova remnant (SNR) G349.7+0.2. The
remnant has an irregular shell morphology and is interacting with a molecular
cloud, evident from the presence of OH(1720 MHz) masers and shocked molecular
gas. The X-ray morphology is consistent with that at radio wavelengths, with a
distinct enhancement in the south. The X-ray emission from the SNR is well
described by a model of a thermal plasma which has yet to reach ionization
equilibrium. The hydrogen column of ~6.0 X 10^{22} cm^{-2} is consistent with
the large distance to the remnant of ~22 kpc estimated from the maser
velocities. We derive an X-ray luminosity of L_x(0.5-10.0 keV)= 1.8 X 10^{37}
d_{22}^2 erg/s, which makes G349.7+0.2 one of the most X-ray luminous
shell-type SNRs known in the Galaxy. The age of the remnant is estimated to be
about 2800 yrs. The ambient density and pressure conditions appear similar to
those inferred for luminous compact SNRs found in starburst regions of other
galaxies, and provides support for the notion that these may be the result of
SNR evolution in the vicinity of dense molecular clouds.Comment: 5 pages, 3 figures. Accepted for publication in Ap
Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
We present observations of HESS J1640-465 with the Fermi-LAT. The source is
detected with high confidence as an emitter of high-energy gamma-rays. The
spectrum lacks any evidence for the characteristic cutoff associated with
emission from pulsars, indicating that the emission arises primarily from the
pulsar wind nebula. Broadband modeling implies an evolved nebula with a low
magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi
emission exceeds predictions of the broadband model, and has a steeper
spectrum, possibly resulting from a distinct excess of low energy electrons
similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap
Revealing New Physical Structures in the Supernova Remnant N63A through Chandra Imaging Spectroscopy
We present Chandra X-ray observations of the supernova remnant (SNR) N63A in
the Large Magellanic Cloud (LMC). N63A, one of the brightest LMC remnants, is
embedded in an H II region and probably associated with an OB association. The
optical remnant consists of three lobes of emission contained within the
approximately three times larger X-ray remnant. Our Chandra data reveal a
number of new physical structures in N63A. The most striking of these are the
several ``crescent''-shaped structures located beyond the main shell that
resemble similar features seen in the Vela SNR. In Vela, these have been
interpreted as arising from high speed clumps of supernova ejecta interacting
with the ambient medium. Another distinct feature of the remnant is a roughly
triangular ``hole'' in the X-ray emission near the location of the optical
lobes and the brightest radio emission. X-ray spectral analysis shows that this
deficit of emission is a result of absorption by an intervening dense cloud
with a mass of ~450 M_sun that is currently being engulfed by the remnant's
blast wave. We also find that the rim of the remnant, as well as the
crescent-shaped features, have considerably softer X-ray spectra than the
interior. Limits on hard X-ray emission rule out a young, energetic pulsar in
N63A, but the presence of an older or less active one, powering a wind nebula
with a luminosity less than ~4e10^34 erg/s, is allowed.Comment: 18 pages, 5 figures (2 color), accepted for publication in Ap
The Slow X-Ray Expansion of the Northwestern Rim of the Supernova Remnant RX J0852.0-4622
The detection of radioactive decay line of 44Ti provides a unique evidence
that the gamma-ray source is a young (< 1,000 yr) supernova remnant because of
its short lifetime of about 90 yr. Only two Galactic remnants, Cassiopeia A and
RX J0852.0-4622, are hitherto reported to be the 44Ti line emitter, although
the detection from the latter has been debated. Here we report on an expansion
measurement of the northwestern rim of RX J0852.0-4622 obtained with X-ray
observations separated by 6.5 yr. The expansion rate is derived to be
0.023+/-0.006% that is about five times lower than those of young historical
remnants. Such a slow expansion suggests that RX J0852.0-4622 is not a young
remnant as has been expected. We estimate the age of 1,700-4,300 yr of this
remnant depending on its evolutionary stage. Assuming a high shock speed of
about 3000 km/sec, which is suggested by the detection of non-thermal X-ray
radiation, the distance of about 750 pc to this remnant is also derived.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
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