345 research outputs found
A Thorough Investigation of Distance and Age of the Pulsar Wind Nebula 3C58
A growing number of researchers present evidence that the pulsar wind nebula
3C58 is much older than predicted by its proposed connection to the historical
supernova of A.D. 1181. There is also a great diversity of arguments. The
strongest of these arguments rely heavily on the assumed distance of 3.2 kpc
determined with HI absorption measurements. This publication aims at
determining a more accurate distance for 3C58 and re-evaluating the arguments
for a larger age. I have re-visited the distance determination of 3C58 based on
new HI data from the Canadian Galactic Plane Survey and our recent improvements
in the knowledge of the rotation curve of the outer Milky Way Galaxy. I have
also used newly determined distances to objects in the neighbourhood, which are
based on direct measurements by trigonometric parallax. I have derived a new
more reliable distance estimate of 2 kpc for 3C58. This makes the connection
between the pulsar wind nebula and the historical event from A.D. 1181 once
again much more viable.Comment: 11 pages, 6 figures, 1 table, accepted for publication in Astronomy &
Astrophysic
A Case Study of Triggered Star Formation in Cygnus X
Radiative feedback from massive stars can potentially trigger star formation
in the surrounding molecular gas. Inspired by the case of radiatively driven
implosion in M16 or Eagle Nebula, we analyze a similar case of star formation
observed in the Cygnus X region. We present new JCMT observations of
CO(3-2) and CO(3-2) molecular lines of a cometary feature located
at 50 pc north of the Cyg OB2 complex that was previously identified in
CO(3-2) mapping. These data are combined with archival H,
infrared, and radio continuum emission data, from which we measure the mass to
be 110 M. We identify Cyg OB2 as the ionizing source. We measure the
properties of two highly energetic molecular outflows and the photoionized rim.
From this analysis, we argue the external gas pressure and gravitational energy
dominate the internal pressure. The force balance along with previous
simulation results and a close comparison with the case of Eagle Nebula favours
a triggering scenario
A Relation Between the Warm Neutral and Ionized Media Observed in the Canadian Galactic Plane Survey
We report on a comparison between 21 cm rotation measure (RM) and the
optically-thin atomic hydrogen column density (N_HI) measured towards
unresolved extragalactic sources in the Galactic plane of the northern sky. HI
column densities integrated to the Galactic edge are measured immediately
surrounding each of nearly 2000 sources in 1-arcminute 21 cm line data, and are
compared to RMs observed from polarized emission of each source. RM data are
binned in column-density bins 4x10^20 cm^-2 wide, and one observes a strong
relationship between the number of hydrogen atoms in a 1 cm^2 column through
the plane and the mean RM along the same line-of-sight and path length. The
relationship is linear over one order of magnitude (from 0.8-14x10^21 atoms
cm^-2) of column densities, with a constant RM/N_HI -23.2+/-2.3 rad m^-2/10^21
atoms cm^-2, and a positive RM of 45.0+/-13.8 rad m^-2 in the presence of no
atomic hydrogen. This slope is used to calculate a mean volume-averaged
magnetic field in the 2nd quadrant of ~1.0+/-0.1 micro-Gauss directed
away from the Sun, assuming an ionization fraction of 8% (consistent with the
WNM). The remarkable consistency between this field and =1.2 micro-Gauss
found with the same RM sources and a Galactic model of dispersion measures
suggests that electrons in the partially ionized WNM are mainly responsible for
pulsar dispersion measures, and thus the partially-ionized WNM is the dominant
form of the magneto-ionic interstellar medium.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letters, July 15, 201
Pulsar Wind Nebulae with Thick Toroidal Structure
We investigate a class of pulsar wind nebulae that show synchrotron emission
from a thick toroidal structure. The best studied such object is the small
radio and X-ray nebula around the Vela pulsar, which can be interpreted as the
result of interaction of a mildly supersonic inward flow with the recent pulsar
wind. Such a flow near the center of a supernova remnant can be produced in a
transient phase when the reverse shock reaches the center of the remnant. Other
nebulae with a thick toroidal structure are G106.6+2.9 and G76.9+1.0. Their
structure contrasts with young pulsar nebulae like the Crab Nebula and 3C 38,
which show a more chaotic, filamentary structure in the synchrotron emission.
In both situations, a torus-jet structure is present where the pulsar wind
passes through a termination shock, indicating the flow is initially toroidal.
We suggest that the difference is due to the Rayleigh-Taylor instability that
operates when the outer boundary of the nebula is accelerating into freely
expanding supernova ejecta. The instability gives rise to mixing in the Crab
and related objects, but is not present in the nebulae with thick toroidal
regions.Comment: 13 pages, 2 Fig., ApJL, accepte
Radio continuum and polarization study of SNR G57.2+0.8 associated with magnetar SGR1935+2154
We present a radio continuum and linear polarization study of the Galactic
supernova remnant G57.2+0.8, which may host the recently discovered magnetar
SGR1935+2154. The radio SNR shows the typical radio continuum spectrum of a
mature supernova remnant with a spectral index of and
moderate polarized intensity. Magnetic field vectors indicate a tangential
magnetic field, expected for an evolved SNR, in one part of the SNR and a
radial magnetic field in the other. The latter can be explained by an
overlapping arc-like feature, perhaps a pulsar wind nebula, emanating from the
magnetar. The presence of a pulsar wind nebula is supported by the low average
braking index of 1.2, we extrapolated for the magnetar, and the detection of
diffuse X-ray emission around it. We found a distance of 12.5 kpc for the SNR,
which identifies G57.2+0.8 as a resident of the Outer spiral arm of the Milky
Way. The SNR has a radius of about 20 pc and could be as old as 41,000 years.
The SNR has already entered the radiative or pressure-driven snowplow phase of
its evolution. We compared independently determined characteristics like age
and distance for both, the SNR and SGR1935+2154, and conclude that they are
physically related.Comment: accepted by The Astrophysical Journal, 16 pages, 10 figure
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