358 research outputs found
Discovery of a 112 ms X-ray Pulsar in Puppis A: Further Evidence of Neutron Stars Weakly Magnetized at Birth
We report the discovery of 112-ms X-ray pulsations from RX J0822-4300, the
compact central object (CCO) in the supernova remnant Puppis A, in two archival
Newton X-Ray Multi-Mirror Mission observations taken in 2001. The sinusoidal
light curve has a pulsed fraction of 11% with an abrupt 180 deg. change in
phase at 1.2 keV. The observed phase shift and modulation are likely the result
of emission from opposing thermal hot spots of distinct temperatures.
Phase-resolved spectra reveal an emission feature at E(line) = 0.8 keV
associated with the cooler region, possibly due to an electron cyclotron
resonance effect similar to that seen in the spectrum of the CCO pulsar 1E
1207.4-5209. No change in the spin period of PSR J0821-4300 is detected in 7
months, with a 2 sigma upper limit on the period derivative less than 8.3E-15.
This implies limits on the spin-down energy loss rate of less than 2.3E35
erg/s, the surface magnetic dipole field strength B_s < 9.8E11 G, and the
spin-down age tau > 220 kyr. The latter is much longer than the SNR age,
indicating that PSR J0821-4300 was born spinning near its present period. Its
properties are remarkably similar to those of the two other known CCO pulsars,
demonstrating the existence of a class of neutron stars born with weak magnetic
fields related to a slow original spin. These results are also of importance in
understanding the extreme transverse velocity of PSR J0821-4300, favoring the
hydrodynamic instability mechanism in the supernova explosion.Comment: 5 pages, 4 figure, Latex, emulateapj style. To appear in the
Astrophysical Journa
New X-ray observations of the Geminga pulsar wind nebula
Previous observations of the middle-aged pulsar Geminga with XMM-Newton and
Chandra have shown an unusual pulsar wind nebula (PWN), with a 20" long central
(axial) tail directed opposite to the pulsar's proper motion and two 2' long,
bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra
observation and a few additional XMM-Newton observations of the Geminga PWN.
The new Chandra observation has shown that the axial tail, which includes up to
three brighter blobs, extends at least 50" (i.e., 0.06 d_{250} pc) from the
pulsar. It also allowed us to image the patchy outer tails and the emission in
the immediate vicinity of the pulsar with high resolution. The PWN luminosity,
L_{0.3-8 keV} ~ 3\times 10^{29} d_{250}^2 erg/s, is lower than the pulsar's
magnetospheric luminosity by a factor of 10. The spectra of the PWN elements
are rather hard (photon index ~ 1). Comparing the two Chandra images, we found
evidence of PWN variability, including possible motion of the blobs along the
axial tail. The X-ray PWN is the synchrotron radiation from relativistic
particles of the pulsar wind; its morphology is connected with the supersonic
motion of Geminga. We speculate that the outer tails are either (1) a sky
projection of the limb-brightened boundary of a shell formed in the region of
contact discontinuity, where the wind bulk flow is decelerated by shear
instability, or (2) polar outflows from the pulsar bent by the ram pressure
from the ISM. In the former case, the axial tail may be a jet emanating along
the pulsar's spin axis, perhaps aligned with the direction of motion. In the
latter case, the axial tail may be the shocked pulsar wind collimated by the
ram pressure.Comment: 16 pages, including 6 figures; minor changes in the text; typos
corrected; published in Ap
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
X-ray analysis of the proper motion and pulsar wind nebula for PSR J1741-2054
We obtained six observations of PSR J1741-2054 using the ACIS-S
detector totaling 300 ks. By registering this new epoch of observations
to an archival observation taken 3.2 years earlier using X-ray point sources in
the field of view, we have measured the pulsar proper motion at in a direction consistent with the symmetry axis of the
observed H nebula. We investigated the inferred past trajectory of the
pulsar but find no compelling association with OB associations in which the
progenitor may have originated. We confirm previous measurements of the pulsar
spectrum as an absorbed power law with photon index =2.680.04,
plus a blackbody with an emission radius of (4.5 km,
for a DM-estimated distance of kpc and a temperature of
eV. Emission from the compact nebula is well described by an
absorbed power law model with a photon index of = 1.670.06, while
the diffuse emission seen as a trail extending northeast of the pulsar shows no
evidence of synchrotron cooling. We also applied image deconvolution techniques
to search for small-scale structures in the immediate vicinity of the pulsar,
but found no conclusive evidence for such structures.Comment: 7 pages, 8 figures, 4 Tables; Accepted by Ap
Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54
We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind
nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks
total exposure, performed over an 8 month period). We investigated the spatial
and spectral properties of the emission coincident with the pulsar, compact
nebula (CN), and extended tail. We find that the CN morphology can be
interpreted in a way that suggests a small angle between the pulsar spin axis
and our line-of-sight, as inferred from the radio data. On larger scales,
emission from the 7' (2 pc) tail is clearly seen. We also found hints of two
faint extensions nearly orthogonal to the direction of the pulsar's proper
motion. The spectrum extracted at the pulsar position can be described with an
absorbed power-law + blackbody model. The nonthermal component can be
attributed to magnetospheric emission, while the thermal component can be
attributed to emission from either a hot spot (e.g., a polar cap) or the entire
neutron star surface. Surprisingly, the spectrum of the tail shows only a
slight hint of cooling with increasing distance from the pulsar. This implies
either a low magnetic field with fast flow speed, or particle re-acceleration
within the tail. We estimate physical properties of the PWN and compare the
morphologies of the CN and the extended tail with those of other bow shock PWNe
observed with long CXO exposures.Comment: 11 pages, 8 figure
Multi-Zone Modeling of The Pulsar Wind Nebula HESS J1825-137
The pulsar wind nebula associated with PSR J1826-1334, HESS J1825-137, is a
bright very high energy source with an angular extent of ~1 degree and
spatially-resolved spectroscopic TeV measurements. The gamma-ray spectral index
is observed to soften with increasing distance from the pulsar, likely the
result of cooling losses as electrons traverse the nebula. We describe analysis
of X-ray data of the extended nebula, as well as 3-D time-dependent spectral
energy distribution modeling, with emphasis on the spatial variations within
HESS J1825-137. The multi-wavelength data places significant constraints on
electron injection, transport, and cooling within the nebula. The large size
and high nebular energy budget imply a relatively rapid initial pulsar spin
period of 13 \pm 7 ms and an age of 40 \pm 9 kyr. The relative fluxes of each
VHE zone can be explained by advective particle transport with a radially
decreasing velocity profile with . The evolution of the
cooling break requires an evolving magnetic field which also decreases radially
from the pulsar, . Detection of 10
TeV flux ~80 pc from the pulsar requires rapid diffusion of high energy
particles with year,
contrary to the common assumption of toroidal magnetic fields with strong
magnetic confinement. The model predicts a rather uniform Fermi LAT surface
brightness out to ~1 degree from the pulsar, in good agreement with the
recently discovered LAT source centered 0.5 degree southwest of PSR J1826-1334
with extension 0.6 \pm 0.1 degree.Comment: Updated to published versio
A Chandra Observation of Supernova Remnant G350.1-0.3 and Its Central Compact Object
We present a new Chandra observation of supernova remnant (SNR) G350.1-0.3.
The high resolution X-ray data reveal previously unresolved filamentary
structures and allow us to perform detailed spectroscopy in the diffuse regions
of this SNR. Spectral analysis demonstrates that the region of brightest
emission is dominated by hot, metal-rich ejecta while the ambient material
along the perimeter of the ejecta region and throughout the remnant's western
half is mostly low-temperature, shocked interstellar/circumstellar medium
(ISM/CSM) with solar-type composition. The data reveal that the emission
extends far to the west of the ejecta region and imply a lower limit of 6.6 pc
on the diameter of the source (at a distance of 4.5 kpc). We show that
G350.1-0.3 is likely in the free expansion (ejecta-dominated) stage and
calculate an age of 600-1200 years. The derived relationship between the shock
velocity and the electron/proton temperature ratio is found to be entirely
consistent with that of other SNRs. We perform spectral fits on the X-ray
source XMMU J172054.5-372652, a candidate central compact object (CCO), and
find that its spectral properties fall within the typical range of other CCOs.
We also present archival 24 um data of G350.1-0.3 taken with the Spitzer Space
Telescope during the MIPSGAL galactic survey and find that the infrared and
X-ray morphologies are well-correlated. These results help to explain this
remnant's peculiar asymmetries and shed new light on its dynamics and
evolution
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