475 research outputs found
Extended Emission from the PSR B1259-63/SS 2883 Binary Detected with Chandra
PSR B1259-63 is a middle-aged radio pulsar (P=48 ms, tau=330 kyr,
Edot=8.3*10^{35} erg/s) in an eccentric binary (P_orb =3.4 yr, e=0.87) with a
high-mass Be companion, SS 2883. We observed the binary near apastron with the
Chandra ACIS detector on 2009 May 14 for 28 ks. In addition to the previously
studied pointlike source at the pulsar's position, we detected extended
emission on the south-southwest side of this source. The pointlike source
spectrum can be described by the absorbed power-law model with the hydrogen
column density N_H = (2.5+/-0.6)*10^{21} cm^{-2}, photon index Gamma =
1.6+/-0.1, and luminosity L_{0.5-8 keV} = 1.3*10^{33} d_3^2 erg/s, where d_3 is
the distance scaled to 3 kpc. This emission likely includes an unresolved part
of the pulsar wind nebula (PWN) created by the colliding winds from the pulsar
and the Be companion, and a contribution from the pulsar magnetosphere. The
extended emission apparently consists of two components. The highly significant
compact component looks like a southward extension of the pointlike source
image, seen up to about 4 arcsec from the pulsar position. Its spectrum has
about the same slope as the pointlike source spectrum, while its luminosity is
a factor of 10 lower. We also detected an elongated feature extended ~15 arcsec
southwest of the pulsar, but significance of this detection is marginal. We
tentatively interpret the resolved compact PWN component as a shocked pulsar
wind blown out of the binary by the wind of the Be component, while the
elongated component could be a pulsar jet.Comment: 13 pages, 7 figures. Submitted to Ap
The Young Pulsar J1357-6429 and Its Pulsar Wind Nebula
We observed the young pulsar J1357--6429 with the {\it Chandra} and {\it
XMM-Newton} observatories. The pulsar spectrum fits well a combination of
absorbed power-law model () and blackbody model
( eV, km at the distance of 2.5 kpc). Strong
pulsations with pulsed fraction of , apparently associated with the
thermal component, were detected in 0.3--1.1 keV. Surprisingly, pulsed fraction
at higher energies, 1.1--10 keV, appears to be smaller, . The small
emitting area of the thermal component either corresponds to a hotter fraction
of the neutron star (NS) surface or indicates inapplicability of the simplistic
blackbody description. The X-ray images also reveal a pulsar-wind nebula (PWN)
with complex, asymmetric morphology comprised of a brighter, compact PWN
surrounded by the fainter, much more extended PWN whose spectral slopes are
and , respectively. The extended PWN with
the observed flux of erg s cm is a factor
of 10 more luminous then the compact PWN. The pulsar and its PWN are located
close to the center of the extended TeV source HESS J1356--645, which strongly
suggests that the VHE emission is powered by electrons injected by the pulsar
long ago. The X-ray to TeV flux ratio, , is similar to those of other
relic PWNe. We found no other viable candidates to power the TeV source. A
region of diffuse radio emission, offset from the pulsar toward the center of
the TeV source, could be synchrotron emission from the same relic PWN rather
than from the supernova remnant.Comment: 18 pages, 12 figures, and 4 tables, Accepted for publication in Ap
Pulsar-wind nebulae in X-rays and TeV gamma-rays
Pulsars are known to be efficient accelerators that produce copious amounts
of relativistic particles and inject them into the Galactic medium. The
radiation emitted by such a pulsar wind can be seen from radio through
gamma-rays as a pulsar-wind nebula (PWN). Here we overview and summarize recent
progress in X-ray and TeV observations of PWNe.Comment: 8 pages, 1 fugure, 2 tables to appear in the proceedings of "X-ray
Astronomy 2009" conference, Bologna, Italy, September, 2009 published by AIP.
Minor changes in the Tables and references. Added acknowledgment
X-ray emission from PSR J1809-1917 and its pulsar wind nebula, possibly associated with the TeV gamma-ray source HESS J1809-193
We detected X-ray emission from the 50-kyr-old pulsar J1809-1917 and resolved
its pulsar wind nebula (PWN) with Chandra. The pulsar spectrum fits PL+BB model
with the photon index of 1.2 and the BB temperature of 2 MK for n_{H}=0.7\times
10^{22} cm^{-2}. The luminosities are(4\pm 1)\times 10^{31} ergs s^{-1} for the
PL component (in the 0.5-8 keV band) and ~1\times 10^{32} ergs s^{-1} for the
BB component (bolometric) at a plausible distance of 3.5 kpc. The bright inner
PWN component of a 3''\times12'' size is elongated in the north-south
direction, with the pulsar close to its south end. This component is immersed
in a larger (20''\times40''), similarly elongated outer PWN component of lower
surface brightness. The elongated shape of the compact PWN can be explained by
the ram pressure confinement of the pulsar wind due to the supersonic motion of
the pulsar. The PWN spectrum fits a PL model with photon index of 1.4\pm0.1 and
0.5-8 keV luminosity of 4\times10^{32} ergs s^{-1}. The compact PWN appears to
be inside a large-scale (~4'\times4') emission more extended to the south of
the pulsar, i.e. in the direction of the alleged pulsar motion. To explain the
extended X-ray emission ahead of the moving pulsar, one has to invoke strong
intrinsic anisotropy of the pulsar wind or assume that this emission comes from
a relic PWN swept by the asymmetrical reverse SNR shock. The pulsar and its PWN
are located within the extent of the unidentified TeV source HESS J1809-193
whose brightest part is offset by ~8' to the south of the pulsar, i.e. in the
same direction as the large-scale X-ray emission. Although the association
between J1809-1917 and HESS J1809-193 is plausible, an alternative source of
relativistic electrons powering HESS J1809-193 might be the serendipitously
discovered X-ray source CXOU J180940.7-192544.Comment: 13 pages, 10 figures and 3 tables, submitted to ApJ. Version with the
high-resolution figures is available at
http://www.astro.psu.edu/users/green/J1809/ms_astroph.pd
Chandra observation of the TeV source HESS J1834-087
Chandra ACIS observed the field of the extended TeV source HESS J1834-087 for
47 ks. A previous XMM-Newton EPIC observation of the same field revealed a
point-like source (XMMU J183435.3-084443) and an offset region of faint
extended emission. In the low-resolution, binned EPIC images the two appear to
be connected. However, the high-resolution Chandra ACIS images do not support
the alleged connection. Instead, in these images XMMU J183435.3-084443 is
resolved into a point source, CXOU~J183434.9--084443 (L=2.5 x 10e33 ergs/s, for
a distance of 4 kpc; photon index 1.1), and a compact (~20'') nebula with an
isotropic morphology and a softer spectrum (L=4.2 x10e33 ergs/s, photon index
2.7). The nature of the nebula is uncertain. We discuss a dust scattering halo
and a pulsar-wind nebula as possible interpretations. Based on our analysis of
the X-ray data, we re-evaluate the previously suggested interpretations of HESS
J1834-087 and discuss a possible connection to the Fermi LAT source 1FGL
J1834.3-0842c. We also obtained an upper limit of 3 x 10e-14 ergs/s cm^2 on the
unabsorbed flux of the SGR J1833--0832 (in quiescence), which happened to be in
the ACIS field of view.Comment: 11 pages, 7 figures, submitted to Ap
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
A possible optical counterpart to the old nearby pulsar J0108-1431
The multi-wavelength study of old (>100 Myr) radio pulsars holds the key to
understanding the long-term evolution of neutron stars, including the advanced
stages of neutron star cooling and the evolution of the magnetosphere.
Optical/UV observations are particularly useful for such studies because they
allow one to explore both thermal and non-thermal emission processes. In
particular, studying the optical/UV emission constrains temperature of the bulk
of the neutron star surface, too cold to be measured in X-ray observations.Aim
of this work is to identify the optical counterpart of the very old (166 Myr)
radio pulsar J0108-1431. We have re-analyzed our original VLT observations
(Mignani et al. 2003), where a very faint object was tentatively detected close
to the radio position, near the edge of a field galaxy. We found that the
backward extrapolation of the PSR J0108-1431 proper motion recently measured by
CHANDRA(Pavlov et al. 2008) nicely fits the position of this object. Based on
that, we propose it as a viable candidate for the optical counterpart to PSR
J0108-1431. The object fluxes (U =26.4+/-0.3; B =27.9; V >27.8) are consistent
with a thermal spectrum with a brightness temperature of 9X10^4 K (for R = 13
km at a distance of 130 pc), emitted from the bulk of the neutron star surface.
New optical observations are required to confirm the optical identification of
PSR J0108-1431 and measure its spectrum.Comment: 5 pages, 4 figures, submitted to A&
- …