212 research outputs found
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
X-ray Observations of Parsec-Scale Tails behind Two Middle-Aged Pulsars
Chandra and XMM-Newton resolved extremely long tails behind two middle-aged
pulsars, J1509-5850 and J1740+1000. The tail of PSR J1509-5850 is discernible
up to 5.6' from the pulsar (6.5 pc at a distance of 4 kpc), with a flux of
2*10^{-13} erg s^{-1} cm^{-2} in 0.5-8 keV. The tail spectrum fits an absorbed
power-law (PL) model with the photon index of 2.3\pm0.2, corresponding to the
0.5-8 keV luminosity of 1*10^{33} ergs s^{-1}, for n_H= 2.1*10^{22} cm^{-2}.
The tail of PSR J1740+1000 is firmly detected up to 5' (2 pc at a 1.4 kpc
distance), with a flux of 6*10^{-14} ergs cm^{-2} s^{-1} in 0.4-10 keV. The PL
fit yields photon index of 1.4-1.5 and n_H=1*10^{21} cm^{-2}. The large extent
of the tails suggests that the bulk flow in the tails starts as mildly
relativistic downstream of the termination shock, and then gradually
decelerates. Within the observed extent of the J1509-5850 tail, the average
flow speed exceeds 5,000 km s^{-1}, and the equipartition magnetic field is a
few times 10^{-5} G. For the J1740+1000 tail, the equipartition field is a
factor of a few lower. The harder spectrum of the J1740+1000 tail implies
either less efficient cooling or a harder spectrum of injected electrons. For
the high-latitude PSR J1740+1000, the orientation of the tail on the sky shows
that the pulsar is moving toward the Galactic plane, which means that it was
born from a halo-star progenitor. The comparison between the J1509 and J1740
tails and the X-ray tails of other pulsars shows that the X-ray radiation
efficiency correlates poorly with the pulsar spin-down luminosity or age. The
X-ray efficiencies of the ram-pressure confined pulsar wind nebulae (PWNe) are
systematically higher than those of PWNe around slowly moving pulsars with
similar spin-down parameters.Comment: 14 pages, 16 figures and 5 table
Chandra Observation of PSR B1823-13 and its Pulsar Wind Nebula
We report on an observation of the Vela-like pulsar B1823-13 and its
synchrotron nebula with Chandra.The pulsar's spectrum fits a power-law model
with a photon index Gamma_PSR=2.4 for the plausible hydrogen column density
n_H=10^{22} cm^{-2}, corresponding to the luminosity L_PSR=8*10^{31} ergs
s^{-1} in the 0.5-8 keV band, at a distance of 4 kpc. The pulsar radiation
likely includes magnetospheric and thermal components, but they cannot be
reliably separated because of the small number of counts detected and strong
interstellar absorption. The pulsar is surrounded by a compact, 25''x 10'',
pulsar wind nebula (PWN) elongated in the east-west direction, which includes a
brighter inner component, 7''x 3'', elongated in the northeast-southwest
direction. The slope of the compact PWN spectrum is Gamma_comp=1.3, and the
0.5-8 keV luminosity is L_comp~3*10^{32} ergs s^{-1}. The compact PWN is
surrounded by asymmetric diffuse emission (extended PWN) seen up to at least
2.4' south of the pulsar, with a softer spectrum (Gamma_ext=1.9), and the 0.5-8
keV luminosity L_ext~10^{33}-10^{34} ergs s^{-1}. We also measured the pulsar's
proper motion using archival VLA data: \mu_\alpha=23.0+/-2.5 mas yr^{-1},
\mu_\delta=-3.9+/-3.3 mas yr^{-1}, which corresponds to the transverse
velocity v_perp=440 km s^{-1}. The direction of the proper motion is
approximately parallel to the elongation of the compact PWN, but it is nearly
perpendicular to that of the extended PWN and to the direction towards the
center of the bright VHE gamma-ray source HESS J1825-137, which is likely
powered by PSR B1823-13.Comment: 13 pages, 8 figures and 3 tables; submitted to 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&
Absorption Features in the X-ray Spectrum of an Ordinary Radio Pulsar
The vast majority of known non-accreting neutron stars (NSs) are
rotation-powered radio and/or gamma-ray pulsars. So far, their multiwavelength
spectra have all been described satisfactorily by thermal and non-thermal
continuum models, with no spectral lines. Spectral features have, however, been
found in a handful of exotic NSs and thought to be a manifestation of their
unique traits. Here we report the detection of absorption features in the X-ray
spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings
bridge the gap between the spectra of pulsars and other, more exotic, NSs,
suggesting that the features are more common in the NS spectra than they have
been thought so far.Comment: 18 pages, 4 color figures, 1 Tabl
Detection of X-ray Emission from the Very Old Pulsar J0108-1431
PSR J0108-1431 is a nearby, 170 Myr old, very faint radio pulsar near the
"pulsar death line" in the P-Pdot diagram. We observed the pulsar field with
the Chandra X-ray Observatory and detected a point source (53 counts in a 30 ks
exposure, energy flux (9+/-2)\times 10^{-15} ergs cm^{-2} s^{-1} in the 0.3-8
keV band) close to the radio pulsar position. Based on the large X-ray/optical
flux ratio at the X-ray source position, we conclude that the source is the
X-ray counterpart of PSR J0108-1431.The pulsar spectrum can be described by a
power-law model with photon index Gamma \approx 2.2 and luminosity L_{0.3-8
keV} \sim 2\times 10^{28} d_{130}^2 ergs s^{-1}, or by a blackbody model with
the temperature kT\approx 0.28 keV and bolometric luminosity L_{bol} \sim
1.3\times 10^{28} d_{130}^2 ergs s^{-1}, for a plausible hydrogen column
density NH = 7.3\times 10^{19} cm^{-2} (d_{130}=d/130 pc). The pulsar converts
\sim 0.4% of its spin-down power into the X-ray luminosity, i.e., its X-ray
efficiency is higher than for most younger pulsars. From the comparison of the
X-ray position with the previously measured radio positions, we estimated the
pulsar proper motion of 0.2 arcsec yr^{-1} (V_\perp \sim 130 d_{130} km
s^{-1}), in the south-southeast direction.Comment: 8 pages, 9 figures, accepted to ApJ; minor revisions in Sections 2.2
and 3.
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