347 research outputs found
Chandra observation of the Galactic supernova remnant CTB 109 (G109.1-1.0)
Context: We study the X-ray emission of the Galactic supernova remnant (SNR)
CTB 109 (G109.1-1.0), which is well-known for its enigmatic half-shell
morphology both in radio and in X-rays and is associated with the anomalous
X-ray pulsar (AXP) 1E2259+586. Aims: We want to understand the origin of the
X-ray bright feature inside the SNR called the Lobe and the details of the
interaction of the SNR shock wave with the ambient interstellar medium (ISM).
Methods: The Lobe and the northeastern part of the SNR were observed with
Chandra ACIS-I. We analysed the spectrum of the X-ray emission by dividing the
entire observed emission into small regions. The X-ray emission is best
reproduced with one-component or two-component non-equilibrium ionisation
models depending on the position. In the two-component model one emission
component represents the shocked ISM and the other the shocked ejecta. Results:
We detect enhanced element abundances, in particular for Si and Fe, in and
around the Lobe. There is one particular region next to the Lobe with a high Si
abundance of 3.3 (2.6 - 4.0) times the solar value. This is the first,
unequivocal detection of ejecta in CTB 109. Conclusions: The new Chandra data
confirm that the Lobe was created by the interaction of the SNR shock and the
supernova ejecta with dense and inhomogeneous medium in the environment of SNR
CTB 109. The newly calculated age of the SNR is t ~ 1.4 x 10^4 yr.Comment: Accepted for publication in A&A. 9 pages, 10 figure
The X-ray nebula of the filled center supernova remnant 3C58 and its interaction with the environment
An \xmm observation of the plerionic supernova remnant 3C58 has allowed us to
study the X-ray nebula with unprecedented detail. A spatially resolved spectral
analysis with a resolution of 8\arcsec has yielded a precise determination of
the relation between the spectral index and the distance from the center. We do
not see any evidence for bright thermal emission from the central core. In
contrast with previous ASCA and {\em Einstein} results, we derive an upper
limit to the black-body 0.5-10 keV luminosity and emitting area of \ergsec and cm, respectively, ruling out
emission from the hot surface of the putative neutron star and also excluding
the "outer-gap" model for hot polar caps. We have performed for the first time
a spectral analysis of the outer regions of the X-ray nebula, where most of the
emission is still non-thermal, but where the addition of a soft (kT=0.2-0.3
keV) optically thin plasma component is required to fit the spectrum at
keV. This component provides 6% of the whole remnant observed flux in the
0.5-10.0 keV band. We show that a Sedov interpretation is incompatible with the
SN1181-3C58 association, unless there is a strong deviation from electron-ion
energy equipartition, and that an origin of this thermal emission in terms of
the expansion of the nebula into the ejecta core nicely fits all the radio and
X-ray observations.Comment: 10 pages, 7 figures, accepted for publication in A&
The distance to the Vela pulsar gauged with HST parallax oservations
The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed
to be 500 pc. Although affected by a significant uncertainty, this value stuck
to both the pulsar and the SNR. In an effort to obtain a model free distance
measurement, we have applied high resolution astrometry to the pulsar V~23.6
optical counterpart. Using a set of five HST/WFPC2 observations, we have
obtained the first optical measurement of the annual parallax of the Vela
pulsar. The parallax turns out to be 3.4 +/- 0.7 mas, implying a distance of
294(-50;+76) pc, i.e. a value significantly lower than previously believed.
This affects the estimate of the pulsar absolute luminosity and of its emission
efficiency at various wavelengths and confirms the exceptionally high value of
the N_e towards the Vela pulsar. Finally, the complete parallax data base
allows for a better measurement of the Vela pulsar proper motion
(mu_alpha(cos(delta))=-37.2 +/- 1.2 mas/yr; mu_delta=28.2 +/- 1.3 mas/yr after
correcting for the peculiar motion of the Sun) which, at the parallax distance,
implies a transverse velocity of ~65 km/s. Moreover, the proper motion position
angle appears specially well aligned with the axis of symmetry of the X-ray
nebula as seen by Chandra. Such an alignment allows to assess the space
velocity of the Vela pulsar to be ~81 km/s.Comment: LaTeX, 21 pages, 5 figures. Accepted for publication in Ap
Caso Fondamenta Srl Le modifiche agli assetti organizzativi, amministrativi e contabili necessarie per il turnaround. Cap.18
Subclinical and asymptomatic atrial fibrillation: Current evidence and unsolved questions in clinical practice
A population of isolated hard X-ray sources near the supernova remnant Kes 69
Recent X-ray observations of the supernova remnant IC443 interacting with
molecular clouds have shown the presence of a new population of hard X-ray
sources related to the remnant itself, which has been interpreted in terms of
fast ejecta fragment propagating inside the dense environment. Prompted by
these studies, we have obtained a deep {\sl XMM-Newton} observation of the
supernova remnant (SNR) Kes 69, which also shows signs of shock-cloud
interaction. We report on the detection of 18 hard X-ray sources in the field
of Kes 69, a significant excess of the expected galactic source population in
the field, spatially correlated with CO emission from the cloud in the remnant
environment. The spectra of 3 of the 18 sources can be described as hard power
laws with photon index <2 plus line emission associated to K-shell transitions.
We discuss the two most promising scenarios for the interpretation of the
sources, namely fast ejecta fragments (as in IC443) and cataclysmic variables.
While most of the observational evidences are consistent with the former
interpretation, we cannot rule out the latter.Comment: 9 pages, 5 figures, A&A in pres
XMM-Newton observation of the supernova remnant Kes 78 (G32.8-0.1):Evidence of shock-cloud interaction
The Galactic supernova remnant Kes 78 is surrounded by dense molecular
clouds, whose projected position overlaps with the extended HESS gamma-ray
source HESS J1852-000. The X-ray emission from the remnant has been recently
revealed by Suzaku observations, which have shown indications for a hard X-ray
component in the spectra, possibly associated with synchrotron radiation. We
aim at describing the spatial distribution of the physical properties of the
X-ray emitting plasma and at revealing the effects of the interaction of the
remnant with the inhomogeneous ambient medium. We also aim at investigating the
origin of the gamma-ray emission, which may be Inverse Compton radiation
associated with X-ray synchrotron emitting electrons or hadronic emission
originating from the impact of high energy protons on the nearby clouds. We
analyzed an XMM-Newton EPIC observation of Kes 78 by performing image analysis
and spatially resolved spectral analysis on a set of three regions. We tested
our findings against the observations of the 12CO and 13CO emission in the
environment of the remnant. We revealed the complex X-ray morphology of Kes 78
and found variations of the spectral properties of the plasma, with
significantly denser and cooler material at the eastern edge of the remnant,
which we interpret as a signature of interaction with a molecular cloud. We
also exclude the presence of narrow filaments emitting X-ray synchrotron
radiation. Assuming that the very high energy gamma-ray emission is associated
with Kes 78, the lack of synchrotron emission rules out a leptonic origin. A
hadronic origin is further supported by evidence for interaction of the remnant
with a dense molecular cloud in its eastern limb.Comment: Accepted for publication in A&
Unveiling pure-metal ejecta X-ray emission in supernova remnants through their radiative recombination continuum
Isolated X-ray -- infrared sources in the region of interaction of the supernova remnant IC 443 with a molecular cloud
The nature of the extended hard X-ray source XMMU J061804.3+222732 and its
surroundings is investigated using XMM-Newton, Chandra, and Spitzer
observations. This source is located in an interaction region of the IC 443
supernova remnant with a neighboring molecular cloud. The X-ray emission
consists of a number of bright clumps embedded in an extended structured
non-thermal X-ray nebula larger than 30" in size. Some clumps show evidence for
line emission at ~1.9 keV and ~3.7 keV at the 99% confidence level. Large-scale
diffuse radio emission of IC 443 passes over the source region, with an
enhancement near the source. An IR source of about 14" x 7" size is prominent
in the 24 um, 70 um, and 2.2 um bands, adjacent to a putative Si K-shell X-ray
line emission region. The observed IR/X-ray morphology and spectra are
consistent with those expected for J/C-type shocks of different velocities
driven by fragmented supernova ejecta colliding with the dense medium of a
molecular cloud. The IR emission of the source detected by Spitzer can be
attributed to both continuum emission from an HII region created by the ejecta
fragment and line emission excited by shocks. This source region in IC 443 may
be an example of a rather numerous population of hard X-ray/IR sources created
by supernova explosions in the dense environment of star-forming regions.
Alternative Galactic and extragalactic interpretations of the observed source
are also discussed.Comment: The Astrophysical Journal, v. 677 (April 2008), in pres
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