394 research outputs found
The Slow X-Ray Expansion of the Northwestern Rim of the Supernova Remnant RX J0852.0-4622
The detection of radioactive decay line of 44Ti provides a unique evidence
that the gamma-ray source is a young (< 1,000 yr) supernova remnant because of
its short lifetime of about 90 yr. Only two Galactic remnants, Cassiopeia A and
RX J0852.0-4622, are hitherto reported to be the 44Ti line emitter, although
the detection from the latter has been debated. Here we report on an expansion
measurement of the northwestern rim of RX J0852.0-4622 obtained with X-ray
observations separated by 6.5 yr. The expansion rate is derived to be
0.023+/-0.006% that is about five times lower than those of young historical
remnants. Such a slow expansion suggests that RX J0852.0-4622 is not a young
remnant as has been expected. We estimate the age of 1,700-4,300 yr of this
remnant depending on its evolutionary stage. Assuming a high shock speed of
about 3000 km/sec, which is suggested by the detection of non-thermal X-ray
radiation, the distance of about 750 pc to this remnant is also derived.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
Discovery of the compact X-ray source inside the Cygnus Loop
We detected an X-ray compact source inside the Cygnus Loop during the
observation project of the whole Cygnus Loop with the ASCA GIS. The source
intensity is 0.11 c s for GIS and 0.15 c s for SIS, which is the
strongest in the ASCA band. The X-ray spectra are well fitted by a power law
spectrum of a photon index of \error{-2.1}{0.1} with neutral H column of
(\error{3.1}{0.6}). Taking into account the
interstellar absorption feature, this source is X-ray bright mainly above 1 keV
suggesting either an AGN or a rotating neutron star. So far, we did not detect
intensity variation nor coherent pulsation mainly due to the limited
observation time. There are several optical bright stellar objects within the
error region of the X-ray image. We carried out the optical spectroscopy for
the brightest source (V=+12.6) and found it to be a G star. The follow up deep
observation both in optical and in X-ray wavelengths are strongly required.Comment: Accepted for Publications of the Astronomical Society of Japan 17
pages, 3 figur
The Plasma Structure of the Cygnus Loop from the Northeastern Rim to the Southwestern Rim
The Cygnus Loop was observed from the northeast to the southwest with
XMM-Newton. We divided the observed region into two parts, the north path and
the south path, and studied the X-ray spectra along two paths. The spectra can
be well fitted either by a one-component non-equilibrium ionization (NEI) model
or by a two-component NEI model. The rim regions can be well fitted by a
one-component model with relatively low \kTe whose metal abundances are
sub-solar (0.1--0.2). The major part of the paths requires a two-component
model. Due to projection effects, we concluded that the low kTe (about 0.2 keV)
component surrounds the high kTe (about 0.6 keV) component, with the latter
having relatively high metal abundances (about 5 times solar). Since the Cygnus
Loop is thought to originate in a cavity explosion, the low-kTe component
originates from the cavity wall while the high-kTe component originates from
the ejecta. The flux of the cavity wall component shows a large variation along
our path. We found it to be very thin in the south-west region, suggesting a
blowout along our line of sight. The metal distribution inside the ejecta shows
non-uniformity, depending on the element. O, Ne and Mg are relatively more
abundant in the outer region while Si, S and Fe are concentrated in the inner
region, with all metals showing strong asymmetry. This observational evidence
implies an asymmetric explosion of the progenitor star. The abundance of the
ejecta also indicates the progenitor star to be about 15 M_sun.Comment: 24 pages, 9 figures, Astrophysical Journal in pres
Parameterization of the Angular Distribution of Gamma Rays Produced by p-p Interaction in Astronomical Environment
We present the angular distribution of gamma rays produced by proton-proton
interactions in parameterized formulae to facilitate calculations in
astrophysical environments. The parameterization is derived from Monte Carlo
simulations of the up-to-date proton-proton interaction model by Kamae et al.
(2005) and its extension by Kamae et al. (2006). This model includes the
logarithmically rising inelastic cross section, the diffraction dissociation
process and Feynman scaling violation. The extension adds two baryon resonance
contributions: one representing the Delta(1232) and the other representing
multiple resonances around 1600 MeV/c^2. We demonstrate the use of the formulae
by calculating the predicted gamma-ray spectrum for two different cases: the
first is a pencil beam of protons following a power law and the second is a
fanned proton jet with a Gaussian intensity profile impinging on the
surrounding material. In both cases we find that the predicted gamma-ray
spectrum to be dependent on the viewing angle.Comment: 8 pages, 7 figures, figure 7 updated, accepted for publication in
ApJ, text updated to match changes by the editor, two refs updated from
preprints to full journal
Discovery of pulsations in the X-ray transient 4U 1901+03
We describe observations of the 2003 outburst of the hard-spectrum X-ray
transient 4U 1901+03 with the Rossi X-ray Timing Explorer. The outburst was
first detected in 2003 February by the All-Sky Monitor, and reached a peak
2.5-25 keV flux of 8x10^-9 ergs/cm^2/s (around 240 mCrab). The only other known
outburst occurred 32.2 yr earlier, likely the longest presently known
recurrence time for any X-ray transient. Proportional Counter Array (PCA)
observations over the 5-month duration of the 2003 outburst revealed a 2.763 s
pulsar in a 22.58 d orbit. The detection of pulsations down to a flux of
3x10^-11 ergs/cm^2/s (2.5-25 keV), along with the inferred long-term accretion
rate of 8.1x10^-11 M_sun/yr (assuming a distance of 10 kpc) suggests that the
surface magnetic field strength is below ~5x10^11 G. The corresponding
cyclotron energy is thus below 4 keV, consistent with the non-detection of
resonance features at high energies. Although we could not unambiguously
identify the optical counterpart, the lack of a bright IR candidate within the
1' RXTE error circle rules out a supergiant mass donor. The neutron star in 4U
1901+03 probably accretes from the wind of a main-sequence O-B star, like most
other high-mass binary X-ray pulsars. The almost circular orbit e=0.036
confirms the system's membership in a growing class of wide, low-eccentricity
systems in which the neutron stars may have received much smaller kicks as a
result of their natal supernova explosions.Comment: 7 pages, 6 figures, accepted by ApJ. Very minor addition in response
to referee's comment; updated author affiliatio
Discovery of a Featureless X-Ray Spectrum in the Supernova Remnant Shell of G330.2+1.0
We report here on the first pointed X-ray observation of the supernova
remnant (SNR) G330.2+1.0. The X-ray morphology is characterized by an extended
shell. Its X-ray spectrum is well represented by a single power-law function
with a photon index of and interstellar absorption of
[cm]. We interpret this emission as
synchrotron radiation from accelerated electrons at the SNR shock, as seen in
SN 1006. The surface brightness of the X-ray emission is anti-correlated with
the radio emission, and the power-law spectrum is dominated at the western
shell where the radio emission is weak. The co-existence of two distinct (radio
bright/X-ray faint and radio faint/X-ray bright) shells in a single supernova
remnant challenges our understanding of the particle acceleration and radiation
mechanisms in different interstellar environments. The object may be a good
target for searching TeV gamma-rays and molecular gas surrounding the blast
shock. We also report on the nature of a bright point-like source (AX
J1601-5143) to the south of the SNR.Comment: PASJ, in pres
Chandra view of Kes 79: a nearly isothermal SNR with rich spatial structure
A 30 ks \chandra ACIS-I observation of Kes 79 reveals rich spatial
structures, including many filaments, three partial shells, a loop and a
``protrusion''. Most of them have corresponding radio features. Regardless of
the different results from two non-equilibrium ionization (NEI) codes,
temperatures of different parts of the remnant are all around 0.7 keV, which is
surprisingly constant for a remnant with such rich structure. If thermal
conduction is responsible for smoothing the temperature gradient, a lower limit
on the thermal conductivity of 1/10 of the Spitzer value can be derived.
Thus, thermal conduction may play an important role in the evolution of at
least some SNRs. No spectral signature of the ejecta is found, which suggests
the ejecta material has been well mixed with the ambient medium. From the
morphology and the spectral properties, we suggest the bright inner shell is a
wind-driven shell (WDS) overtaken by the blast wave (the outer shell) and
estimate the age of the remnant to be 6 kyr for the assumed dynamics.
Projection is also required to explain the complicated morphology of Kes 79.Comment: 12 pages, 6 figures (3 in color), ApJ, in press, April 20, 200
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