706 research outputs found
Discovery of X rays from Class 0 protostar candidates in OMC-3
We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with
the Chandra X-ray Observatory (CXO). The northern part of OMC-3 is found to be
particularly rich in new X-ray features; four hard X-ray sources are located in
and along the filament of cloud cores. Two sources coincide positionally with
the sub- dust condensations of MMS 2 and 3 or an outflow radio source
VLA 1, which are in a very early phase of star formation. The X-ray spectra of
these sources show an absorption column of (1-3) x 10^23 H cm-2. Assuming a
moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is
estimated to be ~10^30 erg s^-1 at a distance of 450 pc. From the large
absorption, positional coincidence and moderate luminosity, we infer that the
hard X-rays are coming from very young stellar objects embedded in the
molecular cloud cores. We found another hard X-ray source near the edge of the
dust filament. The extremely high absorption of 3 x 10^23 H cm^-2 indicates
that the source must be surrounded by dense gas, suggesting that it is either a
YSO in an early accretion phase or a Type II AGN (e.g. a Seyfert 2), although
no counterpart is found at any other wavelength. In contrast to the hard X-ray
sources, soft X-ray sources are found spread around the dust filaments, most of
which are identified with IR sources in the T Tauri phase.Comment: 9 pages, To be appeared in ApJ v554 n2 Jun 20, 2001 issue, related
press release is available at http://science.psu.edu/alert/Tsuboi11-2000.htm,
Figure 1 and figure 2 with the best resolution is available at
ftp.astro.psu.edu/pub/tsuboi/OMC/010205
The distance to the SNR CTB109 deduced from its environment
We conducted a study of the environment around the supernova remnant CTB109.
We found that the SNR is part of a large complex of HII regions extending over
an area of 400 pc along the Galactic plane at a distance of about 3 kpc at the
closer edge of the Perseus spiral arm. At this distance CTB109 has a diameter
of about 24 pc. We demonstrated that including spiral shocks in the distance
estimation is an ultimate requirement to determine reliable distances to
objects located in the Perseus arm. The most likely explanation for the high
concentration of HII regions and SNRs is that the star formation in this part
of the Perseus arm is triggered by the spiral shock.Comment: 6 pages, 6 figures. accepted for publication in the Astrophysical
Journa
Atomic Carbon and CO Isotope Emission in the Vicinity of DR15
We present observations of the 3P1-3P0 fine structure transition of atomic
carbon [CI], the J=3-2 transition of CO, as well as of the J=1-0 transitions of
13CO and C18O toward DR15, an HII region associated with two mid-infrared dark
clouds (IRDCs). The 13CO and C18O J=1-0 emissions closely follow the dark
patches seen in optical wavelength, showing two self-gravitating molecular
cores with masses of 2000 Msun and 900 Msun, respectively, at the positions of
the catalogued IRDCs.
Our data show a rough spatial correlation between [CI] and 13CO J=1-0. Bright
[CI] emission occurs in relatively cold gas behind the molecular cores, neither
in highly excited gas traced by CO J=3-2 emission nor in HII region/molecular
cloud interface. These results are inconsistent with those predicted by
standard photodissociation region (PDR) models, suggesting an origin for
interstellar atomic carbon unrelated to photodissociation processes.Comment: 11 pages Latex, 6 figures, Accepted for publication in The
Astrophysical Journa
XMM-Newton observations of the Galactic Supernova Remnant CTB 109 (G109.1-1.0)
We present the analysis of the X-ray Multi-Mirror Mission (XMM-Newton)
European Photon Imaging Camera (EPIC) data of the Galactic supernova remnant
(SNR) CTB 109 (G109.1-1.0). CTB 109 is associated with the anomalous X-ray
pulsar (AXP) 1E 2259+586 and has an unusual semi-circular morphology in both
the X-ray and the radio, and an extended X-ray bright interior region known as
the `Lobe'. The deep EPIC mosaic image of the remnant shows no emission towards
the west where a giant molecular cloud complex is located. No morphological
connection between the Lobe and the AXP is found. We find remarkably little
spectral variation across the remnant given the large intensity variations. All
spectra of the shell and the Lobe are well fitted by a single-temperature
non-equilibrium ionization model for a collisional plasma with solar abundances
(kT = 0.5 - 0.7 keV, tau = n_e t = 1 - 4 x 10^11 s cm^-3, N_H = 5 - 7 x 10^21
cm^-2). There is no indication of nonthermal emission in the Lobe or the shell.
We conclude that the Lobe originated from an interaction of the SNR shock wave
with an interstellar cloud. Applying the Sedov solution for the undisturbed
eastern part of the SNR, and assuming full equilibration between the electrons
and ions behind the shock front, the SNR shock velocity is derived as v_s = 720
+/- 60 km s^-1, the remnant age as t = (8.8 +/- 0.9) x 10^3 d_3 yr, the initial
energy as E_0 = (7.4 +/- 2.9) x 10^50 d_3^2.5 ergs, and the pre-shock density
of the nuclei in the ambient medium as n_0 = (0.16 +/- 0.02) d_3^-0.5 cm^-3, at
an assumed distance of D = 3.0 d_3 kpc. Assuming CTB 109 and 1E 2259+586 are
associated, these values constrain the age and the environment of the
progenitor of the SNR and the pulsar.Comment: Accepted for publication in ApJ. 9 figures. Figs. 1 + 2 are in color
(fig1.jpg, fig2.jpg
The Most Likely Sources of High Energy Cosmic-Ray Electrons in Supernova Remnants
Evidences of non-thermal X-ray emission and TeV gamma-rays from the supernova
remnants (SNRs) has strengthened the hypothesis that primary Galactic
cosmic-ray electrons are accelerated in SNRs. High energy electrons lose energy
via synchrotron and inverse Compton processes during propagation in the Galaxy.
Due to these radiative losses, TeV electrons liberated from SNRs at distances
larger than ~1 kpc, or times older than ~10^5 yr, cannot reach the solar
system. We investigated the cosmic-ray electron spectrum observed in the solar
system using an analytical method, and considered several candidate sources
among nearby SNRs which may contribute to the high energy electron flux.
Especially, we discuss the effects for the release time from SNRs after the
explosion, as well as the deviation of a source spectrum from a simple
power-law. From this calculation, we found that some nearby sources such as the
Vela, Cygnus Loop, or Monogem could leave unique signatures in the form of
identifiable structure in the energy spectrum of TeV electrons and show
anisotropies towards the sources, depending on when the electrons are liberated
from the remnant. This suggests that, in addition to providing information on
the mechanisms of acceleration and propagation of cosmic-rays, specific
cosmic-ray sources can be identified through the precise electron observation
in the TeV region.Comment: 32 pages, 6 figures, submitted to Ap
Constraints on Thermal Emission Models of Anomalous X-ray Pulsars
Thermal emission from the surface of an ultramagnetic neutron star is
believed to contribute significantly to the soft X-ray flux of the Anomalous
X-ray Pulsars. We compare the detailed predictions of models of the surface
emission from a magnetar to the observed properties of AXPs. In particular, we
focus on the combination of their luminosities and energy-dependent pulsed
fractions. We use the results of recent calculations for strongly magnetized
atmospheres to obtain the angle- and energy-dependence of the surface emission.
We include in our calculations the effects of general relativistic photon
transport and interstellar extinction. We find that the combination of the
large pulsed fractions and the high luminosities of AXPs cannot be accounted
for by surface emission from a magnetar with two antipodal hot regions or a
temperature distribution characteristic of a magnetic dipole. This result is
robust for reasonable neutron star radii, for the range of magnetic field
strengths inferred from the observed spin down rates, and for surface
temperatures consistent with the spectral properties of AXPs. Models with a
single hot emitting region can reproduce the observations, provided that the
distance to one of the sources is ~30% less than the current best estimate, and
allowing for systematic uncertainties in the spectral fit of a second source.
Finally, the thermal emission models with antipodal emission geometry predict a
characteristic strong increase of the pulsed fraction with photon energy, which
is apparently inconsistent with the current data. The energy-dependence of the
pulsed fraction in the models with one hot region shows a wider range of
behavior and can be consistent with the existing data. Upcoming high-resolution
observations with Chandra and XMM-Newton will provide a conclusive test.Comment: 25 preprint pages, 7 color figures, ApJ, in pres
- …