415 research outputs found
A hadronic scenario for HESS J1818-154
Aims: G15.4+0.1 is a faint supernova remnant (SNR) that has recently been
associated with the gamma-ray source HESS J1818-154. We investigate a hadronic
scenario for the production of the gamma-ray emission. Methods: Molecular 13CO
(J=1-0) taken from the Galactic Ring Survey (GRS) and neutral hydrogen (HI)
data from the Southern Galactic Plane Survey (SGPS) have been used in
combination with new 1420 MHz radio continuum observations carried out with the
Giant Metrewave Radio Telescope (GMRT). Results: From the new observations and
analysis of archival data we provided for the first time a reliable estimate
for the distance to the SNR G15.4+0.1 and discovered molecular clouds located
at the same distance. On the basis of HI absorption features, we estimate the
distance to G15.4+0.1 in 4.8+/-1.0 kpc. The 13CO observations clearly show a
molecular cloud about 5 arcmin in size with two bright clumps, labeled A and B,
clump A positionally associated with the location of HESS J1818-154 and clump B
in coincidence with the brightest northern border of the radio SNR shell. The
HI absorption and the 13CO emission study indicates a possible interaction
between the molecular material and the remnant. We estimate the masses and
densities of the molecular gas as (1.2+/-0.5)X10^3 M_sun and (1.5+/-0.4)X10^3
cm^-3 for clump A and (3.0+/-0.7)X10^3 M_sun and (1.1+/-0.3)X10^3 cm^-3 for
clump B. Calculations show that the average density of the molecular clump A is
sufficient to produce the detected gamma-ray flux, thus favoring a hadronic
origin for the high-energy emission.Comment: Accepted to be published in Astronomy and Astrophysics Letter
XMM-Newton observations of the supernova remnant RX J1713.7-3946 and its central source
We present new results from the observations of the supernova remnant (SNR) RX J1713.7–3946 (also G347.3–0.5) performed in five distinct pointings with the EPIC instrument on board the satellite XMM-Newton. RX J1713.7–3946 is a shelltype
SNR dominated by synchrotron radiation in the X-rays. Its emission (emission measure and photon index) as well as the absorption along the line-of-sight has been characterized over the entire SNR. The X-ray mapping of the absorbing column density has revealed strong well-constrained variations (0.4 × 1022 cm−2 ≤ NH ≤ 1.1 × 1022 cm−2) and, particularly, a strong absorption in the southwest. Moreover, there are several clues indicating that the shock front of RX J1713.7–3946 is impacting the clouds responsible for the absorption as revealed for instance by the positive correlation between X-ray absorption and X-ray brightness along the western rims. The CO and H observations show that the inferred cumulative absorbing column densities are in excellent agreement with the X-ray findings in different parts of the remnant on condition that the SNR lies at a distance of 1.3 ± 0.4 kpc, probably in the Sagittarius galactic arm, instead of the commonly-accepted value of 6 kpc. An excess in the CO emission is found in the southwest suggesting that the absorption is due to molecular clouds. A search for OH masers in the southwestern region has been unsuccessful, possibly due to the low density of the clouds. The X-ray mapping of the photon index has also revealed strong variations (1.8 ≤ Γ ≤ 2.6). The spectrum is steep in the faint central regions and
flat at the presumed shock locations, particularly in the southeast. Nevertheless, the regions where the shock impacts molecular clouds have a steeper spectrum than those where the shock propagates into a low density medium. The search for the thermal emission in RX J1713.7–3946 has been unsuccessful leading to a number density upper limit of 2 × 10−2 cm−3 in the ambient medium. This low density corresponds to a reasonable kinetic energy of the explosion provided that the remnant is less than a few thousand years old. A scenario based on a modified ambient medium due to the effect of a progenitor stellar wind is proposed and leads to an estimate of RX J1713.7–3946’s progenitor mass between 12 and 16 M. The X-ray bright central point source 1WGA J1713.4–3949 detected at the center of SNR RX J1713.7–3946 shows spectral properties very similar to those of the Compact Central Objects found in SNRs and consistent in terms of absorption with that of the central diffuse X-ray emission arising from the SNR. It is highly probable that the point source 1WGA J1713.4–3949 is the compact relic of RX J1713.7–3946’s supernova progenitor.Fil: Cassam Chenaï, G.. Centre D; FranciaFil: Decourchelle, A.. Centre D; FranciaFil: Ballet, J.;. Centre D; FranciaFil: Sauvageot, J. L.. Centre D; FranciaFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; Argentin
A molecular shell with star formation toward the supernova remnant G349.7+0.2
A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been
surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO,
using the On-The-Fly technique. The resolution of the observations is 54". We
have found that this remnant is interacting with a small CO cloud which, in
turn, is part of a much larger molecular complex, which we call the ``Large CO
Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of
930,000 solar masses, and a density of 35 cm-3. We investigate the origin of
this structure and suggest that an old supernova explosion ocurred about 4
million years ago, as a suitable hypothesis. Analyzing the interaction between
G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock
front currently driven into the molecular gas is a non-dissociative shock
(C-type), in agreement with the presence of OH 1720 MHz masers. The positional
and kinematical coincidence among one of the CO clouds that constitute the
Large CO Shell, an IRAS point-like source and an ultracompact H II region,
indicate the presence of a recently formed star. We suggest that the formation
of this star was triggered during the expansion of the Large CO Shell, and
suggest the possibility that the same expansion also created the progenitor
star of G349.7+0.2. The Large CO Shell would then be one of the few
observational examples of supernova-induced star formation.Comment: accepted in Astronomical Journal, corrected typo in the abstract (in
first line, 38' instead of 38"
XMM-Newton observation of SNR RX J1713.7-3946
We present the first results of the observations of the supernova remnant RX
J1713.7-3946 (also G347.3-0.5) obtained with the EPIC instrument on board the
XMM-Newton satellite. We show a 5 pointings mosaiced image of the X-ray
synchrotron emission. We characterize this emission by mapping its spectral
parameters (absorbing column density NH and photon index). The synchrotron
spectrum is flat at the shock and steep in the interior of the remnant. NH is
well correlated with the X-ray brightness. A strong NH is found in the
southwest rim of RX J1713.7-3946. We suggest that the SNR is interacting with a
HI region there.Comment: 4 pages, 4 figures, To appear in "Young Neutron Stars and Their
Environments" (IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo
and B. M. Gaensle
The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44
We present radio observations of a region in the vicinity of the young pulsar
PSR B1853+01 in the supernova remnant W44. The pulsar is located at the apex of
an extended feature with cometary morphology. We argue on the basis of its
morphology and its spectral index and polarization properties that this is a
synchrotron nebula produced by the spin down energy of the pulsar. The geometry
and physical parameters of this pulsar-powered nebula and W44 are used to
derive three different measures of the pulsar's transverse velocity. A range of
estimates between 315 and 470 km/s are derived, resulting in a typical value of
375 km/s. The observed synchrotron spectrum from radio to X-ray wavelengths is
used to put constraints on the energetics of the nebula and to derive the
parameters of the pulsar wind.Comment: ApJ Let (in press
A simple model for electron plasma heating in supernova remnants
Context: Multiwavelength observations of supernova remnants can be explained
within the framework of diffusive shock acceleration theory, which allows
effective conversion of the explosion energy into cosmic rays. Although the
models of nonlinear shocks describe reasonably well the nonthermal component of
emission, certain issues, including the heating of the thermal electron plasma
and the related X-ray emission, still remain open.
Methods: Numerical solution of the equations of the Chevalier model for
supernova remnant evolution, coupled with Coulomb scattering heating of the
electrons.
Results: The electron temperature and the X-ray thermal Bremsstrahlung
emission from supernova remnants have been calculated as functions of the
relevant parameters. Since only the Coulomb mechanism was considered for
electron heating, the values obtained for the electron temperatures should be
treated as lower limits. Results from this work can be useful to constrain
model parameters for observed SNRs.Comment: Accepted to A&A as a research not
J16021+3326: New Multi-Frequency Observations of a Complex Source
We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly.Comment: 16 pages, 7 Figures, 2 Tables, accepted to Ap
Advances in the Epidemiological Study of Oral-Facial Diseases
Both demographic patterns and disease distribution are changing rapidly in the United States. These developments have led to the recognition that the epidemiology of many conditions is poorly understood, and that other research has thus been hindered. Four areas of epidemiological study were chosen for detailed analysis of how new technology will affect the conduct of future research. These areas, selected because information about them will be increasingly needed in an aging society, were periodontitis, temporomandibular disorders (TMD) and other orofacial pain, salivary gland disturbances, and health services research. The potential effect of new technology was examined in the short, intermediate, and long term. While the nature of epidemiological study is unlikely to change with the advent of new technology, the scope of potential studies will become broader. Advances in diagnostic techniques from elsewhere will permit far more precise diagnosis than is possible at present. Computer technology will permit an efficient system of epidemiological surveillance to provide current data on trends in tooth loss, caries, and periodontitis—data which will complement the results of national surveys. Analytical studies to produce hypotheses on the etiology of oral conditions, especially in such poorly-understood areas as chronic pain and TMD, will help direct clinical research in those areas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66664/2/10.1177_08959374890030010301.pd
Feasibility Study of Lense-Thirring Precession in LS I +61303
Very recent analysis of the radio spectral index and high energy observations
have shown that the two-peak accretion/ejection microquasar model applies for
LSI+61303. The fast variations of the position angle observed with MERLIN and
confirmed by consecutive VLBA images must therefore be explained in the context
of the microquasar scenario. We calculate what could be the precessional period
for the accretion disk in LSI+61303 under tidal forces of the Be star
(P_{tidal-forces}) or under the effect of frame dragging produced by the
rotation of the compact object (P_{Lense-Thirring}). P_{tidal-forces}R_{tr}r_g$, where the Bardeen-Petterson effect
should align the midplane of the disk. For this truncated radius of the
accretion disk P_{Lense-Thirring} for a slow rotator results in a few days.
Therefore, Lense-Thirring precession induced by a slowly rotating compact
object could be compatible with the daily variations of the ejecta angle
observed in LSI+61303.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
A New Young Galactic Supernova Remnant Containing a Compact Object: G15.9+0.2
We identify the radio-emitting shell-type supernova remnant G15.9+0.2 as a relatively young remnant containing an X-ray point source that may be its associated neutron star. The integrated spectrum of the remnant shell obtained from our 30 ks exploratory Chandra observation shows very strong lines that require elevated element abundances from ejecta, in particular of sulfur. A plane-shock model fit gives a temperature keV, an ionization timescale cm s, and a sulfur abundance of 2.1 (1.7, 2.7) times solar (90% confidence limits). Two-component models with one solar and one enriched component are also plausible, but are not well constrained by the data. Various estimates give a remnant age of order yr, which would make G15.9+0.2 among the dozen or so youngest remnants in the Galaxy. The sparse point source spectrum is consistent with either a steep 4 power law or a 0.4 keV blackbody. The spectrum is absorbed by a H column density cm similar to that required for the remnant shell. The implied 2--9.5 keV source luminosity is about ergs s for an assumed distance of 8.5 kpc consistent with the high absorption column. We suggest that the point source is either a rotation-powered pulsar or a compact central object (CCO)
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