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|X-Ray Spectroscopy of PSR B1951+32 and Its Pulsar Wind Nebula|
We present spatially resolved X-ray spectroscopy of PSR B1951+32 and itspulsar wind nebula (PWN) in supernova remnant (SNR) CTB 80 from aChandra observation. The Chandra X-ray map clearly reveals variouscomponents of a ram-pressure-confined PWN embedded in the SNR ejecta: apoint source representing the pulsar, X-ray emission from the bow shock,a luminous X-ray tail, a 30" diameter plateau whose northwestern part isabsent, and the more diffuse outer X-ray emission. The plateau isclosely surrounded by the radio, [O III], [S II], and [N II] shells, andthe outer diffuse emission is mostly within the Hα shells. Whilethe spectra of all the features are well fitted with power-law models, apower-law plus blackbody model can fit the spectrum of the pulsarsignificantly better than using a power-law model alone. Generally, thespectra of these components obey the trend of steepening from the insideto the outside. However, the edge of the plateau probably has a harderspectrum than the central region of the plateau. The cause of theapparent hard spectrum of the plateau edge is unclear, but we speculatethat it might be due to a shock between the PWN and the SNR ejecta. Thepossible blackbody radiation component from the pulsar has a temperatureof 0.13+/-0.02 keV and an equivalent emitting radius of2.2+1.4-0.8 (d/2 kpc) km, and is thus probablyfrom the hot spots on the pulsar. We also show in this paper that theblackbody temperature of the entire surface of PSR B1951+32 is muchlower than those predicted by the standard neutron star cooling models.
|A search for TeV gamma-ray emission from SNRs, pulsars and unidentified GeV sources in the Galactic plane in the longitude range between -2 deg and 85 deg.|
Using the HEGRA system of imaging atmospheric Cherenkov telescopes, onequarter of the Galactic plane (-2o < l <85o) was surveyed for TeV gamma-ray emission from pointsources and moderately extended sources (φ <= 0.8o).The region covered includes 86 known pulsars (PSR), 63 known supernovaremnants (SNR) and nine GeV sources, representing a significant fractionof the known populations. No evidence for emission of TeV gammaradiation was detected, and upper limits range from 0.15 Crab units upto several Crab units, depending on the observation time and zenithangles covered. The ensemble sums over selected SNR and pulsarsubsamples and over the GeV-sources yield no indication of emission fromthese potential sources. The upper limit for the SNR population is 6.7%of the Crab flux and for the pulsar ensemble is 3.6% of the Crab flux.
|Studies of the ISM in the Vela Supernova Remnant|
Recent observations of the Vela SNR in the ISM species Ca II and Na Iare presented and discussed in the context of the ``break-down'' of theSpitzer-Routly effect. Variations in line profiles with time aredemonstrated, eventually through a statistical approach a description ofcloud structure will be possible. The IS lines in ~ 70 sightlines areused to determine an accurate distance to the Vela SNR of 250 +/- 30 pc.Finally a discussion of future observations are given relatinginformation obtained from measurements of near-by ISM to more distantintergalactic medium.
|Galactic TeV gamma-ray sources|
The observations of galactic TeV objects are summarized with emphasis onthe astrophysical significance of recent positive detections from threepulsar driven nebulae, Crab Nebula, Vela, PSR 1706-44, and a historicalsupernova remnant, SN 1006.
|Accurate Positions for MCG Galaxies|
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
|OH (1720 MHz) Masers as Signposts of Molecular Shocks|
We present observations of molecular gas made with the 15 m James ClarkMaxwell Telescope toward the sites of OH (1720 MHz) masers in threesupernova remnants: W28, W44, and 3C 391. Maps made in the ^12CO J = 3-2line reveal that the OH masers are preferentially located along theedges of thin filaments or clumps of molecular gas. There is a strongcorrelation between the morphology of the molecular gas and therelativistic gas traced by synchrotron emission at centimeterwavelengths. Broad CO line widths (DeltaV = 30-50 km s^-1) are seenalong these gaseous ridges, while narrow lines are seen off the ridges.The ratio of H_2CO line strengths is used to determine temperatures inthe broad-line gas of 80 K, and the ^13CO J = 3-2 column densitysuggests densities of 10^4-10^5 cm^-3. These observations support thehypothesis that the OH (1720 MHz) masers originate in postshock gas,heated by the passage of a supernova remnant shock through densemolecular gas. From the observational constraints on the density,velocity, and magnetic field, we examine the physical properties of theshock and discuss the shock production of OH. These OH (1720 MHz) masersare useful ``signposts'' that point to the most promising locations tostudy supernova remnant/molecular cloud interactions.
|Supernovae and Stellar Wind in the Interstellar Medium|
|Echelle spectroscopy of shocked H_2_ in the L1448 outflow.|
Here we investigate the dynamical properties of the outflow from a Class0 protostar. We have observed H_2_ v=1-0S(1) velocity profiles at eightslit positions in the northern lobe of the outflow driven by L1448-mm(the VLA source L1448C). Complex line profiles are observed throughoutthe region; the peak H_2_ emission is everywhere strongly blue-shifted.The velocities of the line profile peaks also gradually increase alongthe length of the outflow. This we attribute to the bending of the flowtowards the observer. The flow produces numerous bow shocks along itslength (as evidenced by the triangular H_2_ profiles) that areintersperced with a turbulent shear layer (resulting in the moreGaussian profiles). Knot A is a superb example of a bow shock. Itsspatial distribution corresponds to a C-type bow, and this is confirmedby our velocity-position analysis: the profiles are wide anddouble-peaked just behind the bow apex. There is also evidence that allthe H_2_ emission features are produced within an expanding wind of highAlfven speed. Analysis of the main "ridge" of emission suggests thepresence of many small clumps, formed after the wind terminates at anoblique shock. We may therefore be witnessing the shredding anddispersal of the molecular cloud core by the L1448-mm outflow.
|Co/ and HI Associated with the Supernova Remnant G:84.2-0.8?|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..421F&db_key=AST
|Heating and cooling of molecular clouds and their surfaces|
Some of the basic mechanisms of heating molecular clouds and theirsurfaces are reviewed, including cosmic rays, ambipolar diffusion,radiation, and shock waves. Cooling by fine structure transitions ofatoms and ions as well as by vibrational and rotational transitions ofinterstellar molecules is discussed. A theoretical application of theseprocesses is made to the observations of warm CO and vibrationallyexcited H2.
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