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[en] Observations of HZ Her/Her X-1 by the Rossi X-ray Timing Explorer during High State X-ray eclipses are analyzed. After a sharp ingress caused by the neutron star receding behind the companion star HZ Her, X-ray flux smoothly declines to a minimum at mid-eclipse. It then increases smoothly until egress. The mid-eclipse flux implies an extended emission region around the neutron star that is larger than that of HZ Her. The constancy of the X-ray softness ratio is consistent with electron scattering by an ionized corona. The corona is modeled as spherically symmetric with a power-law density profile. We find a best fit of ∝r –1.25 with a normalization of ≅ 1012 cm–3 at r = 2 × 1010 cm. The corona could either be in hydrostatic equilibrium, with heating by Compton scattering, a fast outflow, with a high mass-loss rate of ∼1018 gm s–1, or a hybrid, with an inner hydrostatic region and outer slow flow with a low mass-loss rate. A brightening at orbital phase 0.94 is suggested to be caused by the impact of the accretion stream with the accretion disk
[en] An all-sky survey in the hard x-ray band (3-40 keV) at significantly higher sensitivity than the HEAO A-1 survey would be valuable in finding new sources in a number of categories, both galactic and extragalactic, for more detailed studies. A silicon-strip coded-mask imager for X-rays in this energy band has been proposed, by a team headed by the author, to carry out such an all-sky survey. Recently, the Canadian Space Agency has approved a concept study to carry out a preliminary design of this instrument
[en] Published X-ray emission properties for a sample of 50 supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) are used as input for SNR evolution modeling calculations. The forward shock emission is modeled to obtain the initial explosion energy, age, and circumstellar medium density for each SNR in the sample. The resulting age distribution yields a SNR birthrate of 1/(500 yr) for the LMC. The explosion energy distribution is well fit by a log-normal distribution, with a most-probable explosion energy of erg, with a 1σ dispersion by a factor of 3 in energy. The circumstellar medium density distribution is broader than the explosion energy distribution, with a most-probable density of ∼0.1 cm−3. The shape of the density distribution can be fit with a log-normal distribution, with incompleteness at high density caused by the shorter evolution times of SNRs.
[en] In this paper, we analyze 1420 MHz continuum and H i observations of the supernova remnant (SNR) 3C 397 (G41.1-0.3). The H i absorption spectra show clear absorption up to the tangent point velocity and also the absence of absorption at 50–60 km s"−"1. This yields lower and upper limits to the distances of 6.3 ± 0.1 and 9.7 ± 0.3 kpc, which are better and more robust than previous estimates. We apply generalized SNR models to 3C 397, including the ejecta-dominated phase and the transition-to-Sedov phase. Using emission measures from the X-ray and mean gas density from the infrared, we show that the hard X-ray component has the dominant filling factor and the soft X-ray component has a very small filling factor. The models are required to be consistent with 3C 397's measured properties, including the observed shock temperatures and shock radii. Consistent models are found if 3C 397 has a distance in the range of ≃8–9.7 kpc. For an 8 kpc distance, the estimated age is ≃1350 years and the explosion energy is 1.0 × 10"5"1 erg, while for 9.7 kpc, the the most probable age is ≃1750 years and the energy 1.5 × 10"5"1 erg
[en] Observations of HZ Her/Her X-1 by the Rossi X-Ray Timing Explorer (RXTE) covering high state eclipses of the neutron star are analyzed here. Models of the eclipse are used to measure the radius and atmospheric scale height of HZ Her, the stellar companion to the neutron star. The radius is 2.58-3.01 × 1011 cm, depending on system inclination and mass ratio (q), with an accuracy of ∼1 part in 1000 for given inclination and q. We fit Kurucz model stellar atmosphere models to archival optical observations. The resulting effective temperature (T eff) of the unheated face of HZ Her is determined to be in the 2σ range of 7720 K-7865 K, and metallicity (log (Z/Z ☉)) in the range of –0.27 to +.03. The model atmosphere surface flux and new radius yield a new distance to HZ Her/Her X-1, depending on system inclination and q: a best-fit value of 6.1 kpc with upper and lower limits of 5.7 kpc and 7.0 kpc. We calculate stellar evolution models for the range of allowed masses (from orbital parameters) and allowed metallicities (from optical spectrum fits). The stellar models agree with T eff and the radius of HZ Her for two narrow ranges of mass: 2.15-2.20 M ☉ and 2.35-2.45 M ☉. This lower mass range implies a low neutron star mass (1.3 M ☉), whereas the higher mass range implies a high neutron star mass (1.5-1.7 M ☉).
[en] New distances to the supernova remnants (SNRs) G31.9+0.0 and G54.4−0.3 have been found. The analysis method uses H i absorption spectra and CO channel maps. Individual H i channel maps are used to verify absorption features in the H i absorption spectrum or to determine if they have noise. Both of the SNRs are associated with molecular clouds so accurate kinematic velocities are determined. The H iabsorption is used to resolve the kinematic distance ambiguity. The resulting new distance for G31.9+0.0 is 7.1 ± 0.4 kpc and for G54.4−0.3 it is 6.6 ± 0.6 kpc. These are significant revisions to the previous values.
[en] Analysis of the light curve of Hercules X-1 using the full set of archival observations of Hercules X-1 by the Rossi X-Ray Timing Explorer/Proportional Counter Array (RXTE/PCA) is reported. The observations cover time periods that Her X-1 is in main high, short high, and low states, and an anomalous low state (ALS). They include over 1.4 Ms of net exposure time. We present 35 day and orbital phase folded light curves of the count rates and softness ratios, showing the range of behaviors of Her X-1 with the high sensitivity of the RXTE/PCA. New phenomena are uncovered and previous phenomena are seen in greater detail. For both main high and short high states, the fraction of time in dips is found to be a function of orbital phase and of 35 day phase. It increases steadily with orbital phase past orbital phase 0.3 and is higher at the start and end of both main high and short high states. It is higher for short high state (62%) than for main high state (28%). The normal low state data and ALS data are compared: the low state count rate is ∼twice as high as for ALS data. The 2-4 keV to 9-20 keV softness ratio changes smoothly with orbital phase for low states and ALSs, and is indistinguishable between the two, yet very different than for the high states. This supports models for which the cause of the ALS is changed disk geometry that prevents a direct line of sight from neutron star to observer at all 35 day phases.
[en] We analyze the H I absorption profile for TeV supernova remnant (SNR) G349.7+0.2 based on updated knowledge of the inner Galaxy's structure. We significantly revise its kinematic distance from the previous ∼22 kpc to ∼11.5 kpc, indicating it is in the far 3 kpc arm of the Galactic center. We give a revised age of ∼1800 yr for G349.7+0.2 which has a low explosion energy of ∼2.5 × 1050 erg. This removes G349.7+0.2 from the set of brightest SNRs in radio and X-ray to γ-ray wavebands and helps us to better understand γ-ray emission originating from this remnant. However, one needs to use caution when discussing old kinematic distances of Galactic objects (e.g., SNRs, pulsars, and H II regions) in the range of –12° ≤ l ≤ 12° with distance estimates of ≥5.5 kpc
[en] The recently detected TeV γ-ray source HESS J1923+141 coincides with supernova remnant (SNR) W51C and the star-forming region W51B of the W51 complex. We construct H I absorption spectra of SNR W51C, H II regions G49.2–0.35 and G49.1–0.38 in W51B, and a nearby compact extragalactic source. Our study detects high-velocity (HV) H I clouds (above 83 km s–1) that coincide with W51B, but finds that the clouds are behind W51B. Both W51C and G49.2–0.35 have similar highest velocity absorption features at ∼70 km s–1. The H II region G49.1–0.38 is behind the SNR because its H I absorption spectrum has a feature at 83 km s–1. These new results argue against previous claims that the SNR has shocked the HV H I clouds. Therefore, the TeV emission from the complex should not be associated with the HV H I clouds. W51C has a distance of about 4.3 kpc, smaller than the tangent point distance of 5.5 kpc in that direction, but still in the Sagittarius spiral arm.
[en] The historical supernova remnant (SNR) Tycho SN 1572 originates from the explosion of a normal Type Ia supernova that is believed to have originated from a carbon-oxygen white dwarf in a binary system. We analyze the 21 cm continuum, H I, and 12CO-line data from the Canadian Galactic Plane Survey in the direction of SN 1572 and the surrounding region. We construct H I absorption spectra to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no molecular cloud interaction, which argues against previous claims that a molecular cloud is interacting with the SNR. This new result does not support a recent claim that dust, newly detected by AKARI, originates from such an SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5-3.0 kpc based on a nonlinear rotational curve model. Very high energy γ-ray emission from the remnant has been detected by the VERITAS telescope, so our result shows that its origin should not be an SNR-cloud interaction. Both radio and X-ray observations support that SN 1572 is an isolated Type Ia SNR.