A Monte Carlo Study of the 6.4 keV Emission at the Galactic Center

Strong fluorescent Fe line emission at 6.4 keV has been observed from the Sgr B2 giant molecular cloud located in the Galactic Center region. The large equivalent width of this line and the lack of an apparent illuminating nearby object indicate that a time-dependent source, currently in a low-activity state, is causing the fluorescent emission. It has been suggested that this illuminator is the massive black hole candidate, Sgr A*, whose X-ray luminosity has declined by an unprecedented six orders of magnitude over the past 300 years. We here report the results of our Monte Carlo simulations for producing this line under a variety of source configurations and characteristics. These indicate that the source may in fact be embedded within Sgr B2, although external sources give a slightly better fit to the data. The weakened distinction between the internal and external illuminators is due in part to the instrument response function, which accounts for an enhanced equivalent width of the line by folding some of the continuum radiation in with the intrinsic line intensity. We also point out that although the spectrum may be largely produced by K$\alpha$ emission in cold gas, there is some evidence in the data to suggest the presence of warm (~10^5 K) emitting material near the cold cloud.Comment: 11 pages, 4 figure

Discovery of A New Faint Radio SNR G108.2-0.6

A new faint and large shell-type radio Supernova Remnant (SNR) G108.2-0.6 has been discovered in the Canadian Galactic Plane Survey (CGPS). The SNR shows an elliptical shell-type structure at 1420 MHz, and has a 408-1420 MHz TT-plot spectral index of $\alpha$=-0.5$\pm$0.1 (S$_{\nu}$$\propto$$\nu$$^{\alpha}$), typical of a shell-type SNR. The remnant's flux density at 1420 MHz is 6.6$\pm$0.7 Jy, and at 408 MHz is 11.5$\pm$1.2 Jy. Both of these are corrected for compact sources. An integrated spectral index of $-0.45\pm$0.13 is determined. This new SNR has among the lowest surface brightness of any known remnant ($\Sigma$$_{1 GHz}$=2.4$\times10^{-22}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$). 21 cm Stokes Q and U CGPS data (plus preliminary Effelsberg Q and U maps) show some suggestive features that correlate with total power. \ion{H}{i} observations show structures associated with G108.2$-$0.6 in the radial velocity range $-$53 to $-$58 km s$^{-1}$, and indicate it is located in the Perseus arm shock at a distance of 3.2$\pm$0.6 kpc. At this distance the diameter of G108.2$-$0.6 is 58 pc. IRAS maps (12, 25, 60 and 100\mu m) of the new SNR show rich infrared emission surrounding G108.2$-$0.6.Comment: 10 pages, 6 figs, accepted by A&

The Distance and Age of the SNR Kes 73 and AXP 1E 1841-045

We provide a new distance estimate to the supernova remnant (SNR) Kes 73 and its associated anomalous X-ray pulsar (AXP) 1E 1841-045. 21 cm HI images and HI absorption/ emission spectra from new VLA observations, and 13CO emission spectra of Kes 73 and two adjacent compact HII regions (G27.276+0.148 and G27.491+0.189) are analyzed. The HI images show prominent absorption features associated with Kes 73 and the HII regions. The absorption appears up to the tangent point velocity giving a lower distance limit to Kes 73 of 7.5 kpc, which has previously been given as the upper limit. Also, G27.276+0.148 and G27.491+0.189 are at the far kinematic distances of their radio recombination line velocities. There is prominent HI emission in the range 80--90 km/s for all three objects. The two HII regions show HI absorption at ~ 84 km/s, but there is no absorption in the Kes 73 absorption spectrum. This implies an upper distance limit of ~ 9.8 kpc to Kes 73. This corrected larger distance to Kes 73/ AXP 1E 1841-045 system leads to a refined age of the SNR of 500 to 1000 yr, and a ~ 50% larger AXP X-ray luminosity.Comment: 10 pages, 2 figures, ApJ, dol:10.1086/"529120

A summary of research relating to first grade reading, 1932-1963

Thesis (Ed.M.)--Boston UniversityProblem: An attempt to compare the rate of learning of colorful and abstract words of children in grade one. Materials: 1. Thirty words were selected to be used in three groups of ten words each. Each list consisted of five colorful and five abstract words. Colorful words are those which have much meaning for children and abstract words are those with little meaning. The words were printed on 3 x 11 inch flash cards in lower case letters. 2. Check sheets were made with spaces for checking the retention of words at three different times and pictures were made to enrich the colorful words. 3. Directions were prepared and given to each teacher who participated in the study. 4. Kuhlmann-Anderson Intelligence Test: Battery A. 5. Detroit Word Recognition Test: Form A [TRUNCATED

Enhanced abundances in three large-diameter mixed-morphology supernova remnants

We present an X-ray study of three mixed-morphology supernova remnants (SNRs), HB 21, CTB 1 and HB 3, using archival ASCA and ROSAT data. These data are complemented by archival Chandra X-ray Observatory data for CTB 1 and XMM-Newton X-ray Observatory data for HB 3. The spectra from HB 21 and HB 3 are well-described with a single-temperature thermal plasma in ionization equilibrium, while a two-temperature thermal plasma is found in CTB 1. We found enhanced abundances in all three SNRs. The elemental abundance of Mg is clearly enhanced in CTB 1, while HB 21 has enhanced abundances of Si and S. The situation is not so clear in HB 3 -- the plasma in this SNR either has significantly enhanced abundances of O, Ne and Mg, or it has marginally enhanced abundances of Mg and under-abundant Fe. We discuss the plausibility of mixed-morphology SNR models for the three SNRs and the presence of enhanced abundances. We revise a list of MM SNRs and their properties, compare the three SNRs studied here with other members of this class, and discuss the presence of enhanced elemental abundances in MM SNRs. We also report the ASCA detection of a compact source in the southern part of HB 3. The source spectrum is consistent with a power law with a photon index of ~2.7, and an unabsorbed X-ray flux of ~10^{-12} erg/cm^2/s in the 0.5--10.0 keV band. The column density towards this source differs from that towards the SNR, and it is therefore unlikely they are related.Comment: 26 pages, 15 figures, revised version (minor changes), accepted for publication in ApJ (10 Aug 2006

The Distances of SNR W41 and overlapping HII regions

New HI images from the VLA Galactic Plane Survey show prominent absorption features associated with the supernovae remnant G23.3-0.3 (SNR W41). We highlight the HI absorption spectra and the $^{13}$CO emission spectra of eight small regions on the face of W41, including four HII regions, three non-thermal emission regions and one unclassified region. The maximum velocity of absorption for W41 is 78$\pm$2 km/s and the CO cloud at radial velocity 95$\pm$5 km/s is behind W41. Because an extended TeV source, a diffuse X-ray enhancement and a large molecular cloud at radial velocity 77$\pm$5 km/s are also projected at the center of W41, these yield the kinematic distance of 3.9 to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21 and G23.07+0.25 are at the far kinematic distances ($\sim$9.9 kpc and $\sim$ 10.6 kpc respectively) of their recombination-line velocities (103$\pm$0.5 km/s and 89.6$\pm$2.1 km/s respectively), G23.07-0.37 is at the near kinematic distance (4.4$\pm$0.3 kpc) of its recombination-line velocity (82.7$\pm$2.0 km/s), and G23.27-0.27 is probably at the near kinematic distance (4.1$\pm$0.3 kpc) of its recombination-line velocity (76.1$\pm$0.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A

Correlated radial velocity and X-ray variations in HD 154791/4U 1700+24

We present evidence for approximately 400-d variations in the radial velocity of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The variations are correlated with the previously reported approximately 400 d variations in the X-ray flux of 4U 1700+24, which supports the association of these two objects, as well as the identification of this system as the second known X-ray binary in which a neutron star accretes from the wind of a red giant. The HD 154791 radial velocity variations can be fit with an eccentric orbit with period 404 +/- 3 d, amplitude K=0.75 +/- 0.12 km/s and eccentricity e=0.26 +/- 0.15. There are also indications of variations on longer time scales >~ 2000 d. We have re-examined all available ASM data following an unusually large X-ray outburst in 1997-98, and confirm that the 1-d averaged 2-10 keV X-ray flux from 4U 1700+24 is modulated with a period of 400 +/- 20 d. The mean profile of the persistent X-ray variations was approximately sinusoidal, with an amplitude of 0.108 +/- 0.012 ASM count/s (corresponding to 31% rms). The epoch of X-ray maximum was approximately 40 d after the time of periastron according to the eccentric orbital fit. If the 400 d oscillations from HD 154791/4U 1700+24 are due to orbital motion, then the system parameters are probably close to those of the only other neutron-star symbiotic-like binary, GX 1+4. We discuss the similarities and differences between these two systems.Comment: 6 pages, 2 figures; accepted by Ap