Sgr A East and its surroundings observed in X-rays

We report the results of an XMM-Newton observation of Sgr A East and its surroundings. The X-ray spectrum of Sgr A East is well represented with a two-temperature plasma model with temperatures of ~1 and ~4 keV. Only the iron abundance shows clear spatial variation; it concentrates in the core of Sgr A East. The derived plasma parameters suggest that Sgr A East originated in a single supernova. Around Sgr A East, there is a broad distribution of hard X-ray emission with a superimposed soft excess component extending away from the location of Sgr A East both above and below the plane. We discuss the nature of these structures as well as the close vicinity of Sgr A*.Comment: 7 pages, 3 figures, Accepted for publication in Advances in Space Research, as a proceeding paper for the 34th COSPAR E1.4 "High Energy Studies of Supernova Remnants and Neutron stars" held at Houston, Texas, USA during 10-19 Oct 2002; also found in http://www.star.le.ac.uk/~mas/research/paper/#Sakano2003cos

Interferometric mapping of Magnetic fields: G30.79 FIR 10

We present polarization maps of G30.79 FIR 10 (in W43) from thermal dust emission at 1.3 mm and from CO J=$2 \to 1$ line emission. The observations were obtained using the Berkeley-Illinois-Maryland Association array in the period 2002-2004. The G30.79 FIR 10 region shows an ordered polarization pattern in dust emission, which suggests an hourglass shape for the magnetic field. Only marginal detections for line polarization were made from this region. Application of the Chandrashkar-Fermi method yielded $B_{pos} \approx 1.7$ mG and a statistically corrected mass to magnetic flux ratio $\lambda_{C} \approx 0.9$, or essentially critical.Comment: 11 pages, 2 Figures, Published in Ap

A Model of the EGRET Source at the Galactic Center: Inverse Compton Scattering Within Sgr A East and its Halo

Continuum low-frequency radio observations of the Galactic Center reveal the presence of two prominent radio sources, Sgr A East and its surrounding Halo, containing non-thermal particle distributions with power-law indices around 2.5-3.3 and 2.4, respectively. The central 1-2 pc region is also a source of intense (stellar) UV and (dust-reprocessed) far-IR radiation that bathes these extended synchrotron-emitting structures. A recent detection of gamma-rays (2EGJ1746-2852) from within around 1 degree of the Galactic Center by EGRET onboard the Compton GRO shows that the emission from this environment extends to very high energies. We suggest that inverse Compton scatterings between the power-law electrons inferred from the radio properties of Sgr A East and its Halo, and the UV and IR photons from the nucleus, may account for the possibly diffuse gamma-ray source as well. We show that both particle distributions may be contributing to the gamma-ray emission, though their relevant strength depends on the actual physical properties (such as the magnetic field intensity) in each source. If this picture is correct, the high-energy source at the Galactic Center is extended over several arcminutes, which can be tested with thenext generation of gamma-ray and hard X-ray missions.Comment: latex, 14 pages, 3 figures (accepted for publication in ApJ

Improving the mesomorphic behaviour of supramolecular liquid crystals by resonance-assisted hydrogen bonding

A systematic structure-property relationship study on hydrogen-bonded liquid crystals was performed, revealing the impact of resonance-assisted hydrogen bonds (RAHBs) on the self-assembling behavior of the supramolecular architecture. The creation of a six-membered intramolecular hydrogen-bonded ring acts as a counterpart to the self-organization between hydrogen bond donators and acceptors and determines thus the suprastructure. Variation of the hydrogen-bonding pattern allowed us to significantly improve the temperature range of the reported liquid crystalline assemblies

High-resolution Observations of OH(1720 MHz) Masers Toward the Galactic Center

High-resolution VLA observations of 1720 MHz OH maser emission from Sgr A East and the circumnuclear disk with spatial and spectral resolutions of $\approx$ 2\dasec5 $\times$ 1\dasec3 and 0.27 \kms are reported. This follow-up observational study focuses on the recent discovery of a number of such OH maser features and their intense circularly polarized maser lines detected toward these Galactic center sources. The 1720 MHz maser line of OH arises from collisionally excited gas behind a C-type shock and is an important diagnostic of the interaction process that may occur between molecular clouds and associated X-ray emitting shell-type supernova remnants. The present observations have confirmed that the observed Stokes $V$ signal is due to Zeeman splitting and that the OH masers are angularly broadened by the scattering medium toward the Galactic center. The scale length of the magnetic field fluctuations in the scattering medium toward the Galactic center is estimated to be greater than 0.1-0.2 pc using the correlation of the position angles of the scatter-broadened maser spots. In addition, the kinematics of the maser spots associated with Sgr A East are used to place a 5 pc displacement between this extended radio structure and the Galactic center.Comment: 13 pages, 2 Tables and 2 figures, to be published in Ap

Interferometric Mapping of Magnetic fields: NGC2071IR

We present polarization maps of NGC2071IR from thermal dust emission at 1.3 mm and from CO J=$2 \to 1$ line emission. The observations were obtained using the Berkeley-Illinois-Maryland Association array in the period 2002-2004. We detected dust and line polarized emission from NGC2071IR that we used to constrain the morphology of the magnetic field. From CO J=$2 \to 1$ polarized emission we found evidence for a magnetic field in the powerful bipolar outflow present in this region. We calculated a visual extinction $A_{\rm{v}} \approx 26$ mag from our dust observations. This result, when compared with early single dish work, seems to show that dust grains emit polarized radiation efficiently at higher densities than previously thought. Mechanical alignment by the outflow is proposed to explain the polarization pattern observed in NGC2071IR, which is consistent with the observed flattening in this source.Comment: 17 pages, 4 Figures, Accepted for publication in Ap

The Escape of Ionizing Photons from OB Associations in Disk Galaxies: Radiation Transfer Through Superbubbles

By solving the time-dependent radiation transfer problem of stellar radiation through evolving superbubbles within a smoothly varying HI distribution, we estimate the fraction of ionizing photons emitted by OB associations that escapes the HI disk of our Galaxy into the halo and intergalactic medium (IGM). We consider both coeval star-formation and a Gaussian star-formation history with a time spread sigma_t = 2 Myr. We consider both a uniform H I distribution and a two-phase (cloud/intercloud) model, with a negligible filling factor of hot gas. We find that the shells of the expanding superbubbles quickly trap or attenuate the ionizing flux, so that most of the escaping radiation escapes shortly after the formation of the superbubble. For the coeval star-formation history, the total fraction of Lyman Continuum photons that escape both sides of the disk in the solar vicinity is f_esc approx 0.15 +/- 0.05. For the Gaussian star formation history, f_esc approx 0.06 +/- 0.03, a value roughly a factor of two lower than the results of Dove & Shull (1994), where superbubbles were not considered. For a local production rate of ionizing photons Psi_LyC = 4.95 X 10^7 cm^{-2} s^{-1}, the flux escaping the disk is Phi_LyC approx (1.5-3.0) X 10^6 cm^{-2} s^{-1} for coeval and Gaussian star formation, comparable to the flux required to sustain the Reynolds layer.Comment: Revised version (expanded), accepted for publication by ApJ, 38 pages, 8 figures, aasms4.sty and aabib.sty files include

Probing the Density in the Galactic Center Region: Wind-Blown Bubbles and High-Energy Proton Constraints

Recent observations of the Galactic center in high-energy gamma-rays (above 0.1TeV) have opened up new ways to study this region, from understanding the emission source of these high-energy photons to constraining the environment in which they are formed. We present a revised theoretical density model of the inner 5pc surrounding Sgr A* based on the fact that the underlying structure of this region is dominated by the winds from the Wolf-Rayet stars orbiting Sgr A*. An ideal probe and application of this density structure is this high energy gamma-ray emission. We assume a proton-scattering model for the production of these gamma-rays and then determine first whether such a model is consistent with the observations and second whether we can use these observations to further constrain the density distribution in the Galactic center.Comment: 36 pages including 17 figures, submitted to ApJ, comments welcom

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"

The Distance to the Soft Gamma Repeater SGR 1627-41

We report millimeter observations of the line of sight to the recently discovered Soft Gamma Repeater, SGR 1627-41, which has been tentatively associated with the supernova remnant SNR G337.0-0.1 Among the eight molecular clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is probably interacting with one of the most massive giant molecular clouds (GMC) in the Galaxy, at a distance of 11 kpc from the sun. Based on the high extinction to the persistent X-ray counterpart of SGR 1627-41, we present evidence for an association of this new SGR with the SNR G337.0-0.1; they both appear to be located on the near side of the GMC. This is the second SGR located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a neutron star with a high transverse velocity (~ 1,000 \kms) escaping the young (~ 5,000 years) supernova remnant G337.0-0.1Comment: 17 pages, including 2 figures. Accepted for publication in the Astrophysical Journal Letter