The Evolution of Hydrocarbons in Saturn's Northern Storm Region

The massive storm at 40N on Saturn that began in December 2010 has produced significant and lasting effects in the northern hemisphere on temperature and species abundances (Fletcher et aL 2011). The northern storm region was observed on several occasions between March 2011 and April 2012 by Cassini's Composite Infrared Spectrometer (CIRS) at a spectral resolution (0.5/cm) which permits the study of trace species in Saturn's stratosphere. During this time period, stratospheric temperatures in regions referred to as "beacons" (warm regions at specific longitudes at the latitude of the storm) became significantly warmer than pre-storm values of 140K, peaking near 220K, and subsequently cooling. These warm temperatures led to greatly enhanced infrared emission due to C4H2, C3H4, C2H2, and C2H6 in the stratosphere as well as the first detection of C2H4 on Saturn in the thermal infrared (Hesman et al. 2012). Using CH4 as a thermometer of Saturn's stratosphere in the beacon regions, we can derive the mixing ratios of each of these molecules. The most common hydrocarbons (C2H2 and C2H6) serve as dynamical tracers on Saturn and their abundances may constrain vertical motion in the stratosphere. All of these hydrocarbons are products of methane photolysis. Since many of the photochemical reactions that produce heavier hydrocarbons such as C4H2 and C3H4 are temperature sensitive, the beacon region provides a natural laboratory for studying these reactions on Saturn. We will discuss the time evolution of the abundances of each of these hydrocarbons from their pre-storm values, through the period of maximum heating , and during the period of cooling that is taking place in Saturn's stratosphere

Thermal detection of single e-h pairs in a biased silicon crystal detector

We demonstrate that individual electron-hole pairs are resolved in a 1 cm$^2$ by 4 mm thick silicon crystal (0.93 g) operated at $\sim$35 mK. One side of the detector is patterned with two quasiparticle-trap-assisted electro-thermal-feedback transition edge sensor (QET) arrays held near ground potential. The other side contains a bias grid with 20\% coverage. Bias potentials up to $\pm$ 160 V were used in the work reported here. A fiber optic provides 650~nm (1.9 eV) photons that each produce an electron-hole ($e^{-} h^{+}$) pair in the crystal near the grid. The energy of the drifting charges is measured with a phonon sensor noise $\sigma$ $\sim$0.09 $e^{-} h^{+}$ pair. The observed charge quantization is nearly identical for $h^+$'s or $e^-$'s transported across the crystal.Comment: 4 journal pages, 5 figure

A Compact Supermassive Binary Black Hole System

We report on the discovery of a supermassive binary black hole system in the radio galaxy 0402+379, with a projected separation between the two black holes of just 7.3 pc. This is the closest black hole pair yet found by more than two orders of magnitude. These results are based upon recent multi-frequency observations using the Very Long Baseline Array (VLBA) which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of 0402+379. Multi-epoch observations from the VLBA also provide constraints on the total mass and dynamics of the system. Low spectral resolution spectroscopy using the Hobby-Eberly Telescope indicates two velocity systems with a combined mass of the two black holes of ~1.5 x 10^8 solar masses. The two nuclei appear stationary while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of close binary black holes that might be sources of gravitational radiation. Green Bank Telescope observations at 22 GHz to search for water masers in this interesting system are also presented.Comment: 34 pages, 7 figures, Accepted to The Astrophysical Journa

An antigen-independent contact mechanism as an early step in T cell-proliferative responses to dendritic cells.

The administration ofan antigen to the immune system can lead to the selection and expansion of clones precommitted to respond to that antigen. Antigens are not presented directly to T lymphocytes. Instead, antigens are processed and complexed to transmembrane products of genes in the MHC. The antigen-MHC complexes then are presented on the surface of APC (1-4). How might antigen-MHC complexes on the surface ofAPC find and select clones of T cells that are specific to that antigen, since neither the ligand nor the TCR are free to diffuse in solution? Also, the amount of peptide/MHC complex and the frequency of antigen-specificTcell clones both may be small. Nonetheless, it is evident that antigens on dendritic cells are capable of selecting specificTlymphocytes from a pool of lymphocytes in culture. For example, on the first day of a primary MLR, most of the antigen-specific T cells have formed clusters with dendritic cells (5, 6). The clustered lymphocytes then proliferate and release lymphokines. The specificity of the dendriticT cell binding is evident by the facts that (a) the nonclustered population is selectively depleted of antigen-reactive T cells; and (b) th

EVOLUTION OF THE STRATOSPHERIC TEMPERATURE AND CHEMICAL COMPOSITION OVER ONE TITANIAN YEAR

Since the Voyager 1 (V1) flyby in 1980, Titans exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titan year or 29.5 Earth years was completed in May 2010). In this study we search for temporal variations affecting Titans atmospheric thermal and chemical structure within that year. We process Cassini CIRS data taken during the Titan flybys from 2006-2013 and compare them to the 1980 V1IRIS spectra (re-analyzed here). We also consider data from Earth-based and -orbiting observatories (such as from the ISO, re-visited). When we compare the CIRS 2010 and the IRIS data we find limited inter-annual variations, below the 25 or35 levels for the lower and middle, or the high latitudes, respectively. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50degN to 50degS, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by GCM and photochemical models. However, some exceptions exist among the most complex hydrocarbons (C4H2 and C3H4), especially in the North. In the Southern latitudes, since 2012, we see a trend for an increase of several trace gases, possibly indicative of a seasonal atmospheric reversal. At the Northern latitudes we found enhanced abundances around the period of the northern spring equinox in mid-2009 (as in Bampasidis et al. 2012), which subsequently decreased (from 2010-2012) returning to values similar to those found in the V1 epoch a Titanian year before

Intrinsic Size OF Sgr A*: 72 Schwarzschild Radii

Recent proper motion studies of stars at the very center of the Galaxy strongly suggest that Sagittarius (Sgr) A*, the compact nonthermal radio source at the Galactic Center, is a 2.5 million solar mass black hole. By means of near-simultaneous multi-wavelength Very Long Baseline Array measurements, we determine for the first time the intrinsic size and shape of Sgr A* to be 72 Rsc by < 20 Rsc, with the major axis oriented essentially north-south, where Rsc (= 7.5 x 10^{11} cm) is the Schwarzschild radius for a 2.5 million solar mass black hole. Contrary to previous expectation that the intrinsic structure of Sgr A* is observable only at wavelengths shorter than 1 mm, we can discern the intrinsic source size at 7 mm because (1) the scattering size along the minor axis is half that along the major axis, and (2) the near simultaneous multi-wavelength mapping of Sgr A* with the same interferometer makes it possible to extrapolate precisely the minor axis scattering angle at 7 mm. The intrinsic size and shape place direct constraints on the various emission models for Sgr A*. In particular, the advection dominated accretion flow model may have to incorporate a radio jet in order to account for the structure of Sgr A*.Comment: 15 pages including 2 ps figures and 1 table, to appear in ApJ Letter

PSR J2030+3641: radio discovery and gamma-ray study of a middle-aged pulsar in the now identified Fermi-LAT source 1FGL J2030.0+3641

In a radio search with the Green Bank Telescope of three unidentified low Galactic latitude Fermi-LAT sources, we have discovered the middle-aged pulsar J2030+3641, associated with 1FGL J2030.0+3641 (2FGL J2030.0+3640). Following the detection of gamma-ray pulsations using a radio ephemeris, we have obtained a phase-coherent timing solution based on gamma-ray and radio pulse arrival times that spans the entire Fermi mission. With a rotation period of 0.2 s, spin-down luminosity of 3e34 erg/s, and characteristic age of 0.5 Myr, PSR J2030+3641 is a middle-aged neutron star with spin parameters similar to those of the exceedingly gamma-ray-bright and radio-undetected Geminga. Its gamma-ray flux is 1% that of Geminga, primarily because of its much larger distance, as suggested by the large integrated column density of free electrons, DM=246 pc/cc. We fit the gamma-ray light curve, along with limited radio polarimetric constraints, to four geometrical models of magnetospheric emission, and while none of the fits have high significance some are encouraging and suggest that further refinements of these models may be worthwhile. We argue that not many more non-millisecond radio pulsars may be detected along the Galactic plane that are responsible for LAT sources, but that modified methods to search for gamma-ray pulsations should be productive -- PSR J2030+3641 would have been found blindly in gamma rays if only >0.8 GeV photons had been considered, owing to its relatively flat spectrum and location in a region of high soft background.Comment: Accepted for publication in ApJ, 9 pages, 6 figure

PSRs J0248+6021 and J2240+5832: Young Pulsars in the Northern Galactic Plane. Discovery, Timing, and Gamma-ray observations

Pulsars PSR J0248+6021 (rotation period P=217 ms and spin-down power Edot = 2.13E35 erg/s) and PSR J2240+5832 (P=140 ms, Edot = 2.12E35 erg/s) were discovered in 1997 with the Nancay radio telescope during a northern Galactic plane survey, using the Navy-Berkeley Pulsar Processor (NBPP) filter bank. GeV gamma-ray pulsations from both were discovered using the Fermi Large Area Telescope. Twelve years of radio and polarization data allow detailed investigations. The two pulsars resemble each other both in radio and in gamma-ray data. Both are rare in having a single gamma-ray pulse offset far from the radio peak. The high dispersion measure for PSR J0248+6021 (DM = 370 pc cm^-3) is most likely due to its being within the dense, giant HII region W5 in the Perseus arm at a distance of 2 kpc, not beyond the edge of the Galaxy as obtained from models of average electron distributions. Its high transverse velocity and the low magnetic field along the line-of-sight favor this small distance. Neither gamma-ray, X-ray, nor optical data yield evidence for a pulsar wind nebula surrounding PSR J0248+6021. The gamma-ray luminosity for PSR J0248+6021 is L_ gamma = (1.4 \pm 0.3)\times 10^34 erg/s. For PSR J2240+5832, we find either L_gamma = (7.9 \pm 5.2) \times 10^34 erg/s if the pulsar is in the Outer arm, or L_gamma = (2.2 \pm 1.7) \times 10^34 erg/s for the Perseus arm. These luminosities are consistent with an L_gamma ~ sqrt(Edot) rule. Comparison of the gamma-ray pulse profiles with model predictions, including the constraints obtained from radio polarization data, favor emission in the far magnetosphere. These two pulsars differ mainly in their inclination angles and acceleration gap widths, which in turn explains the observed differences in the gamma-ray peak widths.Comment: 13 pages, Accepted to Astronomy & Astrophysic

Magnetized Iron Atmospheres for Neutron Stars

Using a Hartree-Fock formalism, we estimate energy levels and photon cross sections for atomic iron in magnetic fields B ~ 10^13 G. Computing ionization equilibrium and normal mode opacities with these data, we construct LTE neutron star model atmospheres at 5.5 < Log(T_eff) < 6.5 and compute emergent spectra. We examine the dependence of the emergent spectra on T_eff and B. We also show the spectral variation with the angle between the magnetic field and the atmosphere normal and describe the significant limb darkening in the X-ray band. These results are compared with recent detailed computations of neutron star H model atmospheres in high fields and with low field Fe and H model atmospheres constructed from detailed opacities. The large spectral differences for different surface compositions may be discernible with present X-ray data; we also note improvements needed to allow comparison of Fe models with high quality spectra.Comment: 18 pages with 5 eps figures, accepted for publication in ApJ Replaced due to clerical error only: one more author, no new conten