ALBERT

Description: The present paper investigates the temperature structure of the X-ray emitting plasma in the core of the Perseus cluster using the 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) onboard the Hitomi Observatory. A series of four observations were carried out, with a total effective exposure time of 338 ks and covering a central region _ 7 in diameter. The SXS was operated with an energy resolution of _5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions but also transitions from higher principal quantum numbers are clearly resolved from Si through Fe. This enables us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single temperature thermal plasma model in collisional ionization equilibrium, but detailed line ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with increasing atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures can be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single temperature approximation are due to the effects of projection of the known radial temperature gradient in the cluster core along the line of sight. Comparison with the Chandra/ACIS and the XMM-Newton/RGS results on the other hand suggests that additional lower-temperature components

Description: We present a detailed spectral analysis of XMM-Newton and NuSTAR observations of the accreting transient black hole GRS1739278 during a very faint low hard state at 0.02% of the Eddington luminosity (for a distance of 8.5 kpc and a mass of 10 solar mass). The broadband X-ray spectrum between 0.5 and 60 keV can be well-described by a power-law continuum with an exponential cutoff. The continuum is unusually hard for such a low luminosity, with a photon index of =1.39+/-0.04. We find evidence for an additional reflection component from an optically thick accretion disk at the 98% likelihood level. The reflection fraction is low, with R(sub refl) = 0.043(exp + 0.033)(sub - 0.023). In combination with measurements of the spin and inclination parameters made with NuSTAR during a brighter hard state by Miller et al., we seek to constrain the accretion disk geometry. Depending on the assumed emissivity profile of the accretion disk, we find a truncation radius of 15-35 R(sub g) (5-12 R(sub ISCO)) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.

Description: The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, is greater than 8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.

Description: Arcus will be proposed to the NASA Explorer program as a free-flying satellite mission that will enable high-resolution soft X-ray spectroscopy (8-50 Angstroms) with unprecedented sensitivity-effective areas of greater than 500 sq cm and spectral resolution greater than 2500. The Arcus key science goals are (1) to determine how baryons cycle in and out of galaxies by measuring the effects of structure formation imprinted upon the hot gas that is predicted to lie in extended halos around galaxies, groups, and clusters, (2) to determine how black holes influence their surroundings by tracing the propagation of out-flowing mass, energy and momentum from the vicinity of the black hole out to large scales and (3) to understand how accretion forms and evolves stars and circumstellar disks by observing hot infalling and outflowing gas in these systems. Arcus relies upon grazing incidence silicon pore X-ray optics with the same 12m focal length (achieved using an extendable optical bench) that will be used for the ESA Athena mission. The focused X-rays from these optics will then be diffracted by high-efficiency off-plane reflection gratings that have already been demonstrated on sub-orbital rocked flights, imaging the results with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. The majority of mission operations will not be complex, as most observations will be long (~100 ksec), uninterrupted, and pre-planned, although there will be limited capabilities to observe targets of opportunity, such as tidal disruption events or supernovae with a 3-5 day turnaround. After the end of prime science, we plan to allow guest observations to maximize the science return of Arcus to the community.

Description: Current research carried out with the help of the ASEE-NASA Summer Faculty Program, at NASA-Ames, is concentrated on the dynamics of nuclear regions of galaxies. From a dynamical point of view a galaxy is a collection of around 10(sup 11) stars like our Sun, each of which moves in the summed gravitational field of all the remaining stars. Thus galaxy dynamics becomes a self-consistent n-body problem with forces given by Newtonian gravitation. Strong nonlinearity in the gravitational force and the inherent nonlinearity of self-consistent problems both argue for a numerical approach. The technique of numerical experiments consis of constructing an environment in the computer that is as close as possible to the physical conditions in a real galaxy and then carrying out experiments much like laboratory experiments in physics or engineering, in this environment. Computationally, an experiment is an initial value problem, and a good deal of thought and effort goes into the design of the starting conditions that serve as initial values. Experiments are run at Ames because all the 'equipment' is in place-the programs, the necessary computational power, and good facilities for post-run analysis. Our goal for this research program is to study the nuclear regions in detail and this means replacing most of the galaxy by a suitable boundary condition to allow the full capability of numerical experiments to be brought to bear on a small region perhaps 1/1000 of the linear dimensions of an entire galaxy. This is an extremely delicate numerical problem, one in which some small feature overlook, can easily lead to a collapse or blow-up of the entire system. All particles attract each other in gravitational problems, and the 1/r(sup 2) force is: (1) nonlinear; (2) strong at short range; (3) long-range, and (4) unscreened at any distance.

Description: Trajectory design of the orbit phase of the NEAR mission involves a new process that departs significantly from those procedures used in previous missions. In most cases, a precise spacecraft ephemeris is designed well in advance of arrival at the target body. For NEAR, the uncertainty in the dynamic environment around Eros does not allow the luxury of a precise spacecraft trajectory to be defined in advance. The principal cause of this uncertainty is the limited knowledge oi' the gravity field a,-id rotational state of Eros. As a result, the concept for the NEAR trajectory design is to define a number of rules for satisfying spacecraft, mission, and science constraints, and then apply these rules to various assumptions for the model of Eros. Nominal, high, and low Eros mass models are used for testing the trajectory design strategy and to bracket the ranges of parameter variations that are expected upon arrival at the asteroid. The final design is completed after arrival at Eros and determination of the actual gravity field and rotational state. As a result of the unplanned termination of the deep space rendezvous maneuver on December 20, 1998, the NEAR spacecraft passed within 3830 km of Eros on December 23, 1998. This flyby provided a brief glimpse of Eros, and allowed for a more accurate model of the rotational parameters and gravity field uncertainty. Furthermore, after the termination of the deep space rendezvous burn, contact with the spacecraft was lost and the NEAR spacecraft lost attitude control. During the subsequent gyrations of the spacecraft, hydrazine thruster firings were used to regain attitude control. This unplanned thruster activity used Much of the fuel margin allocated for the orbit phase. Consequently, minimizing fuel consumption is now even more important.

Description: In our search for "hidden" AGN we present results from a Chandra observation of the nearby cluster Abell 2255. Eight cluster galaxies are associated with point-like X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with active galactic nuclei (AGN) with no optical signatures of nuclear activity, with a further two being potential AGN. Of the potential AGN, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies five are associated with luminous (massive) galaxies and the remaining three lie in much lower luminosity systems. We note that the use of X-ray to optical flux ratios for classification of X-ray sources is often misleading, and strengthen the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.

Description: Preliminary results of a continuing search microvariations in a selected sample.

Description: In our search for "hidden" active galactic nuclei (AGNs), we present results from a Chandra observation of the nearby cluster A2255. Eight cluster galaxies are associated with pointlike X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with AGNs with no optical signatures of nuclear activity, with a further two being potential AGNs. Of the potential AGNs, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray-detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies, five are associated with luminous (massive) galaxies, and the remaining three lie in much lower luminosity systems. We note that the use of X-ray-to-optical flux ratios for classification of X-ray sources is often misleading and strengthens the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.

Description: The Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft has obtained numerous spectra of Saturn at varying spectral and spatial resolutions since Saturn Orbit Insertion in 2001. Emission lines due to water vapor in Saturn's stratosphere were first detected using whole-disk observations from the Infrared Space Observatory [1] and subsequently confirmed by the Submillimeter Wave Astronomy Satellite [2], CIRS has detected water and the data permit the retrieval of the latitudinal variation of water on Saturn. Emission lines of H2O on Saturn are very weak in the CIRS data. Thus, large spectral averages as well as improvements in calibration are necessary to detect water vapor. long integrations at the full 0.5/cm spectral resolution were performed at targeted latitudes on Saturn. High emission angles were chosen to enhance stratospheric emission. Over the course of the prime and extended mission a set of observations has been built up spaced roughly every 10 degrees of latitude. Stratospheric temperatures in the 0.5 - 5.0 mbar range were obtained by inverting spectra of CH4 in the v'4 band centered at 1501/cm. The origin of water vapor is believed to be from the ablation of micrometeorites containing eater ice, followed by photochemistry. This external source of oxygen originates either from the Saturn system (from the rings or perhaps from Enceladus) or from the interplanetary medium. Connerney [3] proposed a mechanism to transport water from the inner edge of the B-ring along magnetic field lines to specific latitudes (50N and 44S) on Saturn. Prange et al [4] interpreted a minimum in the abundance of acetylene from ultraviolet spectra gear 41S on Saturn as possibly due to an enhanced influx of water. We will be able to test the "ring rain" mechanism by searching, for localized water vapor enhancement at mid-latitudes. Our results may be used to constrain photochemical models of Saturn's stratosphere [5].