14952591
Constraining the black hole mass spectrum with gravitational wave observations - I. The error kernel
Many scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many of these formation scenarios predict a high-redshift population of intermediate-mass black holes (IMBHs), with masses M • in the range 10 2 ≲ M • ≲ 10 5 M ⊙ A powerful way to observe these IMBHs is via gravitational waves the black holes emit as they merge. The statistics of the observed black hole population should, in principle, allow us to discriminate between competing astrophysical scenarios for the origin and formation of SMBHs. However, gravitational wave detectors such as Laser Interferometer Space Antenna (LISA) will not be able to detect all such mergers nor assign precise black hole parameters to the merger, due to weak gravitational wave signal strengths. In order to use LISA observations to infer the statistics of the underlying population, these errors must be taken into account. We describe here a method for folding the LISA gravitational wave parameter error estimates into an 'error kernel' designed for use at the population model level. The effects of this error function are demonstrated by applying it to several recent models of black hole mergers, and some tentative conclusions are made about LISA's ability to test scenarios of the origin and formation of SMBHs.
73653593
Hands-on gravitational wave astronomy: Extracting astrophysical information from simulated signals
In this article we introduce an activity in which introductory astronomy students act as gravitational wave astronomers by extracting information from simulated gravitational wave signals. The process mimics the way real gravitational wave analysis is handled by using plots of a pure gravitational wave signal. The students measure the properties of the simulated signal and use these measurements to evaluate standard relations for astrophysical source parameters. Although the activity described focuses on circular binaries, the techniques described can be applied to other gravitational wave sources as well. A problem based on the discussion in this paper is available for use in introductory laboratory courses.
118800207
Telescope Array Radar (TARA) Observatory for Ultra-High Energy Cosmic Rays
Abstract Construction was completed during summer 2013 on the Telescope Array RAdar (TARA) bi-static radar observatory for Ultra-High Energy Cosmic Rays (UHECR). TARA is co-located with the Telescope Array, the largest “conventional” cosmic ray detector in the Northern Hemisphere, in radio-quiet Western Utah. TARA employs an 8 MW Effective Radiated Power (ERP) VHF transmitter and smart receiver system based on a 250 MS/s data acquisition system in an effort to detect the scatter of sounding radiation by UHECR-induced atmospheric ionization. TARA seeks to demonstrate bi-static radar as a useful new remote sensing technique for UHECRs. In this report, we describe the design and performance of the TARA transmitter and receiver systems.
118214092
Addressing LISA Science Analysis Challenges
The principal goal of the \emph{LISA Science Analysis Workshop} is to encourage the development and maturation of science analysis technology in preparation for LISA science operations. Exactly because LISA is a pathfinder for a new scientific discipline -- gravitational wave astronomy -- LISA data processing and science analysis methodologies are in their infancy and require considerable maturation if they are to be ready to take advantage of LISA data. Here we offer some thoughts, in anticipation of the LISA Science Analysis Workshop, on analysis research problems that demonstrate the capabilities of different proposed analysis methodologies and, simultaneously, help to push those techniques toward greater maturity. Particular emphasis is placed on formulating questions that can be turned into well-posed problems involving tests run on specific data sets, which can be shared among different groups to enable the comparison of techniques on a well-defined platform.
56410155
LISA data analysis: Source identification and subtraction
The Laser Interferometer Space Antenna will operate as an AM-FM receiver for gravitational waves. For binary systems, the source location, orientation and orbital phase are encoded in the amplitude and frequency modulation. The same modulations spread a monochromatic signal over a range of frequencies, making it difficult to identify individual sources. We present a method for detecting and subtracting individual binary signals from a data stream with many overlapping signals.
118019601
The Resolving Power of LISA: Comparing Techniques for Binary Analysis
Millions of short period binaries in the Milky Way will radiate gravitational waves in the low‐frequency band with enough power to be detectable by LISA, making the foreground of galactic binaries the most prolific source in the band. Characterizing the resolving power of LISA is important for understanding what science will be possible with LISA observations of these binaries (e.g., mass transfer rates in accreting binaries, the structure of the galaxy, etc.) and understanding how well other sources can be resolved amidst the myriad of resolvable LISA sources. This paper reports on a work in‐progress to understand how well different analysis methods can resolve pairs of binary star systems on the sky and in frequency. Preliminary quantitative results described here focus on two methods — gCLEAN and MaxEnt — and their ability to resolve sources of identical frequency as a function of angular separation.
38714824
The structure of tomato aspermy virus by X-ray crystallography.
The three-dimensional structure of tomato aspermy virus (TAV) has been solved by X-ray crystallography and refined to an R factor of 0.218 for 3.4-40 A data (effective resolution of 4A). Molecular replacement, using cucumber mosaic virus (Smith et al., 2000), provided phases for the initial maps used for model building. The coat protein of the 280 A diameter virion has the canonical "Swiss roll" beta-barrel topology with a distinctive amino-terminal alpha-helix directed into the interior of the virus where it interacts with encapsidated RNA. The N-terminal helices are joined to the beta-barrels of protein subunits by extended polypeptides of six amino acids, which serve as flexible hinges allowing movement of the helices in response to local RNA distribution. Segments of three nucleotides of partially disordered RNA interact with the capsid, primarily through arginine residues, at interfaces between A and B subunits. Side chains of cys64 and cys106 form the first disulfide observed in a cucumovirus, including a unique cysteine, 106, in a region otherwise conserved. A positive ion, putatively modeled as a Mg(+)ion, lies on the quasi-threefold axis surrounded by three quasi-symmetric glutamate 175 side chains.
28242232
The RNA of turnip yellow mosaic virus exhibits icosahedral order.
Difference electron density maps, based on structure factor amplitudes and experimental phases from crystals of wild-type turnip yellow mosaic virus and those of empty capsids prepared by freeze-thawing, show a large portion of the encapsidated RNA to have an icosahedral distribution. Four unique segments of base-paired, double-helical RNA, one to two turns in length, lie between 33-A and 101-A radius and are organized about either 2-fold or 5-fold icosahedral axes. In addition, single-stranded loops of RNA invade the pentameric and hexameric capsomeres where they contact the interior capsid surface. The remaining RNA, not seen in electron density maps, must serve as connecting links between these secondary structural elements and is likely icosahedrally disordered. The distribution of RNA observed crystallographically appears to be in agreement with models based on biochemical data and secondary structural analyses.