30 research outputs found
MapScholar: A Web Tool for Publishing Interactive Cartographic Collections
MapScholar is an interactive visualization tool for historic map collections. It offers an open-source portal that gives individual scholars the independent means of gathering high-resolution images, analyzing them in rich geospatial contexts, and using them to illustrate new interpretations in the history of cartography and related humanities fields. It joins together data in industry-standard file formats with free and effective data-serving sites such as Flickr and Google Docs to display its on-the-fly visualizations. MapScholar enhances traditional books and articles by making it possible -- at no cost to publishers -- to mount stunning web displays of map collections assembled from libraries around the world. MapScholar’s key innovation is how it brings maps together -- regardless of the archive in which they sit -- for the purpose of generating new knowledge about human perceptions of geographic space
Blazars in the Fermi Era: The OVRO 40-m Telescope Monitoring Program
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope
provides an unprecedented opportunity to study gamma-ray blazars. To capitalize
on this opportunity, beginning in late 2007, about a year before the start of
LAT science operations, we began a large-scale, fast-cadence 15 GHz radio
monitoring program with the 40-m telescope at the Owens Valley Radio
Observatory (OVRO). This program began with the 1158 northern (declination>-20
deg) sources from the Candidate Gamma-ray Blazar Survey (CGRaBS) and now
encompasses over 1500 sources, each observed twice per week with a ~4 mJy
(minimum) and 3% (typical) uncertainty. Here, we describe this monitoring
program and our methods, and present radio light curves from the first two
years (2008 and 2009). As a first application, we combine these data with a
novel measure of light curve variability amplitude, the intrinsic modulation
index, through a likelihood analysis to examine the variability properties of
subpopulations of our sample. We demonstrate that, with high significance
(7-sigma), gamma-ray-loud blazars detected by the LAT during its first 11
months of operation vary with about a factor of two greater amplitude than do
the gamma-ray-quiet blazars in our sample. We also find a significant (3-sigma)
difference between variability amplitude in BL Lacertae objects and
flat-spectrum radio quasars (FSRQs), with the former exhibiting larger
variability amplitudes. Finally, low-redshift (z<1) FSRQs are found to vary
more strongly than high-redshift FSRQs, with 3-sigma significance. These
findings represent an important step toward understanding why some blazars emit
gamma-rays while others, with apparently similar properties, remain silent.Comment: 23 pages, 24 figures. Submitted to ApJ
The structure and emission model of the relativistic jet in the quasar 3C 279 inferred from radio to high-energy gamma-ray observations in 2008-2010
We present time-resolved broad-band observations of the quasar 3C 279
obtained from multi-wavelength campaigns conducted during the first two years
of the Fermi Gamma-ray Space Telescope mission. While investigating the
previously reported gamma-ray/optical flare accompanied by a change in optical
polarization, we found that the optical emission appears delayed with respect
to the gamma-ray emission by about 10 days. X-ray observations reveal a pair of
`isolated' flares separated by ~90 days, with only weak gamma-ray/optical
counterparts. The spectral structure measured by Spitzer reveals a synchrotron
component peaking in the mid-infrared band with a sharp break at the
far-infrared band during the gamma-ray flare, while the peak appears in the
mm/sub-mm band in the low state. Selected spectral energy distributions are
fitted with leptonic models including Comptonization of external radiation
produced in a dusty torus or the broad-line region. Adopting the interpretation
of the polarization swing involving propagation of the emitting region along a
curved trajectory, we can explain the evolution of the broad-band spectra
during the gamma-ray flaring event by a shift of its location from ~ 1 pc to ~
4 pc from the central black hole. On the other hand, if the gamma-ray flare is
generated instead at sub-pc distance from the central black hole, the
far-infrared break can be explained by synchrotron self-absorption. We also
model the low spectral state, dominated by the mm/sub-mm peaking synchrotron
component, and suggest that the corresponding inverse-Compton component
explains the steady X-ray emission.Comment: 23 pages, 18 figures 5 tables, Accepted for publication in The
Astrophysical Journa
The Cartography of American Colonization Database Project
The Cartography of American Colonization Database (CACD) is a joint effort of S. Max Edelson and the Institute of Computing in the Humanities, Art and Social Science (I-Chass) at the National Center for Supercomputing Applications (NCSA at the University of Illinois. The database provides a highly searchable introduction to the mapping of the western hemisphere in the era of European expansion, ca. 1500-1800. Its first object is to gather and organize metadata, especially bibliographical information and links to high-resolution digital scans of historic maps, plans and charts. By featuring 1,000 Milestone Maps that illustrate colonization in the America's, the CACD will be the first universal digital cartobiliography to organize the increasing digital content available on the Web. Its innovative research modules will showcase the possibilities for map scholarship
The OVRO blazar monitoring program
The OVRO 40 m Telescope monitoring program carries out twice-weekly measurements of the 15 GHz flux density of nearly 1600 blazars and other AGN, including all those associated with northern (declination > −20°) Fermi Large Area Telescope (LAT) detections and a preselected sample ideal for statistical studies. We present some results from the program and describe the statistical method we have developed to assess the intrinsic radio variability of the sources in our sample. We also present a method for assessing the significance of correlations between radio and gamma-ray light curves