Astrophysics Science Colloquium Series
Schedule: July - September 2006

Astrophysics Science Colloquium Series
Schedule: July - September 2006

Through the courtesy of the speakers since 2004, most presentations are available on line.

Future schedules:

  • 2006, Fourth Quarter
  • Past schedules:

  • 2006, Second Quarter
  • 2006, First Quarter
  • 2005, Fourth Quarter
  • 2005, Third Quarter
  • 2005, Second Quarter
  • 2005, First Quarter
  • 2004, Fourth Quarter
  • 2004, Third Quarter
  • 2004, Second Quarter
  • 2004, First Quarter
  • 2003, Fourth Quarter

  • Time: 3:45 pm (Meet the Speaker at 3:30 pm) - Location: Bldg 21, Room 183 - unless otherwise noted.
    To view the abstract of a seminar, click on the title.


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    2 3 4 Federal Holiday: No Colloquium 5 6 7 8
    9 10 11 12 13 Marco Tavani (INFN) - Science Plans for the AGILE Gamma-Ray Observatory 14 15
    16 17 18 Gabriela Gonzalez (Louisiana State Univ.) - Searching for Gravitational Waves with LIGO 19 20 21 22
    23 24 25 26 27 28 29
    30 31


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
       1 2 3 4 5
    6 7 8 Sudip Bhattacharyya (GSFC) - What Thermonuclear X-ray Bursts can tell us about Neutron Stars 9 10 11 12
    13 14 15 Fernando Atrio-Barandela (U Penn / U Salamanca, Spain) - Searching for Missing Baryons with the Thermal Sunyaev-Zeldovich effect 16 17 18 19
    20 21 22 23 24 25 26
    27 28 29 30 31   


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
          1 2
    3 4 5 Robert Benjamin (Univ. of Wisconsin, Whitewater) - New GLIMPSE Results on the Stellar Structure of the Galaxy 6 7 8 9
    10 11 12 13 14 15 16
    17 18 19 Guido Risaliti (Osservatorio Astrofisico di Arcetri, Firenze) - X-ray observations of NGC 1365 20 21 22 23
    24 25 26 Veronica Savu (Yale) - Single UV-Photon Spectrometers Using Superconducting Tunnel Junctions 27 28 Megan Eckart (CalTech) Microwave Kinetic Inductance Detectors 29 30

    AGILE and Its Scientific Program

    Marco Tavani

    Italian Institute for Astrophysics (INFN) and University of Tor Vergata, Rome

    Thursday, July 13, 2006

    Meet-3:30/Talk-3:45pm Bldg21/Rm183


    AGILE is a Scientific Mission (of the SMEX class) dedicated to high-energy astrophysics supported by the Italian Space Agency and the by Italian Institutes of Astrophysics and Nuclear Physics. The AGILE instrument is innovative and designed to simultaneously detect photons in the 30 MeV-50 GeV and 15-45 keV energy bands in a very compact configuration. The instrument is ideal for the detection of hard X-ray/gamma-ray transient emission, and the mission scientific goals include the study of AGNs, GRBs, Galactic compact sources, TeV sources and the diffuse Galactic emission. The AGILE scientific program is complementary and strongly synergic whith that of GLAST.

    The instrument gamma-ray calibration was carried out in November 2005; AGILE is currently completing the satellite qualification tests, and launch by a PSLV rocket is planned in early 2007. AGILE observations will be based on (typically 3-week) fixed sky-pointings, for a scientific program aimed at optimizing the joint imaging capabilities in the hard X-ray and gamma-ray bands. The AGILE scientific program will be open to the international community through a Guest Observer Program whose Announcement is planned to be issued in the Fall of 2006.

    Searching for Gravitational Waves with LIGO

    Gabriela Gonzalez

    Louisiana State University

    Tuesday, July 18, 2006


    The LIGO gravitational wave observatories are now taking data, having reached their design sensitivity. The LIGO Scientific Collaboration is actively searching the data for signals from rotating stars, from stochastic backgrounds, from binary neutron star and black hole systems, and from transient sources like supernovas and collisions of black holes. We will show the sensitivity achieved by the detectors, describe the technology that makes that sensitivity possible, and present the latest results in the search for gravitational waves.

    What Thermonuclear X-ray Bursts can tell us about Neutron Stars

    Sudip Bhattacharyya


    Tuesday, August 8, 2006


    Some of the most extreme conditions of the universe exist in neutron stars, as these stars are very dense, have strong magnetic fields, and sometimes spin very rapidly and emit intense radiation. Many aspects of extreme physics can be studied only by observing and understanding neutron stars, as these problems cannot be addressed by doing experiments in laboratories. One such problem is the lack of knowledge of the nature of dense (5-10 times denser than an atomic nucleus) cold matter at the neutron star cores, and only the accurate measurements of the mass, radius and spin period of a neutron star can resolve this. A promising way to measure these stellar properties is to study type I X-ray bursts, which are produced by thermonuclear burning of matter accumulated on the surfaces of accreting neutron stars. This is because, these intense bursts, which sometimes exhibit timing features (such as millisecond period brightness oscillations from the stellar surfaces) and may show surface spectral features, contain detailed information about the neutron stars. Moreover, X-ray bursts can be helpful for constraining the stellar atmospheric parameters, and for understanding the thermonuclear flame spreading under extreme physical conditions that exist on neutron star surfaces. I will discuss the diagnostic merits of these bursts, the current status of some of their studies, and the future prospects.

    Searching for Missing Baryons with the Thermal Sunyaev-Zeldovich effect

    Fernando Atrio-Barandela

    U Penn, U Salamanca, Spain

    Tuesday, August 15, 2006


    About half the baryons in the local Universe could be in the form of warm-hot intergalactic medium. If a large fraction of the gas is ionized, it could produce significant temperature anisotropies in the Cosmic Microwave Background. Assuming the gas follows a log-normal probability distribution function with a polytropic equation of state, we compute the power spectrum of the predicted temperature anisotropies and its dependence on cosmic and physical parameters. We also discuss prospective ways of detecting this contribution by cross correlating templates constructed from galaxy catalogs with CMB data.

    New GLIMPSE results on the Stellar Structure of the Galaxy

    Robert A. Benjamin

    University of Wisconsin-Whitewater

    Tuesday, September 5, 2006


    I present Spitzer/GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire) results on the global variation of the mid-infrared stellar and diffuse emission over 220 square degrees of the inner Galactic plane from 0<|l|<65 degrees and |b|< 1 degree using IRAC. Principal results include the following: (1) variation of source counts indicate the Galaxy has a radial scale length of H_*= 3.9 +/- 0.6 kpc; (2) there is strong evidence for a Galactic bar with half-length R_bar=4.4 +/- 0.5 kpc, oriented at phi=44 +/- 10 degrees; (3) a major spiral arm of the Galaxy appears to be missing, (4) source counts are depressed even at 4.5 microns by extinction associated with molecular gas; (5) diffuse emission in all four bands is dominated by star formation regions; and (6) there is a significant range in diffuse band ratios: [4.5]/[3.6] varies by a factor of ~10 along the Galactic plane, while [8.0]/[5.8] (the most tightly correlated bands) only varies by a factor of ~2.

    X-ray observations of NGC 1365: highly ionized absorbers and time-resolved eclipse of the X-ray source

    Guido Risaliti

    Osservatorio Astrofisico di Arcetri, Firenze

    Tuesday, September 19, 2006

    Time: 4pm - Location: Bldg 2 / Rm 8


    I present the extraordinary X-ray observations of the Seyfert Galaxy NGC 1365,performed with XMM-Newton and Chandra. This source is unique in two respects:first, the X-ray spectra clearly show the presence of a highly ionized gas close to the source, responsible of Fe XXV and FeXXVI absorption lines; second, changes from Compton-thick to Compton-thin states have been observed in time scales of ~2 days, due to occultations by an intervening cloud. These rapid variation times have strong consequences for the unified model of AGN, implyingan extremely compact structure of the circumnuclear absorber (within the BLR region). Moreover, they provide a direct measurement of the size of the X-ray emitting region, which, for reasonable velocities of the occulting cloud is <~10^14 cm, corresponding to a few gravitational radii according to the black hole mass estimates obtained both with M-sigma and M-L relations.

    Single UV-Photon Spectrometers Using Superconducting Tunnel Junctions

    Veronica Savu


    Tuesday, September 26, 2006


    Superconducting tunnel junction (STJ) spectrometers have been used for single-photon detection, from X-rays to visible light. The detector's response is proportional to the incident photon energy. Thus detection of single UV photons with a high signal-to-noise ratio (S/N) is relatively challenging. This presentation discusses a new, diffusion-engineered approach for signal amplification, using an STJ intrinsic charge-multiplication mechanism. We show that by choosing materials with an appropriate diffusion constant and changing the device geometry, we increase the charge created by a photon, therefore improving the energy resolution (S/N) of our detector.

    Microwave Kinetic Inductance Detectors: Large Format X-ray Spectral Imagers for the Next Generation of X-ray Telescopes

    Megan Eckart


    Thursday, September 28, 2006

    Time: 11am - Location: Bldg2 / Rm8


    Microwave Kinetic Inductance Detectors (MKIDs) have the potential to provide megapixel imagers with few eV spectral resolution for future X-ray missions such as Gen-X. MKIDs offer the advantage over many other cryogenic detector technologies that they can be easily multiplexed, so that arrays with many thousand pixels are readily achievable. In addition, the readout electronics can be operated at room temperature, a significant advantage for space applications. MKIDs exploit the dependence of surface impedance of a superconductor with the quasiparticle density. Quasiparticles are created by absorption of X-rays, with number proportional to the X-ray energy. The impedance change may be sensitively measured using a thin-film resonant circuit.

    The practical application of MKIDs for photon detection requires a method of efficiently coupling the photon energy to the MKID. To this end we have been studying MKIDs in a strip detector architecture. I will present our recent results, discuss ideas for future detector designs and suggest ultimate performance goals for X-ray astronomy applications.

    Jerry Bonnell

    NASA Logo, National Aeronautics and Space Administration