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
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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
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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.
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
Abstract
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.
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Searching for Gravitational Waves with LIGO
Gabriela Gonzalez
Louisiana State University
Tuesday, July 18, 2006
Abstract
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.
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What Thermonuclear X-ray Bursts can tell us about Neutron Stars
Sudip Bhattacharyya
GSFC
Tuesday, August 8, 2006
Abstract
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.
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Searching for Missing Baryons with the Thermal Sunyaev-Zeldovich effect
Fernando Atrio-Barandela
U Penn, U Salamanca, Spain
Tuesday, August 15, 2006
Abstract
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.
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New GLIMPSE results on the Stellar Structure of the Galaxy
Robert A. Benjamin
University of Wisconsin-Whitewater
Tuesday, September 5, 2006
Abstract
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.
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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
Abstract
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.
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Single UV-Photon Spectrometers Using Superconducting Tunnel Junctions
Veronica Savu
Yale
Tuesday, September 26, 2006
Abstract
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.
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Microwave Kinetic Inductance Detectors: Large Format X-ray Spectral
Imagers for the Next Generation of X-ray Telescopes
Megan Eckart
CalTech
Thursday, September 28, 2006
Time: 11am - Location: Bldg2 / Rm8
Abstract
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.
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Jerry Bonnell
