Astrophysics Science Colloquium Series
Schedule: January - March 2006
Astrophysics Science Colloquium Series
Schedule: January - March 2006
Through the courtesy of the speakers since 2004,
most presentations are available on line.
Future schedules:
2006, Second Quarter
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Past schedules:
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.
Connecting Galaxy Evolution, Star Formation and the X-ray Background
Pierre Cox
Institute of Millimeterwave Radio Astronomy,
Grenoble, France
Tuesday, January 17, 2006
Abstract
The study of the molecular gas in quasars and submillimeter galaxies
at high redshift has significantly progressed during the last few
years. From the current detection of CO emission in 38 sources
spanning a range in redshift from $1
For information, the current developments and plans for the IRAM
telescopes will be presented at the end of this talk.
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Infrared Astronomy with NASA's New Spitzer Space Telescope
Robert D. Gehrz
University of Minnesota
Tuesday, February 7, 2006
Abstract
Launched from Kennedy Spaceflight Center in the early morning of August
25, 2003, NASA's Spitzer Space Telescope (formerly Space Infrared
Telescope Facility, SIRTF) is the fourth and final facility in the
Great Observatories Program, joining Hubble Space Telescope (HST,
1990), the Compton Gamma-Ray Observatory (CGRO, 1991-2000), and the
Chandra X-Ray Observatory(CXO, 1999). Spitzer, with a sensitivity that
is orders of magnitude higher than that of any previous ground-based and
space-based infrared (IR)observatories, is expected to revolutionize
our understanding of the creation of the universe, the formation and
evolution of primitive galaxies, the genesis of stars and planets, and
the chemical evolution of the universe. A brief overview of infrared
(IR) astronomy and of Spitzer's role in the NASA's Space IR Astronomy
program for the New Millennium will be given. The construction, launch,
and in-orbit checkout of the observatory will be reviewed. Science
highlights from the first several years of observations will be presented.
Special emphasis will be given to the speaker's GTO and GO observations
of classical novae, SN 1987a, and the Crab Nebula.
Further information about the Spitzer can be found on the WEB at
http://spitzer.caltech.edu/
The speaker's biography and CV may be viewed at
http://webusers.astro.umn.edu/~gehrz/
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Bench-top Simulations of LISA Interferometry
Ira Thorpe
University of Florida
Thursday, February 9, 2006
*** 1:30 PM ***
*** Bldg 2, Rm 8 ***
Abstract
The proposed space-based interferometric gravitational wave detector LISA
will be used to study gravitational waves in the mHz regime. It consists
of three spacecraft located at the vertices of a 5 Gm triangle, each
containing two freely-falling proof masses. The distances between the
proof masses will be monitored using laser interferometry in an effort
to detect modulations due to gravitational waves. Our group is in
the process of developing a bench-top model of LISA interferometry that
includes lasers with LISA-like noise characteristics as well as realistic
light travel delays achieved using an electronic phase delay method
[Class. Quantum Grav. 22 (2005) S227-S234]. The initial goal of this
simulator is to test time-delay interferometry (TDI) and arm-locking,
two laser frequency noise reduction techniques that have been proposed
for LISA. The model could also be expanded to include other aspects of
LISA including gravitational-wave signals, thereby providing a source of
mock LISA data streams with realistic technical noise. Current progress
and results will be presented.
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Early Afterglow Evolution of X-Ray Flashes Observed by Swift
Derek Hullinger
University of Maryland
Tuesday, February 21, 2006
*** 11:00 AM ***
*** Bldg 21, Rm 191 ***
Abstract
Gamma-ray bursts (GRBs) are bright flashes of gamma-ray energy that
originate in distant galaxies and last only a matter of seconds before
fading away, never to appear again. They are accompanied by "afterglows"
made up of longer wavelength radiation that fades away much more gradually
and can be detected for up to several days or even weeks after the
gamma-ray burst has vanished. In recent years, another phenomenon has
been discovered that resembles gamma-ray bursts in almost every way,
except that the radiated energy comes mostly from x-rays instead of
gamma rays. This new class of bursts have been dubbed "x-ray flashes"
(XRFs). There is strong evidence to suggest that GRBs and XRFs are
closely-related phenomena. The Swift mission, launched in November of
2004, is designed to answer many questions about GRBs and their cousins,
XRFs-where they come from, what causes them, and why gamma-ray bursts and
x-ray flashes differ. Swift's ability to study the very early afterglow
emission provides an important key to distinguishing between different
theories that seek to explain the differences between XRFs and GRBs.
I'll describe a study of XRFs and GRBs detected by Swift, including
the first analysis and comparison of the early afterglow properties of
these phenomena. This study reveals interesting differences between the
temporal properties of GRB and XRF afterglows and sets strong constraints
on some theories that seek to explain XRF origins.
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Swift BAT AGN Survey Results
Craig Markwardt and Jack Tueller
University of Maryland, NASA/GSFC
Tuesday, March 14, 2006
Abstract
We present results from the the Swift Burst Alert Telescope (BAT) high
galactic latitude survey in the 14--200 keV band. The survey reaches a
flux of ~10^{-11} erg cm^{-2} s^{-1} and has ~2.7' (90% confidence)
positional uncertainties for the faintest sources. This represents the
most sensitive survey to date (by a factor of ~10) in this energy
band. At 9.5 months, the survey is complete (90% of the sky) to a
sensitivity of <2 milliCrab. At these energies, NH > ~10^{24} is
required to absorb the BAT flux. We have detected 147 AGN, and after
three years of exposure, we expect ~450. Most of the AGN are local
(median redshift ~0.025), although there are some high redshift
blazars. The Swift XRT telescope is used to identify BAT survey
sources that cannot be identified from catalog searches, and to
directly measure NH for sources without previousy x-ray spectra. We
will present x-ray measurements for some of the AGN identified by
Swift. The distributions of NH column densities, luminosities, and
the Log N vs. Log S functions will be presented. We will present the
distributions of Lopt/LBAT, Lx/LBAT, and the hard x-ray spectral index
for the BAT detected AGN. This is a critical test of the completeness
of AGN surveys at other wavelengths. These surveys are the basis for
understanding the evolution of AGN and the origin of the cosmic x-ray
background.
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A Non-Equilibrium Ionization Code and its Application
Li Ji
University of Massachusetts, Amherst
Tuesday, March 7, 2006
Abstract
I will introduce a non-equilibrium ionization code which we developed
based on updated atomic data . A version of the code has been optimized
so that the calculation can be done efficiently and accurately enough
for comparison with X-ray CCD spectra and the coloumn densities of UV
interstellar/intergalactic medium. The atomic process of recombination
into highly excited levels has been self-consistently included, which
is important in some non-equilibrium cases but has generally been
ignored in the past. I will show example applications to illustrate the
characteristics of the code and its combination with various models of gas
dynamics. In particular, I will mainly present results from applications
to massive stellar cluster winds. And I will briefly present other
applications to galactic winds and the UV absorption/emission study with
the radiative cooling scenario.
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A New Search Paradigm for Correlated Neutrino Emission from Discrete
GRBs using Antarctic Cherenkov Telescopes in the Swift Era
Michael Stamatikos
University of Wisconsin
Monday, March 13, 2006
*** 1:30 PM ***
*** Bldg 2, Rm 8 ***
Abstract
Intrinsic neutrino properties qualify them as unique cosmic messengers.
Canonical fireball phenomenology, in the context of hadronic acceleration,
predicts correlated MeV to EeV neutrinos from gamma-ray bursts (GRBs).
The Antarctic Muon and Neutrino Detector Array (AMANDA), has demonstrated
the viability of high energy neutrino astronomy by using the ice at the
geographic South Pole as a Cherenkov medium. Ideal for detection are
TeV-PeV neutrinos, which are expected to be in coincidence with prompt
gamma-ray emission, resulting in a nearly background-free search that
may possibly reveal an acceleration mechanism for the highest energy
cosmic rays. We describe the theoretical modeling and analysis associated
with a search for correlated neutrino emission from a subset of GRBs
detected by the Burst and Transient Source Experiment (BATSE) and High
Energy Transient Explorer-II (HETE-II) burst GRB030329, based upon each
burst's individual (discrete) set of observed electromagnetic parameters,
in the context of constraints on astrophysical models. The effects of
anisotropic emission geometry and non-trivial neutrino mass are addressed.
Implications for future correlated neutrino searches in the era of Swift
and IceCube, AMANDA's km-scale successor, will be discussed.
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Signatures of Electron Acceleration from Nearby Stars
Rachel Osten
GSFC
Tuesday, March 21, 2006
Abstract
Electron acceleration plays in important role in the energetics of
solar and (by implication) stellar flares. Observational signatures
of accelerated electrons appear directly at radio and hard X-ray
wavelengths, and indirectly at optical wavelengths; most stellar work has
concentrated on radio and optical wavelengths due to sensitivity issues.
Finding correspondences in the behavior of accelerated electrons during
solar and stellar flares is important to understanding the physical
processes at work in a variety of stellar environments. New instruments
have expanded the capacity for studying electron acceleration in stars
through both sensivitiy and serendipity. I will review recent results
concerning observational signatures of electron acceleration in solar
neighborhood cool stars at radio and hard X-ray wavelengths, and discuss
the implications for the physics of stellar coronae.
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New GLIMPSE results on the Stellar Structure of the Galaxy
Robert A. Benjamin
University of Wisconsin-Whitewater
POSTPONED
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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GRB 050315: A step in the proof of the uniqueness of the overall GRB
structure
Remo Ruffini
Universit'a di Roma "La Sapienza"
POSTPONED TO April 26
*** 1:30 PM ***
*** Bldg 2, Rm 8 ***
Abstract
Using the Swift data of GRB 050315, we progress in proving the
uniqueness of our theoretically predicted Gamma-Ray Burst (GRB)
structure as composed by a proper-GRB, emitted at the transparency of
an electron-positron plasma with suitable baryon loading, and an
afterglow comprising the "prompt radiation" as due to external
shocks. Detailed light curves for selected energy bands are
theoretically fitted in the entire temporal region of the Swift
observations ranging over 10^6 seconds. The theoretically predicted
instantaneous spectral distribution is presented, confirming a clear
hard-to-soft behavior.
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Jerry Bonnell
