Astrophysics Science Colloquium Series
Schedule: April - June 2006
Astrophysics Science Colloquium Series
Schedule: April - June 2006
Through the courtesy of the speakers since 2004,
most presentations are available on line.
Future schedules:
2006, Third Quarter
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Past schedules:
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.
The Alignment of Grains with the Interstellar Magnetic Field
Joseph C. Weingartner
Dept. of Physics and Astronomy, George Mason University
Tuesday, April 4, 2006
Abstract
Observations of starlight polarization and polarized thermal
emission from dust reveal that interstellar grains are
non-spherical and systematically aligned in space. Despite
over fifty years of effort, no successful alignment theory
has been fully elaborated. I will review the most promising
models and describe recent results on the roles of starlight
torques in aligning grains and fluctuating electric dipole
moments in disaligning grains.
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Exciting Recent Discoveries About Short GRBs and Their Implications
D. Q. Lamb
Chicago
Tuesday, April 18, 2006
Abstract
The localization and observation of several short gamma-ray bursts (GRBs)
by HETE-2 and Swift during the summer of 2005 and the resulting follow-up
observations have largely solved the mystery of short GRBs. In this talk,
I first give an overview of the properties of the 16 short bursts that
have been localized so far by HETE-2 and Swift. I then describe the
properties of GRB 060121, a short burst recently localized by HETE-2.
Many of its properties are similar to those of the well-observed short
bursts GRBs 050709 and 050724. However, many of its other properties
are similar to those of long GRBs -- and are therefore very different
from those of GRBs 050709 and 050724. These results raise the question
of whether short GRBs can have very different properties than previously
thought, or whether GRB 060121 is a different kind of short GRB. I next
discuss the implications of the properties of short GRBs, including their
host galaxies, their offsets from the centers of their host galaxies, and
their redshift distribution for compact binary formation and evolution.
Finally, I discuss the scientific promise of short GRBs as "standard
sirens" for measuring the expansion rate of the universe, and therefore
determining the properties of dark energy.
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The X-ray binary 2S0114+650: X-ray variability due to tidally-induced
pulsations?
Gloria Koenigsberger
Centro de Ciencias Fisica, UNAM, Mexico
Tuesday, April 25, 2006
Abstract
The X-ray source 2S0114+650=LSI+65 010 is a binary system containing a
B-type primary and a low mass companion believed to be a neutron star
and suggested to be a magnetar descendent. The system has three
reported periodicities:
a) the 11.6 day orbital period; b) a ~2.7 hour X-ray
flaring timescale; and c) a 30.7 day ``superorbital" X-ray period.
I will present a model of tidally-driven oscillations of the
B-supergiant star that predicts the observed variability timescales.
I will also discuss the implications of such a model for other
non-synchronously rotating binary systems, particularly those in
eccentric orbits where our model suggests a mechanism for
enhanced activity near periastron passage.
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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"
Wednesday, April 26, 2006
*** 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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The soft X-ray excess and near complete absence of Sunyaev-Zel'dovich
effect
Richard Lieu
University of Alabama, Huntsville
Tuesday, May 2, 2006
Abstract
The soft X-ray excess phenomenon in clusters of galaxies, first seen
by the EUVE, ROSAT, and BeppoSAX missions, is now confirmed by the
high quality data from XMM-Newton. In the present (advanced) stage of
analysis, the simultaneous modeling of ROSAT and Newton data reveal the
existence of a very soft component at all cluster radii. The recent claim
that the outer soft excess is due to missing baryons in the form of a warm
(10^6 - 10^7 K) gas will be examined in detail, and refuted, by emission
and absorption line diagnostics. An even greater puzzle concerns the
inner soft excess, which cannot be explained as warm baryonic emission
unless there is a heat source.
Accompanying these findings is our latest effort to produce the first
in-depth (i.e. radial profile) comparison between X-ray observations
of the hot intracluster gas and WMAP data on the cluster-induced
Sunyaev-Zel'dovich CMB temperature decrement among 31 randomly selected
nearby clusters. The observed SZ effect is four to six times smaller
than X-ray prediction. Since this effect is dominated by the cluster
cores, the only way of avoiding the `non-cosmological CMB origin'
conclusion is to invoke a power-law population of relativistic electrons,
produced by extended Fermi acceleration or neutralino annihilation,
which synchrotron radiates in the microwave passband and, as a bonus,
inverse-Compton scatter the CMB to account for the soft X-ray excess.
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SOFIA: the Stratospheric Observatory for Infrared Astronomy
Edwin F. Erickson
NASA/ARC
Tuesday, May 9, 2006
Abstract
SOFIA is a mobile ground-based observatory which will operate in the
lower stratosphere. It is designed to permit observations at nearly all
wavelengths from 0.3 microns to 1.6 mm, over a 20 year lifetime. Its 2.5 m
effective diameter telescope will be diffraction limited at wavelengths
beyond about 10 microns, providing unprecedented angular resolution
(~8" FWHM at 100 microns) in the far infrared. SOFIA's Boeing 747SP
aircraft platform will allow coverage of the entire sky and enable
unique observations of ephemeral events. Nine first-generation focal
plane instruments are being built, with more to be added later.
A general purpose observatory, SOFIA will enable a vast range of science,
from star and galaxy formation to the properties of Kuiper Belt Objects.
SOFIA's wide wavelength coverage, long lifetime, and accessibility will
enable unmatched continuity of opportunity for infrared observations and
instrument technology development. The program will include a strong
educational component. This talk will describe the observatory, science
instruments and examples, operations planning, and development status.
SOFIA is a joint program of NASA in the U.S. and DLR in Germany.
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Where do intergalactic CR's and magnetic fields come from?
Implications of recent discoveries for coming generations of space- and
ground-based instruments.
Philipp P. Kronberg
Los Alamos National laboratory
Tuesday, May 16, 2006
Abstract
I briefly review the interconnections between extragalactic radio
sources and extragalactic magnetic fields, and (1) describe new
detections of diffuse extragalactic radio emission on degree-scales.
Separately (2), I describe the first attempts to directly detect Faraday
rotation in cosmological large scale structure at low z, and compare
both results with "astrophysical expectation".
Radio techniques, and instrumental advances associated with (1) wil be
described, and I briefly discuss what kind of instrumentation we will
need in future to better characterize IGM magnetic fields and cosmic
rays, that is, the physical state of the intergalactic medium. My talk
will illustrate why radio, X- ray, gamma-ray and UHECR detectors will
more closely synergize with each other in the future.
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X-ray Detection of the Proto Supermassive Binary Black Hole at the
Centre of Abell 400
Daniel S. Hudson
AIfA, Univ. Bonn
Thursday, May 18, 2006
*** 1:30 PM ***
*** Bldg 21, Rm 183 ***
Abstract
We report the first X-ray detection of a proto-supermassive binary black
hole at the centre of Abell 400. Using the Chandra ACIS, we are able to
clearly resolve the two active galactic nuclei in 3C 75, the well known
double radio source at the centre of Abell 400. Through analysis of the
new Chandra observation of Abell 400 along with 4.5 GHz and 330 MHz VLA
radio data, we will show new evidence that the Active Galactic Nuclei in
3C 75 are a bound system. Methods. Using the high quality X-ray data, we
map the temperature, pressure, density, and entropy of the inner regions
as well as the cluster profile properties out to ~18'. We compare
features in the X-ray and radio images to determine the interaction
between the intra-cluster medium and extended radio emission. The
Chandra image shows an elongation of the cluster gas along the
northeast-southwest axis; aligned with the initial bending of 3C 75's
jets. Additionally, the temperature profile shows no cooling core,
consistent with a merging system. There is an apparent shock to the
south of the core consistent with a Mach number of M~1.4 or speed of
v~1200 km s^-1. Both Active Galactic Nuclei, at least in projection, are
located in the low entropy, high density core just north of the shock
region. We find that the projected path of the jets does not follow the
intra-cluster medium surface brightness gradient as expected if their
path were due to buoyancy. We also find that both central AGN are
extended and include a thermal component. Based on this analysis, we
conclude that the Active Galactic Nuclei in 3C 75 are a bound system
from a previous merger. They are contained in a low entropy core moving
through the intra-cluster medium at 1200 km s^-1. The bending of the
jets is due to the local intra-cluster medium wind.
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Third Year WMAP Results
Gary Hinshaw
NASA/Goddard Space Flight Center
Tuesday, May 23, 2006
Abstract
The data from the first three years of operation of the Wilkinson
Microwave Anisotropy Probe (WMAP) satellite provide detailed full-sky
maps of the cosmic microwave background temperature anisotropy and new
full-sky maps of the polarization. Together, the data provide a wealth
of cosmological information, including the age of the universe, the epoch
when the first stars formed, and the overall composition of baryonic
matter, dark matter, and dark energy. The results also provide constraints
on the period of inflationary expansion in the very first moments of time.
These and other aspects of the mission will be discussed.
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Gamma-ray Astrophysics with the MAGIC Telescope
Massimo Persic
INAF and Osservatorio Astronomico di Trieste
Tuesday, May 30, 2006
Abstract
The ground-based MAGIC telescope has been operational, in the
energy band ~0.05-10 TeV, for over a year now. I will highlight
several recent and upcoming MAGIC-based results (both Galactic
and extragalactic), which are relevant to crucial issues of VHE
astrophysics: e.g., the acceleration of cosmic rays, the emission
from millisecond pulsars, the physics of relativistic jets, the
measurement of the extragalactic background light, the nature
of galactic dark matter, tests of quantum gravity. The growing
ability of addressing these issues, made possible by the very
rapid development of Cherenkov techniques in the past few
years, signals the coming of age of TeV astrophysics.
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ASTROSAT: The Indian Multi wavelength Astronomy Satellite
Ravi K. Manchanda
Tata Institute of Fundamental Research
Thursday, June 1, 2006
*** 11:00 AM ***
*** Bldg 2, Rm 8 ***
Abstract
Astrosat is India's first satellite dedicated to multiwavelength
astronomy. Five different payloads on board the satellite permit
simultaneous observations from UV to hard X-ray band. The main x-ray
payloads are designed to provide, high temporal resolution, broad energy
range, and high energy and spatial resolution.
The x-ray instruments on board ASTROSAT include (i) three identical
co-aligned Large Area X-ray Proportional Counters (LAXPC) with an
effective area of 6000 cmA^2 for high resolution timing studies in 3-80 keV
band, (ii) Soft X-ray Imaging Telescope (SXT) based on the use of conical
foil mirrors and x-ray CCD with an effective area of about 200 cmA^2 at
1 keV for X-ray imaging and spectral observations in 0.3 - 8 keV, (iii)
Cadmium- Zinc-Telluride (CZT) array of 1000 cmA^2 area with coded-mask
aperture for hard x-ray imaging and moderate energy resolution x-ray
spectroscopic studies in 10-100 keV band and (iv) a Scanning Sky X-ray
Monitor (SSM) for detection of transient sources and monitoring of known
bright x-ray sources in 2 - 10 keV interval.
The Ultraviolet Imaging Telescope (UVIT) instrument consisting of two
identical telescopes, each with a primary mirror of 38 cm diameter with
a photon counting detector system, is also included in the Astrosat. One
telescope will cover 1300 - 2000 A band while the second one will cover
2000 - 3000 A as well as optical band of 3000 - 6000 A.
In this talk, I will discuss the details of the science payload, their
capabilities and the present status.
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Spitzer Space Telescope Observations of Star- and Planet-Forming
Regions: Ice Cold and Steaming Hot
Ewine van Dishoeck
Leiden Observatory
Friday, June 2, 2006
*** 10:00 AM ***
*** Bldg 21, Rm 183A ***
Abstract
The earliest stages of star- and planet formation are obscured by tens
to hundreds of magnitudes of extinction. Observations of the gas and
dust at long wavelengths often provide the only way to obtain
information on the physical and chemical processes that occur deep
inside these regions. In this talk, an overview of Spitzer
spectroscopic observations of ices, silicates, PAHs and hot gases
obtained in the context of the `Cores to Disks' (c2d) Legacy program
will be given. Spitzer has opened up the possibility to obtain high
quality mid-infrared spectra for large numbers of low-mass protostars
(`Class 0 and I') and disks around low-mass pre-main sequence stars
(`Class II') for the first time. The results will be placed in the
context of other space- and ground-based data and analyzed using
models of protostellar envelopes and (flaring) disks. The diagnostic
values of the various lines and bands will be emphasized, and the
importance of laboratory data to interpret them will be illustrated.
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Peculiar Objects of the Massive Star Population
Yael Naze
Institut d'Astrophysique et de Geophysique,
Universite de Liege
Tuesday, June 6, 2006
Abstract
If you had to chose the queens among the stars, they would certainly
be the O-type stars. With all-time records in temperature, mass and
brightness, these stars truly dominate their host galaxies. Their
intense UV radiation is able to drive massive stellar winds, that are
up to ten billion times stronger than the solar wind. A large fraction
of these stars exist as binaries, and for O-star binaries, one thing
is unavoidable: a powerful collision between the winds. This dramatic
phenomenon was predicted a few decades ago, but is only now beginning
to be observed in detail. These cosmic collisions make an extraordinary
cosmic show throughout the whole electromagnetic spectrum. They give
us a unique insight into the stellar properties, notably by refining
the mass loss rates which are crucial parameters for understanding the
stellar evolution and the chemical enrichment.
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Twin kHz QPOs as a Non-linear Resonance in a Relativistic Accretion Disk
Wlodek Kluzniak
GSFC/UMBC/University Zielona Gora, Poland
Tuesday, June 13, 2006
Abstract
The X-rays from several accreting neutron stars and black holes
are modulated at characteristic pairs of frequencies ("twin QPOs").
In three or four microquasars these frequencies are clearly in a 3:2
ratio, as suggested by us (with M. Abramowicz), and it is now widely
accepted that this could be the result of a resonance. The case of twin
QPOs in neutron stars is more controversial. I will present recent
evidence that the variable kHz QPO frequencies in neutron stars also
point to a 3:2 ratio, in agreement with a model of coupled oscillators.
The oscillators are thought to be two modes of the accretion disk.
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Cosmic acceleration: Dark Energy or Modified gravity?
Mustapha Ishak-Boushaki
University of Texas
Tuesday, June 27, 2006
Abstract
The acceleration of the expansion of the universe is one of the most
important and challenging problems in physics. It is important to
determine if the cosmic acceleration is due to a dark energy component in
the universe or if it is due to a modification in the gravity sector. I
report here results on a procedure that we proposed recently and that will
allow one to make such a distinction. The procedure goes one important
step further than constraining the equation of state. It uses different
combinations of simulated data of CMB, Weak Gravitational Lensing,
and Supernovae. We explored the fact that the effect of dark energy on
the expansion history must be consistent with the effect of dark energy
on the growth factor of large-scale structure. The procedure is able to
detect inconsistencies when present in this relation and thus provides
a test to detect signatures of modified gravity models.
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Jerry Bonnell
