Astrophysics Science Division Colloquium Series
Schedule: July - September 2007
Astrophysics Science Division Colloquium Series
Schedule: July - September 2007
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.
Beyond Einstein: The "DESTINY" mission
Dominic Benford
NASA/Goddard Space Flight Center
Tuesday, July 3, 2007
Abstract
Destiny is a simple, direct, low cost mission to determine the
properties of dark energy by obtaining a cosmologically deep supernova
(SN) type Ia Hubble diagram and by measuring the large-scale mass power
spectrum over time. Its science instrument is a 1.65m space telescope,
featuring a near-infrared survey camera/spectrometer with a large field
of view. During its first two years, Destiny will detect, observe, and
characterize >3000 SN Ia events over the redshift interval 0.4<z<1.7,
thereby constructing a high-precision Hubble diagram to constrain the
dark energy equation of state. Destiny will be used in its third year as
a high resolution, wide-field imager to conduct a weak lensing survey
covering >1000 square degrees to measure the large-scale mass power
spectrum. The combination of surveys is much more powerful than either
technique on its own, and will have over an order of magnitude greater
sensitivity than will be provided by ongoing ground-based projects.
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Fotis Gavriil
NASA/Goddard Space Flight Center NPP
Tuesday, July 24, 2007
Abstract
Magnetars are young, isolated neutron stars with magnetic fields three
orders of magnetar greater than conventional pulsars. Magnetars come
in two flavors: Soft Gamma repeaters (SGRs) and Anomalous X-ray
Pulsars (AXPs); however, what if anything distinguishes the two
classes is getting less and less clear. In this talk I will
concentrate on recent activity from AXPs alone. Activity in AXPs can
consist of bursts, such as those seen from SGRs, long time scale flux
enhancements, rotational anomalies such as glitches, and not to
mention a whole slew of other temporal and radiative changes. I will
report on the recent discovery of six X-ray bursts from the AXP 4U
0142+61, the first ever seen from this AXP. Thus, the number of
bursting AXPs has now surpassed the number of known SGRs. The sixth
burst was the longest and most energetic burst ever observed from an
AXP. The burst spectra were well modeled by simple blackbodies,
however, the sixth burst exhibited a highly significant spectral
emission feature at ~14 keV. Similar features were seen in bursts from
AXPs 1E 1048.1-5937 and XTE J1810-197. I will also present a recent
flux enhancement from one of the most volatile AXPs, 1E 1048.1-5937,
after coming out of a long period of quiescence. The recent detection
of several glitches from AXPs RXS J170849.0-400910 and 1E 1841-045
will also be discussed.
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Al Kogut
NASA/Goddard Space Flight Center
Tuesday, July 31, 2007
Abstract
The polarization of the cosmic microwave background contains a
contribution
from gravity waves excited during the epoch of inflation, shortly after
the
Big Bang. A positive detection of this signal would have extraordinary
consequences for both cosmology and physics: not only would it establish
inflation as a physical reality, but it would also provide a
model-independent
determination of the relevant energy scale. In recognition of this
importance,
NASA's strategic planning includes a mission dedicated to the detection
and
characterization of this gravity-wave signature of inflation: the Beyond
Einstein Inflation Probe. Mission concepts for the Inflation Probe
generically
require thousands of superconducting bolometers in large focal planes,
with mission cost exceeding half a billion dollars. I will discuss the
Absolute Spectrum Polarimeter (ASP), a radically different instrument
that
could measure the polarization signal with sensitivity comparable to the
Inflation Probe but within the mass, cost, and time constraints of the
Small Explorer program.
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Prof. Phillip Kaaret
University of Iowa
Tuesday, August 7, 2007
Abstract
Ultraluminous X-ray sources are extremely bright X-ray sources in
external galaxies that have generated great interest because they may
be intermediate mass black holes. I review recent observational
results on ULXs including a survey of nearby galaxies using XMM-Newton
which has led to the discovery of three distinct classes of ULXs with
differing spectral shapes and the discovery of a 62 day X-ray
periodicity from the ULX in M82.
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Robin "Tuck" Stebbins
NASA/Goddard Space Flight Center
Tuesday, August 14, 2007
Abstract
By mapping the gravitational wave sky over a wide range of low
frequencies, the Laser Interferometer Space Antenna (LISA) mission will:
(1) understand the formation and growth of massive black holes, (2)
trace the merger history of black holes and their host galaxies, (3)
survey binaries of stellar-mass compact objects, (4) test theories of
relativity, and (5) probe new physics and cosmology. LISA will be
capable of acquiring highly accurate astrophysical information about
many binary systems involving massive black holes, intermediate-mass
black holes, and stellar-mass compact objects and about astrophysical
foregrounds and backgrounds. The expected science return will be
summarized, the measurement concept will be explained, and the baseline
architecture and technology will be described.
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AGN/Cluster Feedback
Paul Nulsen
Smithsonian Astrophysical Observatory
Tuesday, August 21, 2007
Abstract
X-ray images have revealed giant cavities and shock fronts
in the hot gas in many elliptical galaxies, groups and clusters.
These provide a direct means of measuring the energy injected into hot
atmospheres by active galactic nuclei (AGN). Average radio jet powers
are near those required to offset radiative losses and suppress
cooling in isolated giant elliptical galaxies, and in larger systems
up to the richest galaxy clusters. This coincidence suggests that
heating and cooling are coupled by feedback, which suppresses star
formation and the growth of luminous galaxies, although the details of
the process remain poorly understood. Outburst energies require
substantial late growth of supermassive black holes. Unless all of the
energy required to suppress star formation is deposited within the
cooling regions of clusters, AGN outbursts must alter large-scale
properties of the intracluster medium.
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Beyond Einstein: The Case for the Black Hole Finder Mission to EXIST
Josh Grindlay
Smithsonian Astrophysical Observatory
Tuesday, August 28, 2007
Abstract
I will describe the principal science drivers for the Black Hole
Finder Probe in the Beyond Einstein program, as originally
formulated. These were originally to "perform a census of
black holes in the nearby universe", presumably with a
hard X-ray wide-field imaging survey. The science case for
BHFP has become even stronger over the past 6y of the BE Program.
I outline the key science objectives, which now include the
origin and evolution of BHs on all scales -- from Pop III BHs
as possibly formed in the most distant GRBs, to nearby "dormant"
supermassive BHs revealed by their tidal disruption of passing
field stars, to the stellar and intermediate mass BHs in the
Milky Way and Local Group galaxies. I then describe how BHFP
as a mission can EXIST as the Energetic X-ray Imaging
Survey Telescope. Our ongoing mission studies and collaborative
instrument development with the ProtoEXIST balloon prototype make
EXIST a compelling candidate for early implementation in the
Beyond Einstein program.
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Understanding Accretion Disks Around Black Holes
Julian Krolik
The Johns Hopkins University
Wednesday, August 29, 2007
Abstract
Although a framework for thinking about relativistic accretion disks
was laid out in the classic papers by Novikov & Thorne and Shakura &
Sunyaev more than thirty years ago, several important questions about
these systems were left unanswered. Most importantly, the actual
mechanism of angular momentum transport, the principal process driving
accretion, was left entirely unspecified. Thanks to the work of
Balbus & Hawley, we now know that this mechanism is correlated MHD
turbulence stirred by the magneto-rotational instability.
Building on this basic fact, it is now possible to construct ever-more
realistic numerical simulations of what happens in accretion disks.
These simulations have revealed a number of surprises: contrary to the
assumption made in both classic papers, the final stages of accretion
are violent, not stress-free, so that the standard numbers for
radiative efficiency may be too small; strong relativistic jets can,
in the right circumstances, arise spontaneously from accretion flows;
and the internal structure of accreting matter is controlled by an
interplay of magnetic and radiation forces far more intricate than
previously imagined, possibly leading to observable effects in the
emitted spectrum.
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"Problem" Means "Opportunity": When X-ray Binaries Distort Winds They
Reveal Them
Bram Boroson
Tuesday, September 4, 2007
Abstract
I will review HST and Chandra observations of X-ray binaries that allow
models of stellar winds to be tested. The X-rays can complicate a
pre-existing wind, or can drive a wind from the companion star or disk.
When X-rays disturb the system, we can use that disturbance to reveal
the kinematics. I will point out ways these methods can be improved,
and put what we can learn in the context of the energy balance between
the emitted X-rays, jets, and accretion rate.
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Tracing the AGN/ICM Connection in Cooling Cores with Low Frequency Radio and
X-ray Observations
Tracy Clarke
Naval Research Laboratory / Interferometrics, Inc.
Tuesday, September 11, 2007
Abstract
X-ray observations of the central regions of cooling core clusters have
revealed spectacular details of the interactions between the AGN-powered
central radio sources and the surrounding thermal intracluster gas. In addition
to depressions and filaments associated with the active central radio source,
there appear to be a number of cases of "ghost cavities" in the thermal gas
which may be the result of aged, buoyantly rising lobes from a past AGN
outburst. These ghost cavities provide a means of studying both the lifecycle
of the central radio source as well as its energy input into the ICM. Our new
low frequency observations appear to reveal multiple cycles of radio outbursts.
I will discuss detailed observations of the central radio sources in several of
these cavity systems. I will present recent multi-frequency observations of the
interaction region as well as details of the total radio galaxy energy output
and outburst timescales. These results show that, at least in some cases, the
AGN outbursts appear to be powerful enough to substantially reduce or quench
cooling flows. Finally I will briefly discuss science goals and technical
specifications of a new low frequency radio telescope (the Long Wavelength
Array - LWA) being built in the US southwest.
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Properties of Late Time X-ray Flares in GRBs
David Morris
Pennsylvania State University
Tuesday, September 18, 2007
Abstract
One of the surprising discoveries of the Swift Gamma-Ray Burst Explorer
Mission has been that of bright flares in the X-ray afterglows of GRBs.
Data from the Swift mission have now shown that X-ray flares are a
common and important component of GRB afterglows, appearing in roughly
40%-50% of GRBs to which Swift slews promptly, appearing in all phases
of the burst, and occasionally emitting as much energy as the prompt
burst phase itself. Much has been learned from the analysis of flares in
remarkable individual bursts, suggesting that flares are produced by a
continuation of activity of the GRB central engine at late times. I will
discuss results from our systematic survey of the X-ray properties of
all flares observed by the Swift XRT during the first 12 months of the
mission and discuss whether this broad sample is consistent with the
idea of X-ray flares as late time central engine activity. I will then
present results from a follow-up study of the broad-band spectral
characteristics of flares and the bursts in which they are observed,
using data from all 3 scientific instruments aboard Swift, and discuss
the implications of this follow-up work on the nature of GRB flares.
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The VLA 1.4GHz Survey of the Extended Chandra Deep Field South
Neal Miller
The Johns Hopkins University
Tuesday, September 25, 2007
Abstract
Observations for the VLA 1.4GHz Survey of the Extended Chandra Deep
Field South (ECDFS) have recently been
completed. Consisting of over 240 hours of VLA time, the survey will
reach an rms sensitivity of 7 uJy per 2" beam across the full area of
the ECDFS (32' x 32')
and thereby provide the deep radio data for this well-
studied deep field. I will present an overview of the program, including
a discussion of the radio data and the challenges that have arisen. Most
of the talk will be dedicated to the science that the radio data will
make possible, including direct testing of the far-IR/radio correlation
at high redshift, additional evaluation of the use of X-ray emission as
a star formation rate indicator, identification of obscured AGN and
their contribution to the X-ray background, and general multiwavelength
studies of galaxy evolution.
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Randall Smith