The Sky Above, the Mud Below -
the UHECR debate:
Technique or Theology?
Dr. Pierre Sokolsky
High Energy Astrophysics Institute, University of Utah
October 1
Abstract
The UHE Cosmic Ray spectrum has been measured by two different techniques
-one based on atmospheric fluorescence(HiRes) and one based on sampling the
shower as it hits the ground(AGASA). The results do not agree well in the
neighborhood of the Greisen-Zatsepin-Kuzmin cut-off. The status of the measurements
and systematics will be discussed and ways to resolve the issue suggested.
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Ultra high frequency peaked BL Lac objects
Dr. Volker Beckmann
INTEGRAL Science Data Centre (ISDC)
Thursday, October 3, 1pm, Building
2, Room 8
Abstract
Blazars are the most extreme class of Active Galactic
Nuclei (AGN) known. The extreme properties which
are observed, such as high polarization and variability,
are believed to result from a highly relativistic
jet, pointing towards the observer. The unification of the blazar sequence
is based on the observation that the differences
between radio and X-ray selected blazars are due to
different peak frequencies of their synchrotron and inverse Compton emission. Based on the
large and complete HRX-BL Lac sample, dependencies of several
physical parameters (such as luminosity, spectral shape, and spectral energy distribution) on the synchrotron emission
peak are shown. It is also possible to explain the different evolutionary
behaviour in a unified scheme. Finally, implications
on the existence of ultra high frequency peaked BL
Lac objects (UHBL) can be made. These objects have
their synchrotron peak at frequencies higher than 100 keV and make them
possible targets for observations in Gamma-rays using INTEGRAL. First encouraging results from studying UHBL candidates
of the HRX-BL Lac sample and from follow-up observations
in the optical domain and with BeppoSAX will be presented. One recently
discovered UHBL is likely to be the counterpart of
an unidentified EGRET source.
Project SEE: A Next-Generation Gravitation Mission
Dr. Alvin Sanders
University of Tennessee
Thursday, October 10, 3pm, Building
2, Room 8
Abstract
Project S.E.E. (Satellite Energy Exchange) is an international effort to
organize a new space mission for fundamental measurements in gravitation,
which entails launching a dedicated satellite and making detailed observations
of free-floating test bodies within its experimental chamber. The planned
experiments include tests of the equivalence principle (EP), both by composition
dependence (CD) and by inverse-square-law (ISL) violations, determination
of G, and a test for non-zero G-dot. The CD tests will be both at intermediate
distances (few meters) and at long distances (radius of the Earth). Thus,
a SEE mission would obtain accurate information self- consistently on a number
of distinct gravitational effects. The EP tests by CD would provide confirmation
of earlier, more precise experiments. All other tests would significantly
improve our knowledge of gravity. In particular, the error in G is projected
to be less than 1 ppm, and the test for non-zero G-dot will be at the level
of less than one part in 10^13
Cosmic Rays and the Search for Extra Dimensions
Dr. Argyris Nicolaidis
Department of Theoretical Physics, University of Thessaloniki
Friday, October 11, 1:15pm, Building
2, Room 8
Abstract
We propose that the cosmic ray spectrum "knee", i.e. the steepening of the
cosmic ray spectrum at energy $E \gsim 10^{15.5}$ eV,
may be the manifestation of the existence of a low fundamental scale for
the gravitational interaction, i.e. that this scale is
of order ~TeV (at the center of mass or 10^{15} eV at the lab frame). The
reduction of the fundamental scale from the commonly accepted Planck
value (10^{19} GeV) to ~ 1 TeV is achieved by considering that the graviton
propagates, besides the usual four dimensions, into an additional $\delta$,
compactified, large radius (~ 1 Fermi) dimensions, as has been recently suggested
in order to account for the hierarchy problem (i.e. the disparity between
the electroweak and gravitational scales) in high energy physics. We compute
the cross section for graviton production in this framework and calculate
the energy lost to gravitons in high energy pp collisions. This energy does
not trigger the cosmic ray detectors and leads to a steepening of the cosmic
ray spectrum at cosmic ray energies greater than that of the fundamental gravity
scale (i.e. 10^{15.5} eV at the Lab frame). Incidentally, this energy scale
is coincident with that of the "knee" of the Cosmic ray spectrum, which thus
finds its explanation in the physics of high energy
particle collisions. By fitting the cosmic ray spectrum data we deduce that
the favorite values for the fundamental scale for gravity
($M_f \sim 5$ TeV) and the number of compactified dimensions ($\delta =4$).
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The Effects of Magnetic Fields
on Line-Driven Hot-Star Winds
Dr. Asif UD-Doula
North Carolina State University
October
15
Abstract
There is extensive evidence that the line-driven
stellar winds of OB-type stars are not the steady, smooth outflows envisioned
in classical models, but instead exhibit extensive structure and variability
on a range of temporal and spatial scales. This talk will examine the possible
role of stellar magnetic fields in forming large-scale wind structure based
on numerical magnetohydrodynamic (MHD) simulations of the interaction of
a line-driven flow with an assumed stellar dipole field. Unlike previous
fixed-field analyses, the MHD simulations here take full account of the
dynamical competition between the field and flow. A key result is that the
overall degree to which the wind is influenced by the field depends largely
on a single, dimensionless, `wind magnetic confinement parameter', $\eta_*$
($=B_{eq}^2 R_*^2/{\dot M} v_\infty$), which characterizes the ratio between
magnetic field energy density and kinetic energy density of the wind. For
weak confinement, $\eta_* \le 1$, the field is fully opened by wind outflow,
but nonetheless, for confinements as small as $\eta_*=1/10$ it can have
a significant back-influence in enhancing the density and reducing the
flow speed near the magnetic equator. For stronger confinement, $\eta_*
> 1$, the magnetic field remains closed over a limited range of latitutde
and height about the equatorial surface, but eventually is opened into nearly
radial configuration at large radii. Within the closed loops, the flow is
channeled toward loop tops into shock collisions that are strong enough
to produce hard X-rays. Within the open field region, the equatorial channeling
leads to oblique shocks that are again strong enough to produce X-rays
and also lead to a thin. dense, slowly outflowing ``disk'' at the magnetic
equator.
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CHANDRA/VLA Follow-up of Unidentified
TeV source TeV J2032+4131
Dr. Yousaf Butt
Center for Astrophysics
October 22
Abstract
The HEGRA Cherenkov telescope group recently reported an extended unidentified
TeV source in the Cyg OB2 region. We obtained a 5 ksec Director's Discretionary
Time (DDT) CHANDRA observation of the region of this source. In addition,
we secured a near-simultaneous VLA B-configuration observation sensitive
to point-like sources. We will present the results of our CHANDRA and VLA
follow-up observations of this source. Preliminary analysis indicates that
the TeV source may be the signature of the cumulative wind-shock of the
>2000 O & B stars in Cyg OB2 accelerating nuclei to TeV energies,
as in the model proposed by Bykov, SSRv, 99, 317 (2001).
New Results of Clusters of Galaxies Observed with XMM-Newton
Dr. Doris Neumann
CEA/Saclay
October 24
Abstract
Clusters of galaxies host huge amounts of hot X-ray emitting gas, which is
an ideal tracer for internal physics and dynamical processes. The X-ray observatory
XMM-Newton with its superb spectro-imaging capabilities offers a unique possiblity
to study in great detail this hot gas. I will show recent results on clusters
observed with XMM-Newton and will thereby address several issues: the dynamical
state of clusters, which is closely linked to structure formation, the dark
matter content of clusters, cluster X-ray shapes, which indicate strong self-similarity
as well as cluster evolution, which is tightly related to cosmological parameters.
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Dr. Olaf Reimer
University of Bochum
October 29
Abstract
We report EGRET upper limits on the high-energy gamma-ray emission from clusters
of galaxies. EGRET observations between 1991 and 2000 were analyzed at positions
of 58 individual clusters from a flux-limited sample of nearby X-ray bright
galaxy clusters.
Subsequently, a cumulative overlay of the data from individual galaxy clusters
has been analyzed utilizing an adequately adapted diffuse gamma-ray background
model. The resulting upper limit is ~ 6 x 10^{-9} cm^{-2} s^{-1} for E >
100 MeV. Implications from the nondetection of prominent individual
clusters and the general inability to detect the X-ray brightest galaxy clusters
as a class of gamma-ray emitters are discussed in comparison with existing
predictions on the high-energy gamma-ray emission and, especially, in respect
of recent contradictory claims about possible associations between gamma-ray
sources and clusters of galaxies.
Interstellar Dust and the X-ray Halo of GX13+1
Dr. Randall Smith
Center for Astrophysics
October 30
Abstract
I will present observations of the X-ray halo around the LMXB GX 13+1 from the Chandra X-ray telescope. The halo is caused by scattering in interstellar dust grains, and we used it to diagnose the line-of-sight position, size distribution, and density of the grains. Using the intrinsic energy resolution of Chandra's ACIS CCDs and the recent calibration observation of the Chandra point spread function (PSF), we were able to extract the halo fraction as a function of energy and off-axis angle. I will present a new quantity, the "halo coefficient," or the total halo intensity relative to the source at 1 keV which we measured to be 1.5+0.5-0.1 for GX 13+1. There is a direct relationship between this value and the dust size, density, and hydrogen column density along the line of sight to GX 13+1. I will also show that our data does not agree with "fluffy" dust models earlier X-ray halo observations have supported, nor does it agree with models including a substantial large dust grain population.
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X-ray Binaries in M101
Dr. Koji Mukai
USRA & GSFC-LHEA
November 5
Abstract
I will present results on X-ray binaies from our Chandra ACIS-S observations of the nearby face-on spiral galaxy, M101. The main aim of the proposal was the study of the diffuse soft X-ray emission in this galaxy (Kuntz et al, submitted) for which the removal of point sources (catalog published by Pence et al) is essential. I will present spectra and light curves of five bright X-ray sources that can be described as bright black hole binaries in M101. The brightest source detected (P098), however, does not fit the norm, although it, too, is likely to be a black hole binary in M101. The observed X-ray photons may have been scattered in an outflow, rather than originating in the accretion disk. I will briefly compare tese results with other studies of Ultraluminous X-ray Sources. Finally, I will compare the X-ray binary population of M101 with that of the Milky Way.
Hot outflows in Seyfert 1's: New results from Chandra HETG
Dr. Barry McKernan
Johns Hopkins University
November 12
Abstract
I present the soft X-ray spectra of several Seyfert 1 AGN as observed recently with Chandra HETG. I discuss the constraints on the warm absorbing gas in these AGN, including composition, location and kinematics. I shall also discuss the link between X-ray and UV warm absorption in Mkn 509 (using simultaneous HST-STIS data), the possibility of a dusty warm absorber in NGC 4593, as well as some intruiging absorption features in the spectrum of the Seyfert 1/BLRG 3c120.
HETE-2 and Swift: Using GRBs as a Probe of Cosmology
Dr. Don Lamb
University of Chicago
Wednesday, November 13, 2:00pm
Abstract
HETE-2 is currently localizing GRBs at a rate of ~ 30 yr^-1, many in near
real-time. About forty percent of the bursts that it has detected and localized
are XRFs. In addition, HETE-2 has localized a short burst, making possible
the first rapid follow-up of such a burst at X-ray, optical, and radio wavelengths.
The results of the HETE-2 mission so far highlight the importance of a spacecraft
and instruments providing accurate, real-time localizations for GRBs, and
imply that Swift will make major contributions to our understanding of GRBs.
In addition, HETE-2, and particularly Swift, hold out the promise of using
GRBs as a probe of cosmology. We describe recent work that we have done in
support of this goal
Sub-millimeter tests of the gravitational
inverse square law: extra dimensions and all that
Dr. Eric Adelberger
University of Washington
2002 William Nordberg Lecturer
Thursday, November 14, 1:00pm
Abstract
Attempts to unify gravity with the other 3 fundamental interactions face
two famous hierarchy problems: the extreme weakness of gravity compared
to electromagnetism and the smallness of the observed "cosmological
constant" compared to the vacuum energy prediction. Proposed solutions to
these two hierarchy problems predict modifications of the Newtonian inverse-square
law at separations less than 1 mm. Recent experimental tests that
test gravity at length scales down to 80 microns will be discussed.
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Infrared and Radio Properties of Dusty Wolf-Rayet Stars
Dr. John Monnier
University of Michigan
November 19
Abstract
The 10-meter Keck-I telescope has been converted into an interferometric
array using aperture masking techniques, allowing near-infrared imaging with
the diffraction-limited resolution of ~50 milli-arcseconds. In this
talk, I will focus on our observations of dust shells around Wolf-Rayet stars,
and what the newly-resolved spatial structure and time evolution reveals
about the underlying systems, the physics of colliding winds, and high mass
stellar evolution in general. We have also used the Very Large Array
to measure the broadband radio spectrum of WR stars in suspected binary systems
and discovered non-thermal emission, which is usually attributed to colliding
winds. Combining the near-IR imaging with the radio results has provided
fresh insights into the nature of colliding winds. Lastly, I will report
new results on WR 140, a 7.9-year binary system known to produce dust for
only a few months per orbit, which we successfully imaged at multiple epochs
during and after its recent periastron passage.
Prospects for Type Ia SN Explosion Mechanism
Identification through Supernova Remnants
Dr. Carles Badenes
Institut d'Estudis Espacials de Catalunya/Universitat Politecnica
de Catalunya
Friday November 22, 1:00pm
Abstract
Thermonuclear supernovae -also known as type Ia SN- have become a key tool
in modern astronomy. The recent spectacular results about the accelerated
expansion of our universe are based on the properties of these objects as
'standard candles', but our knowledge of the physics behind them is far from
being complete. In this talk I will make a short review of type Ia SN explosion
models and how their young supernova remnants might provide clues to learn
more about the explosions themselves.
A Report from the Chandra Calibration Workshop
Dr. Mike Corcoran
NASA GSFC/USRA
November 21; 12:00
Abstract
The first annual Chandra Calibration Workshop was held at the Chandra X-ray
Center on Nov 6 & 7. Topics covered included PSF's and the Telescope,
Detectors and the PSF, ACIS & HRC, spectral imaging, grating spectroscopy
and other issues. This talk will be an informal overview of the results
reported at the workshop.
Long-Term Evolution of Massive Black Hole
Binaries
Dr. Milos Milosavljevic
Caltech
Monday November 25, 3:00pm
Abstract
Air Shower Simulations of High Energy
Cosmic Rays
Dr. Analia Cillis
GSFC LHEA
November 26
Abstract
The history of the study of the cosmic
rays start with Victor Hess in 1912, but it wasn’t until the 30’s when Pierre
Auger observed the particle cascade of the air showers initiated by a cosmic
ray. He identified coincidences between detectors separated 300 m and deduced
that these coincidences were associated with secondary showers produced by
the interaction of a high energy cosmic ray with an atom of the atmosphere.
He thought that the cosmic ray spectrum could be extended beyond 1015eV.
Nowadays these cascades of particles or air showers can be detected by different
techniques like the fluorescent detectors and the surface arrays. But the
detection of air showers is not enough to infer the nature of the primary
particle. Numerical simulations are needed to analyze the different processes
that take place throughout the development of the cascade.
In this seminar I will present some of the results I have obtained during
my PhD work at University of La Plata (Argentina). Several numerical techniques
were developed in order to simulate some of the processes that appear in
the high energy air showers. These algorithms were incorporated in the air
shower simulation system AIRES. The processes studied were: The Landau-Pomeranchuk-Migdal
effect and the dielectric suppression, the electromagnetic processes with
muons, and the deflections produced by the geomagnetic field over the charged
particles in the cascade.
The AIRES program is one of the simulation tools that is being used by the
Pierre Auger team. The Pierre Auger Observatory is now under construction
in Pampa Amarilla (Mendoza, Argentina).
Galaxies in the Chandra Deep Fields
Dr. Ann Hornschemeier
Johns Hopkins University
December 3
Abstract
This talk will cover recent results on the population of normal and starburst
galaxies being detected in extremely deep exposures with the Chandra X-ray
Observatory. This population is diverse, and includes galaxies which are
dominated by an individual off-nuclear X-ray source (e.g., extremely luminous
X-ray binaries or supernova remnants). These sources may provide the first
direct constraints on the prevalence of lower-mass black holes at significantly
earlier times. The X-ray emission from such ``normal" galaxies may also be
a useful star-formation rate indicator, based on radio/X-ray cross-identifications.
Such studies will be greatly improved through the Great Observatories Origins
Deep Survey (GOODS) which covers the two Chandra Deep Fields. The HST Advanced
Camera for Surveys (ACS) observations for the southern field have been partially
completed and I will provide a GOODS ACS "sneak preview" of these publicly
available data. I will also suggest that it is important that the population
of X-ray faint normal and starburst galaxies be well constrained in order
to design the next generation of X-ray observatories.
X-ray Synchrotron
Radiation from Shell Supernova Remnants:
A Diagnostic of Strong-Shock Physics
Dr. Stephen P. Reynolds
Harvard-Smithsonian
Center for Astrophysics and
Physics Department, North Carolina State University
Friday December 6, 2:00pm
Abstract
If supernova-remnant shock waves are responsible for the production of Galactic
cosmic rays, as has long been assumed, they should produce power-law distributions
of electrons, as well as ions, to extremely high energies, possibly to 1000
TeV and beyond. Electrons with energies above a few tens of TeV should radiate
synchrotron radiation in the soft X-ray regime. This contribution to the
complex X-ray spectrum of remnants was predicted over 20 years ago, but only
unambiguously identified in the last seven years. Four or five Galactic
remnants now show strong evidence for synchrotron X-ray emission which can
be interpreted as coming from the cutting-off tail of the same electron distribution
responsible for radio emission. The observed cutoff energies, and the spatial
distribution of synchrotron emission, contain information on both macroscopic
and microphysical parameters of the remnants: shock speed and remnant age,
but also electron diffusion coefficients and the obliquity angle between
the shock normal and the upstream magnetic field. I shall review both theory
and observations of this important new phenomenon, and its contributions
to our understanding of the acceleration of particles to high energies in
astrophysical shock waves in general.
Intermediate Mass Black Holes in the Universe: Formation Mechanisms
and Observational Constraints
Dr. Roeland van der Marel
Space Telescope Science Institute
December 10
Abstract
Astronomers have long believed that black holes naturally form in the Universe
in two mass ranges. Stellar-mass black holes form when a heavy star collapses
under its own weight in a supernova explosion, and have been identified in
X-ray binaries. Super-massive black holes probably form as a byproduct of
galaxy formation, and are found in the centers of galaxies where they sometimes
generate prodigious activity. However, black holes could have formed in the
Universe in different mass ranges. Intermediate mass black holes of 10^2-10^5
solar masses are an especially interesting possibility. I will review the
possible formation mechanisms for such black holes, as well as the observational
constraints on their existence. This includes discussions of recent work
with HST on nearby globular clusters and with Chandra on intermediate luminosity
X-ray objects in nearby galaxies.
Simulating Core-Collapse Supernovae: Understanding the Death
of Massive Stars
Dr. Bronson Messer
Univ. of Tennessee/ORNL
Thursday December 12 1:30pm
Abstract
Core-collapse supernovae are among the most spectacular of astrophysical
events, and their associated phenomenology is
remarkably varied. Not coincidentally, simulating these massive stellar
explosions is one of the most challenging problems in computational astrophysics.
I will describe recent results highlighting the need to enhance the realism
incorporated in supernovae simulations, ranging from improvements in microphysical
inputs to the need for multidimensional models with sophisticated neutrino
transport.
Searching for Gravitational Waves from
Inspiraling
Binaries of Compact Objects with Earth-Based Interferometers
Dr. Alessandra Buonanno
Monday December 16 3:30 pm
Abstract
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Flow Collisions in Astrophysics:
Far from Stationary and Full of Surprises
Dr. Rolf Walder
ETHZ Institut fuer Astronomie
December 17
Abstract
New high resolution observations of colliding flow regions - supernova-remnants,
wind-driven structures, jets, or star- and galaxy-formations - reveal a wealth
of density structures and turbulent motion, in wave-length bands from infrared
to X-rays. Modern, numerical models of such objects indeed show the involved
radiative shocks to develop highly time-dependent and turbulent
structure. These numerical results, although difficult to interpret in detail
and not accounting for all the physics involved, generally fit better with
observations than do stationary models.
In my talk, I present numerical simulations of colliding flows. This comprises
rather theoretical investigations of basic processes as well as simulations
of astrophysical objects. I want to address two main aspects of the physics
of colliding flows: the stability of radiative shocks and the supersonic turbulent
state of the cooled gas. The insights gained here form the basis for a more
thorough understanding of the observed complex shape and internal structure
of interaction zones, with their mixing of hot and cold gas and their clumpy
and filamentary appearance. I will discuss some astrophysical implications
at the example of colliding wind binaries and of wind-driven structures.
This brings me to the last focal point of my talk, namely the collision of
non-homogeneous, clumped flows as they occur for example in hot star binaries.
The possible connection to the observed formation of dust in the immediate
neighborhood of X-ray emitting gas in such systems will be discussed.
Measuring the Evolution of Cosmic Expansion
with SNAP
Dr. Tim McKay
University of Michigan
Thursday December 19 2:00pm
Abstract
Over the last decade we have witnessed the emergence of a 'consensus cosmology' in which the current baryon density, dark matter density, expansion rate, and cosmological constant are reasonably well known. The coming task is to explore the expansion history of the universe.
Details of the expansion history are imprinted on cosmological distance measures and on the growth of structure. I will compare several promising observational signatures, then focus on the most mature; measurements of the luminosity distance using type Ia supernovae. I'll describe details of the proposed Supernova/Acceleration Probe (SNAP); a wide field optical-NIR space telescope designed to enable a precise measurement of the expansion history out to redshifts approaching 2. I'll also comment on the possible impact of such a powerful survey telescope on
other science topics.
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