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
  • 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

  • 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.


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    2 3 4 - Joe Weingartner (GMU), The Alignment of Grains with the Interstellar Magnetic Field 5 6 7 8
    9 10 11 12 - Enrico Ramirez-Ruiz (IAS, Princeton), Cancelled 13 14 15
    16 17 18 - D. Q. Lamb (Chicago), Exciting Recent Discoveries About Short GRBs and Their Implications 19 20 21 22
    23 24 25 Gloria Koenigsberger (UNAM), The X-ray binary 2S0114+650: X-ray variability due to tidally-induced pulsations? 26 Remo Ruffini (U. Rome La Sapienza) - GRB 050315: A step in the proof of the uniqueness of the overall GRB structure 27 28 29


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
      1 2 Richard Lieu (U.Alabama, Hunstville) - The soft X-ray excess and near complete absence of Sunyaev-Zel'dovich effect 3 4 5 6
    7 8 9 Edwin F. Erickson (NASA/ARC) - SOFIA: the Stratospheric Observatory for Infrared Astronomy 10 11 12 13
    14 15 16 Philipp Kronberg (LANL), Where do intergalactic CR's and magnetic fields come from? Implications of recent discoveries for coming generations of space- and ground-based instruments. 17 18 Daniel Hudson (AIfA, U.Bonn) - The Proto Supermassive Binary Black Hole at the Centre of Abell 400 19 20
    21 22 23 Gary Hinshaw (GSFC) - Third Year WMAP Results 24 25 26 27
    28 29 30 Massimo Persic (INAF/Trieste)- Gamma-ray astrophysics with the MAGIC telescope 31    


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
         1 Ravi Manchanda (Tata Inst.) - ASTROSAT: The Indian Multi-wavelength Astronomy Satellite 2 Ewine van Dishoeck (Leiden Obs.) - Spitzer Space Telescope Observations of Star- and Planet-Forming Regions 3
    4 5 6 Yael Naze (Inst. Astro/Geo, Univ. Liege) - Peculiar Objects of the Massive Star Population 7 8 9 10
    11 12 13 Wlodzimierz Kluzniak (GSFC)- Twin kHz QPOs as a Non-linear Resonance in a Relativistic Accretion Disk 14 15 16 17
    18 19 20 21 22 23 24
    25 26 27 Mustapha Ishak-Boushaki (U.Texas)- Cosmic acceleration: Dark Energy or Modified gravity? 28 29 30

    The Alignment of Grains with the Interstellar Magnetic Field

    Joseph C. Weingartner

    Dept. of Physics and Astronomy, George Mason University

    Tuesday, April 4, 2006


    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.

    Exciting Recent Discoveries About Short GRBs and Their Implications

    D. Q. Lamb


    Tuesday, April 18, 2006


    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.

    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


    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.

    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 ***


    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.

    The soft X-ray excess and near complete absence of Sunyaev-Zel'dovich effect

    Richard Lieu

    University of Alabama, Huntsville

    Tuesday, May 2, 2006


    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.

    SOFIA: the Stratospheric Observatory for Infrared Astronomy

    Edwin F. Erickson


    Tuesday, May 9, 2006


    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.

    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


    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.

    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 ***


    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.

    Third Year WMAP Results

    Gary Hinshaw

    NASA/Goddard Space Flight Center

    Tuesday, May 23, 2006


    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.

    Gamma-ray Astrophysics with the MAGIC Telescope

    Massimo Persic

    INAF and Osservatorio Astronomico di Trieste

    Tuesday, May 30, 2006


    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.

    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 ***


    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.

    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 ***


    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.

    Peculiar Objects of the Massive Star Population

    Yael Naze

    Institut d'Astrophysique et de Geophysique,
    Universite de Liege

    Tuesday, June 6, 2006


    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.

    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


    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.

    Cosmic acceleration: Dark Energy or Modified gravity?

    Mustapha Ishak-Boushaki

    University of Texas

    Tuesday, June 27, 2006


    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.

    Jerry Bonnell

    NASA Logo, National Aeronautics and Space Administration