Astrophysics Science Division Colloquium Series
Schedule: July - September 2007

Astrophysics Science Division Colloquium Series
Schedule: July - September 2007

Through the courtesy of the speakers since 2004, most presentations are available on line.

Future schedules:

  • 2007, Fourth Quarter
  • Recent schedules:

  • 2007, Second Quarter
  • 2007, First Quarter
  • 2006, Fourth Quarter
  • 2006, Third Quarter
  • 2006, Second Quarter
  • 2006, First 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
    1 2 3 Dominic Benford (NASA/GSFC) - Beyond Einstein: The "DESTINY" mission 4 5 6 7
    8 9 10 No Talk 11 12 13 14
    15 16 17 No Talk 18 19 20 21
    22 23 24 Fotis Gavriil (NASA/GSFC NPP) - Magnetars Gone Wild 25 26 27 28
    29 30 31 Al Kogut (NASA/GSFC) - The "ASP" mission


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    1 2 3 4
    5 6 7 Phillip Kaaret (U of Iowa)Ultraluminous X-ray Sources 8 9 10 11
    12 13 14 Robin Stebbins (NASA/GSFC) - Beyond Einstein: The "LISA" mission 15 16 17 18
    19 20 21 Paul Nulsen (SAO) - AGN/Cluster Feedback 22 23 24 25
    26 27 28 Josh Grindlay (Harvard) - Beyond Einstein: The Case for the Black Hole Finder Mission to EXIST 29 Julian Krolik (JHU) - Understanding Accretion Disks Around Black Holes 30 31


    Sunday Monday Tuesday Wednesday Thursday Friday Saturday
    2 3 4 Bram Boroson "Problem" Means "Opportunity": When X-ray Binaries Distort Winds They Reveal Them 5 6 7 8
    9 10 11 Tracy Clarke (NRL) Tracing the AGN/ICM Connection in Cooling Cores with Low Frequency Radio and X-ray Observations 12 13 14 15
    16 17 18 David Morris (PSU) Properties of Late Time X-ray Flares in GRBs 19 20 21 22
    23 24 25 Neal Miller (JHU) The VLA 1.4 GHz Survey of the Extended Chandra Deep Field South 26 27 28 29

    Beyond Einstein: The "DESTINY" mission

    Dominic Benford

    NASA/Goddard Space Flight Center

    Tuesday, July 3, 2007


    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.

    Magnetars Gone Wild

    Fotis Gavriil

    NASA/Goddard Space Flight Center NPP

    Tuesday, July 24, 2007


    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.

    The "ASP" mission

    Al Kogut

    NASA/Goddard Space Flight Center

    Tuesday, July 31, 2007


    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.

    Ultraluminous X-ray Sources

    Prof. Phillip Kaaret

    University of Iowa

    Tuesday, August 7, 2007


    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.

    Beyond Einstein -- LISA: The Science and the Instrument

    Robin "Tuck" Stebbins

    NASA/Goddard Space Flight Center

    Tuesday, August 14, 2007


    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.

    AGN/Cluster Feedback

    Paul Nulsen

    Smithsonian Astrophysical Observatory

    Tuesday, August 21, 2007


    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.

    Beyond Einstein: The Case for the Black Hole Finder Mission to EXIST

    Josh Grindlay

    Smithsonian Astrophysical Observatory

    Tuesday, August 28, 2007


    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.

    Understanding Accretion Disks Around Black Holes

    Julian Krolik

    The Johns Hopkins University

    Wednesday, August 29, 2007


    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.

    "Problem" Means "Opportunity": When X-ray Binaries Distort Winds They Reveal Them

    Bram Boroson

    Tuesday, September 4, 2007


    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.

    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


    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.

    Properties of Late Time X-ray Flares in GRBs

    David Morris

    Pennsylvania State University

    Tuesday, September 18, 2007


    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.

    The VLA 1.4GHz Survey of the Extended Chandra Deep Field South

    Neal Miller

    The Johns Hopkins University

    Tuesday, September 25, 2007


    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.

    Randall Smith
    NASA Logo, National Aeronautics and Space Administration