LISA Observations of Supermassive Black Hole Growth

Based on a high resolution cosmological n-body simulation, we track the hierarchical growth of black holes in galaxy clusters from z=20 to z=0. We present a census of black holes as function of redshift and will determine their mass assembly history under a variety of assumptions regarding the importance of gas accretion in black hole growth, from early supercritical Eddington accretion to gas-poor hierarchical assembly. Following a galaxy merger, black holes are expected to form, inspiral and merge after strongly radiating energy via gravitational waves. For each binary black hole inspiral and merger, we determine the expected gravitational wave signal for the Laser Interferometer Space Antenna (LISA), and calculate the LISA event rate as a function of time. We will calculate the black hole mass assembly history for several black hole growth scenerios, so that we can explore tests to characterize each model observationally. In particular, we will study how well LISA observations will be able to distinguish between these very different assembly scenarios.Comment: 5 pages, 11 figures, proceedings, Sixth International LISA Symposium, June 19-23, 2006 Goddard Space Flight Center Greenbelt, Marylan

Interpretation of the 115 Day Periodic Modulation in the X-ray Flux of NGC 5408 X-1

We comment on the recent observation of a 115-day modulation in the X-ray flux of the ultraluminous X-ray source (ULX) NGC 5408 X-1, and in particular, the interpretation of this modulation as the orbital period. We suggest that this modulation may instead be due to a precessing jet, and is thus superorbital in nature. Comparing the properties of this ULX with those of the prototypical microquasar SS 433, we argue that NGC 5408 X-1 is very similar to SS 433: a hyper-accreting stellar mass black hole in a shorter-period binary. If the analogy holds, the 115-day modulation is best explained by the still poorly-understood physics of inner-disc/jet precession and a longer observing baseline would be able to reveal an intrinsic phase jitter that is associated with such a precession.Comment: 5 pages, 1 figure, Accepted for publication in Ap

The Effects of a Shared Vision of Teacher Leadership on Classroom Teachers’ Instruction

Many models of instructional teacher leadership exist in schools with various outcomes for teachers. The aim of this case study was to understand systemic alignment in a formal teacher leadership system and how this alignment impacted instructional change. This dissertation was framed by three research questions: 1) How do the rationales of teachers, teacher leaders, and administrators regarding teacher leadership in their school align? 2) How does the coherence of a system of leadership impact classroom teachers’ abilities to engage with formal teacher leaders? 3) How does the coherence of a system of leadership impact classroom teachers’ abilities to implement instructional changes? A qualitative case study was conducted utilizing semi-structured interviews in one rural school in Minnesota. The participants included one K–12 principal, two high school teacher leaders, two high school teachers, two elementary teacher leaders, and two elementary teachers, and a district Q Comp Coordinator. Role theory (Biddle 1979; Katz & Kahn, 1978; & Turner, 2002) was the theoretical framework used to analyze the data. The findings yielded two scenarios: The elementary in which systemic alignment and a positive engaging culture was associated with the teachers’ willingness to implement instructional change; and the high school in which a slight variation in the shared vision regarding ownership rendered role conflict, periods of teacher-teacher leader disengagement, and teacher instructional changes dependent upon feelings of ownership and relevance