Ultraluminous X-ray Sources and Star Formation

Chandra observations of the Cartwheel galaxy reveal a population of ultraluminous X-ray sources (ULXs) with lifetimes < 10^7 yr associated with a spreading wave of star formation which began some 3 x 10^8 yr ago. A population of high-mass X-ray binaries provides a simple model: donor stars of initial masses M_2 > 15 Msun transfer mass on their thermal timescales to black holes of masses M_1 > 10 Msun. For alternative explanations of the Cartwheel ULX population in terms of intermediate-mass black holes (IMBH) accreting from massive stars, the inferred production rate > 10^-6 yr^-1 implies at least 300 IMBHs, and more probably 3 x 10^4, within the star-forming ring. These estimates are increased by factors eta^-1 if the efficiency eta with which IMBHs find companions of > 15 Msun within 10^7 yr is <1. Current models of IMBH production would require a very large mass (\ga 10^{10}\msun) of stars to have formed new clusters. Further, the accretion efficiency must be low (< 6 x 10^-3) for IMBH binaries, suggesting super-Eddington accretion, even though intermediate black hole masses are invoked with the purpose of avoiding it. These arguments suggest either that to make a ULX, an IMBH must accrete from some as yet unknown non-stellar mass reservoir with very specific properties, or that most if not all ULXs in star-forming galaxies are high-mass X-ray binaries.Comment: 3 pages, no figures; MNRAS accepted with minor amendment

BAL QSOs and Extreme UFOs: the Eddington connection

We suggest a common physical origin connecting the fast, highly ionized winds (UFOs) seen in nearby AGN, and the slower and less ionized winds of BAL QSOs. The primary difference is the mass loss rate in the wind, which is ultimately determined by the rate at which mass is fed towards the central supermassive black hole (SMBH) on large scales. This is below the Eddington accretion rate in most UFOs, and slightly super-Eddington in extreme UFOs such as PG1211+143, but ranges up to $\sim 10-50$ times this in BAL QSOs. For UFOs this implies black hole accretion rates and wind mass loss rates which are at most comparable to Eddington, giving fast, highly-ionized winds. In contrast BAL QSO black holes have mildly super-Eddington accretion rates, and drive winds whose mass loss rates are significantly super-Eddington, and so are slower and less ionized. This picture correctly predicts the velocities and ionization states of the observed winds, including the recently-discovered one in SDSS J1106+1939. We suggest that luminous AGN may evolve through a sequence from BAL QSO through LoBAL to UFO-producing Seyfert or quasar as their Eddington factors drop during the decay of a bright accretion event. LoBALs correspond to a short-lived stage in which the AGN radiation pressure largely evacuates the ionization cone, but before the large-scale accretion rate has dropped to the Eddington value. We show that sub-Eddington wind rates would produce an $M - \sigma$ relation lying above that observed. We conclude that significant SMBH mass growth must occur in super-Eddington phases, either as BAL QSOs, extreme UFOs, or obscured from direct observation.Comment: 8 pages, 5 figures; a higher quality version of Figure 5 available on reques

The ultimate outcome of black hole - neutron star mergers

We present a simple, semi--analytical description for the final stages of mergers of black hole (BH) -- neutron star (NS) systems. Such systems are of much interest as gravitational wave sources and gamma--ray burst progenitors. Numerical studies show that in general the neutron star is not disrupted at the first phase of mass transfer. Instead, what remains of the neutron star is left on a wider, eccentric, orbit. We consider the evolution of such systems as they lose angular momentum via gravitational radiation and come into contact for further phases of mass transfer. During each mass transfer event the neutron star mass is reduced until a critical value where mass loss leads to a rapid increase in the stellar radius. At this point Roche lobe overflow shreds what remains of the neutron star, most of the mass forming a disc around the black hole. Such a disc may be massive enough to power a gamma--ray burst. The mass of the neutron star at the time of disruption (and therefore the disc mass) is largely independent of the initial masses of the black hole and neutron star, indicating that BH--NS star mergers may be standard candles.Comment: MNRAS, in pres

Neutron star binaries and long duration gamma-ray bursts

Cosmological long-duration gamma-ray bursts (LGRBs) are thought to originate from the core collapse to black holes of stripped massive stars. Those with sufficient rotation form a centrifugally-supported torus whose collapse powers the GRB. We investigate the role of tidal locking within a tight binary as a source of the necessary angular momentum. We find that the binary orbit must be no wider than a few solar radii for a torus to form upon core collapse. Comparing this criterion to the observed population of binaries containing two compact objects suggests that rotation may have been important in the formation of up to 50% of the observed systems. As these systems created a neutron star and not a black hole they presumably did not produce highly luminous GRBs. We suggest instead that they make the subset of GRBs in the relatively local universe which have much lower luminosity.Comment: 7 pages, accepted for publication in MNRA

Progenitors of Long Gamma-ray Bursts

Pinpointing the progenitors of long duration gamma-ray bursts (LGRBs) remains an extremely important question, although it is now clear that at least a fraction of LGRBs originate in the core collapse of massive stars in type Ic supernovae, the pathways to the production of these stars, and their initial masses, remain uncertain. Rotation is thought to be vital in the creation of LGRBs, and it is likely that black hole creation is also necessary. We suggest that these two constraints can be met if the GRB progenitors are very massive stars (>20 solar masses) and are formed in tight binary systems. Using simple models we compare the predictions of this scenario with observations and find that the location of GRBs on their host galaxies are suggestive of main-sequence masses in excess of 20 solar masses, while 50% of the known compact binary systems may have been sufficiently close to have had the necessary rotation rates for GRB creation. Thus, massive stars in compact binaries are a likely channel for at least some fraction of LGRBs.Comment: To appear in "Gamma-ray bursts: Prospects for GLAST", AIP Conference proceedings 906, Editors M. Axelsson and F Ryd

Opening the Halls of Power: Implementing a Community Organizing Approach to Parent Engagement in New York City’s Community Schools

Under former Mayor Bill de Blasio, New York City launched a Community Schools Initiative (NYC-CS) in 2014 that now includes more than 300 schools, making it the largest school improvement plan of its kind in the country. Bloomberg, the previous mayor, had championed market-based reform strategies by closing struggling public schools and replacing them with privately run charter schools. In contrast, the community schools model supports struggling schools by providing them with wraparound services to address not only the academic—but also the health, social, and emotional—needs of the “whole child.” Research has shown the NYC initiative has had positive impacts on student performance, test scores, and graduation rates. These services benefited not only students but also their families, drawing parents into the life of the school. From the beginning, a robust parent engagement program was designed to be a central pillar of NYC-CS. My study focused on this crucial component. Research shows strong parent engagement is crucial for school improvement. Yet urban schools are often disconnected from the families they are meant to serve. Racially-based deficit narratives held by many white school staff about black and brown families, along with punitive discipline policies, alienate parents of color from education systems. In response, different approaches have been formulated to foster meaningful parent engagement, yet many remain superficial. Education justice advocates have called for transformative approaches which use an asset-based lens, value the knowledge of marginalized parents, and seek to develop their leadership in school decision-making processes. NYC-CS was shaped by a grassroots visioning process. Many community organizers and parent leaders who led this effort were subsequently hired by the NYC Department of Education to form a citywide Family and Community Outreach Team (FACE). In a distinctive turn, the FACE team took a “community organizing approach” to support parent engagement and leadership in the community schools. Through a mixed-methods study, I investigated and analyzed the processes through which a large urban school district came to adopt such an approach and to understand how it was enacted. In my qualitative research, I conducted in-depth virtual interviews with the FACE team’s Family Outreach Specialists as well as education organizers in order to understand how the family engagement program was developed and implemented. In the quantitative portion, I used Coarsened Exact Matching and linear regression analysis to examine the association between community school status and family engagement levels as measured by parent survey responses. I found that FACE’s Family Outreach Specialists—many of whom were previously “outsiders” who had protested against DOE policies but who now worked on the “inside”—successfully employed political and community organizing strategies to recruit parents and develop them as active leaders in the schools. Through their Ladders of Engagement program, they door-knocked in the neighborhoods to meet marginalized families “where they’re at”; cultivated trusting one-on-one relationships with parents; used phone banking for large-scale outreach; and drew parents into a participatory planning process through Community School Forums. I analyzed four new community school structures that enhanced the capacity for family engagement: a school partnership with a community-based organization; the hiring of a Community School Director; the formation of a Community School Team; and the hosting of Community School Forums. These processes led parents to: form substantial new relationships with one another (building social capital) and with school staff (bridging capital); in some cases, secure employment in the school system; and in other cases, engage in collective action on a broader civic level. However, the program also ran into significant obstacles, including resistance, scaling up and sustaining the model. In my quantitative analysis, I found that community schools, when compared to matched (demographically similar) comparison schools, were positively associated with greater increases in parent survey response rates, higher percentages of self-reported parent volunteer rates, and higher ratings on the DOE’s “Strong Family-Community Ties” category. This study contributes to our understanding of how the community schools strategy and community organizing approaches are able to empower parents and draw them into school leadership and how they can be successfully implemented in mutually reinforcing ways. I demonstrate that these organizing practices, which are often carried out by activists on the “outside” can be brought “inside,” institutionalized, and implemented on a large scale

Superhumps in Low-Mass X-Ray Binaries

We propose a mechanism for the superhump modulations observed in optical photometry of at least two black hole X-ray transients (SXTs). As in extreme mass-ratio cataclysmic variables (CVs), superhumps are assumed to result from the presence of the 3:1 orbital resonance in the accretion disc. This causes the disc to become non-axisymmetric and precess. However the mechanism for superhump luminosity variations in low mass X-ray binaries (LMXBs) must differ from that in CVs, where it is attributed to a tidally-driven modulation of the disc's viscous dissipation, varying on the beat between the orbital and disc precession period. By contrast in LMXBs, tidal dissipation in the outer accretion disc is negligible: the optical emission is overwhelming dominated by reprocessing of intercepted central X-rays. Thus a different origin for the superhump modulation is required. Recent observations and numerical simulations indicate that in an extreme mass-ratio system the disc area changes on the superhump period. We deduce that the superhumps observed in SXTs arise from a modulation of the reprocessed flux by the changing area. Therefore, unlike the situation in CVs, where the superhump amplitude is inclination-independent, superhumps should be best seen in low-inclination LMXBs, whereas an orbital modulation from the heated face of the secondary star should be more prominent at high inclinations. Modulation at the disc precession period (10s of days) may indicate disc asymmetries such as warping. We comment on the orbital period determinations of LMXBs, and the possibility and significance of possible permanent superhump LMXBs.Comment: 6 pages, 1 encapsulated figure. MNRAS in press; replaced to correct typographical error

The analysis of 108mAg, 166mHo and 94Nb in decommissioning waste

Contaminated waste consisting of various materials results from the decommissioning of nuclear power plants. Disposal of Decommissioning Waste requires as much measurement data for the radionuclides contained within the waste as possible. Data that are obtained is then used to create an inventory of the radionuclides in the various types of wastes. This research investigates a route to obtaining additional measurement data for such inventories. The importance of these inventories is to provide as much information as possible so that a reliable risk assessment can be performed on the waste samples and the proposed method of disposal. [Continues.

Post-Fledging Dispersal of Burrowing Owls in Southwestern Idaho: Characterization of Movements and Use of Satellite Burrows

Using radiotelemetry, we monitored dispersing juvenile Western Burrowing Owls (Athene cunicularia hypugaea) within a migratory population in southwestern Idaho during 1994 and 1995. Owls remained within natal areas for an average (± SE) of 58 ± 3.4 days post-hatching before moving permanently beyond 300 m, which was our operational cutoff for dispersal from the natal area. On average, owls dispersed on 27 July (range: 15 July to 22 August), which was approximately 4 weeks after fledging. After initiating dispersal, juveniles continued moving farther away from their natal burrows and, by 61-65 days post-hatching, they had moved 0.6 ± 0.2 km. Each juvenile used 5.1 ± 1.2 satellite burrows, and individual satellite burrows were used for up to 14 days. The average date on which we last sighted radio-tagged juveniles was 13 August, and all but one juvenile departed the study area by early September. Our study illustrates the importance of satellite burrows to dispersing Burrowing Owls