The Spatial Distribution of Coalescing Neutron Star Binaries: Implications for Gamma-Ray Bursts

We find the distribution of coalescence times, birthrates, spatial velocities, and subsequent radial offsets of coalescing neutron stars (NSs) in various galactic potentials accounting for large asymmetric kicks introduced during a supernovae. The birthrates of bound NS-NS binaries are quite sensitive to the magnitude of the kick velocities but are, nevertheless, similar (~10 per Galaxy per Myr) to previous population synthesis studies. The distribution of merger times since zero-age main sequence is, however, relatively insensitive to the choice of kick velocities. With a median merger time of ~100 Myr, we find that compact binaries should closely trace the star formation rate in the Universe. In a range of plausible galactic potentials (M_galaxy > 3 x 10^10 M_solar) the median radial offset of a NS-NS mergers is less than 10 kpc. At a redshift of z=1 (with H_0 = 65 km/s/Mpc and Omega = 0.2), this means that half the coalescences should occur within ~1.3 arcsec from the host galaxy. In all but the most shallow potentials, ninety percent of NS-NS binaries merge within 30 kpc of the host. We find that although the spatial distribution of coalescing neutron star binaries is consistent with the close spatial association of known optical afterglows of gamma-ray bursts (GRBs) with faint galaxies, a non-negligible fraction (~15 percent) of GRBs should occur well outside (>30 kpc) dwarf galaxy hosts. Extinction due to dust in the host, projection of offsets, and a range in interstellar medium densities confound the true distribution of NS-NS mergers around galaxies with an observable set of optical transients/galaxy offsets.Comment: Accepted to MNRAS (12 Jan 1999

Associations of Patient Health-Related Problem Solving with Disease Control, Emergency Department Visits, and Hospitalizations in HIV and Diabetes Clinic Samples

BACKGROUND: Patient problem solving and decision making are recognized as essential to effective self-management across multiple chronic diseases. However, a health-related problem-solving instrument that demonstrates sensitivity to disease control parameters in multiple diseases has not been established. OBJECTIVES: To determine, in two disease samples, internal consistency and associations with disease control of the Health Problem-Solving Scale (HPSS), a 50-item measure with 7 subscales assessing effective and ineffective problem-solving approaches, learning from past experiences, and motivation/orientation. DESIGN: Cross-sectional study. PARTICIPANTS: Outpatients from university-affiliated medical center HIV (N = 111) and diabetes mellitus (DM, N = 78) clinics. MEASUREMENTS: HPSS, CD4, hemoglobin A1c (HbA1c), and number of hospitalizations in the previous year and Emergency Department (ED) visits in the previous 6 months. RESULTS: Administration time for the HPSS ranged from 5 to 10 minutes. Cronbach’s alpha for the total HPSS was 0.86 and 0.89 for HIV and DM, respectively. Higher total scores (better problem solving) were associated with higher CD4 and fewer hospitalizations in HIV and lower HbA1c and fewer ED visits in DM. Health Problem-Solving Scale subscales representing negative problem-solving approaches were consistently associated with more hospitalizations (HIV, DM) and ED visits (DM). CONCLUSIONS: The HPSS may identify problem-solving difficulties with disease self-management and assess effectiveness of interventions targeting patient decision making in self-care