339 research outputs found
Second Mortgages and Household Saving
Second mortgages accounted for 10.8% of the stock of outstanding mortgage debt at the end of 1987, up from 3.6% at the beginning of the 198Os. This paper investigates the determinants of second mortgage borrowing and the characteristics of second mortgage borrowers. We first calculate the outstanding stock of home equity that remains to be borrowed against on tax-preferred terms, recognizing the limits on interest deductions in the 1986 Tax Reform Act and the 1987 Omnibus Budget Reconciliation Act. Despite these limits, we estimate that more than two trillion dollars of housing equity remains to be borrowed against by current homeowners. We then present cross-sectional evidence suggesting that households who obtain second mortgages after purchasing a home ace less wealthy than other households with similar characteristics. Each dollar of second mortgage borrowing is associated with a seventy-five cent reduction in household net worth. While these results cannot be given a causal interpretation, they are consistent with the view that increased access to second mortgages has reduced personal saving.
Assessing the Role of Spin Noise in the Precision Timing of Millisecond Pulsars
We investigate rotational spin noise (referred to as timing noise) in
non-accreting pulsars: millisecond pulsars, canonical pulsars, and magnetars.
Particular attention is placed on quantifying the strength and non-stationarity
of timing noise in millisecond pulsars because the long-term stability of these
objects is required to detect nanohertz gravitational radiation. We show that a
single scaling law is sufficient to characterize timing noise in millisecond
and canonical pulsars while the same scaling law underestimates the levels of
timing noise in magnetars. The scaling law, along with a detailed study of the
millisecond pulsar B1937+21, leads us to conclude that timing noise is latent
in most millisecond pulsars and will be measurable in many objects when better
arrival time estimates are obtained over long data spans. The sensitivity of a
pulsar timing array to gravitational radiation is strongly affected by any
timing noise. We conclude that detection of proposed gravitational wave
backgrounds will require the analysis of more objects than previously suggested
over data spans that depend on the spectra of both the gravitational wave
background and of the timing noise. It is imperative to find additional
millisecond pulsars in current and future surveys in order to reduce the
effects of timing noise.Comment: 16 pages and 6 figures. ApJ, accepte
No Neutron Star Companion To The Lowest Mass SDSS White Dwarf
SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity
white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun;
Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to
originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems.
An optical search for J0917+4638's companion showed that it must be a compact
object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank
Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to
uncover a potential NS companion to the LMWD. No convincing pulsar signal is
detected in our radio data. Our X-ray observation also failed to detect X-ray
emission from J0917+4638's companion, while we would have detected any of the
millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost
certainly another WD.Comment: 4 pages, 1 table; to appear in the Astrophysical Journal Letter
A Binary Millisecond Pulsar in Globular Cluster NGC6544
We report the detection of a new 3.06 ms binary pulsar in the globular
cluster NGC6544 using a Fourier-domain ``acceleration'' search. With an implied
companion mass of ~0.01 solar masses and an orbital period of only P_b~1.7
hours, it displays very similar orbital properties to many pulsars which are
eclipsed by their companion winds. The orbital period is the second shortest of
known binary pulsars after 47 Tuc R. The measured flux density of 1.3 +/- 0.4
mJy at 1332 MHz indicates that the pulsar is almost certainly the known
steep-spectrum point source near the core of NGC6544.Comment: Accepted by ApJ Letters on 11 October 2000, 5 page
Tests of Dynamical Flux Emergence as a Mechanism for CME Initiation
Current coronal mass ejection (CME) models set their lower boundary to be in
the lower corona. They do not calculate accurately the transfer of free
magnetic energy from the convection zone to the magnetically dominated corona
because they model the effects of flux emergence using kinematic boundary
conditions or simply assume the appearance of flux at these heights. We test
the importance of including dynamical flux emergence in CME modeling by
simulating, in 2.5D, the emergence of sub-surface flux tubes into different
coronal magnetic field configurations. We investigate how much free magnetic
energy, in the form of shear magnetic field, is transported from the convection
zone to the corona, and whether dynamical flux emergence can drive CMEs. We
find that multiple coronal flux ropes can be formed during flux emergence, and
although they carry some shear field into the corona, the majority of shear
field is confined to the lower atmosphere. Less than 10% of the magnetic energy
in the corona is in the shear field, and this, combined with the fact that the
coronal flux ropes bring up significant dense material, means that they do not
erupt. Our results have significant implications for all CME models which rely
on the transfer of free magnetic energy from the lower atmosphere into the
corona but which do not explicitly model this transfer. Such studies of flux
emergence and CMEs are timely, as we have new capabilities to observe this with
Hinode and SDO, and therefore to test the models against observations
The Performance and Calibration of the CRAFT Fly's Eye Fast Radio Burst Survey
Since January 2017, the Commensal Real-time ASKAP Fast Transients survey
(CRAFT) has been utilising commissioning antennas of the Australian SKA
Pathfinder (ASKAP) to survey for fast radio bursts (FRBs) in fly's eye mode.
This is the first extensive astronomical survey using phased array feeds
(PAFs), and a total of 20 FRBs have been reported. Here we present a
calculation of the sensitivity and total exposure of this survey, using the
pulsars B1641-45 (J1644-4559) and B0833-45 (J0835-4510, i.e.\ Vela) as
calibrators. The design of the survey allows us to benchmark effects due to PAF
beamshape, antenna-dependent system noise, radio-frequency interference, and
fluctuations during commissioning on timescales from one hour to a year.
Observation time, solid-angle, and search efficiency are calculated as a
function of FRB fluence threshold. Using this metric, effective survey
exposures and sensitivities are calculated as a function of the source counts
distribution. The implied FRB rate is significantly lower than the
\,sky\,day calculated using nominal exposures and
sensitivities for this same sample by \citet{craft_nature}. At the Euclidean
power-law index of , the rate is \,sky\,day above a threshold of \,Jy\,ms, while for the best-fit index for this sample of , it is
\,sky\,day above a threshold of \,Jy\,ms. This strongly suggests that these calculations be performed
for other FRB-hunting experiments, allowing meaningful comparisons to be made
between them.Comment: 21 pages, 15 figures, 2 tables, accepted for publication in PAS
XMM-Newton confirmation of a new intermediate polar: XMMU J185330.7-012815
We report the results from a detailed spectro-imaging and temporal analysis
of an archival XMM-Newton observation of a new intermediate polar XMMU
J185330.7-012815. Its X-ray spectrum can be well-described by a
multi-temperature thermal plasma model with the K-lines of heavy elements
clearly detected. Possible counterparts of XMMU J185330.7-012815 have been
identified in optical and UV bands. The low value of the inferred X-ray-to-UV
and X-ray-to-optical flux ratios help to safely rule out the possibility as an
isolated neutron star. We confirm the X-ray periodicity of ~238 s, but
different from the previous preliminary result, we do not find any convincing
evidence of phase-shift in this observation. We further investigate its
properties through an energy-resolved temporal analysis and find the pulsed
fraction monotonically increases with energy.Comment: 9 pages, 4 figures, 1 table, accepted for publication in MNRA
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