132 research outputs found
Red Noise in Anomalous X-ray Pulsar Timing Residuals
Anomalous X-ray Pulsars (AXPs), thought to be magnetars, exhibit poorly
understood deviations from a simple spin-down called "timing noise". AXP timing
noise has strong low-frequency components which pose significant challenges for
quantification. We describe a procedure for extracting two quantities of
interest, the intensity and power spectral index of timing noise. We apply this
procedure to timing data from three sources: a monitoring campaign of five
AXPs, observations of five young pulsars, and the stable rotator PSR B1937+21.Comment: submitted to the proceedings of the "40 Years of Pulsars" conferenc
Sdss J102347.6+003841: A Millisecond Radio Pulsar Binary that Had a Hot Disk During 2000-2001
The Sloan Digital Sky Survey (SDSS) source J102347.6+003841 was recently revealed to be a binary 1.69 ms radio pulsar with a 4.75 hr orbital period and a ~0.2 M ☉ companion. Here, we analyze the SDSS spectrum of the source in detail. The spectrum was taken on 2001 February 1, when the source was in a bright state and showed broad, double-peaked hydrogen and helium lines—dramatically different from the G-type absorption spectrum seen from 2002 May onward. The lines are consistent with emission from a disk around the compact primary. We derive properties of the disk by fitting the SDSS continuum with a simple disk model, and find a temperature range of 2000-34,000 K from the outer to inner edge of the disk. The disk inner and outer radii were approximately 109 and 5.7×1010 cm, respectively. These results further emphasize the unique feature of the source: it is a system likely at the end of its transition from an X-ray binary to a recycled radio pulsar. The disk mass is estimated to have been ~1023 g, most of which would have been lost due to pulsar wind ablation (or due to the propeller effect if the disk had extended inside the light cylinder of the pulsar) before the final disk disruption event. The system could undergo repeated episodes of disk formation. Close monitoring of the source is needed to catch the system in its bright state again, so that this unusual example of a pulsar-disk interaction can be studied in much finer detail
Toward an Empirical Theory of Pulsar Emission XII: Exploring the Physical Conditions in Millisecond Pulsar Emission Regions
The five-component profile of the 2.7-ms pulsar J0337+1715 appears to exhibit
the best example to date of a core/double-cone emission-beam structure in a
millisecond pulsar (MSP). Moreover, three other MSPs, the Binary Pulsar
B1913+16, B1953+29 and J1022+1001, seem to exhibit core/single-cone profiles.
These configurations are remarkable and important because it has not been clear
whether MSPs and slow pulsars exhibit similar emission-beam configurations,
given that they have considerably smaller magnetospheric sizes and magnetic
field strengths. MSPs thus provide an extreme context for studying pulsar radio
emission. Particle currents along the magnetic polar flux tube connect
processes just above the polar cap through the radio-emission region to the
light-cylinder and the external environment. In slow pulsars radio-emission
heights are typically about 500 km around where the magnetic field is nearly
dipolar, and estimates of the physical conditions there point to radiation
below the plasma frequency and emission from charged solitons by the curvature
process. We are able to estimate emission heights for the four MSPs and carry
out a similar estimation of physical conditions in their much lower emission
regions. We find strong evidence that MSPs also radiate by curvature emission
from charged solitons.Comment: 14 pages, published in Ap
No detectable radio emission from the magnetar-like pulsar in Kes 75
The rotation-powered pulsar PSR J1846-0258 in the supernova remnant Kes 75
was recently shown to have exhibited magnetar-like X-ray bursts in mid-2006.
Radio emission has not yet been observed from this source, but other
magnetar-like sources have exhibited transient radio emission following X-ray
bursts. We report on a deep 1.9 GHz radio observation of PSR J1846-0258 with
the 100-m Green Bank Telescope in late 2007 designed to search for radio
pulsations or bursts from this target. We have also analyzed three shorter
serendipitous 1.4 GHz radio observations of the source taken with the 64-m
Parkes telescope during the 2006 bursting period. We detected no radio emission
from PSR J1846-0258 in either the Green Bank or Parkes datasets. We place an
upper limit of 4.9 \mu Jy on coherent pulsed emission from PSR J1846-0258 based
on the 2007 November 2 observation, and an upper limit of 27 \mu Jy around the
time of the X-ray bursts. Serendipitously, we observed radio pulses from the
nearby RRAT J1846-02, and place a 3\sigma confidence level upper limit on its
period derivative of 1.7 * 10^{-13}, implying its surface dipole magnetic field
is less than 2.6 * 10^{13} G.Comment: 15 pages, 2 figures, submitted to Ap
Common-spectrum process versus cross-correlation for gravitational-wave searches using pulsar timing arrays
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported strong statistical evidence for a common-spectrum red-noise process for all pulsars, as seen in their 12.5-yr analysis for an isotropic stochastic gravitational-wave signal. However, there is currently very little evidence for quadrupolar spatial correlations across the pulsars in the array, which is needed to make a confident claim of detection of a stochastic gravitational-wave background. In this paper, we provide a “back-of-the-envelope” illustration of the NANOGrav 12.5-yr results for the nonexpert reader, using a very simple signal+noise model and frequentist statistics. We show that the current lack of evidence for spatial correlations is consistent with the magnitude of the correlation coefficients for pairs of Earth-pulsar baselines in the array and the fact that pulsar timing arrays are most likely operating in the intermediate-signal regime. We derive analytic expressions that allow one to compare the expected values of the signal-to-noise ratios for both common-spectrum and cross-correlation estimators
Analytic distribution of the optimal cross-correlation statistic for stochastic gravitational-wave-background searches using pulsar timing arrays
We show via both analytical calculation and numerical simulation that the
optimal cross-correlation statistic (OS) for stochastic
gravitational-wave-background (GWB) searches using data from pulsar timing
arrays follows a generalized chi-squared (GX2) distribution-i.e., a linear
combination of chi-squared distributions with coefficients given by the
eigenvalues of the quadratic form defining the statistic. This observation is
particularly important for calculating the frequentist statistical significance
of a possible GWB detection, which depends on the exact form of the
distribution of the OS signal-to-noise ratio (S/N) in the absence of GW-induced cross correlations (i.e., the null
distribution). Previous discussions of the OS have incorrectly assumed that the
analytic null distribution of is well-approximated by a zero-mean
unit-variance Gaussian distribution. Empirical calculations show that the null
distribution of has "tails" which differ significantly from those
for a Gaussian distribution, but which follow (exactly) a GX2 distribution. So,
a correct analytical assessment of the statistical significance of a potential
detection requires the use of a GX2 distribution.Comment: 13 pages, 3 Figure
- …