544 research outputs found
Green Bank Telescope Observations of the Eclipse of Pulsar "A" in the Double Pulsar Binary PSR J0737-3039
We report on the first Green Bank Telescope observations at 427, 820 and 1400
MHz of the newly discovered, highly inclined and relativistic double pulsar
binary. We focus on the brief eclipse of PSR J0737-3039A, the faster pulsar,
when it passes behind PSR J0737-3039B. We measure a frequency-averaged eclipse
duration of 26.6 +/- 0.6 s, or 0.00301 +/- 0.00008 in orbital phase. The
eclipse duration is found to be significantly dependent on radio frequency,
with eclipses longer at lower frequencies. Specifically, eclipse duration is
well fit by a linear function having slope (-4.52 +/- 0.03) x 10^{-7}
orbits/MHz. We also detect significant asymmetry in the eclipse. Eclipse
ingress takes 3.51 +/- 0.99 times longer than egress, independent of radio
frequency. Additionally, the eclipse lasts (40 +/- 7) x 10^{-5} in orbital
phase longer after conjunction, also independent of frequency. We detect
significant emission from the pulsar on short time scales during eclipse in
some orbits. We discuss these results in the context of a model in which the
eclipsing material is a shock-heated plasma layer within the slower PSR
J0737-3039B's light cylinder, where the relativistic pressure of the faster
pulsar's wind confines the magnetosphere of the slower pulsar.Comment: 12 pages, 3 figure
Optimal strategies for continuous gravitational wave detection in pulsar timing arrays
Supermassive black hole binaries (SMBHBs) are expected to emit continuous
gravitational waves in the pulsar timing array (PTA) frequency band
(-- Hz). The development of data analysis techniques aimed at
efficient detection and characterization of these signals is critical to the
gravitational wave detection effort. In this paper we leverage methods
developed for LIGO continuous wave gravitational searches, and explore the use
of the -statistic for such searches in pulsar timing data. Babak &
Sesana 2012 have already used this approach in the context of PTAs to show that
one can resolve multiple SMBHB sources in the sky. Our work improves on several
aspects of prior continuous wave search methods developed for PTA data
analysis. The algorithm is implemented fully in the time domain, which
naturally deals with the irregular sampling typical of PTA data and avoids
spectral leakage problems associated with frequency domain methods. We take
into account the fitting of the timing model, and have generalized our approach
to deal with both correlated and uncorrelated colored noise sources. We also
develop an incoherent detection statistic that maximizes over all pulsar
dependent contributions to the likelihood. To test the effectiveness and
sensitivity of our detection statistics, we perform a number of monte-carlo
simulations. We produce sensitivity curves for PTAs of various configurations,
and outline an implementation of a fully functional data analysis pipeline.
Finally, we present a derivation of the likelihood maximized over the
gravitational wave phases at the pulsar locations, which results in a vast
reduction of the search parameter space.Comment: 11 pages, 5 figure
Locating the intense interstellar scattering towards the inner Galaxy
We use VLBA+VLA observations to measure the sizes of the scatter-broadened
images of 6 of the most heavily scattered known pulsars: 3 within the Galactic
Centre (GC) and 3 elsewhere in the inner Galactic plane. By combining the
measured sizes with temporal pulse broadening data from the literature and
using the thin-screen approximation, we locate the scattering medium along the
line of sight to these 6 pulsars. At least two scattering screens are needed to
explain the observations of the GC sample. We show that the screen inferred by
previous observations of SGR J1745-2900 and Sgr A*, which must be located far
from the GC, falls off in strength on scales < 0.2 degree. A second scattering
component closer to (< 2 kpc) or even (tentatively) within (< 700 pc) the GC
produces most or all of the temporal broadening observed in the other GC
pulsars. Outside the GC, the scattering locations for all three pulsars are ~2
kpc from Earth, consistent with the distance of the Carina-Sagittarius or
Scutum spiral arm. For each object the 3D scattering origin coincides with a
known HII region (and in one case also a supernova remnant), suggesting that
such objects preferentially cause the intense interstellar scattering seen
towards the Galactic plane. We show that the HII regions should contribute >
25% of the total dispersion measure (DM) towards these pulsars, and calculate
reduced DM distances. Those distances for other pulsars lying behind HII
regions may be similarly overestimated.Comment: 16 pages, 10 figures, MNRAS, in pres
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