Publications (7)0 Total impact
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ABSTRACT: PSR J1518+4904 is a recently discovered 40.9 ms pulsar in an 8.6 day, moderately eccentric orbit. We have measured pulse arrival times for this pulsar over 1.4 yr at several radio frequencies, from which we have derived high precision rotational, astrometric, and orbital parameters. The upper limit for the period derivative of the pulsar, P ! 4 Theta 10 Gamma20 , gives a characteristic age of at least 1:6 Theta 10 10 yr, among the highest known. We find the orbit to be precessing at a rate of 0:0111 Sigma 0:0002 ffi yr Gamma1 , which yields a total system mass (pulsar plus companion) of 2:62 Sigma 0:07M fi according to general relativity. Further analysis of the orbital parameters yields a firm upper limit of 1.75M fi on the pulsar mass and constrains the companion mass to the range 0.9 to 2.7 M fi . These masses, together with the sizable orbital eccentricity and other evidence, strongly suggest that the companion is a second neutron star. Subject headings: b...
02/1998;
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ABSTRACT: We have carried out a survey of the northern sky for millisecond pulsars using the Green Bank 140 ft telescope at 370 MHz. Our primary goal was to find the strongest millisecond pulsars in the northern hemisphere. A secondary goal was to study empirically the repeatability of pulsar surveys with well-understood flux-density limits. The flux-density limit of our survey was 8 mJy for slow pulsars with typical pulse shapes and high Galactic latitudes. Spectra were sampled at intervals of 256s, so pulsars with periods as short as 512s were potentially detectable. We obtained high quality data covering 15,900 deg 2 of sky, or 77% of the northern hemisphere. We observed a further 1500 deg 2 with somewhat reduced sensitivity. We detected a total of 84 pulsars, including eight not previously known. The new objects include two recycled pulsars: PSR J1022+1001, a 16.5ms pulsar in a nearly circular 7.8 d orbit with a white dwarf companion, and PSR J1518+4904, a 40.9 ms pulsar in a...
02/1998;
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ABSTRACT: We have made deep searches for pulsed radio signals towards gamma-ray sources detected by the EGRET instrument of the Compton Gamma Ray Observatory. Our observations targeted nineteen sources in the second EGRET source catalog (2EG), primarily sources along the Galactic plane without identified counterparts. Our observations also covered eight locations listed in earlier catalogs but not in 2EG. Data were collected at 370, 770, and 1390 MHz with the Green Bank 140 foot telescope. Flux density limits were 0.5 to 1.0 mJy for slow pulsars, with somewhat less sensitivity at short pulse periods. We discovered no new pulsars. We detected two previously known pulsars, PSR B0611+22 and PSR B1758Gamma23, which are apparently not associated with cataloged gamma-ray sources. Our non-detection of radio pulsars associated with the EGRET sources weakly constrains models of the gamma-ray source population. In particular, we rule out a model in which all the Galactic gamma-ray sources are ...
02/1998;
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ABSTRACT: We have made timing observations of newly discovered binary pulsar PSR
J1518+4904 over a span of five months using the 140ft telescope of
NRAO/Green Bank at frequencies between 320 and 800 MHz. Typical
precision of a pulse time of arrival is 15 mu s in a 1 hour integration
(using a 40 MHz passband at 370 or 575 MHz). The timing data were
reduced using standard techniques, and they fit well to a standard model
of neutron star and orbital behavior. The pulse period is 40.934 ms, and
the period derivative is at most 10(-18) , implying an age of at least
600 Myr and a surface magnetic field no stronger than 6*E(9) Gauss. The
pulsar is in an 8.6 day, eccentric (e=0.249) orbit, with semi-major axis
0.040 AU. Orbital precession of 0.0110+/-0.0008 deg/yr (2sigma
uncertainty) has been detected. This implies a total system mass of
2.6+/-0.3 M_sun. The masses of the pulsar and companion (quite possibly
another neutron star) cannot be fully separated. However, the system
mass, combined with other orbital parameters, implies a pulsar mass of
at most 1.9 M_sun and a companion mass of at least 0.9 M_sun. Precision
of the precession measurement increases at least linearly with the
length of the data series, so further observations of this system will
provide a better measure of the total system mass. It is unlikely that
the estimates of the individual component masses will improve.
02/1995; 27:879.
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ABSTRACT: We have undertaken a program of high sensitivity searches for radio pulsar signals from the directions of otherwise-unidentified gamma ray point sources. Here we present results of observations of five high Galactic latitude (jbj ? 10 ffi ) sources discovered by the EGRET instrument aboard the Compton Gamma Ray Observatory. No pulsed radio signals were detected coincident with these sources. Pulsars are well known sources of high-energy radiation. Indeed, the three strongest sources in the 100 MeV sky are pulsars. One might expect, then, that some of the numerous unidentified gamma ray point sources might also be pulsars. The most secure way of identifying such sources as pulsars is the detection of periodicities in their gamma ray emission. However, the low photon count rate of EGRET makes such a detection very difficult without a priori knowledge of the pulsar's rotational behavior. Such knowledge can come only from observations in another band, typically radio. While all of the ...
02/1970;
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ABSTRACT: We have searched for radio pulsar companions to 40 nearby OB runaway stars. Observations were made at 575 and 770 MHz with the NRAO 140 ft telescope. The survey was sensitive to long-period pulsars with flux densities of 1 mJy or more. No pulsar companions to OB runaways were discovered. One previously unknown pulsar was discovered, PSR J2044+4614, while observing towards target O star BD+45,3260. Follow-up timing observations of the pulsar measured its position to high precision, revealing a 9 0 separation between the pulsar and the target star, unequivocally indicating they are not associated. The pulsar is ordinary, except that its dispersion measure, 315pc cm Gamma3 , is unusually high given its Galactic longitude, l = 85 ffi . The non-detection of pulsars bound to target stars places an upper limit of 8% (95% confidence) for the fraction of runaway OB stars with pulsar companions detectable via pulsed radio emission by surveys such as ours. Assuming standard mode...
02/1970;
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