A. Wolszczan

The Characteristics of Millisecond Pulsar Emission. I. Spectra, Pulse Shapes, and the Beaming Fraction

The extreme physical conditions in millisecond pulsar magnetospheres, as well as an evolutionary history that differs from that of normal pulsars, raise the question whether these objects also differ in their radio emission properties. We have monitored a large sample of millisecond pulsars for a period of 3 yr using the 100 m Effelsberg radio telescope in order to compare the radio emission properties of these two pulsar populations. Our sample comprises a homogeneous data set of very high quality. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. This is contrary to what has previously been thought. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters than normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars, with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars, implying that the different evolutionary history has an influence on the emission properties. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that, contrary to common belief, the millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anticorrelate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model applicable for normal pulsars. Instead, they are systematically smaller, supporting the concept of a critical rotational period below which such a scaling ceases to exist. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birthrate of the Galactic population.

The Characteristics of Millisecond Pulsar Emission. II. Polarimetry

We have made polarimetric monitoring observations of most of the millisecond pulsars visible from the northern hemisphere at 1410 MHz over a period of 3 yr. Their emission properties are presented here and compared with those of normal pulsars. Although we demonstrated in Paper I that millisecond pulsars exhibit the same flux density spectra and a similar profile complexity, the results presented here suggest that millisecond pulsar profiles do not comply with the predictions of classification schemes based on normal pulsars. The frequency development of a large number of millisecond pulsar profiles is abnormal when compared with the development seen in normal pulsars. Moreover, the polarization characteristics suggest that millisecond-pulsar magnetospheres might not simply represent scaled versions of the magnetospheres of normal pulsars, supporting the results of Paper I. However, phenomena such as mode-changing activity in both intensity and polarization are recognized here for the first time (e.g., for J1730-2304). This suggests that while the basic emission mechanism remains insensitive to rotational period, the conditions that regulate the radio emission in the canonical pulsar model might be satisfied at different regions in millisecond pulsar magnetospheres. At least three types of model have been proposed to describe the millisecond pulsar magnetospheres, ranging from distorted magnetic field configurations resulting from the recycled nature of these sources to traditional polar-cap emission and emission from outer gaps. A comparison of the predictions of these models with observations suggests that individual cases are better explained by different processes. However, we show that millisecond pulsars can be grouped according to common emission properties, a grouping that awaits verification with future multifrequency observations.

A Planetary-Mass Companion to the K0 Giant HD 17092

We report the discovery of a substellar-mass companion to the K0 giant HD 17092 with the Hobby-Eberly Telescope. In the absence of any correlation of the observed 360 day periodicity with the standard indicators of stellar activity, the observed radial velocity variations are most plausibly explained in terms of a Keplerian motion of a planetary-mass body around the star. As the estimated stellar mass is 2.3 M_⊙, the minimum mass of the planet is 4.6 M_J. The planets orbit is characterized by a mild eccentricity of e = 0.17 and a semimajor axis of 1.3 AU. This is the tenth published detection of a planetary companion around a red giant star. Such discoveries add to our understanding of planet formation around intermediate-mass stars, and they provide dynamical information on the evolution of planetary systems around post-main-sequence stars.

Discovery of a young, 267 millisecond pulsar in the supernova remnant W44

The discovery of a 267 ms pulsar, PSR 1853+01, in the supernova remnant W44 (G34.7−0.4) is reported. The pulsar is located south of the center of W44, well within its radio shell and at the southern edge of the X-ray emission region which fills the interior of the remnant. The period derivative leads to a characteristic age of ∼ 20000 yr for the pulsar, which agrees well the estimated age of W44 (≥10,000 yr). The data clearly indicate that the two objects are physically related and form the sixth known pulsar-supernova remnant association.

A PLANET IN A 0.6 AU ORBIT AROUND THE K0 GIANT HD 102272

We report the discovery of one or more planet-mass companions to the K0-giant HD 102272 with the Hobby-Eberly Telescope. In the absence of any correlation of the observed periodicities with the standard indicators of stellar activity, the observed radial velocity variations are most plausibly explained in terms of a Keplerian motion of at least one planet-mass body around the star. With an estimated stellar mass of 1.9 M ☉, the minimum mass of the confirmed planet is 5.9 MJ . The planets orbit is characterized by a small but nonzero eccentricity e = 0.05 and a semimajor axis of 0.61 AU, which makes it the most compact planet discovered so far around GK spectral type giants. This detection adds to the existing evidence that, as predicted by theory, the minimum size of planetary orbits around intermediate-mass giants is affected by both planet-formation processes and stellar evolution. The currently available evidence of another planet around HD 102272 is insufficient to obtain an unambiguous two-orbit solution.

Timing and scintillations of the millisecond pulsar 1937+214

Pulse shapes, arrival times, and interstellar scintillations of the 1.56 ms PSR 1937 + 214 pulsar are analyzed at frequencies from 0.32 to 1.4 GHz using data obtained from April 1983 to December 1985. The narrow pulse and small period of the pulsar yield arrival times that are much more precise than those of most other pulsars. Arrival time precision for the pulsar is limited at low frequencies by distortions of the pulse shape imposed by interstellar scintillations. Arrival times at all radio frequencies are affected by variations in dispersion measure and, possibly, additional variations related to variations in angle of arrival. Uncertainties in how the pulse shape varies with frequency influence estimates of dispersion measures. The interstellar scintillation and pulse broadening of the pulsar strongly constrain the spatial power spectrum of electron density variations in the ISM. 70 refs.

The Proper Motion, Age, and Initial Spin Period of PSR J0538+2817 in S147

We present results of the timing observations of the 143 ms pulsar PSR J0538+2817 that provide a proper-motion measurement clearly showing an association of the pulsar with the supernova remnant S147. We measure a proper motion of 67 mas yr-1, implying a transverse velocity of v = 385 km s-1. We derive an age of the pulsar and S147 of only 30 ± 4 kyr, which is a factor of 20 times less than the pulsars characteristic age of τc = 620 kyr. This age implies an initial spin period of P0 = 139 ms, close to the present pulse period and a factor of several larger than what is usually inferred for birth periods. Implications for recent X-ray detections of this pulsar are discussed.

Timing Observations of Four Millisecond Pulsars with the Arecibo and Effelsberg Radio Telescopes

We present long-term timing observations of four millisecond radio pulsars with the 305 m Arecibo and the 100 m Effelsberg radiotelescopes. Our analysis of the combined pulse time-of-arrival data from the two telescopes has led to improvements of the precision of timing parameter determination for all the four pulsars. A new, much more significant measurement of a third-order spin frequency derivative of PSR B1257+12 adds to the existing evidence that a fourth, distant planet may orbit this pulsar. Proper motions have been measured for PSR J1640+2224, PSR B1953+29, and PSR J2229+2643. The derived low transverse velocities of these objects agree with the kinematic characteristics of the observed millisecond pulsar population. Exceptionally low spindown rates of PSR J1640+2224 and PSR J2229+2634 have been used to derive useful limits on the initial spin periods of these objects and on the variation of the gravitational constant G.

A High Galactic Latitude Pulsar Survey of the Arecibo Sky

The results of a 1355 square degree survey of high galactic latitudes conducted from 1990 to 1995 with the Arecibo radio telescope are presented. The majority of the survey was performed at 430 MHz with a 32 channel 250 kHz lter-bank sampled at 4 kHz. A 7 sensitivity of 1 mJy was obtained for pulsars with periods down to 3 ms. This survey yielded 5 millisecond or recycled pulsars and 14 slow period pulsars. In addition, one millisecond pulsar and 4 slow period pulsar candidates have been identiied, but are as yet unconnrmed. One of the new slow period pulsars appears to be associated with the supernova remnant S147 located towards the galactic anti-center.

SUBSTELLAR-MASS COMPANIONS TO THE K-GIANTS HD 240237, BD +48 738 AND HD 96127

We present the discovery of substellar-mass companions to three giant stars by the ongoing Penn State-Torun Planet Search conducted with the 9.2 m Hobby-Eberly Telescope. The most massive of the three stars, K2-giant HD 240237, has a 5.3 M{sub J} minimum mass companion orbiting the star at a 746 day period. The K0-giant BD +48 738 is orbited by a {>=}0.91 M{sub J} planet which has a period of 393 days and shows a nonlinear, long-term radial velocity (RV) trend that indicates a presence of another, more distant companion, which may have a substellar mass or be a low-mass star. The K2-giant HD 96127 has a {>=}4.0 M{sub J} mass companion in a 647 day orbit around the star. The two K2-giants exhibit a significant RV noise that complicates the detection of low-amplitude, periodic variations in the data. If the noise component of the observed RV variations is due to solar-type oscillations, we show, using all the published data for the substellar companions to giants, that its amplitude is anti-correlated with stellar metallicity.