Jason Boyles

A radio pulsar/x-ray binary link

From X-ray Binary to Pulsar Pulsars with millisecond rotational periods are thought to originate from neutron stars in low-mass x-ray binaries that had their spin frequencies increased by long-lasting mass transfer from their companion stars. Using data from a radio pulsar survey, Archibald et al. (p. 1411, published online 21 May; see the Perspective by Kramer) found a neutron star in a low-mass X-ray binary that is in the process of turning into a radio millisecond pulsar. The system, which consists of a solar-like star and a 1.69-millisecond radio pulsar, has gone through a recent accretion phase, characteristic of low-mass X-ray binaries, but it shows no accretion disk anymore, confirming the evolutionary connection between millisecond radio pulsars and low-mass X-ray binaries. Radio observations reveal a system undergoing the transition from a low-mass x-ray binary star to a millisecond radio pulsar. Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray–emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected. Here we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the past decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.

A millisecond pulsar in a stellar triple system

Gravitationally bound three-body systems have been studied for hundreds of years and are common in our Galaxy. They show complex orbital interactions, which can constrain the compositions, masses and interior structures of the bodies and test theories of gravity, if sufficiently precise measurements are available. A triple system containing a radio pulsar could provide such measurements, but the only previously known such system, PSR B1620-26 (refs 7, 8; with a millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of several decades), shows only weak interactions. Here we report precision timing and multiwavelength observations of PSR J0337+1715, a millisecond pulsar in a hierarchical triple system with two other stars. Strong gravitational interactions are apparent and provide the masses of the pulsar (1.4378(13), where is the solar mass and the parentheses contain the uncertainty in the final decimal places) and the two white dwarf companions (0.19751(15) and 0.4101(3)), as well as the inclinations of the orbits (both about 39.2°). The unexpectedly coplanar and nearly circular orbits indicate a complex and exotic evolutionary past that differs from those of known stellar systems. The gravitational field of the outer white dwarf strongly accelerates the inner binary containing the neutron star, and the system will thus provide an ideal laboratory in which to test the strong equivalence principle of general relativity.

THE GREEN BANK TELESCOPE 350 MHz DRIFT-SCAN SURVEY. I. SURVEY OBSERVATIONS AND THE DISCOVERY OF 13 PULSARS

Over the summer of 2007, we obtained 1191 hr of “drift-scan” pulsar search observations with the Green Bank Telescope at a radio frequency of 350 MHz. Here we describe the survey setup, search procedure, and the discovery and follow-up timing of 13 pulsars. Among the new discoveries, one (PSR J1623−0841) was discovered only through its single pulses, two (PSRs J1327−0755 and J1737−0814) are millisecond pulsars, and another (PSR J2222−0137) is a mildly recycled pulsar. PSR J1327−0755 is a 2.7 ms pulsar at a dispersion measure (DM) of 27.9 pc cm −3 in an 8.7 day orbit with a minimum companion mass of 0.22 M� . PSR J1737−0814 is a 4.2 ms pulsar at a DM of 55.3 pc cm −3 in a 79.3 day orbit with a minimum companion mass of 0.06 M� . PSR J2222−0137 is a 32.8 ms pulsar at a very low DM of 3.27 pc cm −3 in a 2.4 day orbit with a minimum companion mass of 1.11 M� . It is most likely a white-dwarf–neutron-star system or an unusual low-eccentricity double neutron star system. Ten other pulsars discovered in this survey are reported in the companion paper Lynch et al.

THE GREEN BANK TELESCOPE 350 MHz DRIFT-SCAN SURVEY II: DATA ANALYSIS AND THE TIMING OF 10 NEW PULSARS, INCLUDING A RELATIVISTIC BINARY

We have completed a 350 MHz Drift-scan Survey using the Robert C. Byrd Green Bank Telescope with the goal of finding new radio pulsars, especially millisecond pulsars that can be timed to high precision. This survey covered ~10,300 deg2 and all of the data have now been fully processed. We have discovered a total of 31 new pulsars, 7 of which are recycled pulsars. A companion paper by Boyles et al. describes the survey strategy, sky coverage, and instrumental setup, and presents timing solutions for the first 13 pulsars. Here we describe the data analysis pipeline, survey sensitivity, and follow-up observations of new pulsars, and present timing solutions for 10 other pulsars. We highlight several sources—two interesting nulling pulsars, an isolated millisecond pulsar with a measurement of proper motion, and a partially recycled pulsar, PSR J0348+0432, which has a white dwarf companion in a relativistic orbit. PSR J0348+0432 will enable unprecedented tests of theories of gravity.

DISCOVERY OF THE OPTICAL/ULTRAVIOLET/GAMMA-RAY COUNTERPART TO THE ECLIPSING MILLISECOND PULSAR J1816+4510

The energetic, eclipsing millisecond pulsar J1816+4510 was recently discovered in a low-frequency radio survey with the Green Bank Telescope. With an orbital period of 8.7?hr and a minimum companion mass of 0.16?M ?, it appears to belong to an increasingly important class of pulsars that are ablating their low-mass companions. We report the discovery of the ?-ray counterpart to this pulsar and present a likely optical/ultraviolet counterpart as well. Using the radio ephemeris, we detect pulsations in the unclassified ?-ray source 2FGL J1816.5+4511, implying an efficiency of ~25% in converting the pulsars spin-down luminosity into ?-rays and adding PSR J1816+4510 to the large number of millisecond pulsars detected by Fermi. The likely optical/UV counterpart was identified through position coincidence (<01) and unusual colors. Assuming that it is the companion, with R = 18.27 ? 0.03?mag and effective temperature 15,000?K, it would be among the brightest and hottest of low-mass pulsar companions and appears qualitatively different from other eclipsing pulsar systems. In particular, current data suggest that it is a factor of two larger than most white dwarfs of its mass but a factor of four smaller than its Roche lobe. We discuss possible reasons for its high temperature and odd size, and suggest that it recently underwent a violent episode of mass loss. Regardless of origin, its brightness and the relative unimportance of irradiation make it an ideal target for a mass, and hence a neutron star mass, determination.

THE PULSAR SEARCH COLLABORATORY: DISCOVERY AND TIMING OF FIVE NEW PULSARS

We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory, a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300?hr of drift-scan survey data taken with the Green Bank Telescope at 350?MHz. These data cover 2876?deg2 of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1?ms to 4.8?s. Among the new discoveries are PSR?J1926?1314, a long period, nulling pulsar; PSR?J1821+0155, an isolated, partially recycled 33?ms pulsar; and PSR?J1400?1438, a millisecond pulsar in a 9.5?day orbit whose companion is likely a white dwarf star.

The Pulsar Search Collaboratory.

The Pulsar Search Collaboratory [PSC, NSF #0737641] is a joint project between the National Radio Astronomy Observatory (NRAO) and West Virginia University (WVU) designed to interest high school students in science, technology, engineering, and mathematics [STEM] related career paths by helping them to conduct authentic scientific research. The 3- year PSC program, which began in summer 2008, teaches students to analyze astronomical radio data acquired with the 100-m Robert C. Byrd Green Bank Telescope for the purpose of discovering new pulsars. We present the results of the first complete year of the PSC, which includes two astronomical discoveries.

A 1.05?M ? Companion to PSR J2222?0137: The Coolest Known White Dwarf?

The recycled pulsar PSR J2222–0137 is one of the closest known neutron stars (NSs) with a parallax distance of 267_(-0.9)^(+1.2) pc and an edge-on orbit. We measure the Shapiro delay in the system through pulsar timing with the Green Bank Telescope, deriving a low pulsar mass (1.20 ± 0.14 M_☉) and a high companion mass (1.05 ± 0.06 M_☉) consistent with either a low-mass NS or a high-mass white dwarf. We can largely reject the NS hypothesis on the basis of the systems extremely low eccentricity (3 × 10^(–4))—too low to have been the product of two supernovae under normal circumstances. However, despite deep optical and near-infrared searches with Southern Astrophysical Research and the Keck telescopes we have not discovered the optical counterpart of the system. This is consistent with the white dwarf hypothesis only if the effective temperature is <3000 K, a limit that is robust to distance, mass, and atmosphere uncertainties. This would make the companion to PSR J2222–0137 one of the coolest white dwarfs ever observed. For the implied age to be consistent with the age of the Milky Way requires the white dwarf to have already crystallized and entered the faster Debye-cooling regime.

The Green Bank North Celestial Cap Pulsar Survey. III. 45 New Pulsar Timing Solutions

We provide timing solutions for 45 radio pulsars discovered by the Robert C. Byrd Green Bank Telescope. These pulsars were found in the Green Bank North Celestial Cap pulsar survey, an all-GBT-sky survey being carried out at a frequency of 350 MHz. We include pulsar timing data from the Green Bank Telescope and Low Frequency Array. Our sample includes five fully recycled millisecond pulsars (MSPs, three of which are in a binary system), a new relativistic double neutron star system, an intermediate mass binary pulsar, a mode-changing pulsar, a 138-ms pulsar with a very low magnetic field, and several nulling pulsars. We have measured two post-Keplerian parameters and thus the masses of both objects in the double neutron star system. We also report a tentative companion mass measurement via Shapiro delay in a binary MSP. Two of the MSPs can be timed with high precision and have been included in pulsar timing arrays being used to search for low-frequency gravitational waves, while a third MSP is a member of the black widow class of binaries. Proper motion is measurable in five pulsars and we provide an estimate of their space velocity. We report on an optical counterpart to a new black widow system and provide constraints on the optical counterparts to other binary MSPs. We also present a preliminary analysis of nulling pulsars in our sample. These results demonstrate the scientific return of long timing campaigns on pulsars of all types.

A POPULATION OF NON-RECYCLED PULSARS ORIGINATING IN GLOBULAR CLUSTERS

We explore the enigmatic population of long-period, apparently non-recycled pulsars in globular clusters, building on recent work by Boyles et al. This population is difficult to explain if it formed through typical core-collapse supernovae, leading many authors to invoke electron capture supernovae. While Boyles et al. dealt only with non-recycled pulsars in clusters, we focus on the pulsars that originated in clusters but then escaped into the field of the Galaxy due to the kicks they receive at birth. The magnitude of the kick induced by electron capture supernovae is not well known, so we explore various models for the kick velocity distribution and size of the population. The most realistic models are those where the kick velocity is 10 km s–1 and where the number of pulsars scales with the luminosity of the cluster (as a proxy for cluster mass). This is in good agreement with other estimates of the electron capture supernovae kick velocity. We simulate a number of large-area pulsar surveys to determine if a population of pulsars originating in clusters could be identified as being separate from normal disk pulsars. We find that the spatial and kinematical properties of the population could be used, but only if large numbers of pulsars are detected. In fact, even the most optimistic surveys carried out with the future Square Kilometer Array are likely to detect <10% of the total population, so the prospects for identifying these as a separate group of pulsars are presently poor.