Members of the double pulsar system PSR J0737-3039: Neutron stars or strange stars (original) (raw)

The aspect of formation and evolution of the recycled pulsar (PSR J0737-3039 A/B) is investigated, taking into account the contributions of accretion rate, radius and spin-evolution diagram (í µí°µ–í µí±ƒ diagram) in the double pulsar system. Accepting the spin-down age as a rough estimate (or often an upper limit) of the true age of the neutron star, we also impose the restrictions on the radius of this system. We calculate the radius of the recycled pulsar PSR J0737-3039 A ranges approximately from 8.14 to 25.74 km, and the composition of its neutron star nuclear matters is discussed in the mass-radius diagram.

Recent timing observations of the double pulsar J0737-3039A/B have shown that its transverse velocity is extremely low, only 10 km s-1, and nearly in the plane of the Galaxy. With this new information, we rigorously re-examine the history and formation of this system, determining estimates of the pre-supernova companion mass, supernova kick and misalignment angle between the pre- and post-supernova orbital planes. We find that the progenitor to the recently formed `B' pulsar was probably less than 2Msolar, lending credence to suggestions that this object may not have formed in a normal supernova involving the collapse of an iron core. At the same time, the supernova kick was likely non-zero. A comparison to the history of the double neutron star binary B1534+12 suggests a range of possible parameters for the progenitors of these systems, which should be taken into account in future binary population syntheses and in predictions of the rate and spatial distribution of short gamma-ray burst events.

We have recently measured the angle between the spin and orbital angular momenta of PSR B1534+12 to be either 25deg+/-4deg or 155deg+/-4deg. This misalignment was almost certainly caused by an asymmetry in the supernova explosion that formed its companion neutron star. Here we combine the misalignment measurement with measurements of the pulsar and companion masses, the orbital elements, proper motion, and interstellar scintillation. We show that the orbit of the binary in the Galaxy is inconsistent with a velocity kick large enough to produce a nearly antialigned spin axis, so the true misalignment must be ~25°. Similar arguments lead to bounds on the mass of the companion star immediately before its supernova: 3+/-1Msolar. The result is a coherent scenario for the formation of the observed binary. After the first supernova explosion, the neutron star that would eventually become the observed pulsar was in a Be/X-ray-type binary system with a companion of at least 10-12 Msolar. During hydrogen (or possibly helium) shell burning, mass transfer occurred in a common envelope phase, leaving the neutron star in a roughly half-day orbit with a helium star with mass above ~3.3 Msolar. A second phase of mass transfer was then initiated by Roche lobe overflow during shell helium burning, further reducing both the helium star mass and orbital period before the second supernova. Scenarios that avoid Roche lobe overflow by the helium star require larger helium star masses and predict space velocities inconsistent with our measurements. The companion neutron star experienced a velocity kick of 230+/-60 km s-1 at birth, leading to a systemic kick to the binary of 180+/-60 km s-1. The direction of the kick was roughly opposed to the instantaneous orbital velocity of the companion.

We are undertaking a high-frequency survey of the Galactic plane for radio pulsars, using the 13-element multibeam receiver on the 64-m Parkes radio telescope. We describe briefly the survey system and some of the initial results. PSR J1811-1736, one of the first pulsars discovered with this system, has a rotation period of 104 ms. Subsequent timing observations using the 76-m radio telescope at Jodrell Bank show that it is in an 18.8-day, highly-eccentric binary orbit. We have measured the rate of advance of periastron which indicates a total system mass of 2.6 +- 0.9 Msun, and the minimum companion mass is about 0.7 Msun. This, the high orbital eccentricity and the recycled nature of the pulsar suggests that this system is composed of two neutron stars, only the fourth or fifth such system known in the disk of the Galaxy.

It is proposed that the small difference between the observed and the theoretically predicted decrease of the orbital period of the Binary Pulsar PSR 1913+16 is not due to the insufficiency of the quadrupole formula and can be attributed to a mass-energy loss due to the contraction of the binary's members. Assuming that the pair's primary is a typical, noncontracting pulsar, is in favour of a slowly contracting, neutron-star companion, thus limiting the member's radii to at most 25 km and 28 km, respectively. The primary's computed total absolute luminosity is in excellent agreement with the observed upper limit of its X-ray and optical luminosities. Moreover, the companion's slow contraction rate implies that its present total absolute luminosity presents a maximum at wavelengths characteristic of X-rays. Finally, it suggests that if the energy-loss remains constant, the duration of the contraction phase will be of the order of 108 y and the final radius about 2...