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Title:
A Massive Neutron Star in the Globular Cluster M5
Authors:
Freire, Paulo C. C.; Wolszczan, Alex; van den Berg, Maureen; Hessels, Jason W. T.
Affiliation:
AA(N.A.I.C., Arecibo Observatory, HC 03 Box 53995, PR 00612; .), AB(Department of Astronomy and Astrophysics, Penn State University, University Park, PA 16802; .), AC(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; .), AD(Astronomical Institute ``Anton Pannekoek'', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands; .)
Publication:
The Astrophysical Journal, Volume 679, Issue 2, pp. 1433-1442. (ApJ Homepage)
Publication Date:
06/2008
Origin:
UCP
ApJ Keywords:
Stars: Binaries: General, Equation of State, Stars: Pulsars: General, Stars: Pulsars: Individual: Alphanumeric: PSR B1516+02A, Stars: Pulsars: Individual: Alphanumeric: PSR B1516+02B, Stars: Neutron
DOI:
10.1086/587832
Bibliographic Code:
2008ApJ...679.1433F

Abstract

We report the results of 19 years of Arecibo timing for two pulsars in the globular cluster NGC 5904 (M5), PSR B1516+02A (M5A) and PSR B1516+02B (M5B). This has resulted in the measurement of the proper motions of these pulsars and, by extension, that of the cluster itself. M5B is a 7.95 ms pulsar in a binary system with a >0.13 Msolar companion and an orbital period of 6.86 days. In deep HST images, no optical counterpart is detected within ~2.5 σ of the position of the pulsar, implying that the companion is either a white dwarf or a low-mass main-sequence star. The eccentricity of the orbit (e=0.14) has allowed a measurement of the rate of advance of periastron: ω˙=0.0142deg+/-0.0007deg yr-1. We argue that it is very likely that this periastron advance is due to the effects of general relativity, the total mass of the binary system then being 2.29+/-0.17 Msolar. The small measured mass function implies, in a statistical sense, that a very large fraction of this total mass is contained in the pulsar: Mp=2.08+/-0.19 Msolar (1 σ) there is a 5% probability that the mass of this object is <1.72 Msolar and a 0.77% probability that 1.2 Msolar<=Mp<=1.44 Msolar. Confirmation of the median mass for this neutron star would exclude most ``soft'' equations of state for dense neutron matter. Millisecond pulsars (MSPs) appear to have a much wider mass distribution than is found in double neutron star systems; about half of these objects are significantly more massive than 1.44 Msolar. A possible cause is the much longer episode of mass accretion necessary to recycle a MSP, which in some cases corresponds to a much larger mass transfer.
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