A Massive Neutron Star in the Globular Cluster M5

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 M companion and an orbital period of 6.86 days. In deep HST images, no optical counterpart is detected within $2.5 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 ¼ 0:14) has allowed a measurement of the rate of advance of periastron:! ¼ 0:0142 AE 0:0007 yr À1 . 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 AE 0:17 M . The small measured mass function implies, in a statistical sense, that a very large fraction of this total mass is contained in the pulsar: M p ¼ 2:08 AE 0:19 M (1 ); there is a 5% probability that the mass of this object is <1.72 M and a 0.77% probability that 1:2 M M p 1:44 M . 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 M . 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.

Radio Timing and Optical Photometry of the Black Widow System PSR J1518+0204c in the Globular Cluster M5

“…M5 (NGC 5904) is a dynamically evolved GC (Ferraro et al 2012) with intermediate central density and concentration (log ρ 0 = 4.0 in units of M /pc 3 ; Pryor & Meylan 1993;c = 1.66;Miocchi et al 2013) and relatively high metallicity ([Fe/H] ∼ −1.3; Carretta et al 2009) located at ∼7.5 kpc from the Earth (Ferraro et al 1999;Harris 1996Harris , 2010. M5 harbors five MSPs (Anderson et al 1997;Hessels et al 2007;Freire et al 2008). Among them, PSR J1518+0204C deserves special attention since it is a BW system.…”

A Puzzling Millisecond Pulsar Companion in NGC 6266

“…The first option is that the pulsar companion is a non-degenerate bloated star, whose mass loss is sustained by ablation of its loosely bound surface layers by the relativistic wind emitted by the pulsar. In this case, PSR 6266B may resemble PSRs B1957ϩ20 (Fruchter et al 1990) and J2051Ϫ0827 (Stappers et al 2001): the optical light curve of their companion star presents a maximum when the side of the companion facing the pulsar points toward the observer (i.e., at the pulsar inferior conjunction:…”

Thermal properties of Non-rotating and Rotating Neutron Stars

“…In this paper the variables P, ε and ρ represent pressure, energy density and number density respectively. binary 4U1538-52 [5] , while the upper limit 2.08 ± 0.19M ⊙ denotes the mass of the potentially very heavy neutron star in the globular cluster M5 [6]. The density-dependent model studied here does not support a neutron star that massive.…”