Eccentric Binary Millisecond Pulsars Paulo C. C. Freire arXiv: v1

INTRODUCTION The importance of the discovery of MSPs in eccentric orbits The context of this work Recent discovery of MSPs in eccentric binaries Prospects

FORMATION OF BINARY PULSARS

Spin Periods –companion mass (‘centi-second pulsar’ CSP, MSP) Magnetic fields –smaller surface magnetic diploe & cleaner rotation Masses –MSPs>CSPs?

How to measure the mass of a neutron star Keplerian orbits – Use doppler shift to measure the orbital velocity changes along the line-of-sight –Fit to determination the five Keplerian parameters: the orbital period P b project of the semi-major axis x the orbital eccentricity e the time of passage through periastron T 0 the longitude of periastron ω

Unknown parameters –two component masses m c, m p –the orbital inclination i The well-known mass function

Post-Keplerian parameters –the rate of advance of periastron ( dω/dt ) –the “Einstein delay” γ –the rate of orbital decay P b –“Shapiro” delay r and s

Use two PK parameters to solve for m p, m c and i test the self-consistency of GR Verification that there are no classical contributions to PK parameters e.g. DNS B –large e =0.617 and small P b =7 h 45 m –dω/dt = (7) ◦ yr −1, γ = (1)s –m p = (3) M ⊙， m c = (3) M ⊙ –dP b /dt = −2.4211(14)× 10 −12 ss −1

Neutron Star Masses –All precise NS mass measurements comes from CSPs located in DNS systems, ranges from (7)M ⊙ to (3) M ⊙ –Is such a narrow distribution of masses also observed for MSPs? small orbital eccentricities (2×10 −3 to 10 −7 ) of MSP-WD system makes the measurement of mass like B impossible(use dω/dt, γ ) dP b /dt will greatly amplified by a) a compact orbit, b) a large orbital eccentricity c) a massive companion Shapiro delay is also use to estimate for the pulsar mass ( of the order of a few µs in the T.O.A.s )

Eccentric binary MSPs in GCs –In GCs LMXB is 3 orders of magnitude more often than in the disk –Since 1987, 140 pulsars found in GCs Interactions with passing stars or even exchange encounters produce binary MSP with large e, and allow the measurement of dω/dt

Early results –The first measurement of dω/dt for a MSP was made in 2003 for PSR J0024−7204H dω/dt = (0.066 ± 0.001) ◦ yr −1 M =(1.61±0.04) M ⊙ m c >(f M 2 ) 1/3 for sin i ≤ 1 m p < 1.52 M ⊙ The maximum mass shows NS can be spun up to MS period with relatively small amounts of matter

J1909−3744 –because it has the narrowest pulse profile for any known pulsar (w50 =43µs); as a result, it is one of the most precisely timed MSPs –the orbital inclination is close to 90 ◦ –precise measurement of Shapiro delay provide m p = (1.438 ±0.024) M ⊙

Recent results

PSR J –a 2.15ms pulsar in a 95-day orbit with ∼ 1M ⊙ main- sequence star companion – e = 0.44 –it is possible that PSR J formed from a hierarchical triple system which the mass donor somehow eliminated –combine dω/dt and s measured give m p =(1.74 ± 0.04)M ⊙, m c = (1.028 ± 0.004)M ⊙

This is the first precisely measured NS mass larger than that of PSR B and the first significantly above the Chandrasekhar mass This pulsar proves that accretion can significantly increase the mass of MSPs compared to the NSs in DNS systems, i.e., the mass distribution for MSPs is definitely wider than the NS mass distribution in DNSs

Study of super-dense matter The precise measurement of MSP masses is so important because –Due to accretion they can be more massive than NSs in DNS systems –This can test our models of how matter behaves at the center of NSs –the mass measured for PSR J is higher than the maximum possible mass predicted by some EOS models

PROSPECTS The increased number of mass Probability distribution functions (pdfs) will assist the statistical studies of the MSP mass distribution. γof Ter 5 I is becoming detectable which we expect the pulsar to be massive (<1.96) Meanwhile, HST time has already been allocated for the study of the environs of these candidate super- massive pulsars The detection of their companions will be important to address the issue of whether the observed dω/dt is purely relativistic or not

Measurements of the spectral line widths of the companion might address once and for all the issue of whether the companion is rotating fast or not and whether it can contribute to the observed advance of periastron

Thanks