New Measurements of MSP masses in Globular Clusters

Paulo C. C. Freire

Max-Planck-Institut für Radioastronomie

MSP Ensemble

• A more sound statistical result is that millisecond pulsars have a much broader mass range than the neutron stars in DNS systems!

• This is much wider than observed for the neutron stars in double neutron star systems.

• The likely reason for this is the accretion of material into the neutron star that was needed to recycle it into a millisecond pulsar.

• Strange new trend: more massive objects have much smaller spin frequencies!

M5B

NG

C 6

440B

0 0.5 1 1.5 2 2.5 3 3.5 4Pulsar Mass (Solar Masses)

Prob

abilit

y de

nsity

From: Freire et al. 2008b, ApJ, 679, 1433

Measuring the Mass of PSR J1903+0327

Apart from presenting an evolutionary puzzle, the unusual characteristics of this binary system are interesting because they allow the measurement of post-Keplerian orbital parameters that lead to a precise determination of the masses of the components of the system.

The eccentricity of this binary system allowed a measurement of the apsidal motion: 86.38 ± 0.08 arcseconds/century . Assuming GR is correct, this gives us the total mass of the system.

The large companion mass, coupled with the good timing precision, allow a measurement of the Shapiro delay.

This is a truly unusual set of circumstances for a MSP binary system!

From: Freire et al. (2011)

The PSR J1903+0327 Binary System

The system is even harder to explain because the companion turns out to be a main sequence (MS) star!

The star shows Doppler shifts that mirror the movement of the MSP (Freire et al. 2011, MNRAS, 412, 2763)

From: Champion et al., Science, 320, 1309 (2008)

From: Freire et al., MNRAS (2011), in press.

Measuring the Mass of PSR J1903+0327

Putting everything together, we obtain a pulsar mass of 1.667 ± 0.021 solar masses (99.7% C. L.). This is the most precise mass measurement of any MSP.

This value is confirmed by four Post-Keplerian parameters, including the two new Shapiro delay parameters, ς and h3 (Freire & Wex, MNRAS, 409, 199, 2010)

From: Freire et al. (2011)

h3h3

/ω. + ’−µ

/ω. + ’−µ

ς

R

R ς

PSR J1614−2230

• Measurement of the Shapiro delay for this pulsar indicates a pulsar mass of 1.97 ± 0.04 solar masses. Not as high as M5B or NGC 6440B, but much more precisely determined!!!

From: Demorest et al. 2010, Nature, 467, 1081

PSR J1614−2230

• Consequences for the study of the EOS are obvious!

• Furthermore, the mass measurements for J1614−2230, J1903+0327 and J1909−3744 confirm that the mass distribution for MSPs is much broader than for “normal” pulsars - presumably, because of accretion!

From: Demorest et al. 2010, Nature, 467, 1081

The lower end of the MSP mass distribution

• PSR J1807-2459B, in the GC NGC 6544, is a 4.18-ms in an eccentric (e = 0.75) orbit!

Mass determination with an awful Shapiro delay

• The Shapiro delay is awful - but combined with the precession of periastron, it yields the most precise MSP mass ever: 1.3649+0.0017-0.0022 solar masses (Lynch, Freire, Ransom & Jacoby 2012, ApJ, 745, 109). Companion is the largest mass around fully recycled MSP (1.2068+0.0022-0.0016 solar masses)

!.

!.h

3

h3"

"

A Millisecond Pulsar in NGC 1851

• In 2003, we (Paulo Freire, Yashwant Gupta and Scott Ransom) used the GMRT to search for pulsars in 11 GCs.

• One pulsar was found: PSR J0514–4002A, in NGC 1851. This object has a spin period of 4.99 ms (Freire et al. 2004, ApJL, 606, 53).

• Previously, nearly all known MSPs had low-eccentricity orbits. NGC 1851A has an orbital eccentricity of 0.89, the highest known at the time!

From: Freire et al. 2004, ApJ Lett., 606. 53

A Millisecond Pulsar in NGC 1851

• These systems were probably formed by an exchange interaction. These are only likely to happen in environments with very high stellar densities, like globular clusters.

• The same mechanism could also form a MSP-MSP system or a MSP-BH system! Such systems would be the ultimate probes of GR, particularly if they could be timed with the SKA!

• The high eccentricity allows a measurement of the periastron advance, indicating a total system mass of 2.453(14) solar masses.

• The pulsar has a maximum mass of 1.5 solar masses (Freire, Ransom and Gupta, 2007, ApJ, 662, 1177). Again, Shapiro delay constraints might be feasible in the very near future for this and 10 other eccentric MSPs. Stay tuned!

From: Freire, Ransom and Gupta, 2007, ApJ 662, 1177