Discovery of a Highly Eccentric Binary Millisecond Pulsar in a Gamma-Ray-Detected Globular Cluster

1. Discovery of a Highly Eccentric Binary Millisecond Pulsar in a Gamma-Ray-Detected Globular Cluster Megan DeCesar (UWM) In collaboration with Scott Ransom (NRAO), Paul Ray (NRL), Paul Demorest (NRAO), David Kaplan (UWM), and the Fermi LAT Collaboration

2. Discovery of a Highly Eccentric Binary Millisecond Pulsar • Pulsars as Extreme Physical Laboratories • Physics of very dense matter • Gravitational physics in weak and strong fields Big Picture • Constraints on EOS from: • Maximum NS mass (binary pulsar timing) • Radius estimates (thermal X-ray emission) NS Equation of State Lattimer+Prakash’04 • Emission: NS-NS, NS-BH mergers • Detection: • Indirect (binary pulsar timing) • Direct (pulsar timing array) Gravitational Waves Weisberg+’10

3. Gamma-ray pulsars with the Fermi Large Area Telescope Young/normal pulsars Saz Parkinson 2009 Abdo+ 2009 (MSPs) Millisecond pulsars (MSPs) http://www.nasa.gov/externalflash/fermipulsar/ Midwest Relativity Meeting 2013

4. Fifty new MSPs discovered in Fermi LAT sources • Several new MSPs for GW searches • All show gamma-ray pulsations Image: P. S. Ray Midwest Relativity Meeting 2013

5. Gamma-ray detections of globular clusters • Many MSPs in globular clusters (GCs) • GCs should be gamma- ray sources with pulsar- like spectra (Venter+ 2008, 2009) • Ter5 (35 MSPs), 47 Tuc(26 MSPs), and several others with known MSPs were detected by the LAT (Abdo+ 2009, Kong+ 2010, Abdo+2010, Tam+ 2011) • Several more were detected that had no known MSPs (Abdo+ 2010, Tam+ 2011) Abdo+ 2009 Midwest Relativity Meeting 2013

6. Discovery of PSR J1835-3259A • Searched NGC 6388 and NGC 6652 with the NRAO Green Bank Telescope (GBT) • Found 1 MSP in NGC 6652 Midwest Relativity Meeting 2013

7. Estimating the orbitof PSR J1835-3259A Circular orbit Eccentric orbit NGC 6652A has a highly eccentric orbit. Pulsar timing is needed to accurately determine the orbital parameters. Midwest Relativity Meeting 2013

8. Pulsar timing • Basic idea: Use measured pulse arrival times to find a function (the timing solution) that accurately predicts future pulse arrival times. • Timing solution depends on pulsar properties. Frequency, frequency derivative (spin parameters) Solitary pulsar • Spin parameters + orbital parameters: • Orbital period, Pb • Pulsar’s projected semimajor axis, x = apsin(i) • Eccentricity, e • Epoch of periastron, T0 • Longitude of periastron, ω Binary pulsar Midwest Relativity Meeting 2013

9. Initial timing solution of NGC 6652A !!! Midwest Relativity Meeting 2013

10. An exotic, relativistic binary system • High eccentricity implies companion exchange in the past, • common in dense environments of globular clusters. Mass function Midwest Relativity Meeting 2013

11. An exotic, relativistic binary system 90% confidence mc ~ 0.7 – 2.9 Msun 1.4 Msun Midwest Relativity Meeting 2013

12. An exotic, relativistic binary system Roche lobe is smaller than MS radius for all companion masses.  Companion cannot be MS star; must be compact object. Midwest Relativity Meeting 2013

13. An exotic, relativistic binary system • High eccentricity implies companion exchange in the past, • common in dense environments of globular clusters. Mass function Companion is compact object with min. mass ~ 0.7 Msun Midwest Relativity Meeting 2013

14. An exotic, relativistic binary system • High eccentricity implies companion exchange in the past, • common in dense environments of globular clusters. Mass function Companion is compact object with min. mass ~ 0.7 Msun • System is relativistic  Measure Post-Keplerian parameters. Midwest Relativity Meeting 2013

15. Post-Keplerian parameters Rate of periastron advance Einstein delay Shapiro delay Orbital decay (due to GWs) • Measure 2 PK parameters •  pulsar, companion masses • Measure 3+ PK parameters •  test GR Midwest Relativity Meeting 2013

16. Post-Keplerian parameters: γ, dPb/dt, and dω/dt Comparison with Hulse-Taylor pulsar Midwest Relativity Meeting 2013

17. An exotic, relativistic binary system • High eccentricity implies companion exchange in the past, • common in dense environments of globular clusters. Mass function Companion is compact object with min. mass ~ 0.7 Msun • System is relativistic  Measure Post-Keplerian parameters. Einstein delay and dPb/dt ~5x larger than PSR B1913+16. Might also measure dω/dt. There is real potential to measure pulsar mass and test GR. Midwest Relativity Meeting 2013

18. Conclusions and Future • PSR J1835-3259A is the most eccentric binary MSP known. • It has undergone one or more companion exchanges. Its current companion is a compact object with minimum mass ~ 0.7 Msun, likely a massive white dwarf or a neutron star. • Two PK parameters, γ and dPb/dt, are ~5x larger than those of Hulse-Taylor pulsar, so are likely measurable. May be able to measure the neutron star mass and test GR. • We are currently investigating feasibility of measuring PK parameters. • We have proposed for GBT observations to better determine the timing solution and measure PK parameters. Thank you! Midwest Relativity Meeting 2013