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

This study presents the discovery of an eccentric binary millisecond pulsar in a gamma-ray-detected globular cluster. The pulsar acts as an extreme physical laboratory, revealing insights into gravitational physics and dense matter. Constraints on the equation of state are derived from various pulsar characteristics, such as mass and emission types. The research explores indirect and direct detection methods, including the detection of gravitational waves. The detection of gamma-ray pulsars using the Fermi Large Area Telescope expands understanding of young and normal pulsars, particularly millisecond pulsars found in globular clusters. The study uncovers a highly eccentric orbit in NGC 6652A, highlighting the need for precise orbital parameters estimation through pulsar timing. Various pulsar and binary system properties are examined, emphasizing the exotic and relativistic nature of the discovered system and its potential to measure pulsar mass and test general relativity.

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

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  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

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