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Discovery of a Highly Eccentric Binary Millisecond Pulsar in a Gamma-Ray- Detected Globular Cluster Megan DeCesar (UWM) In collaboration with Scott Ransom.

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Presentation on theme: "Discovery of a Highly Eccentric Binary Millisecond Pulsar in a Gamma-Ray- Detected Globular Cluster Megan DeCesar (UWM) In collaboration with Scott Ransom."— Presentation transcript:

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

3 Midwest Relativity Meeting 2013 Gamma-ray pulsars with the Fermi Large Area Telescope Saz Parkinson 2009 Abdo (MSPs) Young/normal pulsars Millisecond pulsars (MSPs)

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

5 Midwest Relativity Meeting 2013 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)  Ter 5 (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

6 Midwest Relativity Meeting 2013 Discovery of PSR J A  Searched NGC 6388 and NGC 6652 with the NRAO Green Bank Telescope (GBT)  Found 1 MSP in NGC 6652

7 Midwest Relativity Meeting 2013 Estimating the orbit of PSR J A NGC 6652A has a highly eccentric orbit. Pulsar timing is needed to accurately determine the orbital parameters. Circular orbitEccentric orbit

8  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. Midwest Relativity Meeting 2013 Pulsar timing Solitary pulsar Frequency, frequency derivative (spin parameters) Binary pulsar Spin parameters + orbital parameters:  Orbital period, P b  Pulsar’s projected semimajor axis, x = a p sin(i)  Eccentricity, e  Epoch of periastron, T 0  Longitude of periastron, ω

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

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

11 Midwest Relativity Meeting 2013 An exotic, relativistic binary system m c ~ 0.7 – 2.9 M sun 1.4 M sun 90% confidence

12 Midwest Relativity Meeting 2013 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.

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

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

15 Midwest Relativity Meeting 2013 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

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

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

18 Midwest Relativity Meeting 2013 Conclusions and Future  PSR J A 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 M sun, likely a massive white dwarf or a neutron star.  Two PK parameters, γ and dP b /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!


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