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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 (NRAO), Paul Ray (NRL), Paul Demorest (NRAO), David Kaplan (UWM), and the Fermi LAT Collaboration

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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

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

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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

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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

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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

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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

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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

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

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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.

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

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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.

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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

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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.

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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

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

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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.

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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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