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

Discovery of a Highly Eccentric Binary Millisecond Pulsar

Big PicturePulsars 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 mergersDetection:

Indirect (binary pulsar timing) Direct (pulsar timing array)

Gravitational Waves

Lattimer+Prakash’04

Weisberg+’10

Midwest Relativity Meeting 2013

Gamma-ray pulsars with the Fermi Large Area Telescope

http://www.nasa.gov/externalflash/fermipulsar/

Saz Parkinson 2009Abdo+ 2009 (MSPs)

Young/normal pulsars

Millisecond pulsars (MSPs)

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

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

Midwest Relativity Meeting 2013

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

Estimating the orbit of PSR J1835-3259A

NGC 6652A has a highly eccentric orbit. Pulsar timing is needed to accurately determine the

orbital parameters.

Circular orbit Eccentric orbit

Midwest Relativity Meeting 2013

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.

Pulsar timing

Solitary pulsar

Frequency, frequency derivative (spin parameters)

Binary pulsar

Spin parameters + orbital parameters: Orbital period, Pb Pulsar’s projected semimajor axis, x

= ap sin(i) Eccentricity, e Epoch of periastron, T0 Longitude of periastron, ω

Midwest Relativity Meeting 2013

Initial timing solution of NGC 6652A

!!!

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.

Midwest Relativity Meeting 2013

An exotic, relativistic binary system

mc ~ 0.7 – 2.9 Msun

1.4 Msun

90% confidence

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.

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 Msun

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 Msun

System is relativistic Measure Post-Keplerian parameters.

Midwest Relativity Meeting 2013

Post-Keplerian parameters

Rate of periastron advanceEinstein 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

Post-Keplerian parameters: γ, dPb/dt, and dω/dt

Comparison with Hulse-Taylor pulsar

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 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

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!