Discovery of a Highly Eccentric Binary
Millisecond Pulsar in a Gamma-RayDetected 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
Pulsars as Extreme Physical Laboratories
Big Picture
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Physics of very dense matter
Gravitational physics in weak and strong fields
Constraints on EOS from:
NS Equation
of State
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Maximum NS mass
(binary pulsar timing)
Radius estimates
(thermal X-ray emission)
Lattimer+Prakash’04
Emission: NS-NS, NS-BH mergers
Gravitational
Waves
Detection:
 Indirect (binary pulsar timing)
 Direct (pulsar timing array)
Weisberg+’10
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/
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Fifty new MSPs discovered in Fermi LAT sources
 Several new MSPs
for GW searches
 All show gammaray pulsations
Image: P. S. Ray
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Gamma-ray detections of globular clusters

Many MSPs in globular clusters (GCs)
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GCs should be gammaray sources with pulsarlike 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)
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Abdo+ 2009
Discovery of PSR J1835-3259A
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Searched NGC 6388
and NGC 6652 with the
NRAO Green Bank
Telescope (GBT)
Found 1 MSP in
NGC 6652
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Estimating the orbit of PSR J1835-3259A
Circular orbit
Eccentric orbit
NGC 6652A has a highly eccentric orbit. Pulsar timing is needed to
accurately determine the orbital parameters.
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Pulsar timing

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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.
Solitary pulsar
Frequency, frequency derivative (spin parameters)
Binary pulsar
Spin parameters + orbital parameters:

Orbital period, Pb
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Pulsar’s projected semimajor axis, x = ap sin(i)

Eccentricity, e
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Epoch of periastron, T0
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Longitude of periastron, ω
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Initial timing solution of NGC 6652A
!!!
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An exotic, relativistic binary system
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High eccentricity implies companion exchange in the past,
common in dense environments of globular clusters.
Mass function
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An exotic, relativistic binary system
90% confidence
mc ~ 0.7 – 2.9 Msun
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1.4 Msun
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

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
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.
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Post-Keplerian parameters
Rate of periastron
advance
Einstein delay
Shapiro delay
Orbital decay (due
to GWs)
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Measure 2 PK parameters
 pulsar, companion masses
Measure 3+ PK parameters
 test GR
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Post-Keplerian parameters: γ, dPb/dt, and dω/dt
Comparison with
Hulse-Taylor pulsar
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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.
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Conclusions and Future
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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 HulseTaylor 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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