Transcript Document

NANOGrav
Long-term timing of two faint millisecond pulsars at Arecibo
Text text text.
Paulo C. C. Freire (Arecibo Observatory / West Virginia University),
for the NANOGrav Collaboration
Introduction
•The two millisecond pulsars (MSPs) described here, J1738+0333
and J1741+1351,were discovered in 2001 in a Parkes survey of
the intermediate Galactic latitudes. These MSPs were amongst
the faintest discovered in that survey.
•Both objects can be seen with the Arecibo radio telescope. The
sensitivity provided by this telescope has now made these two of
the most precisely timed pulsars ever: averaging the Times of
Arrival of the pulses (TOAs) for 100 MHz and 1 hour, we get
weighted r.m.s. residuals of 200 and 110 ns for J1738+0333 and
PSR J1741+1351 respectively. These values make these objects
valuable for the detection of gravitational waves.
•These pulsars demonstrate the capacity of the Arecibo
telescope to produce useful scientific results with pulsars that
are too faint to be timed with other radio telescopes. These
objects are interesting studies in themselves ->
• PSR J1738+0333 is in a binary system with an orbital
period of 8.5 hours. The orbital eccentricity is smaller than
0.0000001 – the orbit does not deviate from a circle by more
than ~2 μm.
• The white dwarf companion of this pulsar has been detected at
optical wavelengths. The orbital variability of its redshift
allowed a measurement of its mass ratio:
 R = m /M
P
WD = 8.1 +/- 0.3.
•Arecibo timing carried out since 2003 has shown that the orbit
appears to become shorter by (1.7 +/- 0.10) x 10-14 s/s, i.e., the
orbital period decreases by about 0.5 μs per year.
•The timing also allows a precise determination of the proper
motion and parallax. Subtracting the kinetic effect of the
pulsar's velocity and the Galactic potential, we obtain the
orbital decay due to the emission of gravitational waves: -(2.5
+/- 0.10) x 10-14 s/s.
•Above : Pulse profiles for the two MSPs. The presence of sharp
features allows for precise timing.
•Above : Mass-mass diagram for the PSR J1738+0333 binary system. The
component masses are more likely to be located at the intersection of
the regions limited by the mass ratio measurement (R, with +/- 1 σ) and
the relativistic orbital decay (calculated assuming GR applies, also +/- 1
σ). Note that the pulsar mass is similar to the masses derived for neutron
stars in double neutron star systems (green bar).
•An independent determination of mass of the companion of PSR
J1738+0333 (which is, unfortunately, not possible to determine
from the Shapiro delay, given the low orbital inclination i) could
make this one of the best laboratories for testing gravitational
theories: the system would then impose very strong constraints
on the emission of dipolar gravitational waves, which are
predicted by alternative theories of gravitation.
•Left : Companion mass – cos i plot for PSR J1741+1351. The contours
include 99.7, 95.4 and 68.3 % of all probability, the constraints are
derived from a measurement of the Shapiro delay for this 16.3-day
binary system. The companion appears to have a mass of 0.27 +/- 0.02
M⊙ (1 -σ) and the pulsar a mass of 1.55 +/- 0.15 M⊙ (1-σ).