Long-Term Timing of Globular Cluster Pulsars Sergio Smith National Radio Astronomy Observatory Green Bank, West Virginia Summer 2016 Long-Term Timing of Globular Cluster Pulsars

Research objectives Learn to do pulsar astronomy Time some pulsars How to Time a Pulsar Time some pulsars Update the timing model for these pulsars Study timing models Find and study interesting physics

So…what’s a pulsar? Neutron Star Strong magnetic fields Bill Saxton, RAO/AUI/NSF So…what’s a pulsar? Neutron Star Supernova Remnant Strong magnetic fields Up to 1015 Gauss Produces radio emission from magnetic poles Rotating Rapidly Up to 700 times per second Trove of questions… …but also answers!

What is pulsar timing? Careful tracking of pulsar rotations When do we EXPECT pulses to arrive? Monitoring changes in pulse arrivals over time Learning more about pulsars and their environment

What’s a timing model? “Set of parameters” List of numbers Describes several properties of the pulsar Rotational period, orbital information, proper motion… Leads to “derived parameters” Pulsar mass, companion mass, relativistic effects…

Times of Arrival (TOAs) What’s a timing model? More Science! TEMPO2 Timing Model Pulse Times of Arrival (TOAs) Some Science

Getting TOAs – Observation Scheme Observations using the Robert C. Byrd Green Bank Telescope (GBT) L-band frequencies (1500 MHz center, with 800 MHz bandwidth) Observations over ~5 years 2011-2015 ~30 Observation dates Lots of data processing

Getting TOAs – RFI zapping Removing Radio Frequency Interference (RFI) from data

Getting TOAs – RFI zapping Removing Radio Frequency Interference (RFI) from data

Getting TOAs – Calibration Calibrate for absolute flux as well as polarization Compares data to intensity of known object Allows us to measure brightness of pulsar Useful for studying energy dissipation, changes in flux over time, etc. Assumes orthogonal polarizations Measures circular as well as linear polarization

Getting TOAs – Derotation Removes Faraday rotation from signal Rotation in linear polarization polarization Caused by interstellar medium (ISM)

Timing results – Residuals Difference between expected TOA and measured TOA Post-Fit Residuals for NGC 6544A

Timing Results – Parameters

Timing Results – Dispersion Measure Effect of ISM Smearing of signal in time Frequency dependent http://astronomy.swin.edu.au/pulsar/noteshome/reduction/p2.html

Timing Results – Dispersion measure Jumps in data suggested DM was possibly changing over time Calculated DM for each day

Timing Results – Dispersion measure B Fluctuations in dispersion measure over observation span

Timing Results – Jerk Effect of neighboring stars on rate of rotation Mean Field and Nearest Neighbor contributions Seen in second period (or frequency) derivative Fitted in timing model F2A≈10-26 s-3 F2B≈10-25 s-3

Mean field contribution Timing Results – Jerk Full equation for second period derivative Mean field contribution F2mf≈10-27 s-3 (too small) Large nearest neighbor contribution?

Summary Revisited values of certain timing parameters Close agreement with published results Dispersion measure as possible cause for residual jumps Possible measurement of jerk Nearest neighbor contribution? Tests of general relativity? Shapiro delay

Acknowledgements Dr. Ryan Lynch (advisor) National Radio Astronomy Observatory Green Bank staff members National Astronomy Consortium Attendees and participants Thank you!