UR: Quick–LOOK: Pulsar Data!

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Katherine Zine/Blaise Veres

Indiana University Bloomington/Gettysburg College

Katherine worked on this research during the 2021 Astrophysics REU at West Virginia University’s Center for Gravitational Waves and Cosmology. Her advisor was Dr. Maura McLaughlin and she is a rising senior majoring in astronomy and physics at Indiana University Bloomington. Katherine loves to read and plans to attend graduate school in astronomy.

Blaise is a rising senior studying physics at Gettysburg College. He completed this research during the 2021 Astrophysics REU program at West Virginia University’s Center for Gravitational Waves and Cosmology, working under Dr. Maura McLaughlin. In his free time, Blaise enjoys playing niche sports, making music, and reading non-fiction.

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a collaboration of astronomers across North America that uses pulsars to try to detect gravitational waves, which are ripples in spacetime produced by accelerating massive objects. Pulsars are rapidly-rotating, highly magnetized neutron stars which emit radio beams from their magnetic poles that cross our sightline like a lighthouse as the star rotates. This rotation is very periodic, so we can calculate exactly when the next pulse will occur. NANOGrav “times” pulsars, or calculates the time of arrival of their pulses. If a gravitational wave comes through, we will detect it in the times of arrival because the pulse signal will come at a slightly different time than predicted. To look for any interesting changes relating to the pulsar observations, the software called Quicklook, in the form of a Jupyter Notebook, quickly generates various graphs of different properties of the pulsar. Our project aimed to add two new plots that look at additional properties: dispersion measure (DM), which is the integrated column density of electrons between us and the pulsar, and changes in the intensity of the pulsar profile, which plots the energy of the pulsar beam over its rotation.

We added Python code to the Quicklook notebook to create our graphs. The first plot we added showed profile residuals (example shown in Figure 1), which are the differences between the observation profile and the average template for that pulsar. The second plot (example shown Figure 2) uses the times of arrival of the pulses, calculates their DM, and then graphs the difference between the measured DM and the average, which is called DMX, along with historical values. We used NANOGrav data for pulsars J2145-0750 and J1613-1224 as test cases for our code. The new graphs make it easier to see any interesting variations in the profiles or DM and allow for follow-up. Future work may include making the running of the Quicklook notebook automatic, and, since the data we used was only obtained by the Green Bank Telescope, to make it work with other telescopes as well


Profile residuals (difference between model and data) for pulsar J2145, showing just a noisy straight line
Figure 1: An example of our profile residual plot for pulsar J1643-1224 on July 14, 2017 (MJD 57948). This shows the difference between the profile for the observation and the template average for the pulsar. This residual plot allows changes from the average in the intensity profile to be easily seen.
Dispersion measure changes for pulsar J2145-0750, showing the change in dispersion measure over time, showing an upward trend
Figure 2: An example of our DMX plot for pulsar J2145-0750 on April 1, 2020 (MJD 58940). This shows how the DM on each date varies from the average DM for this pulsar. Historical and previously calculated points are in blue, and the value for the current date is in orange.

Astrobite edited by: Haley Wahl

Featured image credit: Katherine Zine, Blaise Veres

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