Student Research Projects

Funding sources for these research projects are acknowledged at the bottom of the page.

Kristina Rolph (F&M '15)

Kristina is working with me as a summer student on a search of the Triangulum Galaxy (M33) for dispersed radio pulses from compact objects using the Arecibo telescope. A new wide-bandwidth backend has been installed at Arecibo, making a new search of M33 for pulses feasible with Arecibo. We hope to discover extragalactic radio pulsars from M33, which would be the first confirmed pulses from a compact object in another spiral galaxy. Apart from detecting signals from bright pulsars, our search may be sensitive to bright bursts from other sources, such as rotating radio transients and magnetars. The search is also sensitive to the extremely luminous extragalactic bursts that have been observed previously in some pulsar surveys. More details can be found here.

Chris Morrow (F&M '15)

Chris is working with me as summer student on a project to support modeling of the detection of gravitational waves using pulsar timing. This modeling work is being led by Xavier Siemens from the University of Wisconsin - Milwaukee. This in turn is part of a larger effort to directly detect gravitational waves by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) consortium. Gravitational waves are distortions in space-time that are predicted by General Relativity to be generated by the acceleration of masses. Very massive black holes in binary systems that undergo inspiral and coalescence are sources of these waves. These inspiral and merger events early in the evolution of the universe ought to have left a background signal of gravitational waves which may be detectable today with pulsar timing. The idea is that pulses coming from an array of pulsars in space may experience delays (timing residuals) of such a magnitude and with such a correlated relationship that it would indicate the presence of gravitational waves. Currently just a handful of known pulsars with very precisely measured residuals are used in the detection models since these are the most sensitive to slight delays. However, other less precisely measured pulsars may also be useful to include. Nobody has yet compiled a complete census of the characteristics and information relevant for gravitational wave detection for the known pulsar population. Chris will track down and compile this information for the known pulsars, and we will determine whether any of these pulsars may be useful to add to the gravitational wave modeling and detection effort. More details can be found here.

Jack Madden (F&M '14)

Jack worked with me as an independent study student and summer research student identifying pulsar candidates from both the PALFA survey (see below) and a high-resolution radio pulsar survey of the Large Magellanic Cloud (LMC). The LMC survey data were taken with the Parkes 64-m radio telescope in Australia, and this is the first survey of the LMC that is sensitive to fast-spinning, millisecond pulsars (MSPs) that have been recycled from accretion from a companion star. To date no MSP has been discovered outside of our Galaxy, and we hope that this survey will find the first one. Some initial results from this survey were presented in a conference talk at an American Astronomical Society meeting. Most MSPs reside in binary systems, and in order to detect binaries, the survey is being processed using a search in acceleration parameter space. The acceleration search expands the data processing task by orders of magnitude, so Jack's summer work was to determine a feasible range of parameter space to search with our Beowulf clusters. He then processed the survey data using his chosen search parameters. Jack did not find any pulsars in his search of these data, but he did find a new pulsar in the LMC from reprocessed archival data. His discovery was reported in articles in The Diplomat and in The College Reporter. The pulsar discovery is also presented along with several others in a forthcomng paper (Ridley et al. 2013).

Ryan Anella (F&M '13)

Ryan worked with me on processing pulsar survey data from observations that were coincident with cataloged HMXBs located in the Magellanic Clouds. He looked for faint, pulsed radio emission and radio bursts, which are not generally expected to be detectable from active X-ray binary systems. The data were searched on our Beowulf cluster at a wide range of dispersion trials as well as a large range of acceleration trials to account for any binary oribital motion effects. Detection of radio emission from these systems would have implications for the physics of how accretion from a companion onto a neutron star suppresses the radio emission mechanism. We found no radio pulsars associated with any HMXBs. His work is described in a forthcoming paper announcing the discovery of several pulsars in the Large Magellanic Cloud (Ridley et al. 2013).

Hannan Li (F&M '14)

Han worked with me as a summer student investigating the modulation characteristics of PSR J0529-6652, a very luminous pulsar in the Large Magellanic Cloud that has shown unusual variability on short time-scales. This is a continuation of work that was first started by Dean Altemose (F&M '09) (see Dean's project below). Han modified and extended some of Dean's code to take a different approach toward characterizing the pulsar variability that was outlined by Jenet & Gil (2003) and Jenet & Gil (2004), and more recently by Weltevrede, Edwards, & Stappers (2006) and Weltevrede, Johnston, & Espinoza (2011). The results from this study were presented in Crawford et al. (2013).

Zach Robinson (F&M '11)

Zach worked as an independent study student continuing our investigation and classification of pulsar candidates produced in the processing at F&M of survey data from the PALFA survey project (see below for more details about candidate analysis work for the PALFA survey). He also was responsible for evaluating the quality of PALFA candidates produced by Dominik Rastawicki's automated pulsar detection algorithm (see below).

Dominik Rastawicki (F&M '11)

For his independent study project, Dominik took a set of algorithms that he had previously developed to detect cavities/voids in maps of the solar corona and applied them to the classification of pulsar candidate plots from the PALFA survey. One goal was to determine whether this artificial detection algorithm can be used to effectively discriminate between real and fake (interference) signals in the PALFA survey candidates at F&M (the answer is yes!). A second goal was to apply this algorithm to identify good pulsar candidates in our existing database of processed data at F&M, which currently has several hundred thousand plots and is growing each month. Investigating the plots one at a time is too big of a task for one or two students without some kind of automation. We also applied Dominik's algorithm to the collection of PALFA candidates produced by the Einstein@Home radio pulsar search project, which processes PALFA survey data in a distributed fashion and is particularly sensitive to finding highly-accelerated binaries with short orbital periods. Dominik's algorithms have proven to be a promising approach to candidate identification, and a modified version of the code was used by the Einstein@Home group to identify roughly half of the 23 new pulsars found in Parkes Multibeam Pulsar Survey data. These results are presented in a forthcoming paper (Knispel et al. 2013).

Claire and Debbie worked as independent study students, and apart from their continuing work on the PALFA survey (see below) and assisting with timing observations for the binary pulsar PSR J1723-28 (Crawford et al. 2010), they were responsible for regular observations using the NRAO 140-ft (43-meter) telescope in Green Bank, WV. For this project, we collected high-resolution pulsar search data on 92 unidentified radio sources from the FIRST and NVSS VLA surveys that are both bright and highly linearly polarized. This project is a joint collaboration between F&M and NRAO and augments a previous search of these same sources with Jodrell Bank (Crawford et al. 2000). Some of these unidentified sources may be pulsars undiscovered in previous large-scale surveys, perhaps owing to very fast spin periods (i.e., millisecond, or possibly sub-millisecond periods). Discovery of a sub-millisecond pulsar would indeed be very exciting, and the payoff of the search in this case would be huge. Our new search at NRAO used a different frequency than the previous Jodrell Bank search, had a much wider bandwidth, and employed some software tools and observing and computational developments that were not available for the previous search. The 140-ft telescope and data acquisition software were operated remotely from F&M by the students, and the huge amount of data acquired in these sessions has been processed at both NRAO and F&M. Debbie completed the analysis of this survey for her senior thesis project, including a search for single pulse candidates and radio bursts. More details can be found here. Aspects of this work have been presented by Mickaliger et al. (2011), Crawford et al. (2011), Schmidt et al. (2012), and the final project results were presented by Schmidt et al. (2013).

Debbie and J.B. worked as summer students on the ongoing effort at F&M to process data and analyze pulsar candidates from the PALFA survey project. This work was started the previous semester by Claire Gilpin and Matt Jaffee, both of whom also worked on this project during the summer (see the description of their work below). Debbie worked full-time as a research student while J.B. supplemented his internship in another field with some part-time work on this project. In addition to this, J.B. worked on developing an algorithm to determine the spatial location (with uncertainty) of a putative radio signal that had been detected simultaneously in multiple beams of the Parkes multibeam receiver. The signal strengths in the 13 beams vary depending on the location of the source and other factors, including the different beam gains and the signal attenuation as a function of distance from the beam center, both of which must be modeled. The fitted signal position in the model must reproduce the observed ratios of the 13 different signal strengths (within their uncertainties). If no solution to this set of ratios can be found, then this could indicate that the signal might not be celestial in origin. In addition to her PALFA survey work, Debbie re-analyzed some Parkes timing data taken of the binary millisecond pulsar PSR J1723-28 in order to see if additional timing detections could be made with these data. This work supported a new pulsar timing campaign that collaborators and I began on PSR J1723-28 (see Crawford et al. 2010). Debbie accompanied me to an AAS meeting as well.

Claire and Matt both worked as independent study students (and subsequently as summer research students) processing and analyzing PALFA survey data at F&M. A good fraction of their their work was identifying promising pulsar candidates from the thousands of output plots that are automatically produced in our batch processing of the survey data with our Beowulf cluster. To help with this, they used a python GUI developed by the pulsar group at McGill University. They also downloaded raw data from Cornell for processing, operated the batch processing of survey data on the computer cluster, and uploaded the resulting candidates to the Cornell PALFA database. In addition, Matt worked on writing scripts which parse the headers of the processed beams in order to extract useful information from them, as well as writing scripts to help automate the review of the single pulse plots produced in the processing. Claire worked on writing up a manual for PALFA data analysis at F&M which can be used by future research students. Claire also assisted with several other ongoing projects. One was a search for very long-period pulsations (8-25 sec) in a radio pulsar survey that had targeted unidentified gamma-ray sources (see Crawford et al. 2006). Slowly-spinning neutron stars, for instance, could be detectable in this way and might have been missed with other search techniques. The other project was an investigation of the orbital phases of observations of PSR J1723-28 taken with the Parkes Observatory and Green Bank Telescope. PSR J1723-28 is a binary millisecond pulsar that has proved difficult to detect regularly in previous observations (possibly due to eclipsing from the companion star), and my collaborators and I have begun a timing study of this pulsar system. Claire spent some time in Australia, and Claire and Matt both accompanied me to an AAS meeting.

Dean worked with me as a summer student analyzing the nulling behavior of a very luminous radio pulsar (PSR J0529-6652) in the Large Magellanic Cloud. The pulsar was discovered in a radio pulsar survey of the Magellanic Clouds some years ago (McCulloch et al. 1983), but its nulling behavior has not been studied as far as we can tell. Apart from being very luminous (and having some kind of nulling behavior), this pulsar is not particularly unusual, and it is not yet clear exactly how PSR J0529-6652 is connected to the population of known nulling pulsars, or whether its behavior represents something new. Dean developed code in IDL to turn the raw data we collected at the Parkes telescope into individual phase-resolved pulses, and he applied his software to PSR J0529-6652 as well as several bright test pulsars we also observed. His work was continued by Han Li (F&M '14) (see Han's project above). The results from this study were presented in Crawford et al. (2013).

Jen worked with me on two different summer projects. The first project was finishing up the analysis of candidates in a search for highly-dispersed single radio pulses and bursts in archival survey data taken of mid-latitude EGRET sources with the Parkes telescope (see Crawford et al. 2006, Burke-Spolaor et al. 2011, and also below). Jen also worked on developing a procedure for doing the photometry of variable K-dwarfs in the Pleiades using IRAF. This latter project is part of F&M's long-term collaboration to monitor several variable dwarf stars (see Krishnamurthi et al. 1998). Jen reduced data that F&M students and I had collected at the NURO 31-inch telescope in March 2008, and she created a photometry cookbook that we can use for data reduction in the future. Jen's work on the search for dispersed radio pulses was presented in an AAS conference poster.

Chase's project as a summer research student was searching for a periodic signal from the pulsar candidate J1928+15, which was discovered in the PALFA survey. The discovery observation of J1928+15 showed a single set of three dispersed pulses. Subsequent follow-up observations showed no periodicity in the expected period range. Chase and I searched these follow-up observations for additional single pulses and for a long-period periodicity using the Fast Folding Algorithm. This latter analysis is more sensitive than a Fourier search to very long periods (i.e., more than a couple of seconds). This pulsar may belong to a new observational (and possibly physical) class of serendipitous intermittent objects. This search work was reported in a larger paper on intermittent and transient radio pulsars found in the PALFA survey (Deneva et al. 2009).

Brian worked with me as a summer student searching for highly-dispersed single radio pulses and bursts in archival Parkes survey data taken of mid-latitude EGRET sources (see Crawford et al. 2006, Burke-Spolaor et al. 2011, and also below). Brian modified and ran PERL scripts to process the raw data, and extended the search to a higher dispersion range than what was covered in the prior analysis of these data. The extension in the dispersion range was motivated by the discovery of a highly-dispersed, extragalactic millisecond radio burst in another archival Parkes survey (see Lorimer et al. 2007) which indicated that such bursts might be present in other pulsar data sets. Brian's work on this project was presented in an AAS conference poster. Brian also accompanied me to the Parkes observatory to collect data for several pulsar projects, including a study of a nulling pulsar (see above) and a search for pulsed radio emission from two X-ray sources (including one transient source) in the Magellanic Clouds (see Crawford et al. 2009).

For her senior project, Elisabeth worked on the calibration, editing, and mapping of archival radio interferometry data from the Australia Telescope Compact Array. These data were taken of a young, energetic pulsar (PSR J1301-6305) that was first discovered in the Parkes Multibeam Survey (see also Chelsea Tiffany's project below). The radio observation field happened to include the error circle of a newly discovered TeV gamma-ray source, HESS J1303-631 (Aharonian et al. 2005), so her analysis aimed to determine whether there were any faint extended radio sources within the error circle (such as a pulsar wind nebula) that could be powering the gamma-ray emission. We carefully repeated the prior calibration and editing of the raw data, and we created maps of the region at both 1384 MHz and 2496 MHz. We found a small extended object that had been only hinted at in a previous, low-resolution map taken at 843 MHz. However, further analysis indicated that this source was not a pulsar wind nebula or supernova remnant and is not associated with the TeV source. Some of Elisabeth's calibration work on the PSR J1301-6305 data was used in the polarization analysis of two energetic radio pulsars that was written up in a journal article (Crawford & Tiffany 2007).

Tim's senior project was to search through single pulse plots from a Parkes survey for pulsars in the Magellanic Clouds (see Manchester et al. 2006). The goal was to look for highly dispersed single pulses or bursts from transient neutron stars. Our collaborators were also searching these plots at the same time, and they discovered a very luminous, highly-dispersed millisecond burst in several of the beams. This probably represents a new kind of source, and follow-up search observations revealed no additional signals . The burst discovery and discussion were subsequently written up in a journal article (Lorimer et al. 2007).

Brian's senior project was to model a high-pass filter present in the multibeam receiver system of the Parkes telescope. This filter is modeled as a two-pole filter (see Manchester et al. 2001), and it attenuates variable signals (such as pulses) having characteristic times longer than a few seconds. This receiver has been widely used for pulsar searches and other observations, but the filtering effect is particularly relevant for searches for radio pulses from anomalous X-ray pulsars (see, for example, Crawford et al. 2007) and from other sources having long spin periods. In these cases, the filter can significantly degrade the sensitivity of the search observations. Brian's project was to quantify the effect of the filter on the sensitivity of radio search observations with this system by creating synthetic pulse trains in software having a range of periods and duty cycles. He then passed these signals through a model software filter. Brian developed scripts in Mathematica to do this, and his results were included in a paper in which we reported the results of a sensitive radio search of a long-period transient X-ray source (XTE J0103-728) in the Small Magellanic Cloud (Crawford et al. 2009).

Apart from helping with the maintenance of our distributed Linux cluster (see Cantino et al. 2004 and also below), Peter assisted me with survey observations for the PALFA survey, a survey of the Galactic plane for pulsars being using done with the Arecibo telescope. Peter and I went to Arecibo to conduct some of these observations, and he accompanied me to an AAS conference as well.

All of these students worked with me on troubleshooting and expanding a distributed Linux cluster that we constructed from a collection of decommissioned PCs that were connected to each other through standard ethernet ports throughout the science building (see Cantino et al. 2004 and below). Since the machines were old and no mechanism was in place to automatically synchronize the machine configurations as changes were made, these students spent a lot of time adding and checking software, handling network and system administration tasks, rebooting and resetting machines, dealing with power issues, and adding new machines to the cluster as they became available. During the course of this work, some of the processing of the Parkes survey data taken of mid-latitude EGRET sources was also done (see Crawford et al. 2006).

Gabe worked with me as a summer student on several pulsar projects. He wrote a monitoring script for our distributed Linux cluster in PERL which periodically polled the node machines and recorded the machine loads in a publicly accessible file. This was useful for checking on the status of the cluster during data processing. Gabe also began a modeling study of the Parkes Multibeam Survey sensitivity, comparing model predictions with the sample of observed pulsar detection strengths from both the blind Fourier search and folded-profile detections. Accurately modeling the sensitivity of the survey is important for population modeling work which aims to understand the underlying radio pulsar population in the Galaxy. He also conducted some of the processing of the data from the Parkes survey of mid-latitude EGRET sources (see Crawford et al. 2006).

Steve and Ryan worked over the summer on developing PERL scripts to handle the processing of the data from the Parkes survey of mid-latitude EGRET sources (see Crawford et al. 2006) using the distributed Linux cluster we constructed from decommissioned PCs (see Cantino et al. 2004 and below). These data were loaded from DVD and processed on the cluster, with a range of trial dispersions determined for each individual beam from the NE2001 Galactic electron model (Cordes & Lazio 2002). By separately calculating the dispersion range to be searched for each individual beam, we could more efficiently use the available cluster cycles and more quickly complete the processing.

Cole's senior project was to search for radio emission from PSR J0537-6910, an X-ray pulsar with a period of 16 ms in the Large Magellanic Cloud that was first discovered by Marshall et al. (1998). This is the fastest non-recycled rotation-powered pulsar known and is one of the few "Crab-like" pulsars that are known. A previous search for radio emission from this pulsar was unsuccessful (Crawford et al. 1998), so we undertook a more sensitive observation of this pulsar with the Parkes telescope using higher time and frequency resolution. In addition, there is reason to believe that PSR J0537-6910 could be emitting giant single radio pulses. Detection of either giant or regular radio pulses from PSR J0537-6910 would be important for understanding the connection between giant radio pulses, the light-cylinder magnetic field strength, and high-energy and radio emission. Cole searched for periodic emission using both a Fourier search and a folding search at a range of trial dispersions (a computationally demanding problem) while our colleagues searched for single-pulse emission. We made no detections and set upper limits on the radio luminosity of the pulsar. Cole accompanied me to a COSPAR conference meeting in Paris to present these results, which were also written up in a journal article (Crawford et al. 2005).

Andrew's summer project was jointly sponsored by the physics and computer science departments (myself and John Dougherty) to develop a distributed Linux cluster for pulsar data processing and network efficiency analysis. This cluster was to be constructed from decommissioned PCs connected to each other through the standard ethernet ports present throughout the science building. Essentially, this was a simple, low cost solution to the processing problem which used a client-based approach to the data distribution. Andrew also was responsible for writing the majority of the software (in PERL) through which the processing of data from a Parkes pulsar survey of unidentified EGRET sources would be handled. Andrew presented our work at a refereed computer science conference (see Cantino et al. 2004), and the results from the EGRET pulsar survey were later published in a journal article (Crawford et al. 2006). Andrew also presented this work in a KNAC symposium paper.

For his summer project, Reid worked on producing a database archive of the raw data collected in a survey of unidentified mid-latitude EGRET sources for radio pulsars conducted with the Parkes telescope (see Crawford et al. 2006). The data were originally stored on DLT tape when they were acquired at the telescope. Reid read off the survey data files from tape, unpacked them, and archived each set of unpacked beams onto DVD with an additional file that included relevant information about the beams (e.g., sky positions) and instructions for retrieval. Reid created a portable archive of 232 DVDs containing the whole survey (see Cantino et al. 2004), and this archive was used in the processing of the survey data by our group. Reid also created a set of master files containing all of the survey information. This database is publicly accessible here. Reid presented his work in a KNAC symposium paper, and he also went to the Parkes observatory for an extended observing session, which included assistance with pulsar survey observations as well as planetary satellite tracking work.

For Saurav's summer project, he worked on developing code in IDL to cross-check the catalog of known radio pulsars with the positions of the beams from a survey of unidentified mid-latitude EGRET sources for radio pulsars taken with the Parkes telescope. This was important for making sure that we detected the pulsars in the survey that we expected to detect and that our pulsar search code was working properly. Saurav also assisted with the construction of the DVD survey archive (see Reid Sherman's work above). Saurav presented his work in a KNAC symposium presentation and paper.

Chelsea worked me me as a summer student on the analysis of interferometric radio imaging data taken with the Australia Telescope Compact Array. These observations targeted several young, energetic pulsars that were discovered in the Parkes Multibeam Survey. Chelsea worked on the calibration of these data, and she constructed maps of the observed regions at two frequencies (1384 and 2496 MHz) in order to look for extended radio emission associated with the pulsars. These data were taken in pulsar gating mode, which allowed us to separate out the pulsed radio emission of the pulsar itself. The pulsar-gated data was used to construct phase-resolved polarization profiles and determine polarization fractions and rotation measures for two of the pulsars. This work was presented in her KNAC symposium presentation and paper, an AAS conference poster, and a subsequent journal article (Crawford & Tiffany 2007).

Nathan's summer project was to work on the analysis of radio polarization data taken of PSR J1119-6127, a young, high-magnetic field pulsar that was discovered by Camilo et al. (2000) in the Parkes Multibeam Survey. These polarization data were used to constrain the emission geometry of the pulsar and to test a theoretical model of pulsar spin-down proposed by Melatos (1997). Nathan constructed a 1400 MHz polarization profile, measured the polarization fraction and rotation measure for the pulsar, and determined the position angle swing of the pulsar as a function of pulse phase. He also used the measured position angle data to make constraints on the pulsar geometry using the rotating-vector model of Radhakrishnan & Cooke (1969). This work was presented in his KNAC symposium presentation and paper, an AAS conference poster, and a subsequent journal article (Crawford & Keim 2003).

Lindsey's UROP project was looking through plots of pulsar candidates that were produced from the processing of the Parkes Multibeam Survey. Promising candidates were tagged for follow-up confirmation with the Parkes telescope.

Funding

Our work has been supported in part by funds from the following sources:

• American Astronomical Society (AAS)
• Australia Telescope National Facility (ATNF)
• Franklin & Marshall Committee on Grants (COG)
• Franklin & Marshall Hackman Scholars Program
• Fund for Astrophysical Research, Inc.
• Haverford College Zweifler Family and Green Research Funds
• Keck Northeast Astronomy Consortium (KNAC)
• Mount Cuba Astronomical Foundation
• National Aeronautics and Space Administration (NASA)
• National Astronomy and Ionosphere Center (NAIC)
• National Radio Astronomy Observatory (NRAO)
• National Science Foundation (NSF)
• Pennsylvania Space Grant Consortium
• Research Corporation
• Sigma Xi Grants-in-Aid of Research Program