Student Research Projects
Fronefield Crawford
Below are descriptions of the various research projects that my
student colleagues and I have undertaken (presented in reverse
chronological order). Students interested in learning more about
getting involved in research projects with me at
F&M are invited to contact me
directly. My contact information can be found
here.
I also manage the
NANOGrav Student
Teams of Astrophysics ResearcherS (NANOStars) program at F&M in
which students participate in various research activities with the
Arecibo telescope.
Funding sources for these research projects are acknowledged at the
bottom of the page.
Mckenzie Golden
(F&M '25),
Eric Baldwin
(F&M '25),
and
Sergio-Marin Miralles
(F&M '26)
The Arecibo PALFA pulsar survey was very successful at discovering
dozens of new pulsars in the plane of our Galaxy. A new analysis of
this survey that these students are undertaking looks to find very
highly accelerated pulsar systems in which the pulsar is in a tight
binary with, e.g., a black hole. Such systems are expected to be very
rare (but are very interesting from a physics standpoint). The
previous survey analysis could have missed such systems if their
accelerations were outside of the search parameter space. The new
analysis splits the integrations into small sub-integrations to allow
exploration of very high accelerations in the search. This helps
manage the computational task, which is significant even with this
sub-integration approach.
Youssef El Gharably
(F&M '26),
Inna Shapovalenko
(F&M '26),
and
Kelvin Larty
(F&M '26)
Youssef, Inna, and Kelvin worked on investigating the possibility of
using rugged GoPro cameras for real-time tripwire detection in
minefields. Our prototype tripwire detection system that we
previously demonstrated to NATO used a fairly fragile Canon DSLR
camera, which is not well suited for work in a more rugged combat
environment. We are trying to determine if we could replace this
existing camera with a GoPro and reproduce the successful detections.
The soldiers and deminers in Ukraine are using GoPros on helmets, and
in principle the techniques we are testing could ultimately be useful
in tripwire detection in their ongoing fight through minefields.
See the description below, the
Landmine Detection at F&M
web site, or the NATO project websites
G5014 and
G5731 for more
complete details about this project.
Mckenzie Golden (F&M '25)
Wenky Xia
(F&M '24)
Wenky searched for exotic pulsars in the nearby spiral galaxy
M33. M33 has been observed with long integrations with the Arecibo
radio telescope, and an initial search for dispersed bursts and
periodicities in the data has been completed. Wenky revisited these
data sets and applied
stack search approach (outlined below in Zach Nusbickel's project and
in
Cadelano
et al. 2018) to combine multiple observations that targeted the
nucleus of M33. Combining the power spectra from these observations
enhanced the sensitivity to any faint periodic signals from
pulsars that may be present but would otherwise be undetectable in any
single observation.
An additional analysis of the M33 Arecibo data is searching for
periodic signals that might briefly be made brighter by scintillation
in short portions of the (long) total integration and for pulses from
highly accelerated and/or partially eclipsed binary systems. This is
accomplished by separately searching individual small sections of each
integration, where such systems could be more easily detected.
Melanie Ficarra
(F&M '24)
Mel is searching three newly characterized Galactic binary
systems which may harbor neutron star companions. Binary pulsars are
valuable systems to discover owing to the many physical applications
possible from their study. We are proposing deep, sensitive
observations with the GBT at a low observing frequency (350 MHz) to
try and detect pulsed radio emission from the compact companions. In
the cae of non-detecitons, our observations will improve the existing
sensitivity limits on these systems to a luminosity level comparable
to the lowest luminosities of the known Galactic binary pulsar
population. All three target systems are relatively near to us and
have small expected dispersion measures. Thus, using a low observing
frequency is desirable to take advantage of a likely steep spectrum
while not suffering significantly from dispersive and scattering
effects. These latter effects can be particularly deleterious for
recycled, millisecond pulsars having small spin periods.
Yuta
Shiohira (Ph.D. student,
Kumamoto University)
Yuta searched for periodic technosignatures in the Parkes 70-cm
survey archive (PKS70; see below and
here for survey
details). In terms of transmission power efficiency, periodic pulse
signals are considered one of the promising targets in the radio
search for extraterrestrial intelligence. Yuta used the software
package BLIPSS (see
Suresh
et al. 2023) which is based on the Fast Folding Algorithm (FFA),
and he searched for pulsed signals with periods between 3 and 56
seconds. No signals were detected, but he set constraints on the
number of extraterrestrial transmitters.
He presented his work at the conference Interstellar
Frontiers: Bridging Technosignatures, Astrobiology, and the SKA
in Perth, Australia.
Liv Young
(F&M '23),
Dani Zoeller
(F&M '23),
Andrew Lara
(F&M '24),
and
Gavi Fischer
(F&M '25)
These students helped finalize the cooperative robots system we
developed and are got things ready for our demonstration of the
working system for NATO at a test site at F&M. This involved the
following: (1) Making sure the automated navigation of the robot in
the test minefield was working, including verifying the GPS
localization, running the graphical user interface that controls the
robot, and running the robot in test lanes with simulated buried
mines; (2) Finishing and testing the camera sensor system on the robot
which was used to detect tripwires in minefields. This required that
the camera be mountable and controllable from the robot, that the
robot had access to frames the camera was taking, and that real-time,
automated analysis of the camera frames to detect linear features such
as tripwires was tested and could run properly. (3) Collecting LIDAR
frames of surface objects under different field conditions (e.g.,
lighting, angle, distance, scene background). This will be used in an
artificial intelligence approach under development to identify mines
and other ground objects.
See the description below, the
Landmine Detection at F&M
web site, or the NATO project websites
G5014 and
G5731 for more
complete details about this project.
Ziyu Mo
(F&M '23)
Ziyu was in charge is creating a gallery of heat maps for various
objects under investigation with a Fisher M-101 metal detector. These
objects are both landmine simulants of various types and different
forms of clutter (like a crushed can, knife, and shell casing). The
heat maps consist of the signal strength (voltage output form the
metal detector) as a function of horizontal position offset between
the metal detector coil center and the object center. These maps are
also created at different offset heights between the metal detector
and object, to measure how the overall sensitivity will change with
distance. The heat map gallery will be useful in determining whether
such information can be used to help distinguish landmines from buried
clutter in real surveys of minefields as part of our multi-sensor
approach to landmine detection and identification. His work can be
viewed on the Landmine
Detection at F&M web site.
Alex Sobey-Strick
(F&M '23)
Alex worked on developing a matched filtering program that will detect
particular kinds of exposed landmines using LIDAR imagery. The
landmines in question are the
PMA-2 type, which
has a small starfish-type plunger extension on top of the mine which
acts as the trigger, and the
PFM-1 type, which
is typically scattered onto the ground and has a distinctive
butterfly-like shape. The PMA-2 mine is typically planted in such a
way that the starfish is poking up above the ground surface, making it
visible. In a real scene with such mines, other shapes that are
present on the ground, such as leaves, blades of grass, or ground
bumps, make the identification of these mines very difficult since
they blend in. Color similarity with the background (camouflage) also
inhibits detection through imagery. However, preliminary
investigation of LIDAR imagery taken with an iPhone indicates that
these mine shapes are in fact distinguishable in high-resolution
imagery if one knows where to look. One approach for reliable
detection in the absence of a known mine location is to convolve a
kernel (consisting of a LIDAR image of the starfish or butterfly on a
flat, smooth background) with the scene image to enhance the location
of the mine in the convolved (filtered) image, where the starfish or
butterfly kernel would match the mine shape. Alex developed test
imagery as well as convolution code to test this idea, and he explored
exploring whether this can work in real scenes as part of a
multi-sensor landmine identification approach.
Mia Gironda
(F&M '23)
Maggie Shaw (F&M '24)
and Wenky Xia (F&M '24)
Gillian Leeds
(F&M '25)
and
Melanie Ficarra
(F&M '24)
Gillian and Mel were investigating pulsar candidates
generated in a search of unidentified Fermi gamma-ray sources for
radio millisecond pulsars. This survey is being conducted with the
Green Bank Telescope and is one of the
NANOGrav pulsar search projects.
Shinnosuke
Hisano (Ph.D. student,
Kumamoto University)
Shin reprocessed the high-resolution survey of the LMC done with
Parkes
(Ridley
et al. 2013) to search for single pulses. This reprocessing was
done with the new FETCH
software package, which is well-suited to finding and identifying
realistic dispersed signals in pulsar survey data. This work was
published in
Hisano et
al. (2022). Shin is also looking through the
PALFA survey archive
to look for single-pulse events, rotating radio transients (RRATs),
and fast radio bursts (FRBs) that may have been missed in the original
survey processing. This reprocessing also used the
FETCH software package.
In addition, Shin also helped with the reprocessing of the Parkes
PKS70 survey (see below) and a search for millisecond pulsars in
unidentified Fermi gamma-ray sources with the Green Bank Telescope
(see above).
Adem Imamovic (F&M '22),
Andrew Lara (F&M '24),
Ethan Senatore (F&M '24),
Yihao Zhang (F&M '23),
Erik Lillegard (F&M '23),
David Li (F&M '24),
and
Joey Buck (F&M '24)
These students all continued work on our landmine detection project
(see below). Each student focused on a different aspect of the system
under development. See the description below, the
Landmine Detection at F&M
web site, or the NATO project websites
G5014 and
G5731 for more
complete details about this project.
Zach Nusbickel
(F&M '23)
Zach worked on modifying python code that was originally developed
for a so-called stack search of pulsars in a globular cluster so that
we can use it in a search for pulsars in the neighboring galaxy M33,
the Triangulum Galaxy. The stack search is a method in which multiple
separate obervations of the same object (or location on the sky) can
be combined to improve the sensitivity to periodic signals relative to
what can be achieved in any single observation. This is accomplished by
adding (stacking) the power spectra computed for each separate
observation into a single summed spectrum. This stack search will be
applied to about a dozen long integrations that were taken of the core
of M33 with the Arecibo radio telescope. Very luminous pulsars residing
in the core of M33 may be detectable in this way.
Don Fasce
(F&M '21)
Don worked on analyzing observations of several millisecond pulars
(MSPs) taken with the Long Wavelength
Array (LWA). The goal of the project is to determine if several
regularly observed MSPs in the
NANOGrav pulsar
timing array can be reliably detected with this instrument at very low
frequencies (below 100 MHz). If that were the case, then LWA
observations could be used for monitoring changes in the pulsar
dispersion measure that occur from changes in the interstellar
medium. Such corrections to dispersion measures are more easily
estimated at low frequiencies and are necessary to achieve the highest
possible timing precision for the detection of gravitational waves
through pulsar timing.
Mckenzie Golden (F&M '25),
Dani Zoeller
(F&M '23),
Aubrey Laity
(Millersville '21),
Jamie Margeson
(F&M '21), and
Tomonosuke Kikunaga
(Ph.D. student, Kumamoto University)
These students have been searching archival data from the Parkes
radio telescope to hunt for new pulsars and impulsive signals such as
fast radio bursts. The archival data is from a 70 cm survey (called
PKS70) conducted at the Parkes telescope in the early 90's which
covered much of the southern sky. This data was processed at the time
it was taken, and a large number of pulsars were discovered and
published. The raw data were recently downloaded and reprocessed at
F&M. There are two reasons for doing this reprocessing. The first is
that the newer software is better tuned in some ways to find pulsars
than the old software from the time of the survey, so there may be
pulsars lurking in the data that were missed. The second is that the
the newer software searches for radio bursts as well as periodicities,
whereas the old software did not. So impulsive signatures such as
giant single pulses from neutron stars or fast radio bursts (FRBs)
from distant galaxies that were previously undetected may now be
discoverable. The signals detected in the reprocessed data (either as
periodicities or single-pulse events) need to be checked against the
known pulsar catalog to see if it they are in fact new signals. The
tasks include viewing and checking all of the plots and other output
from the processing, identifying known signals, identifying any
promising new candidates, and keeping meticulous bookkeeping records
about what has been investigated and checked.
Four new FRBs were found in the analysis The new FRBs have several
distinguishing features. All four of the FRBs discovered have
significantly larger widths (> 50 ms) than almost all of the FRBs
detected and cataloged to date. One of the FRBs has a DM of 3338 pc
cm^-3, which is the DM largest measured for any FRB to date. These
are the first FRBs detected by any radio telescope (so far), and they
predate the Lorimer Burst by almost a decade.
More details can be found in
Crawford
et al. (2022). Several F&M students were co-authors on this paper.
More information about this project can be found
here and
here.
Jack Sinton
(F&M '20),
Ileane Ho
(F&M '20), and
Aaron DiGregorio
(F&M '21)
Jack, Ileane, and Aaron continued work on the robotic landmine
detection project outlined below. Specific tasks included the
following: (1) Development of tripwire detection techniques using
cameras to be mounted on the robot. This involves camera testing,
developing appropriate image processing algorithms, and field tests to
test effectiveness. (2) Investigation, purchase, field testing, and
integration of a metal detector for inclusion in the robotic platform
(in consultation with partners in Jordan). (3) Design and
implementation of a database for real-time storage of position
coordinates and auxiliary information from the robot via GPS. This is
needed to identify locations of possible explosive ordnace prior to
disposal (this work will be conducted in consultation with our robot
vendor, ClearPath). (4) Field testing of the robot to identify buried
simulated landmines and buried harmless clutter of different
varieties.
See the description below, the
Landmine Detection at F&M web
site, or the NATO project websites G5014
and G5731
for more complete details about this project.
Gaby Sallai
(F&M '19),
Stasia Kuske
(F&M '19), and
Jack Sinton
(F&M '19)
Gaby, Stasia, and Jack worked as summer and independent study
students with Tim
Bechtel (Earth and Environment Department) and me on the
development of a practical next-generation robotic landmine
identification system using a cyber-physical connected systems
approach to the problem of mine identification and removal.
The detection and removal of landmines and other unexploded ordnance
in current and former conflict zones is a major humanitarian task that
can be leveraged by the use of technology to address the complexities
and difficulties in correctly identifying mines. Typically more than 99%
of a deminer's time is spent identifying and removing inert
underground clutter. Sophisticated identification and imaging of
underground objects (whether they be landmines or junk; either plastic
or metal) can reduce this wasted time and mitigate the physical danger
to the deminer. This demining technology comes in multiple forms and
needs to work together in a single system to be maximally
effective. This technology includes imaging (with LIDAR-enabled
cameras for landscapes, and holographic radars for underground
objects), ground-penetrating radar for object detection, robotics and
field mobility assessments, real-time communication between different
parts of the overall system, user databases that are populated in
real-time with field data and which are accessible worldwide, wireless
data transfer and communication between robots, sensors, users, and
databases, and interfaces between users and the instrumentation.
With rapid advances of commercial technology, the costs are reduced
while reliability and capability are increased (these are important
considerations since cost, ease of use, and reliability are important
for the end users of the technology in typically poor and/or
underdeveloped conflict zones). Real-world conditions also dictate
that the technology be field-ready and simple to use in order to be
practical as a tool. These developments and the requirements of the
overall problem point to an integrated technology approach, dubbed
Industry 4.0 in engineering and industry parlance, which represents a
fourth technology revolution. In this paradigm, cyber and physical
systems communicate, merge, and integrate into a single, connected,
decentralized system that is simple, cheap, and reliable. The name we
give to this integrated cyber-physical approach to the landmine
problem is Landmine Detection 4.0.
Our research group at F&M is working in tandem with colleagues from
Italy and the Ukraine as a NATO-funded team (Projects
G5014
and
G5731)
to enhance existing and proven technology and the techniques that have
been developed to address demining in the Ukraine conflict zone of
Donbass. The
existing work of this team has been successful in testing imaging
techniques with holographic radars and with terrain analysis in the
Ukraine conflict zone. The integration of these aspects of the system
and others are beginning to get underway.
We plan to take the next steps in this project and begin development,
testing, and integration of an effective and widely-used demining
system. Our work at F&M will initially focus on several aspects of
the system development, including LIDAR imaging and digital elevation
models (DEMs) for the terrain in the Ukraine conflict zone, and how
the robot can use these for navigation and movement decisions. This is
necessary because the terrain is generally uneven with lots of
obstacles, which can block the robot or get it stuck in the
minefield. In addition, accurate cm-scale real-time mapping of the
ground in the vicinity of the robot is necessary to correct the
holographic radar images for the non-planar ground-air interface
through which the radar signal propagates. Additional tasks that our
group will tackle are: investigating the possibility of tripwire
detection (imaging of wires) using experiments with different infrared and visible cameras and
with different wire configurations, wire types, and distances from the
camera, determining the feasibility of using publicly available
algorithms for automatic wire detection and implementing these; using actual Ukraine terrain
data and DEM maps to assess robot maneuverability in the Ukraine mine
fields; determining the fraction of area suitable for the selected
robot design and ensuring readiness for real-field conditions to
maximize usefulness of the robot by local operators; and assisting
with the holographic ground-penetrating radar imaging correction work
being led by the Italian group by conducting radar and camera
detection scans in a soil test bed at F&M under different field
assumptions (underground target configuration, shape, size, and depth,
background material type, scanning angle, and distance to target.
The project has been described in two news articles published in the
F&M News in 2018. These articles can be acccessed
here
and
here
You can learn more about the project at the Landmine Detection at F&M page.
Tori Bonidie
(F&M '20)
Tori continued a search for millisecond pulsars and fast radio
bursts in the LMC from data taken with the Parkes radio telescope (see
the paper by
Ridley et
al. 2013 which describes this survey). She did this as an
independent study project and processed additional data sets on
our Beowulf clusters after they were observed and received from Parkes.
Faisal Alam
(F&M '19)
Faisal worked with me as a summer student on several projects
involving extragalactic pulsars. He examined pulsar search candidates
produced from a recent high-resolution Parkes survey of the LMC, he
worked on determining timing solutions for a number of LMC pulsars
discovered by
Ridley et
al. (2013), and he compiled a list of the most luminous radio
pulsars currently known in the Galaxy and the Magellanic Clouds in
order to compare them to our luminosity detection threshold in an
Arecibo search for pulsars in the Triangulum Galaxy (M33) (see
Kristina Rolph's project below). In addition, Faisal conducted regular
Arecibo pulsar search and timing observations for the
PALFA survey and the
NANOGrav search for
gravitational waves. Faisal also classified a number of single
pulse candidate plots from the
PALFA survey for the
purpose of creating a training set for an automatic classification
scheme being developed by the
pulsar group at McGill
University.
Benjamin Nguyen
(F&M '18)
and
Tanya Saigal
(F&M '19)
Ben and Tanya's work was to expand the search of the radio data that
we previously collected with the
NRAO 140-ft (43-meter)
telescope at Green Bank which targeted 91 bright, polarized, but
still unidentified point-like radio sources that might be undetected
pulsars (see Debbie Schmidt's project below and also
Schmidt et
al. 2013). Their processing of the survey data went to a much
higher dispersion measure (DM) range than the previous processing did
(a maximum of 1000 vs. 100 pc cm-3), and it had full sensitivity to a
larger range of binary accelerations (up to 1000 m/s^2) for small DMs.
This acceleration range makes very tightly orbiting binary pulsars
near to Earth more likely to be detected. The high DM range searched
ensured that no high-DM pulsars were missed in the search and that
highly dispersed (bright) fast radio bursts (FRBs; see
Lorimer et
al. 2007) originating from outside our Galaxy were also
detectable (if present). This work was written up and published by
Crawford et al. (2021).
Ben also classified a number of single pulse
candidate plots from the PALFA
survey for the purpose of creating a training set for an automatic
classification scheme being developed by the pulsar group at McGill
University.
Rachel Umberger
(F&M '17)
Rachel worked with me on two pulsar projects as a summer student. The
first project was sifting through timing observations of known pulsars
discovered in the Large Magellanic Cloud to search for new, previously
undetected pulsars in the data. The timing data in question used the
Parkes multibeam receiver, so there are 12 beams in addition to the
one timing beam in each observation that have good sky data. We hoped
to find a millisecond pulsar in these data and also looked for
possible fast radio bursts in the data. The second project was to
identify and confirm millisecond pulsar candidates from the PALFA
Arecibo survey. These candidates were selected from the PALFA-3
processing pipeline database to have promising visual features in the
folded plots. This project used Dominik Rastawicki's IDL code to
identify the promising pulsar candidates (see also Jack Madden's PALFA
project below). Once harmonics of known pulsars were eliminated and
any candidates already identified in a previous analysis of the data
have removed from the list, the remaining handful of candidates were
selected for confirmation observations at Arecibo.
Lam Tran
(F&M '17)
Lam finished the analysis of data from several Parkes pulsar surveys
to look for the presence of millisecond-scale radio bursts (fast radio
bursts, or FRBs) at very large dispersion measures (see Kristina
Rolph's project below). You can read more about F&M's involvement in
FRBs here. A large
dispersion measure corresponds to a large (cosmological) distance in
this case. There have been a number of FRB detections by others at
smaller (but still large) DMs in other surveys, but no FRBs have been
detected so far at very large DMs. Finding a burst at a very large DM
would indicate the presence of millisecond burst progenitors at a much
larger distance and at an earlier time in the universe than what has
been seen so far. We found no new FRBs in our surveys, but from our
non-detections, we have been able to improve upon the upper limit for
the all-sky rate of occurrence of FRBs. This results of this work were
published by Crawford et al. (2016).
Kristina Rolph
(F&M '15)
Kristina worked with me 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
kind of extremely luminous extragalactic bursts that have been
observed in some pulsar surveys (see below). More details can be found
here.
Kristina also analyzed data from several Parkes pulsar surveys to look
for the presence of millisecond-scale radio bursts (called fast radio
bursts, or FRBs) at very large dispersion measures. You can read more
about F&M's involvement in FRBs
here. A large
dispersion measure corresponds to a large (cosmological) distance in
this case. There have been several burst detections of this kind by
others at smaller (but still large) DMs, but no bursts have been
detected so far at very large DMs. Finding a burst at a very large DM
would indicate the presence of millisecond burst progenitors at a much
larger distance and at an earlier time in the universe than what has
been seen so far. No new FRBs were found on these surveys, but the
results of this work (including new improved upper limits on the
all-sky rate of FRBs) were presented by Crawford et al. (2016).
Chris Morrow
(F&M '15)
Chris worked with me as summer student on a project to support
modeling of the detection of gravitational waves using pulsar timing.
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 one source 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 had yet
compiled a complete census of the characteristics and information
relevant for gravitational wave detection for the known pulsar
population. Chris tracked down and compiled 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.
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
(Ridley et
al. 2013).
For a senior project, Jack returned to the
PALFA survey and
applied the IDL pulsar finder code that was developed by Dominik
Rastawicki (see below) to the PALFA "Pipeline 2" database of survey
candidates. We wanted to see if we could detect any new pulsars that
were missed in the usual candidate inspection (we found only two new
weak candidates). In addition, he is applied the filter to select for
low dispersion, bright millisecond pulsars that might have been missed
in the analysis if they were mistaken for terrestrial radio
interference (RFI). Such pulsars could be useful to include in the
North American Nanohertz Observatory
for Gravitational Waves (NANOGrav) pulsar timing array in the
search for gravitational waves. He also evaluated the effectiveness of
the code in detecting all known pulsars in these data, and this code
is ready to be applied to the latest set of survey candidates being
generated by the PALFA survey ("Pipeline 3").
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 orbital
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
paper announcing the discovery of several pulsars in the Large
Magellanic Cloud
(Ridley et
al. 2013).
Hannan Li
(F&M '14)
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
24
new pulsars found in Parkes Multibeam Pulsar Survey data. These
results were presented in
Knispel et
al. (2013).
Debbie Schmidt (F&M '12) and
Claire Gilpin (F&M '12)
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 J1723-2837
(Crawford et
al. 2010 and
Crawford et
al. 2013), 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 Schmidt (F&M '12) and Justin "J.B." Brown (F&M '11)
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 J1723-2837 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 J1723-2837 (see
Crawford et
al. 2010 and
Crawford et
al. 2013). Debbie accompanied me to an
AAS meeting as well.
Claire Gilpin (F&M '12) and Matt Jaffee (F&M '10)
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 J1723-2837 taken with the
Parkes Observatory and
Green Bank Telescope. PSR
J1723-2837 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 Altemose (F&M '09)
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 Moses (F&M '11)
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 Morgan (F&M '08)
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 Devour (F&M '10)
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).
Elisabeth Bardenett (F&M '07)
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 Falkner (F&M '07)
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 Takacs (F&M '07)
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).
Peter O'Malley (Haverford '08)
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.
Sarah Burke (Haverford '06), Peter Forshay (Haverford '05), Nathaniel Grabman (Haverford '07), and Megan Roscioli (Haverford '05)
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 Roxby (Wesleyan '06)
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 Gilhool (Vassar '05) and
Ryan Sajac (Haverford '06)
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 Sorrelgreen (Haverford '04)
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 Cantino (Haverford '05)
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.
Reid Sherman (Haverford '04)
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.
Saurav Dhital (Swarthmore '06)
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 Tiffany
(Wellesley '04)
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 Keim (Haverford '04)
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 Malcom (MIT '01)
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:
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