Professor of Astronomy, Director of Grundy Observatory, Chair of Physics & Astronomy



Office: HAC424

Current Students

Emma Handzo '14 and Jennie Anne Simson '14

Emma (shown at right at the Jodrell Bank Telescope in Manchester, UK) and Jennie Anne think of the Pulsar Timing Arrays (PTA) as an instrument and such are working to characterize the noise in the system much like an engineer would when working to make her instrument as sensitive as possible.  Most engineering experiments fit in a building, or at least in a small city - ours takes up most of the galaxy!  The basic premise they are working on is that as one looks at longer and longer integrations of the pulsars, the noise should decrease as the square root of the length of the integration.   This effect is crucial in making the PTA more and more sensitive. In the pulsars they are looking at, this appears to be mostly the case, but not always.  Their attention to this issue will be crucial in optimizing the experiment in the future.

Abigail Polin NYU '13 and Joe Simon '07

Abi (pictured with Emma above) and Joe are looking for a gravitational wave 'hotspot' in the galaxy.  It may sound a little bit funny to be talking about a 'hotspot' when no gravitational wave has ever been detected, but we have a good sense of what is producing these gravitational waves - mostly massive black hole binaries at the center of galaxies.  So it stands to reason that if you find a direction with more galaxies there are probably more gravitational waves coming from that direction, and we may want to 'tune' our detector to that direction.  For example, the Virgo cluster is nearby, and it may well turn out to provide the 'hotspot'.   Joe and Abi are looking in many galactic databases in order to determine this information.  We were surprised to find out how hard it is to piece this information together.  Various regions of the local universe have been surveyed in various ways, but a uniform survey of the entire sky does not exist, so Abi and Joe are using clever means to answer this important question.

Former Students

Stephanie Douglas '12

Stephanie (shown here at the 64-m Parkes Telescope in Australia) conducted a study of the delays caused by the interstellar medium (ISM) which is basically clouds of ionized hydrogen in between us and the pulsars we are studying.  The problem with the ISM delay is that it changes by as much as microseconds from day to day, so in order to detect gravitational waves, which will cause delays of more like 100s of nanoseconds, we need to measure this delay.  Stephanie is investigating how this could be accomplished using 1 or 2-dimensional dynamic spectra.  Her work took her to Australia for 3 weeks this summer where she worked with George Hobbs and Dick Manchester at the Australia Telescope National Facility.  Because of her involvement in ourMARIE outreach program, she also worked with Dave McKinnon and Lena Denaia in Bathurst, Australia who run extensive outreach programs with similar components (such as remote observing.)

Brian Burt '10

Brian (shown at right on the platform 500 ft above Arecibo's 300 meter dish) worked with Sam Finn at the Center for Gravitational Wave Physics at Penn State university to create sensitivity maps for various pulsar timing arrays.  We are currently working on publishing his work (it is available on astroph currently) and he has also created a web interface herewhich you can use to create your own sensitivity maps.

In 2008 July, Brian and Isaac Waldstein (see below) left for Australia for 2 weeks to assist Brett Reid, Jim Palfreyman, Aidan Hotan, and John Dickey in obtaining the largest, most continuous data set of single pulses of the Vela pulsar using both the Hobart and Ceduna radio telescopes.  The observing run was timed to coincide with the pointed mode of the Gamma-Ray Large Area Space Telescope (GLAST).  With the combined data set of radio and gamma-ray telescopes, we hope to do experiments similar to those done by Jen Donovan (see below) and myself.

Brian is now in graduate school in astrophysics at Northern Arizona University.

Arpita Roy '09

Arpita investigated the possibility that OJ287 which some people suspect harbors a massive binary black hole  (see Valtonen et al 2008) would be detectable in pulsar timing.  She determined that the residual signature for that object would be about 10ns, too small to be detectible with current pulsar timing, but it brings up an interesting question that Arpita has answered in her honors thesis:  What sorts of objects like OJ287 would be detectable and what's the likelihood that we'll find one in the near future?  Arpita and I are getting this manuscript ready for publication.  Arpita spent the summer of 2008 at the Harvard Center for Astrophysics, and will be spending the next year (09-10) working with Alex Wolszczan at Penn State University.

Michael Johnson, UCSB Graduate Student

Michael Johnson is on loan to us from the University of California at Santa Barbara.  He is installing psrchive at F&M and creating a pipeline for data processing so that future generations of F&M students can monitor and reduce pulsar data from our Green Bank and Arecibo millisecond pulsar observing programs.

Isaac Waldstein '08

Isaac is investigating the detectability of the formation of massive black holes in pulsar timing.  If, when massive black holes formed, they formed with spherical symmetry, we would see no effect, but it turns out that we believe they are asymmetrically formed.  Isaac did a directed reading in General Relativity with Professor Christie Larochelle in the spring, and is now applying his experience to this problem. 

Isaac also traveled to Australia in the summer of 08 to take data on the Vela pulsar (see the paragraph about Isaac and Brian's adventure under Brian Burt's name, above.)

 Rebecca Sobel '08

Rebecca is tackling the problem of how one might detect a brief burst of gravitational waves. She takes advantage of the quadrupolar spatial signature of gravitational waves.  Remember those spherical harmonics: the Ylms? For gravitational waves the l=2 terms dominate. Rebecca is writing computer ce that fits spherical harmonics to a collection of pulsar data to search for gravitational waves.  In the picture she is looking at penguins (not spherical harmonics) near the Australia Telescope National Facility where she and Tim Falkner spent a month this summer. 

Rebecca is currently at MIT earning her PhD in astrophysics.

 Tim Falkner ’07

Tim (shown here at the Koala petting zoo near the Australia Telescope National Facility) is working on the problem of the solar wind mucking up the precision with which we can time the pulsars.The solar wind is essentially a bunch of charged particles coming from the sun.  This plasma changes the index of refraction and therefore the light-travel time from the sun.  As the pulsar signal passes near the sun, it can be slowed down substantially.  Tim is working to improve our models of the solar wind, such that it can be better corrected for in pulsar timing.

In the picture at the right we see Tim taking a break from collaborating with folks at the Australia Telescope National Facility to pet a Koala

 Richard Kipphorn ’06

(Rick is shown here with Jana Bilikova in the control room of the Arecibo 300m Telescope).  The pulsar that Richard worked on,  J0030+0451, spins much faster than a blender – about 200 times per second (that’s about “A-flat” below middle-C for those who are musically inclined).   Richard improved the timing model of this pulsar by reducing and analyzing data from the Arecibo 300-m radio telescope in Puerto Rico.  He has also measured the proper motion of the pulsar to be one of the smallest ever for a millisecond pulsar.  Somehow the supernova which resulted in this pulsar did not impart a large ‘kick’ to the pulsar.  Strange!  Even stranger is the fact that J0030+0451 is an isolated pulsar, i.e. it has no companion.  So somehow the pulsar was spun up by a companion and then the companion disappeared.  Rick received departmental honors for his work and has been published in the Astrophysical Journal:  "Parallax and Proper Motion of J0030+0451,"  Lommen, A.N., Kipphorn, R.A., Nice, D.J., Splaver, E.M., Stairs, I.H., and Backer, D.C. (2006) ApJ, 10 May 2006, v642 2.

Rick earned a master's degree in astrophysics at Cornell University and now works for a large firm in Manhattan, NY, 1010data,  that provides analytical tools for customers doing all sorts of varied research.  The picture shows Rick and Jana ('04 below) observing at the Arecibo Telescope, in Puerto Rico.

Frederika Edgington-Giordano ’05

Frederika is continuing the work that Jana began (see below) by including a new calculation that shows that perhaps it doesn’t matter how close the pulsar is to the black hole binary but rather only how close the electro-magnetic radiation from the pulsar passes to the black hole binary.

Frederika is now earning her PhD in astrophysics at the Northern Arizona University.

Jana Bilikova ’04

Pulsars can be thought of as interstellar clocks as they pulse with stunning regularity, more accurately than atomic clocks.  As clocks, they can be used as gravitational wave detectors; any gravitational wave impinging on a pulsar will cause an irregularity in the observed clock-rate.   In theory this is straight forward, but in practice the irregularities are often much smaller than the intrinsic jitter in the pulsar clock.  For example, we can measure the arrival time of pulses to within 100 nanoseconds, but there are many situations that will produce irregularities of 1 nanosecond.  However, some recent discoveries of black hole binaries in the center of globular clusters have led us to ask whether a pulsar in a globular cluster could detect gravitational radiation coming from two black holes at the center of the globular cluster.  Jana modeled the gravitational radiation from one of these putative black holes in order to determine how large the black hole binary must be, and how close the pulsar must be to the black hole binary, in order for the gravitational radiation to be detectable.

Jana received departmental honors for her thesis and also co-authored an article in the proceedings of a conference in Aspen, Co in January 2004.  She is now earning her PhD in astrophysics at the University of Illinois, Urbana-Champagne.

 Jen Donovan ’03

Jen (shown in the control room of the Arecibo 300m Telescope) received departmental honors for her work on the Vela pulsar.  She combined data from the Rossi X-ray Timing Explorer (very high energy radiation) and the Tasmanian Radio Telescope (very low energy radiation) and showed that on a pulse-by-pulse basis, the mechanisms for producing the high and the low energy radiation knew about each other.   Why is this interesting?  Well it turns out that we don’t know much about pulsar emission mechanisms in general and we certainly don’t know whether the high energy x-rays we receive from them are emitted via the same mechanism as the low-energy radio waves we receive from them.  Jen’s work provides the first evidence that in fact these mechanisms are related.

Jen presented her work at the International Astronomy Union meeting in Sydney, Australia in 2003 and will earn her PhD this summer (2009) in astrophysics at Columbia University.  She will be going on to do a post-doctoral fellowship at SUNY Stony Brook.  In 2007 our work together in the Astrophysical Journal in an article entitled "Correlation between X-Ray Light-Curve Shape and Radio Arrival Time in the Vela Pulsar".