The PULSE@Parkes project: A new observing technique for long-term pulsar monitoring
G. Hobbs, R. Hollow, D. Champion, J. Khoo, D. Yardley, M. Carr, M. Keith, F. Jenet, S. Amy, M. Burgay, S. Burke-Spolaor, J. Chapman, L. Danaia, B. Homewood, A. Kovacevic, M. Mao, D. McKinnon, M. Mulcahy, S. Oslowski, W. van Straten
aa r X i v : . [ a s t r o - ph . S R ] J u l The PULSE@Parkes project: A new observing technique forlong-term pulsar monitoring
G. Hobbs A , R. Hollow A , D. Champion A , J. Khoo A , D. Yardley A , B , M. Carr A ,M. Keith A , F. Jenet C , S. Amy A , M. Burgay D , S. Burke-Spolaor A , E , J.Chapman A , L. Danaia F , B. Homewood G , A. Kovacevic H , M. Mao A , I , J , D.McKinnon F , M. Mulcahy A , S. Oslowski A , E and W. van Straten E A Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping, NSW 1710 Australia. B Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW 2006,Australia C Center for Gravitational Wave Astronomy, University of Texas at Brownsville, 80 Fort Brown,Brownsville, TX 78520 D Universit`a di Cagliari, Dipartimento di Fisica, SP Monserrato-Sestu km 0.7, 09042 Monserrato(CA), Italy E Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218,Hawthorn VIC 3122, Australia F Charles Sturt University, Bathurst, Australia G Braemar College, Woodend, Victoria, Australia H Department of Physics, Macquarie University, Sydney, NSW 2109, Australia I Anglo-Australian Observatory, PO Box 296, Epping, NSW, 1710, Australia J School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, 7001, Australia
Abstract:
The PULSE@Parkes project has been designed to monitor the rotation of radio pulsarsover time spans of days to years. The observations are obtained using the Parkes 64-m and 12-mradio telescopes by Australian and international high school students. These students learn the basisof radio astronomy and undertake small projects with their observations. The data are fully calibratedand obtained with the state-of-the-art pulsar hardware available at Parkes. The final data sets arearchived and are currently being used to carry out studies of 1) pulsar glitches, 2) timing noise, 3)pulse profile stability over long time scales and 4) the extreme nulling phenomenon. The data are alsoincluded in other projects such as gamma-ray observatory support and for the Parkes Pulsar TimingArray project. In this paper we describe the current status of the project and present the first scientificresults from the Parkes 12-m radio telescope. We emphasise that this project offers a straightforwardmeans to enthuse high school students and the general public about radio astronomy while obtainingscientifically valuable data sets.
Keywords: pulsars: general
Long-term and frequent observations of radio pulsarshave led to a large number of important and diverseastrophysical results. For instance, long-term timingexperiments have generated studies of basic physicssuch as providing stringent tests of the theory of gen-eral relativity (Kramer et al. 2006), and have madeimportant astrophysical discoveries including the firstextra-Solar planet (Wolszczan & Frail 1992). Pulsartiming experiments have also led to an improved un-derstanding of pulsars and their surroundings includ-ing 1) an understanding of the pulsar velocity distri-bution (Hobbs et al. 2005), 2) the discovery of pulsarglitch events (e.g. Shemar & Lyne 1996) and spin-down irregularities (e.g. Hobbs, Lyne & Kramer 2006)and 3) the first evidence of ion-neutral damping in the interstellar medium (You et al. 2007). Existing long-term pulsar timing programs are attempting even moreambitious experiments, such as making the first directdetection of gravitational wave signals (e.g. Manch-ester 2006). Pulsar timing observations are also es-sential for gamma-ray telescopes such as the Gamma-ray Large Area Space Telescope (previously knownas GLAST and now re-named Fermi) and the Astro-rivelatore Gamma a Immagini LEggero (AGILE). Inorder for these observatories to detect and study theemission from pulsars they need accurate pulsar tim-ing models that can only be supplied from radio timing(Smith et al. 2008).The basic process of pulsar timing has been de-scribed numerous times in the literature. In brief, pul-sar observations give us measurements of pulse times-of-arrival (TOAs) at an observatory. Computer soft- Publications of the Astronomical Society of Australia ware (for instance, tempo2 ; Hobbs, Edwards, Manch-ester 2006, Edwards, Hobbs & Manchester, 2006) isrequired for carrying out the complex calculations toconvert the measured TOAs to the proper time of emis-sion. The calculations include converting the measuredsite arrival times to Solar System barycentric arrivaltimes and adding excess propagation delays caused bythe interstellar medium. The tempo2 software is usedto compare the derived time of emission with a pulsarmodel to form “timing residuals”, the deviations be-tween the observed TOAs and the model predictions.For a perfect pulsar model and random receiver noise,these timing residuals will be uncorrelated and willhave a flat spectrum. The pulsar model can be im-proved by model-fitting to the timing residuals. How-ever, any remaining residuals correspond to unmod-elled physics affecting the measured TOAs. These mayindicate calibration or instrumental errors or may becaused by unmodelled binary companions to the pulsar(such as planetary companions), or the effect of grav-itational wave signals on the pulsar and/or the Earth.Long-term pulsar timing experiments rely on thededication of the observing team and the willingnessof the time allocation committee to allocate telescopetime over many years often without immediate sci-entific results. This is particularly difficult for tele-scopes such as the 64-m diameter Parkes radio tele-scope which are not only oversubscribed, but also re-quire that at least two observers be present at the tele-scope for every observation.The importance of public outreach work in presentand future large-scale projects is clear. Even thoughsome major radio astronomy projects have specific fund-ing for outreach it often takes the form of websitesdescribing the research and its results and/or publictalks given by the team members. However, the im-pact of this form of outreach cannot easily be anal-ysed and, without large-scale advertising, only reachesa relatively small number of people. For optical astron-omy, numerous student projects have been developedthat make use of optical telescopes that are controlledremotely by students (e.g. McKinnon & Mainwaring2000; Roche et al. 2005). The majority of these projectshave great educational value, but often have little im-pact on mainstream scientific research. Recently aproject was started at the University of Texas, Brownsville(the
ARCC project ) that allows high school studentsto observe with the Arecibo radio telescope as part ofan ongoing pulsar survey (Cordes et al. 2006). A sim-ilar project allows high school students in West Vir-ginia, U.S.A., to search for pulsars using observationstaken with the GreenBank telescope.The PULSE@Parkes project officially started inDecember 2007 (Hollow et al. 2008). The project makesuse of the Parkes radio telescopes with the aim of 1)obtaining research quality pulsar timing data-sets ap-plicable to many long-term pulsar timing programs, 2)testing remote observing capabilities of the antennaeand 3) providing a way to engage many high school stu-dents in science. The students carry out the relativelystraightforward observations. This allows the students http://arcc.phys.utb.edu/ARCC/ Figure 1: A period–period-derivative diagram forthe 40 pulsars in the PULSE@Parkes sample ob-served using the 64-m telescope (filled circles) andthe three pulsars observed with the 12-m telescope(filled triangles) overlaid on the known pulsar pop-ulation. The dashed lines indicate characteristicmagnetic field strengths. to develop their understanding of science, at the sametime providing data sets for professional researchers.In contrast to the ARCC project, the PULSE@Parkesproject does not select students based on their currentacademic standing. PULSE@Parkes also uses pulsartiming observations instead of pulsar survey observa-tions. A summary of the PULSE@Parkes project canbe obtained from our web-site .This paper provides an overview of the project.A detailed analysis of the educational impact of thisproject will be published elsewhere. Here, we describethe pulsar sample chosen, describe the new observingtechniques, provide initial scientific results and high-light possible results obtainable in the near future. The PULSE@Parkes observations have been dividedinto those obtained using the 64-m telescope and thoseobtained with the 12-m telescope. The larger telescopeprovides much higher quality data sets for a large sam-ple of pulsars. We typically obtain a two-hour observ-ing session per month which yields several observationsof a given pulsar over the course of a year. The 12-mtelescope allows far more frequent observations, albeitwith poorer sensitivity, allowing no more than a few,bright pulsars to be studied. http://outreach.atnf.csiro.au/education/pulseatparkes ww.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia
A sample of 40 pulsars has been chosen for observa-tion with the 64-m telescope. These pulsars were se-lected 1) because they are useful for long-term tim-ing campaigns, 2) because they span the entire rangeof pulsar properties from millisecond pulsars to slowpulsars (their basic spin-properties are summarised inFigure 1) and 3) because they provide short, straight-forward data sets that can be accessed and analysedby the high school students involved. In Table 1 we listeach pulsar’s B1950 and J2000 names, a flag indicatingwhether this pulsar is part of long-term timing pro-grams for gamma-ray (‘G’) mission support (see § § PSRCHIVE suite of software (Hotan, van Straten & Manchester2004) that allows polarimetric and flux density cali-bration. Pulsar timing models and the resulting timingresiduals are obtained using tempo2 .The majority of these observations have been car-ried out remotely by the high school students fromschools listed in Table 2 (in this table we list the dateof observation, the name of the school, the region con-taining the school, the approximate number of stu-dents that attended, N s , and the number of pulsarsthat were observed, N psr ). Currently, the students un-dertake the observations from the ATNF headquartersin Sydney or from existing science centres (to date, ob-servations have been undertaken from Sydney, the Uni-versity of Western Australia, the University of Texasat Brownsville and the University of Milwaukee. How-ever, it is expected that we will be able to provide ac-cess from science centres around Australia in the nearfuture). This project has become possible by the high-speed network links recently installed between Parkesand Sydney and the installation of web cameras at theobservatory that do not create radio interference. Thestudents can access the telescope control software andmonitor the observations via web cameras set up out-side the telescope and inside the observatory controlroom. A professional astronomer at Parkes interactswith the students throughout their observations and isresponsible for telescope safety. The Parkes-based as-tronomer can immediately take control of the telescopeif required.In Figure 2 we plot a typical total intensity foldedpulse profile for each of the 40 pulsars at an observ- Figure 3: Timing residuals for PSR J1003 − ing frequency close to 1.4 GHz. The signal-to-noiseratio of the profiles is typical of that obtained in aPULSE@Parkes observing session. For some pulsarswe now have more than a year’s worth of monthly ob-servations. For other pulsars we currently have signif-icantly reduced sampling. An example of the timingachieved is shown in Figure 3 for PSR J1003 − The 12-m telescope at Parkes is a prototype antennafor the Australian Square Kilometre Array Pathfindertelescope (ASKAP) and is being used for engineeringtesting of phased array feeds. The PULSE@Parkesproject has obtained the first scientific data using thistelescope which has been used to test and characterisethe antenna. All the data described in this paper thatwere taken with this telescope were obtained using asimple feed providing a 20 MHz bandwidth around anobserving frequency of 1.4GHz, with a system temper-ature ∼ ww.publish.csiro.au/journals/pasa P ˙ P DM P b S (s) (10 − ) (cm − pc) (d) (mJy)B0031 −
07 J0034 − − − −
16 J0152 − −
40 J0206 − − −
18 J0452 − −
18 J0729 − −
28 J0742 − − − −
47 J1003 − − − − − − −
64 J1453 − − −
06 J1543 − − −
45 J1637 − − −
35 J1721 − − −
27 J1807 − −
14 J1818 − −
04 J1820 − −
17 J1829 − −
11 J1830 − −
72 J2053 − − Publications of the Astronomical Society of Australia
Table 2: Student groups that have taken part in the PULSE@Parkes projectDate School Region † N s N psr † the regions included are the United States of America (U.S.A.), the Sydney region (Syd.), New SouthWales not counting the Sydney region (N.S.W.) and Western Australia (W.A.)Table 3: The PULSE@Parkes sample of pulsars observed using the Parkes 12-m antenna.PSR B PSR J P ˙ P DM S (s) (10 − ) (cm − pc) (mJy)B0833 −
45 J0835 − −
68 J1456 − −
45 J1644 − − − − ww.publish.csiro.au/journals/pasa The main scientific aims of the PULSE@Parkes projectare to study 1) the long-term timing stability of ra-dio pulsars, 2) glitch events, 3) pulse profile stabilityover long time scales and 4) the extreme nulling phe-nomenon. To achieve these aims data spanning manyyears are required. Despite only running the programfor one year we have already achieved some resultswhich we present in this section. − The Vela pulsar, PSR J0835 − ∼
30 s and to study the post-glitchrecovery in detail. In Figure 5 we show the timingresiduals obtained over 40 d of observing. No glitchhas so far been discovered in our data. − PSR J1107 − − PSR J1717 − ∼
20% of thetime. However, this source has not yet been studiedin detail. We have attempted to observe this sourcefour times and seen it twice. In Figure 6 we show twoobservations of the source taken 15 minutes apart bystudents from Lithgow High School in Australia. Inthe first observation the pulsar is ‘on’ and is brightwithin one minute of observing. However, in the sec-ond observation the pulsar has switched ‘off’ and iscompletely undetectable even after observing for fiveminutes.
14 of the PULSE@Parkes pulsars are also being ob-served as part of the Parkes gamma-ray support project.The PULSE@Parkes observations are automaticallybeing processed with the gamma-ray data processingpipeline and the resulting observations and timing so-lutions being supplied to the Fermi and AGILE missionteams for folding of the gamma-ray photons. Many ofthese pulsars show large period variability implyingthat it is difficult to obtain a coherent timing solutionover many weeks or months. The PULSE@Parkes ob-servations improve the data sampling for these pulsars.
The Parkes Pulsar Timing Array (PPTA) project be-gan in the year 2003. The three main aims of thisproject are 1) to detect gravitational wave signals, 2)to establish a pulsar-based time scale for comparisonwith terrestrial time standards and 3) to improve theSolar system planetary ephemeris. An overview of theproject has been published by Manchester (2008) andrecent details of the gravitational wave aspects of theproject by Hobbs et al. (2009). This project requiresnumerous observations of very stable millisecond pul-sars in order to achieve the aims. The PULSE@Parkesproject contains three pulsars (PSRs J0437 − − Publications of the Astronomical Society of Australia
Figure 6: Two observations of PSR J1717 − test the hardware, software and calibration methodsused for the PPTA project. PULSE@Parkes aims to engage high school studentsin science by providing them with a stimulating exam-ple of real science using a major national facility. Thestudents interact directly and via video conferencingwith active research scientists. Within the context ofradio astronomy the students develop skills in science,information and communication technology, problemsolving and group work. Prior to their observing ses-sion, a school visit takes place in which the studentsand their teachers are given an overview of radio as-tronomy, pulsars and basic astronomy. At the start ofthe observing sessions the students are given a shorttalk which includes detailed information on how theyuse the telescope control software and a short moviethat provides a virtual tour of the telescope. Duringtheir observations the students are exposed to real ob-servational issues that affect the quality of data andresults. They are expected to keep an online log thatdescribes the pulsars being studied, impulsive radio in-terference and any hardware failures. Each group ofstudents observes a few pulsars. The data they col-lect are immediately available online allowing the stu-dents to carry out small projects. Under supervisionfrom a professional astronomer the students determinethe distance to their pulsars from the pulsars’ disper-sion measures. New projects are being developed thatwill allow the students to compare their observationswith previous data in order to estimate pulsar ages andsearch for glitch events. Post-observing collaborationsamong students from different schools will be encour-aged in these new projects. There is also opportunityfor the students to explore the topic further in theirschool science classs. For example, under the guidanceof their teacher, they could develop their own investi-gations for use in programs such as the various statescience investigation awards. Currently the program is offered to students in Years 10 - 12, is open to anyschool to apply and is non-academically selective. Atypical two-hour observing session involves up to 24students, split into groups of four.PULSE@Parkes is the first stage in developing,testing and implementing educational projects plannedfor larger-scale schemes in the future using new facili-ties such as ASKAP and the Square Kilometre Array(SKA). Given that there has been much less work onhigh school student use and understanding of radio as-tronomy compared with optical astronomy, a key com-ponent of the project has been to conduct educationalresearch to evaluate the scheme and guide ongoing de-velopment. The results of this research will shortlybe published in appropriate science education researchjournals.
PULSE@Parkes is a new, international project withboth scientific and educational impact. It demonstratesa new observing model that shares with high schoolstudents the excitement of carrying out scientific ob-servations using state-of-the-art instrumentation, whileproviding essential observations for cutting-edge sci-ence.The project uses the high-speed networking sys-tems now available to allow remote observations to becarried out at the Parkes telescope and demonstratesthe manner in which educational programs and scien-tific studies can be linked together. The PULSE@Parkesmodel is already being considered for carrying out otherexperiments, such as pulsar or neutral hydrogen sur-veys, in the future.
Acknowledgments