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Drift Scan Survey for Pulsars, FRBs, Radio Transients, and Gas in Galaxies

Image: Photon Grabbers; P.Vosteen (NSF/BGO/AUI); photograph of green bank telescope with star trails

The Drift Scan Survey for Pulsars, FRBs, Radio Transients, and Gas in Galaxies is looking to perform drift scans using the 342 MHz, 800 MHz, and L-Band receivers during GBT filler time and the 2019 summer maintenance time. One of these three configurations will be assigned depending on receiver availability. The configurations will be similar to the drift scans performed in 2016 and 2018, with suitable time and frequency resolution for discovering pulsars and transient sources to large distances. Simultaneous spectral line observations will be taken whenever using the L-band receiver to search for galaxies via their λ 21 cm HI emission. The observations will require minimal monitoring by the operator, once they have been started. General oversight of the observations will be managed by the Green Bank Observatory team members. For the pulsar data, high time-resolution data will be copied from Green Bank directly to WVU, using the high-speed link, so as to not congest the available storage space at Green Bank. This data will be processed on a high performance cluster at WVU and students of the PSC program will inspect plots to identify candidate pulsars, FRBs, and other transient sources. The HI data will be copied to an external drive and reduced at Green Bank using GBTIDL.

The studies of pulsars, Fast Radio Bursts (FRBs), and other radio transients will greatly benefit from additional sources.  Currently there are about 70 detected FRBs, with one being definitely confirmed as extra-galactic in origin. While the neutron star population sums up to over 2700, various all-sky surveys are still finding new pulsars and other exotic sources which can be used to test many aspects of fundamental physics and general relativity.  Therefore, continuing to perform these searches would greatly enhance these fields of study.

Blind neutral-hydrogen searches for external galaxies conducted at several telescopes over the past decade have contributed immensely to our understanding of the properties of the extra-galactic population in the nearby universe. These surveys have also generated new questions about gas-rich dwarf galaxies, almost ‘dark galaxies’, and details of the low-end of the HI-mass function. Continuation of similar surveys can only benefit the research in these areas, and several such projects are currently underway at SKA-precursor telescopes.

The Green Bank Telescope (GBT), even with its single-pixel feed at L-Band and below,  is an excellent instrument for the above searches, given its high sensitivity, large sky coverage, cutting edge receivers and backends, and its location in the National Radio Quiet Zone (NRQZ). It also offers an unique opportunity for a simultaneous pulsar, FRB, Transients Sources, and HI search in drift mode during the summer months when for three nights per week the telescope is parked at a fixed position for painting the structure. In this proposal, we describe our request for such a multi-purpose commensal project.

Drift scans are an efficient way to utilize a telescope when it cannot be moved or would otherwise be idle.  Drift scans are widely used at other large single dish antennas.  AO327, an ongoing drift scan survey at Arecibo has resulted in the discovery of 81 pulsars, including 9 millisecond pulsars (MSP) and 13 RRATs.

There are many occasions, whether due to weather or some other circumstance, that the GBT is unable to move or needs to be parked for a period of time.  These are opportune occasions to perform drift scans.  There will be some restrictions in positioning, again due to weather and weather positioning, but minor control of the azimuth and elevation, whenever possible, is suitable.  This would allow us to adopt a standard mapping scheme of set declination intervals, based on frequency, ensuring that we cover as much sky as possible, increasing our chances of making new discoveries.  This mapping scheme can be carried to future observations as well, and is adaptable to different telescope restrictions.  We estimate that there will be about 180 hours of additional filler time, throughout the semester.  We are able to use any filler time that is made available.

The additional filler time observations may be performed at multiple frequencies: Prime Focus-1 342 MHz, using GUPPI with a bandwidth of 200 MHz, Prime Focus-1 800 MHz using GUPPI with a bandwidth of 200 MHz, L-Band at 1500 MHz using GUPPI and VEGAS simultaneously with a bandwidth of 800 MHz for GUPPI and a bandwidth of 187.5 MHz for VEGAS, and FLAG if available.  This frequency agility ensures that we will be able to use any time granted under multiple telescope configurations.  This is useful in reducing time lost from retracting or extending the boom. We will be pointing as often as possible towards the galactic plane.

Data Reduction

West Virginia University (WVU) will transfer the pulsar data from the Green Bank servers to WVU, via the high speed link.  This will be done relatively quickly to keep the Green Bank servers open and available. The raw PSRFITS files will be divided into filterbank files of  length equal to the source transit time at a particular frequency. These beams will overlap by 50% so any source will appear in two beams.  The data from the filterbank files will then be searched for both periodic  and  transient/single-pulse sources via well-tested pulsar search pipelines using the PRESTO software package.
    The VEGAS spectral line data will be moved to an extra hard drive within a day or two of the data being taken.  The  data reduction will take place mostly using GBTIDL.

Current Sky Coverage

Drift Scan Spreadsheet

Publicly Released Datasets

Coming Soon

Team Members

Amber Bonsall, Green Bank Observatory, PI

Tapasi Ghosh, Green Bank Observatory

Andrew Seymour, Green Bank Observatory

Robert Minchin, SOFIA Science Center

Christopher Salter, Green Bank Observatory

Maura McLaughlin, West Virginia University

Natalia Lewandowska, West Virginia University

Nathaniel Garver-Daniels, West Virginia University

Ryan Lynch, Green Bank Observatory

Sue Ann Heatherly, Green Bank Observatory

Pulsar Search Collaboratory

    Search analysis will be done at  WVU, with the diagnostic plots being set aside for analysis by high-school students in the Pulsar Search Collaboratory (PSC) program.  With the number of students and teachers joining the PSC each year increasing, there is a necessity for large amounts of additional data for them to work on.  There are about 200 students in the PSC that are able to reduce data.  PSC students and teachers have discovered seven pulsars, including one double neutron star system and one millisecond pulsar in the 20% of the 2007 350 MHz drift scan data allocated to the PSC.  Each year about 1,000 datasets are completed, with each dataset requiring 5 students to analyze them.  The PSC encompasses at total of 17 states, each with students who can access and reduce this data.  In addition, data that contains known pulsars is used for educational outreach by the PSC.

Pulsar Search Collaboratory Official Webpage