ALFA Pulsar Studies


Pulsar surveys
The ALFA Pulsar Consortium


Most of the advances in pulsar astronomy were due to the discovery of new objects. A major increase in search sensitivity in comparison to any previous surveys created a great era of discovery at the Arecibo Observatory.
This increase in search sensitivity was due first and foremost to the Arecibo L-band Feed Array (ALFA), a 7-pixel receiver similar in design to the very successful Parkes Multibeam system. This allowed us to search for pulsars much deeper into our Galaxy. Preliminary estimates (see below) indicated that the Arecibo Galactic plane survey using ALFA could find many hundreds of new pulsars. The survey started in 2004 and ended in 2020, with the end of operation of the Arecibo telescope. By May 2021, we have already discovered a total of 208 new pulsars, and counting, as processing of the survey data continues.

Survey region in the Galaxy
Figure 1: Sky map in Galactic coordinates showing (in green) the portions of the Galactic plane being targeted by the PALFA survey. This region corresponds to most of the Galactic plane visible with the Arecibo telescope. The dots correspond to known pulsars, their color indicates their inferred distance.

Credit: Emilie Parent.

Because of the superior spectral and time resolution of the survey, it discoved of many distant millisecond pulsars (the number of discoveries with spin periods smaller than 25 ms is 39 as of May 2021), which were beyound reach of pervious surveys because of dispersive smearing. A fine example of such systems is PSR J1903+0327, the first eccentric binary millisecond pulsar in the Galactic plane. This system is also unusual for having a main-sequence companion. It is the first of a new class of systems that is thought to have started their evolution as triple systems. Another unusual system is PSR J1950+2414, a MSP-WD system with a low-mass companion, an orbital period of 22 days and orbital eccentricity of 0.08. The origin of this new class of systems is still mysterious.

Given the very high sensitivity of the Arecibo telescope, we could combine very high sensitivity with very short (5 minute) pointings. This allowed us to retain sensitivity to extremely compact binary systems, which are likely to represent the best laboratories for the study of gravitational physics. Great examples of this are PSR J1946+2052, the most compact pulsar - neutron star system known (the orbital period is only 1h 53m), PSR J1913+1102, discovered in PALFA data by the Einstein@Home pipeline, a member of a new population of merging, asymmetric double neutron stars, and PSR J1906+0746 - which is by far the youngest pulsar known to be in a binary system. The companion to this pulsar is likely to be a recycled pulsar, but it could also be a heavy white dwarf.

Apart from pulsars, one of the types of objects targeted by the PALFA survey is fast radio bursts (FRBs). The first FRB to be discovered with a telescope other than the Parkes radio telescope was found in the PALFA survey. However, the unparallelled sensitivity of the Arecibo telescope has allowed us to see what no other telescope had been able to see before: some FRBs repeat!

New pulsar discoveries in the Galaxy
Figure 2: Galactic location of the new P-ALFA pulsar survey discoveries. The center of the Galaxy is indicated by the center of the coordinates, the position of the Solar System is indicated by the red dot on the left. The PALFA search areas are indicated in light blue. The dots indicate pulsars, this time colored according to their DM. The new PALFA discoveries are indicated by the larger dots. The PALFA millisecond pulsars have, on average, considerably larger distances than the previously known millisecond pulsar population in the same section of the Galaxy.

Credit: Emilie Parent.

New pulsar discoveries in DM

Figure 3: Positions of the pulsars as a function of Galactic longitude and DM. The black curve indicates the maximum Galactic column density according to the Cordes and Lazio (2001) model of the electron distribution of the Galaxy. Orange dots indicate positions of known pulsars that appear in the ATNF pulsar catalog (Manchester, R. N., Hobbs, G.B., Teoh, A. & Hobbs, M., AJ, 129, 1993-2006, 2005) with Galactic latitude smaller than 5 degrees, and purple indicates new discoveries by the Arecibo P-ALFA survey. There seems to be a deficiency in the number of pulsars at Galactic latitudes of 60 degrees.

Credit: Emilie Parent.

Pulsar Surveys

Data acquisition

With ALFA, we need about 47 pointings to cover one square degree, compared to about 330 pointings needed to cover one square degree with similar density with a single-pixel feed. Until 2009, we were using the Wideband Arecibo Pulsar Processors (WAPPs) to detect the signal from ALFA's seven beams. These cover 100 MHz of band (with dual polarization capability), initially centered at 1420 MHz and later at 1440 MHz. In 2009, the survey transitioned to new and improved back-ends, the Mock polyphase filterbank spectrometers, which are capable of covering 300 MHz (from 1225 MHz to 1525 MHz, the bandwidth covered by ALFA) for each of the seven beams (see detailed technical specifications here). This has resulted in greatly increased search sensitivity, but only for pointing where we can effectively deal with all the radio frequency interference.
From August 1 to October 8 2004, we conducted a preliminary survey that covered the two regions closest to the Galactic plane (|b| < 1 degrees) visible from Arecibo: the "Inner Galaxy" (40 < l < 75 degrees) and the "Anti-center" (170 < l < 210 degrees). Each pointing was 134 seconds for the Inner Galaxy and 67 seconds for the Anti-center. This was done in sparse mode, where we do only 1/3 of the pointings needed to cover the whole region. This preliminary survey found a total of 11 new pulsars, and detected 30 previously known pulsars. For a detailed description of this survey, and the strategy of the present survey, see Cordes et al. (2006).

The survey will cover the Galactic plane (|b| < 5 degrees) visible with the Arecibo 305-m radio telescope (35 < l < 75 degrees, see Fig. 1). Each pointing lasts about 268 seconds in the Inner Galaxy and 134 seconds in the Anti-center.

Data processing and storage

This survey has generated over 1000 Terabytes of data. The data is stored at the Cornell University Center for Advanced Computing, the publicly available data can be retrieved here. These are processed by three independent software pipelines: The data processed thus far has revealed that the radio frequency interference (RFI) environment at Arecibo significantly affects the detection threshold of the survey, creating unforseen challenges in identifying the many weak pulsars that are likely lurking in the data. To address this, the PALFA consortium is actively developing novel techniques for identification, mitigation, and excision of RFI. We are also implementing a variety of heuristics as well as machine learning algorithms for identifying real pulsars among the millions of signal candidates, most of which appear to be due to RFI. The inevitable growth in the incidence and variety of man-made RFI suggests that this problem will likely be important for all future radio pulsar surveys.

Outreach Efforts

The Arecibo Remote Command Center (ARCC) at the University of Texas at Brownsville and the University of Wisconsin at Miwaukee is currently engaged in searching for radio pulsars in ALFA data. ARCC is an integrated research/education facility that allows students at the high school and undergraduate level to be directly involved with the research at the Arecibo telescope. Web based tools have been developed so that students could rank the pulsar candidates created by the PRESTO analysis.


* 2020 Dec. 1: End of data taking phase of the survey - collapse of the 305-m Arecibo radio telescope
* A new population of merging, asymmetric double neutron stars!!
* The most compact pulsar - neutron star system ever!!
* A pulsar - neutron star discovered by Einstein@Home!
* A Repeating Fast Radio Burst!
* The disappearance of the cosmic spinning top!
* Arecibo confirms Fast Radio Bursts from outer space!
* First Pulsar Discovery by Global Volunteer Computing!
* ALFA Finds its first MSP! This is the first eccentric binary millisecond pulsar in the galactic plane!
* ALFA Finds the Youngest Binary Pulsar Ever! (see also Jodrell Bank Observatory press release),
* PSR J1928+1746: First pulsar discovered with ALFA!
* ALFA pulsar surveys start!


See our list of discoveries.

See also PALFA public library at ADS

Refereed (36):

* Discovery of 72 pulsars in the PALFA survey: Timing analysis, glitch activity, emission variability, and a pulsar in an eccentric binary (Parent et al. 2022, ApJ, 924, 135).
* Asymmetric mass ratios for bright double neutron-star mergers (Ferdman et al., 2020, Nature, 583, 211).
* Eight Millisecond Pulsars Discovered in the Arecibo PALFA Survey (Parent et al., 2019, ApJ, 886, 148).
* Mass measurements for two binary pulsars discovered in the PALFA survey (Zhu et al., 2019, ApJ, 881, 165).
* PALFA Single-Pulse Pipeline: New Pulsars, Rotating Radio Transients and a Candidate Fast Radio Burst (Patel et al., 2018, ApJ, 869, 181).
* A novel single-pulse search approach to detection of dispersed radio pulses using clustering and supervised machine learning (Pang et al., 2018, MNRAS, 480, 3302).
* The implementation of a Fast-Folding pipeline for long-period pulsar searching in the PALFA survey (Parent et al., 2018, ApJ, 861, 44).
* PALFA Discovery of a Highly Relativistic Double Neutron Star Binary (Stovall et al., 2018, ApJ Lett, 854, 22).
* Timing of 29 Pulsars Discovered in the PALFA survey (Lyne et al., 2017, ApJ, 834, 137).
* Two long-term intermittent pulsars discovered in the PALFA survey (Lyne et al., 2017, ApJ, 834, 72).
* Timing of Five PALFA-Discovered Millisecond Pulsars (Stovall et al. 2016, ApJ, 833, 192).
* The repeating Fast Radio Burst FRB 121102: Multi-wavelength observations and additional bursts (Scholz et al., 2016, ApJ, 833, 177).
* Einstein@Home discovery of a Double-Neutron Star Binary in the PALFA survey (Lazarus et al. 2016, ApJ, 831, 150).
* A repeating fast radio burst (Spitler et al., 2016, Nature, 531, 202).
* Arecibo Pulsar Survey Using ALFA. IV. Mock Spectrometer Data Analysis, Survey Sensitivity, and the Discovery of 40 Pulsars (Lazarus et al., 2015, ApJ, 812, 81).
* Einstein@Home Discovery of a PALFA Millisecond Pulsar in an Eccentric Binary Orbit (Knispel et al. 2015, ApJ, 806, 140).
* Timing of five millisecond pulsars discovered in the PALFA survey (Scholz et al. 2015, ApJ, 800, 123).
* The Binary Companion of Young, Relativistic Pulsar J1906+0746 (van Leeuwen et al. 2015, ApJ, 798, 115).
* Fast Radio Burst Discovered in the Arecibo Pulsar ALFA Survey (Spitler et al. 2014, ApJ, 790, 101).
* Arecibo Pulsar Survey Using ALFA. III. Precursor Survey and Population Synthesis (Swiggum et al. 2014, ApJ, 787, 137).
* Searching for pulsars using image pattern recognition (Zhu et al. 2014, ApJ, 781, 117).
* Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion (P. Lazarus et al. 2014, MNRAS, 437, 1485).
* The Einstein@home Search for Radio Pulsars and PSR J2007+2022 Discovery (B. Allen et al. 2013, ApJ, 773, 91).
* Properties of Thirty-Five Pulsars Discovered in the PALFA Survey (D. Nice et al. 2013, ApJ, 772, 50).
* PEACE: Pulsar Evaluation Algorithm for Candidate Extraction - A software package for post-analysis processing of pulsar survey candidates (Lee et al. 2013, MNRAS, 433, 688).
* Four Highly Dispersed Millisecond Pulsars Discovered in the Arecibo PALFA Galactic Plane Survey (F. Crawford et al. 2012, ApJ, 757, 90).
* Two Millisecond Pulsars Discovered by the PALFA Survey and a Shapiro Delay Measurement (J. Deneva et al. 2012, ApJ, 757, 89).
* Arecibo PALFA Survey and Einstein@Home: Binary Pulsar Discovery by Volunteer Computing (B. Knispel et al. 2011, ApJ, 732, 1).
* On the Nature and Evolution of the Unique Binary Pulsar J1903+0327 (P. Freire et al. 2011, MNRAS, 412, 2763).
* Pulsar Discovery by Global Volunteer Computing (B. Knispel et al. 2010, Science, 329, 1305).
* Arecibo Pulsar Survey Using ALFA: Probing Radio Pulsar Intermittency And Transients (J. S. Deneva et al., 2009, ApJ, 703, 2259).
* PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV Gamma-ray Source HESS J1857+026 (J. W. T. Hessels et al. 2008, ApJ, 703, 2259).
* An Eccentric Binary Millisecond Pulsar in the Galactic Plane (D. Champion et al. 2008, Science, 320, 1309).
* Arecibo and the ALFA Pulsar Survey (J. van Leeuwen et al., 2006, ChJAS, 6b, 311, see .pdf presentation here).
* Arecibo Pulsar Survey Using ALFA. II. The young, highly relativistic binary pulsar J1906+0746 (Lorimer et al., 2006, ApJ 640, 428),
* Arecibo Pulsar Survey Using ALFA. I. Survey Strategy and First Discoveries (Cordes et al., 2006, ApJ, 637, 446).

In Conference Proceedings:

* The PALFA Survey: Going to great depths to find radio pulsars (P. Lazarus and the ALFA Pulsar Consortium).
* Two Millisecond Pulsars Discovered by the PALFA Survey and a Shapiro Delay Measurement (J. Deneva and the ALFA Pulsar Consortium).
* Two Pulsar Discoveries from the Einstein@Home Distributed Computing Project (J. Deneva and the ALFA Pulsar Consortium).
* An Update on the Status of the Pulsar-ALFA Survey (P. Lazarus).
* Finding Pulsars with Einstein@Home (B. Knispel and the ALFA Pulsar Consortium).
* Arecibo Multibeam Pulsar Surveys: Overview and Discovery of a Young Relativistic Binary (F. Camilo and the ALFA Pulsar Consortium).
* ALFA pulsar surveys: Searching for fundamental laboratories of extreme physics (P. Freire and the ALFA Pulsar Consortium, see powerpoint presentation).
* ALFA Arecibo Pulsar Surveys (P. Freire and the ALFA Pulsar Consortium, see powerpoint presentation).

The ALFA Pulsar Consortium

The ALFA Pulsar Consortium is open to all researchers interested in observations of radio pulsars and related science, regardless of country or origin and level of expertise. The Consortium manages its collaboration on the CyberSKA portal.

* Membership and Affiliations

Bruce Allen Albert Einstein Institute - Hannover / University of Wisconsin - Milwaukee / Einstein@Home
Slavko Bogdanov Columbia University
Adam Brazier Cornell University
Fernando Camilo Columbia University
Fernando Cardoso West Virginia University
Shami Chatterjee Cornell University
Jim Cordes Cornell University
Fronefield Crawford Franklin and Marshall College
Julia Deneva Navy Research Laboratory
Gregory Desvignes Max-Planck-Institut für Radioastronomie
Robert Ferdman University of East Anglia
Paulo Freire Max-Planck-Institut für Radioastronomie
Jason Hessels ASTRON
Frederick Jenet University of Texas at Brownsville and Texas Southmost College
Victoria Kaspi McGill University
Benjamin Knispel Albert Einstein Institute
Joeri van Leeuwen ASTRON
Andrea Lommen Franklin & Marshall College
Maura McLaughlin West Virginia University
Ryan Lynch National Radio Astronomy Observatory
David Nice Lafayette College
Scott Ransom National Radio Astronomy Observatory
Paul Scholz McGill University
Xavier Siemens University of Wisconsin - Milwaukee
Laura Spitler Max-Planck-Institut für Radioastronomie
Ingrid Stairs University of British Columbia
Ben Stappers Jodrell Bank Center for Astrophysics
Kevin Stovall University of New Mexico
Weiwei Zhu Max-Planck-Institut für Radioastronomie



Date Title Author
2006 May 4 Tiling strategy for P-ALFA (being updated) Freire
2005 Apr 25 Specifications of new spectrometer. PALFA Consortium
2004 Jul 5 Cornell Simulation of P-ALFA survey. Vlemmings and Cordes
2004 Jul McGill Simulation of P-ALFA survey. Faucher-Giguère and Kaspi
2003 Jan 14 A Report on the First ALFA Pulsar Consortium Workshop PALFA Consortium


Pulsar Astronomy at the Arecibo Observatory
More information on ALFA and its performance.
Proposal submitted for large-scale P-ALFA survey (Now being scheduled with number P2030)
PALFA public data server
Einstein@Home Pulsar Search
The Arecibo Remote Command Center


At the Arecibo Observatory: Julia Deneva
At Cornell University: Jim Cordes