The Einstein@Home Gamma-ray Pulsar Survey. I. Search Methods, Sensitivity and Discovery of New Young Gamma-ray Pulsars (1611.01015v2)

Abstract: We report on the results of a recent blind search survey for gamma-ray pulsars in Fermi Large Area Telescope (LAT) data being carried out on the distributed volunteer computing system, Einstein@Home. The survey has searched for pulsations in 118 unidentified pulsar-like sources, requiring about 10,000 years of CPU core time. In total, this survey has resulted in the discovery of 17 new gamma-ray pulsars, of which 13 are newly reported in this work, and an accompanying paper. These pulsars are all young, isolated pulsars with characteristic ages between 12 kyr and 2 Myr, and spin-down powers between $10^{34}$ and $4\times10^{36}$ erg/s. Two of these are the slowest spinning gamma-ray pulsars yet known. One pulsar experienced a very large glitch $\Delta f/f \approx 3.5\times10^{-6}$ during the Fermi mission. In this, the first of two associated papers, we describe the search scheme used in this survey, and estimate the sensitivity of our search to pulsations in unidentified Fermi-LAT sources. One such estimate results in an upper limit of 57% for the fraction of pulsed emission from the gamma-ray source associated with the Cas A supernova remnant, constraining the pulsed gamma-ray photon flux that can be produced by the neutron star at its center. We also present the results of precise timing analyses for each of the newly detected pulsars.

The Einstein@Home Gamma-ray Pulsar Survey

The paper "The Einstein@Home Gamma-ray Pulsar Survey. I. Search Methods, Sensitivity and Discovery of New Young Gamma-ray Pulsars" by Clark et al. outlines a substantial effort to detect gamma-ray pulsars using data from the Fermi Large Area Telescope (LAT). The research leverages the distributed computing resources of the Einstein@Home project to undertake a large-scale blind search for pulsations in 118 unidentified pulsar-like sources in Fermi LAT data. This endeavor has resulted in the discovery of 17 new gamma-ray pulsars.

Search Methodology

The survey adopts a sophisticated search strategy to identify pulsations from potential gamma-ray pulsars. The process involves several key components:

• Data Selection: Gamma-ray data from the Fermi LAT over several years is used, focusing on photons with energies above 100 MeV collected from regions centered around each target source.
• Search Space Definition: The examination spans a range of frequencies and spin-down rates, operating over a four-dimensional parameter space that includes two angular coordinates (R.A. and declination), spin frequency, and spin-down rate.
• Semicoherent Detection Techniques: The initial survey stage employs semicoherent methods to manage the extensive computational demand. This approach balances sensitivity and efficiency by combining coherent integration over segments of data with follow-up stages analyzing shortlisted candidates.
• Follow-up Analysis: Candidates from initial searches undergo further scrutiny using more sensitive fully coherent search techniques.

Results and Discoveries

The survey discovered 17 gamma-ray pulsars, 13 of which are reported explicitly in this paper, with characteristic ages ranging from 12 kyr to 2 Myr and spin-down powers between 10<sup\>34</sup> and 4 × 10<sup\>36</sup> erg s^-1. Notable among these are the slowest spinning gamma-ray pulsars yet identified and a pulsar that exhibited a substantial glitch during the Fermi mission.

The paper also achieves critical sensitivity estimates, setting an upper limit of 57% for the fraction of pulsed emission from the gamma-ray source associated with the Cas A supernova remnant. This result constrains the pulsed gamma-ray photon flux attributable to the neutron star at its center.

Implications and Future Directions

The discoveries underline the efficacy of the advanced search methods employed and highlight the potential of distributed computing efforts like Einstein@Home in detecting faint and previously unobserved pulsars. The survey signifies progress in characterizing the population of gamma-ray pulsars, particularly distinguishing between radio-loud and radio-quiet variants, essential for understanding magnetospheric particle acceleration and emission mechanisms.

Future developments may involve:

• Enhanced search methodologies that increase sensitivity to pulsars with complex timing behaviors, such as those in binary systems or with significant timing noise.
• Leveraging improvements in Fermi LAT data calibration and processing (such as the Pass 8 enhancements) to refine sensitivity further and lower detection thresholds.
• Expanding the search to include sources with lower characteristic brightness, constrained by thoughtful optimization of computing resources and parameter space coverage.

This research significantly contributes to the pulsar detection landscape, providing a framework for identifying and studying the gamma-ray sky's energetic pulsar population. The successful detection of pulsars with challenging observational profiles opens pathways for nuanced explorations of pulsar physics and their roles in galactic structure and evolution.