Fermi Gamma-ray Space Telescope

Searching For Eclipsing Neutron Star Binaries

Matthew Kerr
(Roger Romani, Elizabeth Ferrara, Colin Clark, Lars Nieder)


Among the nearly 90 millisecond gamma-ray pulsars discovered by Fermi are a surprising number of compact binaries with light main sequence or white dwarf companions and orbital periods ranging from hours to days. The intense pulsar wind and radiation in these "redback" and "black widow" systems ablates material from the companion surface, partially filling the Roche lobe. In nearly edge-on systems, the filled Roche lobe directly eclipses the gamma-ray emission from the pulsar, yielding a notched light curve modulated at the orbital period. Many Fermi sources remain unidentified but have spectral and variability features similar to known pulsars. Detection of eclipses would immediately identify them as neutron star binaries and enable searches for optical modulation and gamma-ray pulsations. Conversely, limits on eclipses of both known and candidate pulsar systems constrain the distribution of inclination angles. Here, we present results from a sensitive search for eclipses of all pulsar-like Fermi sources, including known systems, to limiting periods as fast as a few minutes.