Fermi Gamma-ray Space Telescope

DISCOVERY OF SIXTEEN MILLISECOND PULSARS IN FERMI LAT UNASSOCIATED SOURCES WITH THE GBT TELESCOPE

Siraprapa Sanpa-arsa
(Scott Ransom, Fernando Camilo, Paul Ray, Tyrel Johnson, Elizabeth Ferrara, Mallory Roberts, Matthew Kerr, Megan Decesar)

Abstract:

We would like report the discovery and initial timing solutions of sixteen millisecond pulsars (MSPs) from radio searches in the direction of 198 unassociated Fermi LAT sources, conducted with the Green Bank Telescope (GBT) at 350 MHz, 820 MHz and 2 GHz. Eleven MSPs are in binary systems with likely degenerate He-core white dwarf (He-WD) companions (except for the isolated J0533+6759). All twelve of the pulsars are shown to have gamma-ray pulsations after folding LAT events using our radio ephemerides. Combining the gamma-ray and radio data for all Fermi LAT MSPs detected in the radio band, we find that there is no correlation between gamma-ray and radio flux densities. We also examine the assumption that the inclination angles (i) of the orbital planes of MSPs with He-WD companions are distributed randomly. Using the orbital period-companion mass relation together with Monte Carlo simulations, we find that the distribution of cos(i) of 81 such systems is not flat, but favors higher cos(i) (i.e. more face-on orbits). For the four MSPs in compact orbits, we examined flux density variability, as well as their optical light curves. We found that all four MSPs are eclipsing and that two of them exhibit strong diffractive scintillation. Finally, we found optical counterparts for two MSPs, one of which shows ellipsoidal modulations in its light curve, suggesting that the companion is filling its Roche lobe.