Constraints on the emission geometries and spin evolution of gamma-ray millisecond pulsars
Date
2014Author
Johnson, T.J.
Venter, C.
Harding, A.K.
Guillemot, L.
Smith, D.A.
Metadata
Show full item recordAbstract
Millisecond pulsars (MSPs) are a growing class of gamma-ray emitters. Pulsed gamma-ray signals have been
detected from more than 40 MSPs with the Fermi Large Area Telescope (LAT). The wider radio beams and more
compact magnetospheres of MSPs enable studies of emission geometries over a broader range of phase space than
non-recycled radio-loud gamma-ray pulsars. We have modeled the gamma-ray light curves of 40 LAT-detected
MSPs using geometric emission models assuming a vacuum retarded-dipole magnetic field. We modeled the radio
profiles using a single-altitude hollow-cone beam, with a core component when indicated by polarimetry; however,
forMSPs with gamma-ray and radio light curve peaks occurring at nearly the same rotational phase, we assume that
the radio emission is co-located with the gamma rays and caustic in nature. The best-fit parameters and confidence
intervals are determined using amaximum likelihood technique.We divide the light curves into three model classes,
with gamma-ray peaks trailing (Class I), aligned (Class II), or leading (Class III) the radio peaks. Outer gap and slot
gap (two-pole caustic) models best fit roughly equal numbers of Class I and II, while Class III are exclusively fit
with pair-starved polar cap models. Distinguishing between the model classes based on typical derived parameters
is difficult. We explore the evolution of the magnetic inclination angle with period and spin-down power, finding
possible correlations. While the presence of significant off-peak emission can often be used as a discriminator
between outer gap and slot gap models, a hybrid model may be needed
URI
http://hdl.handle.net/10394/15863https://doi.org/10.1088/0067-0049/213/1/6
http://iopscience.iop.org/0067-0049