Evidence of TeV halos around millisecond pulsars

Abstract

Using data from the HAWC gamma-ray telescope, we have studied a sample of 37 millisecond pulsars (MSPs), selected for their spindown power and proximity. From among these MSP, we have identified four which favor the presence of very high-energy gamma-ray emission at a level of $(2\mathrm{\ensuremath{\Delta}}\mathrm{ln}\mathcal{L}{)}^{1/2}\ensuremath{\ge}2.5$. Adopting a correlation between the spindown power and gamma-ray luminosity of each pulsar, we performed a stacked likelihood analysis of these 37 MSPs, finding that the data supports the conclusion that these sources emit very high-energy gamma-rays at a level of $(2\mathrm{\ensuremath{\Delta}}\mathrm{ln}\mathcal{L}{)}^{1/2}=4.24$. Among sets of randomly selected sky locations within HAWC's field-of-view, less than 1% of such realizations yielded such high statistical significance. Our analysis suggests that MSPs produce very high-energy gamma-ray emission with a similar efficiency to that observed from the Geminga TeV-halo, ${\ensuremath{\eta}}_{\mathrm{MSP}}=(0.39\ensuremath{-}1.08)\ifmmode\times\else\texttimes\fi{}{\ensuremath{\eta}}_{\text{Geminga}}$. This conclusion poses a significant challenge for pulsar interpretations of the Galactic Center gamma-ray excess, as it suggests that any population of MSPs potentially capable of producing the GeV excess would also produce TeV-scale emission in excess of that observed by HESS from this region. Future observations by CTA will be able to substantially clarify this situation.

Topics & Concepts