Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess

TL;DR

This study provides evidence that millisecond pulsars (MSPs) can produce TeV halos similar to young pulsars, suggesting many MSPs are detectable via TeV emission and could explain the Galactic Center gamma-ray excess.

Contribution

First detection of TeV halos around MSPs through a stacked analysis, indicating their potential role in high-energy astrophysics and Galactic gamma-ray phenomena.

Findings

MSPs are surrounded by TeV halos with 2.6-3.2 sigma significance.

TeV halo production efficiency in MSPs is comparable to young pulsars.

Unresolved MSPs' TeV halos could dominate high-latitude diffuse emission.

Abstract

Observations by HAWC indicate that many young pulsars (including Geminga and Monogem) are surrounded by spatially extended, multi-TeV emitting regions. It is not currently known, however, whether TeV emission is also produced by recycled, millisecond pulsars (MSPs). In this study, we perform a stacked analysis of 24 MSPs within HAWC's field-of-view, finding between 2.6-3.2 sigma evidence that these sources are, in fact, surrounded by TeV halos. The efficiency with which these MSPs produce TeV halos is similar to that exhibited by young pulsars. This result suggests that several dozen MSPs will ultimately be detectable by HAWC, including many "invisible" pulsars without radio beams oriented in our direction. The TeV halos of unresolved MSPs could also dominate the TeV-scale diffuse emission observed at high galactic latitudes. We also discuss the possibility that TeV and radio observations could be used to constrain the population of MSPs that is present in the inner Milky Way, thereby providing us with a new way to test the hypothesis that MSPs are responsible for the Galactic Center GeV excess.