Millisecond pulsars, TeV halos, and implications for the Galactic Center gamma-ray excess

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 2.6-3.2σ 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.

The Hunt for Pevatrons: The Case of Supernova Remnants

“…This result as been confirmed by other instruments such as VERITAS [118]. Various interpretations of the gamma-ray emission of this pevatron candidate have been proposed, including e.g., supernovae and clusters of massive stars [94,119], millisecond pulsars [120][121][122], or particle acceleration from the supermassive black hole [123,124].…”

Deep observations of the globular cluster M15 with the MAGIC telescopes

“…We suggest that the acceleration/radiation processes within the atmospheres of classical γ -ray pulsars and the MSPs are different. Note that up to now no isolated TeV γ -ray Pulsar Wind Nebula around a MSP has been firmly detected (Ahnen, Ansoldi & Antonelli 2017;Hooper, D & Linden 2018). This, combined with the limits derived by the MAGIC observations of M15, suggests that the winds of the MSPs might not accelerate leptons as efficiently as the winds around classical pulsars.…”

Revival of the Dark Matter Hypothesis for the Galactic Center Gamma-Ray Excess

“…Introduction.-There has been an extensive debate in the literature over the origins of the galactic center excess (GCE), an extended and roughly spherically symmetric gamma-ray source filling the region within ∼1.5 kpc of the galactic center (GC), with energy spectrum peaking at 1-3 GeV [1][2][3][4][5][6][7]. Leading hypotheses include a new population of unresolved gamma-ray pulsars, individually too faint to be detected but in aggregate yielding the excess [8][9][10][11][12][13][14][15][16][17][18][19], cosmic-ray injection [20][21][22], or alternatively a signal from annihilating dark matter (DM) (e.g., [1,5,23]). The latter explanation, if confirmed, would be of extraordinary importance for our understanding of the Universe, as the first nongravitational probe of the properties of DM and its interactions with visible particles.…”