November 16, 2017 — HAWC has captured the first wide-angle view of very-high-energy light emanating from two rapidly spinning stars. The fresh perspective on these stellar neighbors — which are both close to Earth in cosmic terms — casts serious doubt on one possible origin for a mysterious excess of particles near Earth whose origin has tantalized scientists in recent years.
Scientists have debated the cause of an unexpectedly high number of positrons — the anti-matter cousins of electrons — near the Earth since a space-borne detector measured the anomaly in 2008. Some have speculated that the extra positrons have an exotic source, perhaps originating from as-yet undetected processes involving dark matter — the invisible but pervasive substance seen only through its gravitational pull. Others have suggested something more pedestrian: The extra particles might originate from nearby collapsed stars, called pulsars, that spin around several times a second and throw off electrons, positrons and other matter with violent force.
Left: spatial morphology of TeV emission from Geminga and its neighbor PSR B0656+14. Right: schematic illustration of the observed region and the line of sight to Earth. Positrons from Geminga and PSR B0656+14 must diffuse 250 pc to affect the local flux.
Using new data from the HAWC Gamma-Ray Observatory, an international team of researchers has made the first detailed measurements of two extended pulsars, Geminga and its neighbor PSR B0656+14, that had been identified as possible sources of the mysterious excess of positrons. These measurements demonstrate the capability of the HAWC detector to observed such very extended objects. Relatively close galactic objects, like these two pulsars, appear so extended that one can only see them with an instrument with a wide field-of-view. Using data from the HAWC Observatory, we provide a unique and complementary view of these very extended sources that is not possible with the more pointed gamma-ray telescopes. The results appeared in the Nov. 17 issue of the journal Science.
