The low cosmic-ray density in Polaris Flare

TL;DR

This study reports a gamma-ray observation of Polaris Flare, revealing a significantly lower cosmic ray density and a softer spectrum compared to local measurements, suggesting a gradient or suppression of cosmic rays in this region.

Contribution

It provides the first detailed measurement of cosmic ray density and spectrum in Polaris Flare, highlighting regional variations in cosmic ray distribution.

Findings

Cosmic ray density in Polaris Flare is significantly lower than local values.

The cosmic ray spectrum in Polaris Flare is softer than the local spectrum.

Results suggest a large gradient or suppression of cosmic rays in molecular clouds.

Abstract

We reported the gamma-ray observation towards the giant molecular cloud Polaris Flare. Together with the dust column density map, we derived the cosmic ray density and spectrum in this cloud. Compared with the CR measured locally, the CR density in Polaris Flare is significantly lower and the spectrum is softer. Such a different CR spectrum reveals either a rather large gradient of CR distribution in the direction perpendicular to the Galactic plane or a suppression of CR inside molecular clouds.