Fermi Gamma-ray Space Telescope

Suzaku observations of the Fermi Cygnus Cocoon: search for a signature of young cosmic ray electrons

Tsunefumi Mizuno
Toshiaki Tanabe, Hiromitsu Takahashi, Katsuhiro Hayashi, Ryo Yamazaki, Isabelle Grenier, Luigi Tibaldo

Abstract:

The origin of Galactic cosmic rays (GCRs) has still to be completely understood, but star-forming regions are promising source candidates. We report on a series of in-depth observations of the nearby star-forming region Cygnus-X in X-rays by {it Suzaku}-XIS, focusing on the extended GeV $gamma$-ray source "Cygnus Cocoon" revealed by {it Fermi}-LAT. After excluding point sources and small-scale structures, and subtracting the non-X-ray and cosmic X-ray backgrounds, the 2--10~keV X-ray intensities were found to monotonically decrease with increasing Galactic latitude. This indicates that most of the remaining extended emission constitutes the Galactic ridge X-ray emission (GRXE), an apparently diffuse X-ray glow along the Galactic plane. We derived upper limits on the possible diffuse X-rays from the cocoon in the 2--10 keV range. The limits are consistent with an electron spectral cutoff at several TeV inferred by multiwavelength data up to TeV energies. The properties of the GRXE in the region observed are also discussed.