Observations of the Large Magellanic Cloud with Fermi

Fukazawa Yasushi

Hanabata Yoshitaka

Katagiri Hideaki

Mizuno Tsunefumi

Ohsugi Takashi

Takahashi Hiromitsu

Astronomy & Astrophysics

Context. The Large Magellanic Cloud (LMC) is to date the only normal external galaxy that has been detected in high-energy gamma rays. High-energy gamma rays trace particle acceleration processes and gamma-ray observations allow the nature and sites of acceleration to be studied.

Aims. We characterise the distribution and sources of cosmic rays in the LMC from analysis of gamma-ray observations.

Methods. We analyse 11 months of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope and compare it to tracers of the interstellar medium and models of the gamma-ray sources in the LMC.

Results. The LMC is detected at 33σ significance. The integrated >100 MeV photon flux of the LMC amounts to (2.6 ± 0.2) × 10-7 ph cm-2 s-1 which corresponds to an energy flux of (1.6 ± 0.1) × 10-10 erg cm-2 s-1, with additional systematic uncertainties of 16%. The analysis reveals the massive star forming region 30 Doradus as a bright source of gamma-ray emission in the LMC in addition to fainter emission regions found in the northern part of the galaxy. The gamma-ray emission from the LMC shows very little correlation with gas density and is rather correlated to tracers of massive star forming regions. The close confinement of gamma-ray emission to star forming regions suggests a relatively short GeV cosmic-ray proton diffusion length.

Conclusions. The close correlation between cosmic-ray density and massive star tracers supports the idea that cosmic rays are accelerated in massive star forming regions as a result of the large amounts of kinetic energy that are input by the stellar winds and supernova explosions of massive stars into the interstellar medium.

acceleration of particles

cosmic rays

Magellanic Clouds

gamma rays: galaxies

Astronomy. Space sciences [ 440 ]

eng

EDP Sciences S A

Copyright (c) 2010 The European Southern Observatory

[ISSN] 0004-6361

[DOI] 10.1051/0004-6361/200913474

[NCID] AA00553195

[DOI] http://dx.doi.org/10.1051/0004-6361/200913474