Context. The flux of gamma rays with energies greater than 100 MeV is dominated by diffuse emission coming from cosmic-rays (CRs) illuminating the interstellar medium (ISM) of our Galaxy through the processes of Bremsstrahlung, pion production and decay, and inverse-Compton scattering. The study of this diffuse emission provides insight into the origin and transport of cosmic rays. Aims.We searched for gamma-ray emission from the Small Magellanic Cloud (SMC) in order to derive constraints on the cosmic-ray population and transport in an external system with properties different from the Milky Way. Methods.We analysed the first 17 months of continuous all-sky observations by the Large Area Telescope (LAT) of the Fermi mission to determine the spatial distribution, flux and spectrum of the gamma-ray emission from the SMC. We also used past radio synchrotron observations of the SMC to study the population of CR electrons specifically. Results.We obtained the first detection of the SMC in high-energy gamma rays, with an integrated >100MeV flux of (3.7±0.7)×10-8 ph cm-2 s-1, with additional systematic uncertainty of ≤16%. The emission is steady and from an extended source ∼3. in size. It is not clearly correlated with the distribution of massive stars or neutral gas, nor with known pulsars or supernova remnants, but a certain correlation with supergiant shells is observed. Conclusions.The observed flux implies an upper limit on the average CR nuclei density in the SMC of ∼15% of the value measured locally in the Milky Way. The population of high-energy pulsars of the SMC may account for a substantial fraction of the gamma-ray flux, which would make the inferred CR nuclei density even lower. The average density of CR electrons derived from radio synchrotron observations is consistent with the same reduction factor but the uncertainties are large. From our current knowledge of the SMC, such a low CR density does not seem to be due to a lower rate of CR injection and rather indicates a smaller CR confinement volume characteristic size.
|Autori:||Abdo AA; Ackermann M; Ajello M; Baldini L; Ballet J; Barbiellini G; Bastieri D; Bechtol K; Bellazzini R; Berenji B; Blandford D; Bloom ED; Bonamente E; Borgland AW; Bouvier A; Brandt TJ; Bregeon J; Brez A; Brigida M; Bruel P; Buehler R; Buson S; Caliandro GA; Cameron RA; Caraveo PA; Carrigan S; Casandjian JM; Cecchi C; Celik O; Charles E; Chekhtman A; Cheung CC; Chiang J; Ciprini S; Claus R; Cohen-Tanugi J; Conrad J; Dermer CD; de Palma F; Digel SW; Silva EDE; Drell PS; Dubois R; Dumora D; Favuzzi C; Fegan SJ; Fukazawa Y; Funk S; Fusco P; Gargano F; Gasparrini D; Gehrels N; Germani S; Giglietto N; Giordano F; Giroletti M; Glanzman T; Godfrey G; Grenier IA; Grondin MH; Grove JE; Guiriec S; Hadasch D; Harding AK; Hayashida M; Hays E; Horan D; Hughes RE; Jean P; Johannesson G; Johnson AS; Johnson WN; Kamae T; Katagiri H; Kataoka J; Kerr M; Knodlseder J; Kuss M; Lande J; Latronico L; Lee SH; Lemoine-Goumard M; Garde ML; Longo F; Loparco F; Lovellette MN; Lubrano P; Makeev A; Martin P; Mazziotta MN; McEnery JE; Michelson PF; Mitthumsiri W; Mizuno T; Monte C; Monzani ME; Morselli A; Moskalenko IV; Murgia S; Nakamori T; Naumann-Godo M; Nolan PL; Norris JP; Nuss E; Ohsugi T; Okumura A; Omodei N; Orlando E; Ormes JF; Panetta JH; Parent D; Pelassa V; Pepe M; Pesce-Rollins M; Piron F; Porter TA; Raino S; Rando R; Razzano M; Reimer A; Reimer O; Reposeur T; Ripken J; Ritz S; Romani RW; Sadrozinski HFW; Sander A; Parkinson PMS; Scargle JD; Sgro C; Siskind EJ; Smith DA; Smith PD; Spandre G; Spinelli P; Strickman MS; Strong AW; Suson DJ; Takahashi H; Takahashi T; Tanaka T; Thayer JB; Thayer JG; Thompson DJ; Tibaldo L; Torres DF; Tosti G; Tramacere A; Uchiyama Y; Usher TL; Vandenbroucke J; Vasileiou V; Vilchez N; Vitale V; Waite AP; Wang P; Winer BL; Wood KS; Yang Z; Ylinen T; Ziegler M|
|Titolo:||Detection of the Small Magellanic Cloud in gamma-rays with Fermi/LAT|
|Anno del prodotto:||2010|
|Digital Object Identifier (DOI):||10.1051/0004-6361/201014855|
|Appare nelle tipologie:||1.1 Articolo in rivista|