We present results from gamma-ray observations of the Coma cluster incorporating six years of Fermi-LAT data and the newly released "Pass 8" event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the gamma-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100MeV are 1.7 x 10(-9) ph cm(-2) s(-1) and 5.2 x 10(-9) ph cm(-2) s(-1) respectively (the latter corresponds to residual emission at the level of 1.8 sigma). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray (CR) models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of CRs and magnetic field properties. The minimal expected.-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.
SEARCH FOR GAMMA-RAY EMISSION FROM THE COMA CLUSTER WITH SIX YEARS OF FERMI-LAT DATA / Ackermann M; Ajello M; Albert A; Atwood WB; Baldini L; Ballet J; Barbiellini G; Bastieri D; Bechtol K; Bellazzini R; Bissaldi E; Blandford RD; Blooms ED; Bonino R; Bottacini E; Bregeon J; Bruel P; Buehler R; Caliandro GA; Cameron RA; Caragiulo M; Caraveo PA; Casandjian JM; Cavazzuti E; Cecchi C; Charles E; Chekhtman A; Chiaro G; Ciprini S; Cohen-Tanugi J; Conrad J; Cutini S; DAmmando F; de Angelis A; de Palma F; Desiante R; Digel SW; Di Venere L; Drell PS; Favuzzi C; Fegan SJ; Fukazawa Y; Funk S; Fusco P; Gargano F; Gasparrini D; Giglietto N; Giordano F; Giroletti M; Godfrey G; Green D; Grenier IA; Guiriec S; Hays E; Hewitt JW; Horan D; Johannesson G; Kuss M; Larsson S; Latronico L; Li J; Li L; Longo F; Loparco F; Lovellette MN; Lubrano P; Madejski GM; Maldera S; Manfreda A; Mayer M; Mazziotta MN; Michelson PF; Mitthumsiri W; Mizuno T; Monzani ME; Morselli A; Moskalenko IV; Murgia S; Nuss E; Ohsugi T; Orienti M; Orlando E; Ormes JF; Paneque D; Pesce-Rollins M; Petrosian V; Piron F; Pivato G; Porter TA; Raino S; Rando R; Razzano M; Reimer A; Reimer O; Sanchez-Conde M; Sgro C; Siskind EJ; Spada F; Spandre G; Spinelli P; Tajima H; Takahashi H; Thayer JB; Tibaldo L; Torres DF; Tosti G; Troja E; Vianello G; Wood KS; Zimmer S; Rephaeli Y. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - STAMPA. - 819:2(2016), pp. 149.149-149.158. [10.3847/0004-637X/819/2/149]
SEARCH FOR GAMMA-RAY EMISSION FROM THE COMA CLUSTER WITH SIX YEARS OF FERMI-LAT DATA
D'AMMANDO, FILIPPO;
2016
Abstract
We present results from gamma-ray observations of the Coma cluster incorporating six years of Fermi-LAT data and the newly released "Pass 8" event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the gamma-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100MeV are 1.7 x 10(-9) ph cm(-2) s(-1) and 5.2 x 10(-9) ph cm(-2) s(-1) respectively (the latter corresponds to residual emission at the level of 1.8 sigma). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray (CR) models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of CRs and magnetic field properties. The minimal expected.-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
