The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN= dS, of extragalactic.-ray sources at E > 50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (8 x 10(-12) ph cm(-2) s(-1)). We employ a one-point photon fluctuation analysis to constrain the behavior of dN= dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, Sb, in the range [8 x 10-12; 1.5 x 10-11] ph cm(-2) s(-1) and power-law indices below and above the break of a 2. [1.60; 1.75] and a 1 +/- 2.49 +/- 0.12, respectively. Integration of dN= dS shows that point sources account for at least 86_16 -14 % of the total extragalactic gamma-ray background. The simple form of the derived source count distribution is consistent with a single population (i. e., blazars) dominating the source counts to the minimum flux explored by this analysis. We estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.
Resolving the Extragalactic gamma-Ray Background above 50 GeV with the Fermi Large Area Telescope / Ackermann M; Ajello M; Albert A; Atwood WB; Baldini L; Ballet J; Barbiellini G; Bastieri D; Bechtol K; Bellazzini R; Bissaldi E; Blandford RD; Bloom ED; Bonino R; Bregeon J; Britto RJ; Bruel P; Buehler R; Caliandro GA; Cameron RA; Caragiulo M; Caraveo PA; Cavazzuti E; Cecchi C; Charles E; Chekhtman A; Chiang J; Chiaro G; Ciprini S; Cohen-Tanugi J; Cominsky LR; Costanza F; Cutini S; DAmmando F; de Angelis A; de Palma F; Desiante R; Digel SW; Di Mauro M; Di Venere L; Dominguez A; Drell PS; Favuzzi C; Fegan SJ; Ferrara EC; Franckowiak A; Fukazawa Y; Funk S; Fusco P; Gargano F; Gasparrini D; Giglietto N; Giommi P; Giordano F; Giroletti M; Godfrey G; Green D; Grenier IA; Guiriec S; Hays E; Horan D; Iafrate G; Jogler T; Johannesson G; Kuss M; La Mura G; Larsson S; Latronico L; Li J; Li L; Longo F; Loparco F; Lott B; Lovellette MN; Lubrano P; Madejski GM; Magill J; Maldera S; Manfreda A; Mayer M; Mazziotta MN; Michelson PF; Mitthumsiri W; Mizuno T; Moiseev AA; Monzani ME; Morselli A; Moskalenko IV; Murgia S; Negro M; Nuss E; Ohsugi T; Okada C; Omodei N; Orlando E; Ormes JF; Paneque D; Perkins JS; Pesce-Rollins M; Petrosian V; Piron F; Pivato G; Porter TA; Raino S; Rando R; Razzano M; Razzaque S; Reimer A; Reimer O; Reposeur T; Romani RW; Sanchez-Conde M; Schmid J; Schulz A; Sgro C; Simone D; Siskind EJ; Spada F; Spandre G; Spinelli P; Suson DJ; Takahashi H; Thayer JB; Tibaldo L; Torres DF; Troja E; Vianello G; Yassine M; Zimmer S. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - STAMPA. - 116:15(2016), pp. 151105.1-151105.8. [10.1103/PhysRevLett.116.151105]
Resolving the Extragalactic gamma-Ray Background above 50 GeV with the Fermi Large Area Telescope
D'AMMANDO, FILIPPO;
2016
Abstract
The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN= dS, of extragalactic.-ray sources at E > 50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (8 x 10(-12) ph cm(-2) s(-1)). We employ a one-point photon fluctuation analysis to constrain the behavior of dN= dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, Sb, in the range [8 x 10-12; 1.5 x 10-11] ph cm(-2) s(-1) and power-law indices below and above the break of a 2. [1.60; 1.75] and a 1 +/- 2.49 +/- 0.12, respectively. Integration of dN= dS shows that point sources account for at least 86_16 -14 % of the total extragalactic gamma-ray background. The simple form of the derived source count distribution is consistent with a single population (i. e., blazars) dominating the source counts to the minimum flux explored by this analysis. We estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
