We report on the detection of high-energy gamma-ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmic-ray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(> 100 MeV) = (1.04 +/- 0.01 [statistical error] +/- 0.1 [systematic error]) x 10(-6) cm(-2) s(-1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(> 100 MeV) approximate to 5 x 10(-7) cm-2 s-1, when solar activity was relatively high. The higher gamma-ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.
FERMI OBSERVATIONS OF gamma-RAY EMISSION FROM THE MOON / Abdo AA; Ackermann M; Ajello M; Atwoo WB; Baldini L; Ballet J; Barbiellini G; Bastieri D; Bechtol K; Bellazzini R; Berenji B; Blandford RD; Bonamente E; Borgland AW; Bottacini E; Bouvier A; Bregeon J; Brigida M; Bruel P; Buehler R; Buson S; Caliandro GA; Cameron RA; Caraveo PA; Casandjian JM; Cecchi C; Charles E; Chekhtman A; Chiang J; Ciprini S; Claus R; Cohen-Tanugi J; Conrad J; Cutini S; DAmmando F; de Angelis A; de Palma F; Dermer CD; Digel SW; Silva EDE; Drell PS; Drlica-Wagner A; Dubois R; Favuzzi C; Fegan SJ; Focke WB; Fortin P; Fukazawa Y; Funk S; Fusco P; Gargano F; Gehrels N; Germani S; Giglietto N; Giommi P; Giordano F; Giroletti M; Glanzman T; Godfrey G; Gomez-Vargas GA; Grenier IA; Grove JE; Guiriec S; Hadasch D; Hays E; Hill AB; Horan D; Hou X; Hughes RE; Iafrate G; Jackson MS; Johannesson G; Johnson AS; Kamae T; Katagiri H; Kataoka J; Knodlseder J; Kuss M; Lande J; Larsson S; Latronico L; Lemoine-Goumard M; Longo F; Loparco F; Lott B; Lovellette MN; Lubrano P; Mazziotta MN; McEnery JE; Mehault J; Michelson PF; Mitthumsiri W; Mizuno T; Moiseev AA; Monte C; Monzani ME; Morselli A; Moskalenko IV; Murgia S; Naumann-Godo M; Nolan PL; Norris JP; Nuss E; Ohno M; Ohsugi T; Okumura A; Omodei N; Orienti M; Orlando E; Ormes JF; Ozaki M; Paneque D; Panetta JH; Parent D; Pesce-Rollins M; Pierbattista M; Piron F; Pivato G; Poon H; Porter TA; Prokhorov D; Raino S; Rando R; Razzano M; Razzaque S; Reimer A; Reimer O; Reposeur T; Rochester LS; Roth M; Sadrozinski HFW; Sanchez DA; Sbarra C; Schalk TL; Sgro C; Share GH; Siskind EJ; Spandre G; Spinelli P; Stawarz L; Takahashi H; Tanaka T; Thayer JG; Thayer JB; Thompson DJ; Tibaldo L; Tinivella M; Torres DF; Tosti G; Troja E; Uchiyama Y; Usher TL; Vandenbroucke J; Vasileiou V; Vianello G; Vitale V; Waite AP; Wang P; Winer BL; Wood DL; Wood KS; Yang Z; Zimmer S. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - STAMPA. - 758:2(2012), pp. 140.140-140.147. [10.1088/0004-637X/758/2/140]
FERMI OBSERVATIONS OF gamma-RAY EMISSION FROM THE MOON
D'AMMANDO, FILIPPO;
2012
Abstract
We report on the detection of high-energy gamma-ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmic-ray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(> 100 MeV) = (1.04 +/- 0.01 [statistical error] +/- 0.1 [systematic error]) x 10(-6) cm(-2) s(-1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(> 100 MeV) approximate to 5 x 10(-7) cm-2 s-1, when solar activity was relatively high. The higher gamma-ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
