Fermi Large Area Telescope observations of the supernova remnant G8.7-0.1

Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Charles, E.; Chekhtman, A.; Ciprini, S.; Claus, R.; Cohen Tanugi, J.; Cutini, S.; De Angelis, A.; De Palma, F.; Dermer, C. D.; Do Couto, E. Silva E.; Drell, P. S.; Drlica Wagner, A.; Dubois, R.; Favuzzi, Cecilia; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Fukui, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, Nicola; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashi, K.; Hays, E.; Itoh, R.; Johannesson, G.; Johnson, A. S.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knoedlseder, J.; Kubo, H.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S. H.; Lionetto, A. M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; Mehault, J.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Parent, D.; Pelassa, V.; Pesce Rollins, M.; Pierbattista, M.; Piron, F.; Porter, T. A.; Raino, S.; Rando, R.; Reimer, A.; Reimer, O.; Reposeur, T.; Roth, M.; Sadrozinski, H. F. W.; Sgro, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibaldo, L.; Tibolla, O.; Torres, D. F.; Tosti, G.; Tramacere, A.; Troja, E.; Uchiyama, Y.; Uehara, T.; Usher, T. L.; Vandenbroucke, J.; Van Etten, A.; Vasileiou, V.; Vianello, G.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Yamamoto, H.; Yamazaki, R.; Yang, Z.; Yasuda, H.; Ziegler, M.; Zimmer, S.

doi:10.1088/0004-637X/744/1/80

We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. An investigation of the relationship between G8.7-0.1 and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. TheGeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.1 and a lesser part located outside the western boundary of G8.7-0.1. The region of the gamma-ray emission overlaps spatially connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200MeV-100GeV can be described by a broken power-law function with a break of 2.4 ± 0.6 (stat) ± 1.2 (sys)GeV, and photon indices of 2.10 ± 0.06 (stat) ± 0.10 (sys) below the break and 2.70 ± 0.12 (stat) ± 0.14 (sys) above the break. Given the spatial association among the gamma rays, the radio emission of G8.7-0.1, and the molecular clouds, the decay of π0s produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains theGeV gamma-ray spectrum. We also find that theGeV morphology is not well represented by the TeV emission from HESS J1804-216 and that the spectrum in theGeV band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV spectrum originates from the interaction of particles accelerated in G8.7-0.1 with molecular clouds, and we constrain the diffusion coefficient of the particles.

Fermi Large Area Telescope observations of the supernova remnant G8.7-0.1 / Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Berenji, B., Blandford, R.D., Bloom, E.D., Bonamente, E., Borgland, A.W., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G.A., Cameron, R.A., et al.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 744:1(2012). [10.1088/0004-637X/744/1/80]