Gamma-Ray Emission from the Shell of Supernova Remnant W44 Revealed by the Fermi LAT

A A Abdo,N Giglietto,N Giglietto,D J Thompson,M Ajello,A W Borgland,C C Cheung,D Bastieri,D Bastieri,E Hays,M Ziegler,M Kuss,T Kamae,M Ackermann,M Razzano,F De Palma,W Mitthumsiri,A Reimer,A Reimer,J Knödlseder,C Venter,C Venter,B Giebels,N Vilchez,P D Smith,M Roth,I Cognard,C Farnier,S Murgia,G Barbiellini,A S Johnson,Y Hanabata,T Reposeur,M N Mazziotta,B L Winer,D Dumora,G Tosti,A Sander,R Rando,R Rando,E Nuss,F Piron,J Kataoka,J Kataoka,E Do Couto E Silva,C Meurer,S Cutini,B W Stappers,J Conrad,J Conrad,E Orlando,D F Torres,D F Torres,G Spandre,T J Johnson,G Godfrey,C Sgrò,M S Jackson,J Ballet,L Guillemot,L Guillemot,S Buson,P F Michelson,S Guiriec,A Makeev,N Omodei,C Favuzzi,E Bonamente,W N Johnson,V Pelassa,T Mizuno,I V Moskalenko,P Fortin,D Paneque,T A Porter,M Pesce-Rollins,A G Lyne,R E Hughes,D Gasparrini,A Brez,J Chiang,N Gehrels,J E Mcenery,M S Jackson,A K Harding,G Giavitto,S W Digel,P M Saz Parkinson,P S Drell,J Bregeon,H Takahashi,Y Uchiyama,G M Madejski,T Ylinen,K Bechtol,S Funk,A Y Rodriguez,B Berenji,E J Siskind,J Cohen-Tanugi,R D Blandford,W B Focke,S J Fegan,N Kawai,M.-H Grondin,M.-H Grondin,E D Bloom,G Barbiellini,P Lubrano,C D Dermer,R Dubois,S Germani,L Tibaldo,L Tibaldo,L Tibaldo,O Tibolla,M S Strickman,P Fusco,A Morselli,H Tajima,D Parent,T Ohsugi,F Longo,T J Johnson,M Brigida,P A Caraveo,I A Grenier,M E Monzani,T Reposeur,K S Wood,J F Ormes,V Vasileiou,A De Angelis,S Rainò,A Chekhtman,C Cecchi,C Cecchi,G Theureau,F W Stecker,J M Casandjian,G A Caliandro,T H Burnett,D J Suson,J E Grove,M N Lovellette,A Tramacere,D Parent,A Noutsos,P Wang,V Vitale,B Lott,B Lott,F Ryde,F Ryde,P Spinelli,E Bonamente,Ö Çelik,Ö Çelik,Ö Çelik,F Gargano,M S Jackson,D Dumora,R A Cameron,R Bellazzini,M Kerr,T Glanzman,F Giordano,F Giordano,R Claus,H Katagiri,S Ciprini,S Ciprini,J P Norris,J B Thayer,C Monte,B M Baughman,L Latronico,P L Nolan,A P Waite,M Frailis,J D Scargle,M Hayashida,J Katsuta,F Loparco,Matthew G Baring ,Pascal Bruel ,L Cominsky ,Ryo Yamazaki ,M Pepé ,David Sánchez ,Takeshi Nakamori ,M Kocian ,Takaaki Tanaka ,David Stanley Smith ,H F-W Sadrozinski ,C M Espinoza ,T Usher ,Luca Baldini ,M Lemoine‐Goumard ,Roger W Romani ,M Krämer ,G Jøhannesson ,Yasushi Fukazawa ,J Landé ,Lynn Rochester ,Tadayuki Takahashi

doi:10.1126/science.1182787

Abstract

Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close to ~10(15) electron volts. However, the nature of the particles that produce the emission remains ambiguous. We report observations of SNR W44 with the Fermi Large Area Telescope at energies between 2 x 10(8) electron volts and 3 x10(11) electron volts. The detection of a source with a morphology corresponding to the SNR shell implies that the emission is produced by particles accelerated there. The gamma-ray spectrum is well modeled with emission from protons and nuclei. Its steepening above approximately 10(9) electron volts provides a probe with which to study how particle acceleration responds to environmental effects such as shock propagation in dense clouds and how accelerated particles are released into interstellar space.

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