The supernova remnant W44: Confirmations and challenges for cosmic-ray acceleration

被引:55
作者
Cardillo, M. [1 ,2 ]
Tavani, M. [1 ,2 ,3 ]
Giuliani, A. [3 ,4 ]
Yoshiike, S. [5 ]
Sano, H. [5 ]
Fukuda, T. [5 ]
Fukui, Y. [5 ]
Castelletti, G. [6 ]
Dubner, G. [6 ]
机构
[1] INAF IAPS, I-00133 Rome, Italy
[2] Univ Roma Tor Vergata, Dip Fis, I-00133 Rome, Italy
[3] CIFS Torino, I-10133 Turin, Italy
[4] INAF IASF Milano, I-20133 Milan, Italy
[5] Nagoya Univ, Dept Phys & Astrophys, Chikusa Ku, Nagoya, Aichi 4648601, Japan
[6] Inst Astron & Fis Espacio, RA-1428 Buenos Aires, DF, Argentina
来源
ASTRONOMY & ASTROPHYSICS | 2014年 / 565卷
关键词
acceleration of particles; astroparticle physics; shock waves; radiation mechanisms: non-thermal; ISM: supernova remnants; gamma rays: ISM; LARGE-AREA TELESCOPE; VERY-HIGH-ENERGY; TEV GAMMA-RAY; MHZ OH MASERS; PARTICLE-ACCELERATION; MOLECULAR CLOUDS; RX J1713.7-3946; FERMI-LAT; AGILE DETECTION; ATOMIC GAS;
D O I
10.1051/0004-6361/201322685
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. For the first time for a SNR, the gamma-ray missions AGILE and Fermi have established the spectral continuum below 200 MeV, which can be attributed to a neutral pion emission. Confirming the hadronic origin of the gamma-ray emission near 100 MeV is then of the greatest importance. Our paper is focused on a global re-assessment of all available data and models of particle acceleration in W44 with the goal of determining the hadronic and leptonic contributions to the overall spectrum on a firm ground. We also present new gamma-ray and CO NANTEN2 data on W44 and compare them to recently published AGILE and Fermi data. Our analysis strengthens previous studies and observations of the W44 complex environment and provides new information for more detailed modeling. In particular, we determine that the average gas density of the regions emitting 100 MeV-10 GeV gamma-rays is relatively high (n similar to 250-300 cm(-3)). The hadronic interpretation of the gamma-ray spectrum of W44 is viable and supported by strong evidence. It implies a relatively large value for the average magnetic field (B >= 10(2) mu G) in the SNR surroundings, which is a sign of field amplification by shock-driven turbulence. Our new analysis establishes that the spectral index of the proton energy distribution function is p(1) = 2.2 +/- 0.1 at low energies and p(2) = 3.2 +/- 0.1 at high energies. We critically discuss hadronic versus leptonic-only models of emission taking radio and gamma-ray data into account simultaneously. We find that the leptonic models are disfavored by the combination of radio and gamma-ray data. Having determined the hadronic nature of the gamma-ray emission on firm ground, a number of theoretical challenges remain to be addressed.
引用
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页数:12
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