期刊
ASTROPHYSICAL JOURNAL
卷 749, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/749/1/54
关键词
binaries: close; gamma rays: general; stars: variables: general; X-rays: binaries; X-rays: individual (LS I+61 303); X-rays: individual (LS 5039)
资金
- National Aeronautics and Space Administration
- Department of Energy in the United States
- Commissariat a l'Energie Atomique
- Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France
- Agenzia Spaziale Italiana
- Istituto Nazionale di Fisica Nucleare in Italy
- Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- High Energy Accelerator Research Organization (KEK)
- Japan Aerospace Exploration Agency (JAXA) in Japan
- K. A. Wallenberg Foundation
- Swedish Research Council
- Swedish National Space Board in Sweden
- Istituto Nazionale di Astrofisica in Italy
- Centre National d'Etudes Spatiales in France
- Spanish CSIC
- MICINN
- Generalitat de Catalunya [AYA2009-07391, SGR2009-811]
- Formosa Program [TW2010005]
- National Natural Science Foundation of China [NSFC-10325313, 10521001, 10733010, 10821061, 11073021, 11133002]
- 973 program [2009CB824800]
- European Community [ERC-StG-200911]
- EU [2010-275861]
- STFC
- University of Cambridge
- ICREA Funding Source: Custom
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1109911] Funding Source: National Science Foundation
The Fermi Large Area Telescope (LAT) reported the first definitive GeV detections of the binaries LS I + 61 degrees 303 and LS 5039 in the first year after its launch in 2008 June. These detections were unambiguous as a consequence of the reduced positional uncertainty and the detection of modulated gamma-ray emission on the corresponding orbital periods. An analysis of new data from the LAT, comprising 30 months of observations, identifies a change in the gamma-ray behavior of LS I + 61 degrees 303. An increase in flux is detected in 2009 March and a steady decline in the orbital flux modulation is observed. Significant emission up to 30 GeV is detected by the LAT; prior data sets led to upper limits only. Contemporaneous TeV observations no longer detected the source, or found it-in one orbit-close to periastron, far from the phases at which the source previously appeared at TeV energies. The detailed numerical simulations and models that exist within the literature do not predict or explain many of these features now observed at GeV and TeV energies. New ideas and models are needed to fully explain and understand this behavior. A detailed phase-resolved analysis of the spectral characterization of LS I + 61 degrees 303 in the GeV regime ascribes a power law with an exponential cutoff spectrum along each analyzed portion of the system's orbit. The on-source exposure of LS 5039 is also substantially increased with respect to our prior publication. In this case, whereas the general gamma-ray properties remain consistent, the increased statistics of the current data set allows for a deeper investigation of its orbital and spectral evolution.
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