VARIABILITY AND SPECTRAL MODELING OF THE HARD X-RAY EMISSION OF GX 339-4 IN A BRIGHT LOW/HARD STATE
- CESR, Universite de Toulouse, UPS, 9 avenue du Colonel Roche, F-31028 Toulouse (France)
We study the high-energy emission of the Galactic black hole candidate GX 339-4 using INTEGRAL/SPI and simultaneous RXTE/PCA data. By the end of 2007 January, when it reached its peak luminosity in hard X-rays, the source was in a bright hard state. The SPectrometer on INTEGRAL (SPI) data from this period show a good signal-to-noise ratio, allowing a detailed study of the spectral energy distribution up to several hundred keV. As a main result, we report on the detection of a variable hard spectral feature ({>=}150 keV) which represents a significant excess with respect to the cutoff power-law shape of the spectrum. The SPI data suggest that the intensity of this feature is positively correlated with the 25-50 keV luminosity of the source and the associated variability timescale is shorter than 7 hr. The simultaneous Proportional Counter Array data, however, show no significant change in the spectral shape, indicating that the source is not undergoing a canonical state transition. We analyzed the broadband spectra in the lights of several physical models, assuming different heating mechanisms and properties of the Comptonizing plasma. For the first time, we performed quantitative model fitting with the new versatile Comptonization code BELM, accounting self-consistently for the presence of a magnetic field. We show that a magnetized medium subject to pure non-thermal electron acceleration provides a framework for a physically consistent interpretation of the observed 4-500 keV emission. Moreover, we find that the spectral variability might be triggered by the variations of only one physical parameter, namely the magnetic field strength. Therefore, it appears that the magnetic field is likely to be a key parameter in the production of the Comptonized hard X-ray emission.
- OSTI ID:
- 21457122
- Journal Information:
- Astrophysical Journal, Vol. 717, Issue 2; Other Information: DOI: 10.1088/0004-637X/717/2/1022; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ACCELERATION
ACCRETION DISKS
BLACK HOLES
EMISSION
ENERGY SPECTRA
HARD X RADIATION
KEV RANGE 10-100
LUMINOSITY
MAGNETIC FIELDS
POLAR-CAP ABSORPTION
PROPORTIONAL COUNTERS
SIGNAL-TO-NOISE RATIO
SIMULATION
SPECTROMETERS
ABSORPTION
DIMENSIONLESS NUMBERS
ELECTROMAGNETIC RADIATION
ENERGY RANGE
IONIZING RADIATIONS
KEV RANGE
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATION DETECTORS
RADIATIONS
SORPTION
SPECTRA
X RADIATION