TY - JOUR
T1 - A Hard X-Ray View of Scorpius X-1 with INTEGRAL: Nonthermal Emission?
AU - Robba, Natale
AU - Di Salvo, Tiziana
AU - Israel, Gianluca
AU - Ubertini, Pietro
AU - Farinelli, null
AU - Van Der Klis, null
AU - Goldoni, null
AU - Burderi, null
AU - Mirabel, null
AU - Lewin, null
AU - Stella, null
AU - Frontera, null
AU - Méndez, null
AU - Bazzano, Angela
AU - Sizun, null
PY - 2006
Y1 - 2006
N2 - We present here simultaneous INTEGRAL/RXTE observations of Sco X-1 and in particular a study of the hard X-ray emission of the source and its correlation with the position in the Z track of the X-ray color-color diagram. We find that the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a power-law component with a photon index of ~3. The flux in the power-law component slightly decreases when the source moves in the color-color diagram in the sense of increasing inferred mass accretion rate from the horizontal branch to the normal branch/flaring branch vertex. It becomes not significantly detectable in the flaring branch, where its flux has decreased by about an order of magnitude. These results present close analogies to the behavior of GX 17+2, one of the so-called Sco-like Z sources. Finally, the hard power law in the spectrum of Sco X-1 does not show any evidence of a high-energy cutoff up to 100-200 keV, strongly suggesting a nonthermal origin of this component.
AB - We present here simultaneous INTEGRAL/RXTE observations of Sco X-1 and in particular a study of the hard X-ray emission of the source and its correlation with the position in the Z track of the X-ray color-color diagram. We find that the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a power-law component with a photon index of ~3. The flux in the power-law component slightly decreases when the source moves in the color-color diagram in the sense of increasing inferred mass accretion rate from the horizontal branch to the normal branch/flaring branch vertex. It becomes not significantly detectable in the flaring branch, where its flux has decreased by about an order of magnitude. These results present close analogies to the behavior of GX 17+2, one of the so-called Sco-like Z sources. Finally, the hard power law in the spectrum of Sco X-1 does not show any evidence of a high-energy cutoff up to 100-200 keV, strongly suggesting a nonthermal origin of this component.
UR - http://hdl.handle.net/10447/32236
UR - http://iopscience.iop.org/article/10.1086/508489/meta
M3 - Article
VL - 649
SP - 91
EP - 94
JO - THE ASTROPHYSICAL JOURNAL
JF - THE ASTROPHYSICAL JOURNAL
SN - 0004-637X
ER -