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Bibliographical reference
The Astrophysical Journal Letters, Volume 735, Issue 1, article id. L5 (2011).
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7
2011
Citations
15
Refereed citations
10
Description
The acceleration of particles up to GeV or higher energies in
microquasars has been the subject of considerable theoretical and
observational efforts in the past few years. Sco X-1 is a microquasar
from which evidence of highly energetic particles in the jet has been
found when it is in the so-called Horizontal Branch (HB), a state when
the radio and hard X-ray fluxes are higher and a powerful relativistic
jet is present. Here we present the first very high energy gamma-ray
observations of Sco X-1, obtained with the MAGIC telescopes. An analysis
of the whole data set does not yield a significant signal, with 95% CL
flux upper limits above 300 GeV at the level of 2.4 ×
10-12 cm-2 s-1. Simultaneous RXTE
observations were conducted to provide the X-ray state of the source. A
selection of the gamma-ray data obtained during the HB based on the
X-ray colors did not yield a signal either, with an upper limit of 3.4
× 10-12 cm-2 s-1. These upper
limits place a constraint on the maximum TeV luminosity to non-thermal
X-ray luminosity of L VHE/L ntX <~ 0.02 that
can be related to a maximum TeV luminosity to jet power ratio of L
VHE/L j <~ 10-3. Our upper limits
indicate that the underlying high-energy emission physics in Sco X-1
must be inherently different from that of the hitherto detected
gamma-ray binaries.