Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 735, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/735/1/L5
Keywords
acceleration of particles; gamma rays: stars; stars: individual (Sco X-1); X-rays: binaries
Categories
Funding
- German BMBF
- MPG
- Italian INFN
- Swiss National Fund SNF
- Spanish MICINN
- Spanish Consolider-Ingenio [CSD2007-00042, CSD2009-00064]
- Bulgarian NSF [DO02-353]
- Academy of Finland [127740]
- Helmholtz Gemeinschaft
- DFG
- Polish MNiSzW [745/N-HESS-MAGIC/2010/0]
- ICREA Funding Source: Custom
- Grants-in-Aid for Scientific Research [22840030] Funding Source: KAKEN
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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 x 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 x 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 less than or similar to 0.02 that can be related to a maximum TeV luminosity to jet power ratio of L-VHE/L-j less than or similar to 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.
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