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Observation of the HMXB LS I +61 303 in GeV/TeV gamma rays with the MAGIC telescope

This study presents the observation of the high-mass X-ray binary (HMXB) system LS I +61 303 using the MAGIC telescope. The LS I +61 303 system consists of a B0 V star with a disc (Be) and an unknown compact object with an orbital period of 26.496 days. The distance to the system is around 2 kpc, with a periastron at φ = 0.23 and an eccentricity of 0.73. The observation detected LS I +61 303 in various wavelengths, including radio, optical, X-ray, high-energy gamma rays (E < 10 GeV), and Very High Energy (VHE) gamma rays. The system shows strong variability in flux and spectral shape, making it a potential cosmic ray accelerator and a valuable laboratory for studying Pulsar Wind/Stellar Wind interactions.

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Observation of the HMXB LS I +61 303 in GeV/TeV gamma rays with the MAGIC telescope

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  1. T 302.6 Observation of the HMXB LS I +61 303 in GeV/TeV gamma rays with the MAGIC telescope T. Jogler, K. Berger for the MAGIC Collaboration

  2. HMXBs HMXB: Binary systems with massive star and lighter compact object orbiting the massive star • LS I +61 303 • B0 V star with disc (Be) • Compact object unknown • Orbital period 26.496 days • Distance ~ 2 kpc • Periastron at  = 0.23 • Eccentricity e = 0.73

  3. Periodic Periodic variable Periodic Periodic radio, x-ray optical + infrared HE (E< 10 GeV) Paredes et al. 1997 Tavani et al. 1998 Mendelson et al. 1989 LS I Observation Detected in radio, optical, x-ray, HE (E< 10 GeV) gamma rays

  4. MAGIC Observation • LS I was observed for 6 orbits between Oct 05 and March 06 • In total 54 hours of data, 22% ofdata taken during moon • Clear detection with8.7 sigma • Excess position:RA=2h 40m 34s DEC= + 6115’ 25” In agreement with LS I position • Possible association with variable EGRET source

  5. Periastron Oct2005 Nov2005 Dec2005 Jan 2006 Feb 2006 Mar 2006 Source isquiet at periastron and loud before apastron ! Average Maximum flux 16% of Crab Nebula at 0.5 - 0.7 Orbital Light Curves Albert et al. Science 312, 1771 (2006) Phases 0.8 – 0.1 not observed due to bright moon Strong variability between phases Probability of a constant flux < 3 x 10-5

  6. Spectrum from phase 0.4 - 0.7 VHE Gamma Ray Spectrum • Spectral shape compatible with power law • Spectral index 2.6 0.2 stat.  0.2 syst. • VHE (E > 200 GeV)luminosity ~ 7 x 10 33 erg s-1for distance =2 kpc

  7. e +  e +  • from synchrotron radiation • or from companion star p + Ion 0 +    Mirabel 2006 LS I - a Microquasar ? Production of -rays: Features: - accretion disc - jets - modulation with accretion rate

  8. p + Ion 0 +    Mirabel 2006 LS I a Binary Pulsar ? Production of -rays: e +  e +   from companion star e from relativistic PW Features: - no accretion disc needed - no jet needed

  9. VHE measurements are very important to understand LS I Broad Band Spectrum Chernyakova et al. 2006 Simple IC scenario can not explain MAGIC measurements additional VHE  - ray production due to hadronic mechanism

  10. Conclusion • 2nd detection of an variable galactic source in VHE  - rays • LS I is more luminous in GeV-TeV energies than in x-ray • Spectral break between 10 and 200 GeV • Possibly a cosmic ray accelerator • Nice laboratory for studying Pulsar Wind / Stellar Wind interactions

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