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Detection of LS I+61 303 in a low VHE gamma-ray emission state with the MAGIC telescopes

Detection of LS I+61 303 in a low VHE gamma-ray emission state with the MAGIC telescopes. Tobias Jogler and O. Blanch Bigas for the MAGIC Collaboration. Very sensitive instrument to study faint VHE gamma ray sources. The MAGIC Telescopes. La Palma, asl. 2200m 17 m diameter mirror

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Detection of LS I+61 303 in a low VHE gamma-ray emission state with the MAGIC telescopes

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  1. Detection of LS I+61 303 in a low VHE gamma-ray emission state with the MAGIC telescopes Tobias Jogler and O. Blanch Bigas for the MAGIC Collaboration

  2. Very sensitive instrument to study faint VHE gamma ray sources The MAGIC Telescopes La Palma, asl. 2200m 17 m diameter mirror 3.5 ° FoV camera Trigger threshold of E = 50 GeV Sensitivity of 0.8 % Crab flux Can operate under moonlight conditions

  3. Microquasar vs Binary Pulsar Different scenarios for the VHE gamma-ray emission from binaries Mirabel 2006

  4. LS I +61 303 • Gamma ray binary discovered by MAGIC (E > 300 GeV) in 2005/2006 • Compact object unknown • B0Ve star as optical companion • Highly eccentric orbit e = 0.54 (Argona et al. 2009) • Orbital period 26.5 days • Periastron phase 0.275 (Aragona et al. 2009) circumstellar disc Be to observer

  5. Light Curve of LS I +61 303 • MAGIC (mono) measurements • Tobs= 166 h (2005-2006) • Highest emission phase 0.6-0.7 • Quiet at periastron Albert et al. 2009 Periastron Periodic with P=26.6 ± 0.2 days average campaign 1average campaign 2

  6. sometimes emission periodicoutburst 2005-2007 averaged flux 2007 Fall campaign adapted from Aragona et al 2009 Periodicity • Periodic outburst in phase 0.6-0.7 modulated with orbital period • Additional fluxes measured in phase 0.8-1.0 not periodic

  7. Evidence for correlation linear correlation coefficientr = 0.81 (pfap ~ 5 x 10-3) VHE / X-ray correlation H. Anderhub et al. 2009 Simultaneously obtained LC averaged flux in orbital phasebin 0.6 - 0.7 EFX-rays ~ 2 EFVHE X-ray VHE

  8. integral data set signalS = 6.3 σ Tobs= 48.4 h 2009 Observations Aimed to study short time variability and spectral behavior between different phase intervals with the very improved stereo sensitivity. That was not what we expected

  9. Observation in 2009 Periastron Tobs ~ 48 hours Emission level dropped significantly F (E >300 GeV) = (1.4 ± 0.3stat ± 0.4sys) x10-12 cm-2 s-1 (total average flux) Difficult to study details of emission since very lowflux and sensitivity per night very limited average VERITAS did not detect LSI at all in 2008 and 2009.Acciari et. al. 2011

  10. Spectral index is stable independent of flux state! Spectral behavior Well fitted by power-law with spectral index Γ=-2.6 ± 0.2stat± 0.2sys high state 2006low state 2009

  11. LS I+61 303 shows again high VHE flux! 2010/2011 measurements Observed by MAGIC from Fall 2010 to Spring 2011 to monitor VHE behavior

  12. Even after several years of detailed study, the nature of the VHE emission is not understood and the system can still surprise us Conclusions • LS I +61 303 exhibits different VHE gamma-ray flux states • The spectrum is compatible with a power law for all observations ( Γ= -2.6 ± 0.2 ± 0.2) at all emission levels • Simultaneously obtained LC in X-ray and VHE gamma-rays present evidence for a flux correlation between the two energy emissions in “high VHE flux state” • Low VHE flux state duration up to 2 years • Since Fall 2010 back at high flux state in VHE gamma-rays • The reason for these flux states and their changes is unknown

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