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

TL;DR

This study reports a significant reduction in very high energy gamma-ray emission from LS I +61 303 during a low emission state, contrasting previous periodic outbursts, and discusses implications for future observations.

Contribution

First detailed VHE gamma-ray observations of LS I +61 303 during a low emission state with MAGIC telescopes, revealing a substantial flux decrease and constant flux level.

Findings

VHE gamma-ray flux decreased by nearly an order of magnitude.

No significant outburst observed in 2009, flux remained constant.

Implications for gamma-ray emission models of LS I +61 303.

Abstract

The gamma-ray binary system LS I +61 303 was studied in great detail in VHE gamma-rays in the last years by the MAGIC telescope. The VHE emission of the system exhibited a prominent periodic outburst in the orbital phases 0.6-0.7 between September 2005 to January 2008. In Fall 2008 the Fermi collaboration reported as well periodic emission in the MeV to GeV energy range, but with a shifted outburst in the phases 0.35-0.45. MAGIC observed again LS I+61 303 in 2009 with the twice more sensitive stereo mode to allow for detailed correlation studies between the VHE gamma-ray and Fermi/LAT energy band. Here we present our new results, which show a significant reduction in the VHE gamma-ray flux in the phase of the periodic outburst by almost one order of magnitude compared to our previous measurements. Furthermore, the 0.1-phase averaged light curve shows no significant outburst, but a rather constant flux. Here we will discuss the implications of our results for future gamma-ray studies of LS I +61 303.