Measurement of the Crab Nebula spectrum over three decades in energy with the MAGIC telescopes
Abstract
The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between October 2009 and April 2011. Analysis of this data sample using the latest improvements in the MAGIC stereoscopic software provided an unprecedented precision of spectral and nightbynight light curve determination at gamma rays. We derived a differential spectrum with a single instrument from 50 GeV up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC results, combined with FermiLAT data, show a flat and broad Inverse Compton peak. The overall fit to the data between 1 GeV and 30 TeV is not well described by a logparabola function. We find that a modified logparabola function with an exponent of 2.5 instead of 2 provides a good description of the data (χ_{red}^{2} = 35 / 26). Using systematic uncertainties of the MAGIC and FermiLAT measurements we determine the position of the Inverse Compton peak to be at (53 ±3_{stat} +31_{syst} 13_{syst}) GeV, which is the most precise estimation up to date and is dominated by the systematic effects. There is no hint of the integral flux variability on daily scales at energies above 300 GeV when systematic uncertainties are included in the flux measurement. We consider three stateoftheart theoretical models to describe the overall spectral energy distribution of the Crab Nebula. The constant Bfield model cannot satisfactorily reproduce the VHE spectral measurements presented in this work, having particular difficulty reproducing the broadness of the observed IC peak. Most probably this implies that the assumption of the homogeneity of the magnetic field inside the nebula is incorrect. On the other hand, the timedependent 1D spectral model provides a good fit of the new VHE results when considering a 80 μG magnetic field. However, it fails to match the data when including the morphology of the nebula at lower wavelengths.
 Publication:

Journal of High Energy Astrophysics
 Pub Date:
 March 2015
 DOI:
 10.1016/j.jheap.2015.01.002
 arXiv:
 arXiv:1406.6892
 Bibcode:
 2015JHEAp...5...30A
 Keywords:

 Crab Nebula;
 Pulsar wind nebulae;
 MAGIC telescopes;
 Imaging atmospheric Cherenkov telescopes;
 Very high energy gamma rays;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 accepted by JHEAp, 9 pages, 6 figures