MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context

Abstract

We present a study of the very high energy (VHE; E > 100 GeV) gamma-rayemission of the blazar PKS 1424+240 observed with the MAGIC telescopes. Theprimary aim of this paper is the multiwavelength spectral characterization andmodeling of this blazar, which is made particularly interesting by the recentdiscovery of a lower limit of its redshift of z > 0.6 and makes it a promisingcandidate to be the most distant VHE source. The source has been observed withthe MAGIC telescopes in VHE gamma rays for a total observation time of ~33.6 hfrom 2009 to 2011. The source was marginally detected in VHE gamma rays during2009 and 2010, and later, the detection was confirmed during an opticaloutburst in 2011. The combined significance of the stacked sample is ~7.2sigma. The differential spectra measured during the different campaigns can bedescribed by steep power laws with the indices ranging from 3.5 +/- 1.2 to 5.0+/- 1.7. The MAGIC spectra corrected for the absorption due to theextragalactic background light connect smoothly, within systematic errors, withthe mean spectrum in 2009-2011 observed at lower energies by the Fermi-LAT. Theabsorption-corrected MAGIC spectrum is flat with no apparent turn down up to400 GeV. The multiwavelength light curve shows increasing flux in radio andoptical bands that could point to a common origin from the same region of thejet. The large separation between the two peaks of the constructednon-simultaneous spectral energy distribution also requires an extremely highDoppler factor if an one zone synchrotron self-Compton model is applied. Wefind that a two-component synchrotron self-Compton model describes the spectralenergy distribution of the source well, if the source is located at z~0.6.