The 2010 VERY HIGH ENERGY Γ-Ray FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

Abstract

The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3−6)×10 9 M ) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ -ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ -ray emitter since 2006. The VHE γ -ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE γ -ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of τ rise (1-3) × 10 −11 photons cm −2 s −1 ), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ∼3 days after the peak of the VHE γ -ray emission reveal an enhanced flux from the core (flux increased by factor ∼2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE γ -ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: [2002][2003][2004][2005][2006][2007][2008][2009]). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE γ -ray emission from M 87 are reviewed in the light of the new data.

Minimal variability time scale – central black hole mass relation of theγ-ray loud blazars

“…Observations of fast variability for a number of blazars have already been reported in the literature (Aharonian et al 2007;Albert et al 2007;Abramowski et al 2010Abramowski et al , 2012Acciari et al 2010Acciari et al , 2008Arlen et al 2013). As there is no unique way of measuring the variability, the time scales reported in the literature are often derived in different manners and have to be put into the same scale.…”

The minijets-in-a-jet statistical model and the rms-flux correlation

“…Narayan & Piran (2012) considered a turbulent process, modelled by a random motion of minijets inside the jet. Models involving minijets have also been invoked to explain the fast variations in the emission of radio galaxies (Giannios et al 2010), though the time scales of variations observed at VHE are much longer than for blazars, approximately a day for M 87 (Abramowski et al 2012). A&A 548, A123 (2012) These models are additive (the flux is given by the sum of the contributions of several regions) and, provided there are finite moments for the individual components, the central limit theorem (CLT) can be applied.…”

Study of High Energy Emission from Relativistic Jets with VERITAS

“…[18] and triggered an extensive multiwavelength campaign at lower energies. Figure 5b shows results from the coordinated observation with VERITAS, H.E.S.S., and MAGIC during the bright VHE flare in 2010 [15]. This TeV flare was very well sampled, and the light curve shows a single isolated flare characterized by two-sided exponential decay τ rise ∼ 1.7 days and τ decay ∼ 0.6 days.…”

“…The source has exhibited three distinct VHE flares with similarities in the VHE behaviour, but no unique multi-wavelength correlation. Figure 5a shows the multiwavelength light curves of M 87 over ten years of observations [15]. The exact location of the VHE gamma-rayemitting region in M 87 remains elusive.…”