Observations of Active Galactic Nuclei at very high energies with H.E.S.S.

Observations of Active Galactic Nuclei at very high energies with H.E.S.S. Robert Wagner for the H.E.S.S. Collaboration http://www.mpi-hd.mpg.de/hess/ @hesstelescopes 1

H.E.S.S. High Energy Stereoscopic System International Collaboration of 260 Scientists, 11 Countries Four 12-m Telescopes: CT1 4 (HE.S.S.-I: 2002 2012) Khomas Highlands, near Windhoek, Namibia + One 28-m Telescope: CT5 (H.E.S.S.-II: Sept. 2012)

Cherenkov Telescopes Blue Cherenkov light beamed forward Illuminates ~105 m2 on the ground Short flash of few nanoseconds Intensity O(10 photons/m2) @ 1 TeV R. WagnerR. AGN OKC-Stockholm Observations with H.E.S.S Telescope AGN workshop ESO 2016 Wagner, University: Cherenkov Array (UiO Seminar, Oslo, 160511)

The Imaging Air Cherenkov Technique ~ 1o Ch e re n ko vl igh tc on e 10 15 km 120 m huge detection area typical: approx. 1000 h/yr duty cycle 10% Simulation: Superimposed images from 8 cameras R. Wagner, OKC-Stockholm University: Cherenkov Telescope Array (UiO Seminar, Oslo, 160511)

Extragalactic source classes for H.E.S.S. 1. HBL, IBL, LBL (blazars) 2. FSRQs (blazars) 3. FR1s 4. Starburst galaxies Large portion of H.E.S.S. results have come from the first of these classes Will focus predominantly on first class

Extragalactic Source Classes TeV Blazars before 2004: detection of 6 TeV Blazars, extraordinary outbursts of Mkn 501 in 1999, variation on <1h timescales; initiated huge interest in AGN and EBL communities today: more than 30 TeV blazars; quite unexpectedly: TeV γ-rays from distant blazars; strong impact on both AGN/jet physics and on the diffuse Extragalactic Background Light (EBL) models most exciting results: variability on minute timescales extremely compact acceleration regions unusually hard gamma-ray spectra (internal) γγ absorption less than thought particularly relevant in FSRQs that feature strong internal photon fields

HBL: Archetypical H.E.S.S. Example TeV Blazar PKS 2155 304

Temporal Structure During Flare temporal structure down to minutes found ct var r Schwarzschild HESS Collaboration: Aharonian et al., Astrophys. Journal, 664 (2007)

Flaring SED and Evolution A bimodality is emerging in the flaring modes for HBL: either synchrotron dominated or Compton dominated ( orphan flare ) events Correlation between X-ray and gamma-ray a key probe to testing SSC acceleration models HESS Collaboration: A&A 502, 749-770 (2009)

Long-term monitoring of known TeV blazars 13-year time line since H.E.S.S.-I first light H.E.S.S VHE PKS 2155-304 Fermi-LAT HE Swift, RXTE XMM R-band

Temporal Structure for Ensemble of Flares Distribution of different flux states appears bimodal Quiescent state Flaring state HESS Collaboration: Astron. Astrophys. 520 (2010) A83

Long-term monitoring of known TeV blazars PKS 2155-304 Excess rms variability σ xs ~ flux Φ Multiplicative process Fractional variability amplitude F var increasing throughout SED components

Mkn 501 at multi-tev energies 2004-2014 No obvious correlation of the variability in different bands No correlation of optical and X-rays two or more zones/mechanisms needed (G. Cologna)

Rapid variability at multi-tev energies Major flaring state in June 2014 Run-by-run light curve

Rapid variability at multi-tev energies Major flaring state in June 2014 4-minute binned light curve τ min (> 2 TeV) < 10 min! Flux doubling time scale < 10 minutes 4 x TeV flux in 90 min X-ray data taken simultaneously, under analysis

Statistical Analysis of Time-Domain Behavior Probability Distribution Function: Lognormality Flux probability distribution function: PDF of F(E>2 TeV) lognormal distribution multiplicative processes (vs. additive processes/normal distribution) similar to PKS 2155-304 flaring in 2006 with very similar linear excess flux RMS correlation may be a natural outcome of a cascade-like hadronic scenario or an intrinsic jet-disk connection Abramowski+10 Chevalier+15 Power Spectral Density (PSD): single power law of index 1.7 similar to the flaring state of PKS 2155-304 that had an red-noise index of 2.0 bin size of 4 minutes: fluctuations at frequencies higher than 2 10 3 are suppressed.

H.E.S.S. Phase II: Lower Energies Challenge: Good overlap to cover high-energy part of SED Cross-calibration of Fermi-LAT and ground based instruments PKS 2155-304 H.E.S.S. I z = 0.116 Importance: Improvement in statistics during flaring events (particularly relevant for AGN/GRB) Search for unexpected spectral features at low energies EBL studies of AGN at high redshift

CT 5 Mono Observations of Blazars Significant overlap with Fermi-LAT Excellent agreement with H.E.S.S. Phase I z = 0.116 energy threshold 80 GeV

Multi-Instrument Campaigns 19 2001 2011 VHE HE Core X-RAY HST-1 OPTICAL RADIO Campaign on the radio galaxy M87 (misaligned blazar) Instruments: H.E.S.S., MAGIC, VERITAS, Fermi-LAT Chandra HST, Liverpool VLBA, Mojave, VLA, EVN Three large flares detected 2005 coincident with X-ray brightening of the knot HST-1, 100pc away 2008, 2010 coincident with X-ray brightening and VLBA radio brightening of the core Abramowski+12 (H.E.S.S, MAGIC, Veritas++) Joint venture ongoing. 2008 flare in some more detail...

Revealing the Origin of TeV Gamma-Rays VLBA Monitoring M87 jet during flare mas Resolution: 0.43x0.21 100 Schwarzschild radii Jet formation @ 30 60 RS VHE flare accompanied by radio flare from BH vicinity (~100 RS) Core flux peaks HST-1 very low all-time high VERITAS, MAGIC, HESS++ Science 325 (2009) 444 20

Wrap-Up Ground-based gamma-ray facilities allow observation of highest energy e/m radiation from AGNs Temporal studies showed bimodality in flux levels Variability detected down to timescales smaller than the light-crossing time of the event horizon Spectral evolution during flares shows X-ray and gamma-ray brightness correlations Access to low energies (<100 GeV) allow complete characterization of HE part of SED in MWL contexts MWL efforts, like M87 campaign, allow location of blazar engine. In the 2008 campaign: ~100 Rs from SMBH Bright TeV Gamma-Ray Future: H.E.S.S. Phase II & coming soon: Cherenkov Telescope Array http://www.mpi-hd.mpg.de/hess/ @hesstelescopes 21