Two exceptional γ-ray flares of PKS 2155-304 and their implications on blazar and fundamental physics Rolf Bühler MPIK Heidelberg KIPAC Tea Talk SLAC 9th December 2008
H.E.S.S. Telescopes Located in Namibia (1800 a.s.l.) Energy threshold of ~150 GeV Sensitivity of 5 σ detection of 5% crab in one hour Point spread function of ~0.1o Energy resolution of ~15%
Blazars at VHE From R. Wagner 25 detected at VHE (E>100 GeV) to date: All (but four) High Frequency Peaked BL Lacs Typical flux of ~2% crab Mkn 421, Mkn 501, PKS 2155-304 brighter (~10% crab)
Synchrotron Self Compton E2 dn/de ~ev Synchrotron ~GeV Inverse Compton E Preferred model to explain EM emission: X-rays and gamma-rays correlate Synchrotron dominated Radio to X-ray emission
PKS 2155-304 in 2005-2007 Runwise (28 min) flux Excess events Observed for 74.4 hours with 82222 excess events Typical flux of I0 = 4 10-11 cm-2 s-1 (compatible with 2002-2004 data)
Lightcurve in 2005-2007 monthly flux 2005 2006 2007 nightly flux June July August September Close to I0 in 2005-2006. Highly active in 2006 with extreme outburts in July
Lightcurve in 2005-2007 nightly flux June July runwise flux August September Chandra Flare Big Flare Exceptional flares on 28 and 30 July with flux values more the >100 I0 and fast flux variability
The Big Flare 1 min bins F. Aharonian et al. Arp. J. L. 664 (2007) 10 I0 Five sub-bursts with rise/fall times of ~200s Causality connects Doppler factor and size of emitting region: 60 120 R RS
The Chandra Flare 4 min bins Unprecedented MWL coverage: High correlation between X-rays and rays Optical flare starts at the same time and evolves slower
The Chandra Flare Max. sim. Min. sim. Max. VHE 2003 Large Compton dominance during the flare (Lγ / Lx ~5) Increasing variability with energy: 20 at γ-rays, 2 at X-rays, 1.15 at optical
The Chandra Flare 7-14 min bins VHE X-ray a Fγ Fx High flux and spectral correlation, cubic flux correlation during decreasing phase No one zone SSC [1] Likely several X-ray emitting regions [1] K. Katarzynski et al., A&A (2005)
Summary PKS 2155-304 underwent two exceptional VHE flares in July 2006: Peak flux values >100 more then typical Fast flux variability (~200 s) Multi-wavelength observations during the second flare reveals: A cubic decrease of the VHE with X-ray flux No one zone SSC Likely several X-ray emitting regions The inverse Compton component dominates the energy output No time delays seen between X-rays and γ-rays Energy spectrum hardens at VHE with increasing flux Inverse Compton SED peak shifts to higher energies during flare Publication in preparation..
Is the speed of light constant? Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body
Is the speed of light constant? Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body Are you sure?
Is Is cc energy energy dependent dependent?? Several Quantum Gravity models have predicted energy dependence of the speed of light. General parametrization:, with Leads to dispersion of poly-energetic signals: Linear: Quadratic:
Measurable Measurable effect effect?? High Energ y Low Energ y Time Requirements: Long distance, fast variability GRB's (X-ray) and AGN (VHE) Caveat: Cancellation due to source intrinsic effect (unlikely if no dispersion) Population studies
Current limits Time of flight measurements GRB's [1,2] : AGN's [3] : ( population studies: ) Vacuum Birefringence Radio Galaxies [4] : ( if sign helicity dependent ) Modified thresholds UHECR [5] : Crab Nebula [6] : [1]Boggs et al., Ap. J. L. (2004) [2]Ellis et al., Astr. Part. Phys (2006) ( if sign negative ) ( for electrons ) [3]Albert et al., Phys. Lett. B (2008) [5]Galaverni et al., PRL (2008) [4]Fan et al., MNRAS (2007) [6]Maccione et al., JCAP (2007)
Probing c(e) with the Big Flare Oversampled, 2-min bins 200-800 GeV >800 GeV ΔEmean = 1 TeV
Dispersion measurement RMS = 28 s τpeak= 20 s 21% < 73 s TeV-1 ( 95% confidence )
Systematic tests Recovery of injected dispersion in data Confirmed with bootstrap simulations & independent analysis
Limits Dispersion limit translates into: Linear: Quadratic: Most stringent linear limit from time of flight measurements Finally rule out possibility of time delay cancellation requires population studies For more details see Aharonian et al., Phys. Rev. Lett. 101 (2008) Reminder:
Summary & Conclusions Summary PKS 2155-304 underwent two exceptional VHE flares in July 2006: Peak flux values >100 more then typical Fast flux variability (~200 s) Multi-wavelength observations during the second flare reveals: A cubic decrease of the VHE with X-ray flux No one zone SSC Likely several X-ray emitting regions The inverse Compton component dominates the energy output The absence of dispersion during the first flare results in stringent limits on speed of light modifications:
Backup slides
E2 dn/de Correlations in SSC SSC electrons Fγ ne(eγ) nph ne(eγ) nx(ex) Fx ne (Ex) Thomson regime (electrons upscatter E2 dn/de E their own synchrotron): Fγ Fx photon s 2 Klein-Nishina regime in decaying phase (electrons upscatter synchrotron from lower energies) : Synch. IC E nph = const. Fγ Fx Generally: [1] K. Katarzynski et al., A&A (2005) F F γ x 3 [1]
Simplest solution X-ray emission from (at least) two regions:
Blazar population [2] [1] No redshift dependent trend (yet) [1] Biller et al., PRL (1999) [2] Albert et al., Phys. Lett. B (2008)
Blazar population Derived from 232 +- 54 s lag between 0.15-0.25 and 0.6-1.2 TeV [3] [1] [2] [1] Biller et al., PRL (1999) [2] Albert et al., Phys. Lett. B (2008) [3] Albert et al., Ap. J. (2007)
Simulation of of bin bin correlations correlations Simulation Throw random numbers on a fine grid Add and multiply with measurement error on coarse grids