Comment on two topics related to fundamental “exotic” physics with AGN Alessandro De Angelis Brera, March 2012 Testing fundamental spacetime symmetries AGN spectra and photon/ALP oscillation

Rapid variability and LIV MAGIC, Mkn 501 Doubling time ~ 2 min astro-ph/0702008 arXiv:0708.2889 HESS PKS 2155 z = 0.116 July 2006 Peak flux ~15 x Crab ~50 x average Doubling times 1-3 min RBH/c ~ 1...2.104 s H.E.S.S. arXiV:0706.0797

GRBs Another probe Interesting for astrophysical reasons, for propagation physics, for rapid variability Fermi is changing our view, due to its unprecedented range, self-pointing, dedicated instrument MAGIC is the best IACT, due to its fast movement & low threshold De Angelis, Galanti, Roncadelli 2011 with Franceschini EBL modeling MAGIC H.E.S.S. redshift z g ray energy (TeV) t = 1 (GRH) > 1 region of opacity No VHE g emission from GRB positively detected yet... (all observed GRB very short or at very high z) But how many can we expect/year? 0.02 < N < 0.5

Mkn501 flare: violation of the Lorentz Invariance Mkn501 flare: violation of the Lorentz Invariance? Light dispersion expected in some QG models, but interesting “per-se” V = c [1 +- x (E/Es1) +– x2 (E/Es2)2 +- …] 1st order 0.15-0.25 TeV 0.25-0.6 TeV 0.6-1.2 TeV 1.2-10 TeV > 1 GeV < 5 MeV 4 min lag

LIV in Fermi vs. MAGIC+HESS GRB080916C at z~4.2 : 13.2 GeV photon detected by Fermi 16.5 s after GBM trigger. At 1st order The MAGIC result for Mkn501 at z= 0.034 is Dt = (0.030 +- 0.012) s/GeV; for HESS at z~0.116, according to Ellis et al., Feb 09, Dt = (0.030 +- 0.027) s/GeV Dt ~ (0.43 ± 0.19) K(z) s/GeV Extrapolating, you get from Fermi (26 +- 11) s (J. Ellis et al., Feb 2009) SURPRISINGLY CONSISTENT: DIFFERENT ENERGY RANGE DIFFERENT DISTANCE ~z

Fermi: GRB 090510 GRB 090902 z = 0.903 ± 0.003 prompt spectrum detected, significant deviation from Band function at high E High energy photon detected: 31 GeV at To + 0.83 s [expected from Ellis & al. (12 ± 5) s] tight constraint on Lorentz Invariance Violation: Es1 = MQG > several MPlanck z = 1.8 ± 0.4 one of the brightest GRBs observed by LAT after prompt phase, power-low emission persists in the LAT data as late as 1 ks post trigger: highest E photon so far detected: 33.4 GeV, 82 s after GBM trigger [expected from Ellis & al. (26 ± 13) s] much weaker constraints on LIV Es => Fermi rules, but 1st order violations appear unlikely

2nd order? Cherenkov rules! Es2 > 6 10-10 GeV (10-9 MP) (HESS, MAGIC) Difficult to improve by 9 orders of magnitude 

Interpretation of the results on rapid variability The most likely interpretation is that delays are due to physics at the source However We are sensitive to linear effects at the Planck mass scale 2nd order effects: the realm of Cherenkov detectors Anisotropy? More observations of flares might clarify the situation (or complicate it)

Propagation of g-rays e+ e- gVHEgbck  e+e- Mean free path x gVHEgbck  e+e- dominant process for absorption: maximal for: Heitler 1960 s(b) ~ ≈ For gamma rays, relevant background component is optical/infrared (EBL) different models for EBL: minimum density given by cosmology/star formation (Galanti et al. 2012) Mean free path Measurement of spectral features permits to constrain EBL models (Dominguez et al. 2011)

Are our AGN observations consistent with theory? Selection bias? New physics ? Measured spectra affected by attenuation in the EBL: observed spectral index ~ E-2 redshift (DA, Galanti, Roncadelli; PRD 2011) The most distant: MAGIC 3C 279 (z=0.54) Alessandro De Angelis

Attempts to quantify the problem overall Analysis of AGN For each data point, a corresponding lower limit on the optical depth t is calculated using the minimum EBL model of Kneiske & Dole 2010 Nonparametric test of consistency Disagreement with data: overall significance of 4.2 s => Understand experimentally the outliers (Horns , Meyer 2011)

If there is a problem Explanations from the standard ones very hard emission mechanisms with intrinsic slope < 1.5 (Stecker 2008) Very low EBL, plus observational bias to almost standard gamma-ray fluxes enhanced by relatively nearby production by interactions of primary cosmic rays or n emitted from the same source to possible evidence for new physics Oscillation to a light “axion”? (DA, Roncadelli & MAnsutti [DARMA], PLB2008, PRD2007, PRD2011) Axion emission (Hooper et al., PRD2008) A combination of the above (Sanchez Conde et al.)

Recent confirmation

PKS1222: an alternative detailed discussion of the problem Tavecchio, Roncadelli, Galanti, Bonnoli 2012: the g → a conversion occurs before most of the photons reach the BLR. Accordingly, ALPs traverse this region unimpeded and Outside, the re-conversion a → g takes place either in the same magnetic field of the source or in that of the host galaxy Resulting parameters of the ALP needed to fit the data consistent with DARMA

Summarizing: if the expected photon yield at VHE is different from what we think, what might be wrong? Emission models are more complicated than we think VHE photons are generated on the way Something is wrong in the gg -> e+e- rate calculation gg -> e+e- cross section Boost (relativity) QED (2nd order effects due to vacuum energy could not decrease the absorpyion probability) Vacuum energy (new sterile particles coupling to the photons) “Se non e’ vero e’ ben pensato”: consistent values for m, (1/M) in a range not experimentally excluded But explanations are expensive: an ALP

We are (maybe) making two extraordinary claims A possible relation between arrival time and energy Signal from sources far away hardly compatible with EBL But warning: how hardly? We should keep in mind that Extraordinary claims require extraordinary evidence New Scientist, SciAm blog/news, …, and then? Claims must be followed up If we see this in such sources, what else do we expect? Fundamental implications of unexpected findings? Are we seeing a part of the same big picture? Warning: this is a very connected world… If you touch dispersion relations, the Universe might become transparent to photons beyond the GZK (Galaverni & Sigl 2008)

ce = cg(1+d), 0 < abs(d) << 1 Coleman & Glashow; Stecker and Glashow If d<0 => ce < cg => decay g -> e+e- kinematically allowed for gamma with energies above Emax = me sqrt(2/abs(d)) - Eg > 100 TeV => abs(d) < 5 x 10-17 2. If d>0 => ce > cg => electrons become superluminal for energies larger than Emax/sqrt(2) => Vacuum Cherenkov Radiation. - Ee > 2 TeV from cosmic electron radiation => abs(d) < 2 x 10-14 Modification of g g -> e+e- threshold. Using Mkn 501 and Mkn 421 spectra observations up to Eg > 20 TeV => abs(d) < 1.3 x 10-15 From MAGIC Mkn501 (taken as a LIV signal): |d| ~ 2 10-15

A no-loss situation: if propagation is standard, cosmology with AGN GRH depends on the –ray path and there the Hubble constant and the cosmological densities enter => if EBL density and intrinsic spectra are known, the GRH might be used as a distance estimator GRH behaves differently than other observables already used for cosmology measurements. Blanch & Martinez 2004 Simulated measurements Mkn 421 Mkn 501 1ES1959+650 Mkn 180 1ES 2344+514 PKS2005-489 1ES1218+304 1ES1101-232 H2356-309 PKS 2155-304 H1426+428 EBL constraints are paving the way for the use of AGN to fit WM and WL …

Determination of H0, M , L Using the foreseen precision on the GRH (distance at which t(E,z)=1) measurements of 20 extrapolated AGN at z>0.2, cosmological parameters can be fitted. => The Dc2=2.3 2-parameter contour might improve by a factor 2 the 2004’ Supernovae combined result !

Conclusions When we were young we have been happy: we found possible hints of new physics in 2 of the most promising AGN channels However, it looks to me that we are a bit stuck now What should we do if we don’t want to keep repeating the same talks and we believe on what we are doing? Gamma propagation and transparency of the Universe: Detect well some 20-30 AGN at z > 0.2 (one of the goals to consider for focusing our scientific objectives) Know better the relevant astrophysics: make the best possible computation of the VHE SED at the source, and of EBL (and of magnetic fields?) (a no-loss situation in which we improve in the worst case our knowledge of cosmological parameters) Gamma propagation and possible LIV Detect more rapid flares (how?), possibly far away from us Have reliable models on the energy profile of the emission at different times (a no-loss in which we improve in the worst case the limits on 2nd order LIV)