Explaining extreme TeV blazar observations with ultrahigh energy cosmic rays

Transcription

1 Explaining extreme TeV blazar observations with ultrahigh energy cosmic rays Foteini Oikonomou (Penn State) Oikonomou, Murase & KK, submitted to A&A Kumiko Kotera - Institut d Astrophysique de Paris KICP - 11/06/2014

2 IR/X-rays: synchrotron from e + e - TeV gamma-rays: IC on synchrotron? Unusually hard spectrum de-absorption correction + interesting time variability (day-year) Tavecchio 2013 Extreme Hard Spectrum TeV Blazars 2

3 TeV emission from blazars Cascade in IGM D. Giannios & T. Venters talk e.g., Aharonian et al. 94,, 06, Coppi & Aharonian 97, Tavecchio et al leptonic acceleration UHECR acceleration pair production Inverse Compton... γtev-gev no more interactions interactions with Extragalactic Background Light (EBL) UHECR + γ bg UHECR vs leptonic cascade E 2 F E [erg cm -2 s -1 ] e +-, γ UHE interactions with CMB/IR photons Essey & Kusenko 10, 13, Essey et al. 10, 11, Murase et al. 12, Takami et al. 13 γ-induced (low IR) γ-induced (best fit) CR-induced (low IR) CR-induced (best fit) attenuation deflections dilution of signal Cosmic Magnetic fields inhomogeneous B: flux dilution according to fraction of Universe where BIGM > 3x10-11 G ( ) E 2 dn γ Photon L cr E 1/2 spectrum γ attenuation γ f 1d (< B θ ) χ e de γ 8πd 2 H.E.S.S. I KUV (z = 0.61) Takami et al K.K., Allard & Lemoine 2010 CTA E γ,max 1 Oikonomou, PhD thesis,

4 cal energy flux dependence Eγ up to some maximal enaxis, at 1 Gpc and LE,19 = 1046 erg s 1 (black solid line), and at 100 Mpc ergy E γ,max 1 10 TeV beyond which the Universe is opaque 44 1 to gamma rays on the distance scale d (Ferrigno et al. 2004). and erg sencore (green blacket stars and green Ryu et al.l(2008) utilisent une dashed fois la m line). ethodethe de Ryu al. (1998), mais estiment E,19 = 10 crosses present theecorresponding flux up to adegiven angular Neglecting any redshift dependence for simplicity, the gammadirectement l intensit du champ magn integrated etique en chaque point l espace en utilisant la extension in the sky θ. ray energy flux per unit energy interval may then be approxivorticit e et la densit e d energie de turbulence calcul ee `a partir de la cin etique du gaz. Ils as: mated se d ebarrassent ainsi de la normalisation arbitraire pr esente dans les autres simulations. inhomogeneous B: flux dilution according to fraction of Universe Das et al. (2008) adoptent egalement cette m ethode dans leur etude.-11! "1/ Inve rse C om pton ca sca de swhere BIGM > 3x10 G dn E L γ γ cr Eγ2 f1d (< Bθ ) χe deγ 8πd2 Eγ,max Let us briefly discuss the gamma rayallard signal& expected K.K., Lemoine from 2010 Compton cascades of ultra-high energy photons and pairs in" GeV cm 2 s 1 f1d (< Bθ )χe jected in the intergalactic medium. The physics of these cas" 2!! "1/2 E L d γ E,19 cades has been discussed in detail in Wdowczyk et al. (1972);. (6) Mpc E 10 erg/s Protheroe (1986); Protheroe & Stanev (1993); Aharonian et al. γ,max large uncertainties (1994); Ferrigno et al. (2004). These cascades have been conin underdense regions sidered in the study of Armengaud et al. (2006) (for a source located in asigl cluster of galaxies) but dismissed in the study of where f1d (< Bθ ) denotes the one-dimensional filling factor, i.e. et al. (2004) Gabici & Aharonian (2005) because of the dilution of the emit- the fraction of the line of sight in which the magnetic field is ted flux through the large deflection of the pairs in the low energy smaller than the value Bθ such that the deflection of the low enrange of the cascade. Indeed, the effective inverse Compton cool- ergy cascade is θ. For reference, Bθ " G for θ = 1. ing length of electrons of energy Ee! 100 TeV can be written as In general, one finds in the literature the three-dimensional fillxeγ " 3.5 kpc (Ee /100 TeV) 1 and on this distance scale, the de- ing factor f3d, but f1d (< Bθ ) f3d (< Bθ ) up to abertone numerical et al. (2006) flection imparted by a magnetic field of coherence length λb # prefactor of order unity that depends on the geometry of the xeγ reads θe xeγ /rl,e (Ee /100 TeV) 2 (B/10 12 G). structures. Interestingly enough, the amount of magnetization of Then, assuming that thedelast paire duofchamp the magn cascade Figure 3.8 Coupes dans le mˆ eme plan l intensit etique (`acarries gauche) etan de laendensit e the baryo-voids of large scale structure is directly related to the origin TeV that photon produced through thee baryonique of large scale magnetic fields. Obviously, if galactic and clusfin e nique (`aergy droite)esimul es par20sigl et al.(so (2004). Les the champs magn etiques sont en Gauss et la densit Das et al. (2008) interaction with the CMB carries a typical energy! 1 TeV), one ter magnetic fields originate from a seed field produced in a en unit e de densit e baryonique moyenne. finds that a magnetic field larger than G isotropizes the homogeneous way with a present day strength B # G, low energy cascade, in agreement with the estimates of Gabici then the above gamma ray flux will be diluted to large angular & Aharonian (2005). scales, hence below detection threshold. However, if the seed field, This modified one into accountmagn theetique Une deuxi` emesituation cat egorie deis travaux a faitwhen l hypoth` ese takes d un ensemencement ho- extrapolated to present day values is much lower than thisde value, or if most of the magnetic enrichment of the indistribution fields, asa cause mog`eneinhomogeneous dans l Univers `a haut redshift (z of10extra-galactic 20). Dolag et al.magnetic (2002) ont montr e qu ` Dolag et al. (2005) forming we now discuss. Primary cosmic rays, upon traveling through tergalactic medium results from the pollution by star Donnert et al. (2008) la nature chaotique des processus d accr e tion lors de la formation des structures, toute trace de the voids of large scale structure may inject secondary pairs galaxies and radio-galaxies, then one should expect f1d (< Bθ ) la configuration initiale duinverse champ est e ac ee aucascades cours de l ein volution Ceci implique to be non negligible.normalization: For instance, Donnert et al. (2009) obtain which undergo Compton thesecosmologique. unmagnetized K.K. & Olinto G) 0.03observations in such models. Given tentative the sensitivity of If ces thesimulations field in ne such regions smaller than du thechamp above 3d (< 10 modeling of primordial origins magnetic quead-hoc lesregions. r e 12 sultats de d epend que de is l intensit e comobile magn eftique future gammaof raygalaxies experiments, thepollution inverse Compton 10 G, then simulations the cascade will transmit its energy in forward current and of from clusters B0.+Lacosmological normalisation peut donc ˆetre arbitraire, tant que l energie magn etique reste petite par cascades might then produce degree-size detectable halos for!tev photons. Of course, depending on the exact value of B + evolution of B field coupled to matter astrophysical sources 43 2 rapportwhere `a l energie condition image assure que le champ magn etique source luminosities " 2 10 (d/100 Mpc) erg/s. We note that the thermique. cascade Cette ends,derni` theere resulting will be spread by n influe magnetic fields of strength B < G might be finite angle. Since interesteddes in sharply peaked pas sursome la dynamique du plasma. Dewe plus,are l amplification champs magn etiquesimayant intergalactic lieu `a probed through the delay time of the high energy afterglow of ages,(zlet uslesconsider a d typical sizeduθmoment and ignore thoseles germes bas redshift. 3), r esultats ne ependentangular pas non plus pr ecis auquel regions in which the magnetic field is large enough to give a gamma-ray bursts (Plaga 1995; Ichiki et al. 2008) or the GeV 1 100structures GeV averaged over3.8). angular bins, for a filament seen along its grandes (voir figure Uncertainties on the Intergalactic Magnetic Fields (IMF) 4

5 UHECR pair echo/halo Cascade in IGM leptonic acceleration UHECR acceleration pair production Inverse Compton... γtev-gev no more interactions interactions with Extragalactic Background Light (EBL) UHECR + γ bg e +-, γ UHE interactions with CMB/IR photons magnetized filament e +- γgev no more interactions Synchrotron on B xsyn xsyn NB: Confined UHECRs should produce UHE neutrals (e.g, photons) at source (Murase 2009, Murase 2012, Dermer et al. 2012) Mean free path (Mpc) xic guaranteed if xsyn > xic Gabici & Aharonian 06 5

6 UHECR pair echo/halo Oikonomou, Murase & KK, submitted to A&A 1ES ( Coll. 2007, Coll. 2010, 2013) lepton seeded cascade in IGM Proton UHECRs B3 Mpc = 316 ng Injection spectral index = 2 EMAX = 1 ev LCR,j = erg s -1 UHECR seeded cascade in IGM UHECR seeded synchrotron RGB J (L CR,ISO = erg s 1 ) Attenuated ES (L CR,ISO = erg s 1 ) RGB J ES B 3 Mpc = 100 ng Injection spectral index = 2 EMAX = 0.5 ev B 3 Mpc = 100 ng Injection spectral index = 2 EMAX = 0.5 ev Attenuated MAGIC 6

7 Robustness to B, EBL, Emax Oikonomou, Murase & KK, submitted to A&A Robustness to particle Emax E max = 1 ev L CR, iso = erg s 1 E max = 0.5 ev, L CR, iso = erg s 1 compatible source = producer of UHECRs Inoue et al ES uncertainties on the EBL Y. Inoue s talk Robustness to particle EBL 1ES Kneiske 08 Inoue 13 Franceschini 08 Robustness to IGMF B filament >100 ng weak dependence on B in underdense regions B = 6nG B = 16nG B = 100nG B = 316nG UHECR/UHE photons ES not distinguishable by spectrum UHECR, B =100 ng UHECR, B = 316 ng UHE, B=100 ng UHE, B = 316 ng 7

8 Time Variability Oikonomou, Murase & KK, submitted to A&A be small. Noting d 2 Mpc, Murase (2012) obtained t 2 ed/2c yr (E syn /.5 GeV)(min[d, ]/Mpc), where d is the characteristic scale of the magnetised region. In deflection in B d = magnetised region ~ few Mpc, λγγ ~ 2 Mpc E 2 dn/de [ev s 1 cm 2 2 ] ] ES Attenuated Franceschini Attenuated Kneiske ES RGB J (L CR,ISO = erg s 1 ) E [ev] 1ES ES (L CR,ISO = erg s 1 ) Attenuated Kneiske Attenuated Franceschini MAGIC UHE photons Injection spectral index = 1.5 B 3 Mpc = 316 ng Eγ,MAX = 9.5 ev Lγ = erg s -1 A&A proofs: manuscript no. OMK14 Attenuated Franceschini Attenuated Attenuated Kneiske Attenuated MAGIC UHE protons ~ year? Aliu et al 2014 Fig. 8. Top panel: Same as Fig. 7 but zooming in at the arriving phofavour neutral beams as the population responsible for this emission, as discussed in the next section Time variability BThe 3 Mpc main = 100 observable ng di erences between UHECR or UHE photon seeding spectral in theindex magnetised = 2 region should be related to the Injection None EMAX di erent = 10deflection 20.5 ev properties and as a result time delays experienced by the UHE photons and their products in the magnetised region. In the UHE photon channel any deflections will come from the secondary electrons and should be approximately: e D syn /r Lar (E e /9 ev) 2 (B/10 ng) 1. (3) Typically this is a very small angle, smaller than typical values of jet hence the emission from this channel is expected to be UHE beamed. photons If UHE photons can escape into intergalactic space, the mean free path to pair production is 2 Mpc, i.e., smaller Injection than the p spectral energy index loss length = 1.5 of UHECRs, so the pair halo/echo Bsignal 3 Mpc = from 100 UHE ng neutrals is dominant when the photopion production Eγ,MAX = in10the 19.5 source ev is e cient (Murase 2012). As a result of the small deflections, Lγ = 8x10 45 erg s -1 the time spread of the signal should also be small. Noting d 2 Mpc, Murase (2012) obtained t 2 ed/2c yr (E syn /.5 GeV)(min[d, ]/Mpc), where d is the characteristic scale of the magnetised region. In comparison the deflections su ered by UHECRpprotons in the If confirmed: - disfavours UHECR synchrotron cascade - rules out UHECR IC cascade ~ day Acciari et al 2010 UHE neutrals could account for ~ day variability if emission region < pc size detailed modeling needed 8

9 Extreme Hard Spectrum blazars and UHECRs Oikonomou, Murase & KK, submitted to A&A leptonic and UHECR Inverse Compton channels strongly subject to uncertainties on K.K., Allard & Lemoine 2010 Extragalactic Background Light Intergalactic Magnetic fields If blazar in mildly magnetized region (e.g. filament) and injects UHE protons robust synchrotron signal fits spectral shape Lcr,19 = erg s -1 d = 1 Gpc /CTA at 10 GeV: ~ GeV cm -2 s -1 (θsource /1 ) If UHE protons --> UHE photons inside source fits spectral shape time variability can be explained D = 100 Mpc at level of total CR flux Signatures: time variability extended halos around source CTA HAWC D = 1 Gpc 10% of total CR flux * + flux integrated up to angular extension θ Kumiko Kotera - Institut d Astrophysique de Paris KICP - 11/06/2014 9