Gamma-ray Observations of Galaxy Clusters! a! Fabio Zandanel! (GRAPPA Institute University of Amsterdam)! f.zandanel@uva.nl! SnowCluster 2015 The Physics Of Galaxy Clusters! Snowbird (Utah, US) March 15-20, 2015!
NON-THERMAL EMISSION:! SOME KEY QUESTIONS CIZA J2242.8+5301! 610 MHz van Weeren et al. (2010)! COMA! 1.4 GHz Deiss et al. (1997)! PERSEUS! 1.4 GHz Pedlar et al. (1990)! Origin of radio-emitting electrons?! Contribution of CR protons?! Impact on cluster environment?! 2!
HADRONIC PROTON-PROTON INTERACTIONS! Radio Synchrotron &! X-ray Inverse Compton! Neutrinos! Gamma-rays! 3!
WHERE DO WE STAND?! space-based observations (100 MeV 100 GeV)! EGRET 2003 (Reimer et al.); Fermi-LAT Coll. (2010, 2014);! Han et al. (2012); Ando & Nagai (2012); Huber et al. (2013);! FZ & Ando (2014); Prokhorov & Churazov (2014);! Griffin et al. (2014; see poster)! ground-based observations (> 100 GeV)! WHIPPLE 2006! (Perkins et al.);! VERITAS 2008 (Perkins), 2009 (Galante et al.); VERITAS Coll. (2009, 2012);! HESS Coll. (2009; 2012); CANGAROO 2009! (Kiuchi et al.);! MAGIC Coll. (2010, 2012);! Brunetti & Jones (2014)! 4!
MAGIC OBSERVATIONS: PERSEUS! cool-core = high icm target density for p-p interactions! PERSEUS! 1.4 GHz Pedlar et al. (1990)! Perseus hosts brightest radio mini-halo! 19/03/2015! Fabio Zandanel (GRAPPA)! Pinzke & Pfrommer (2010)! 5!
MAGIC OBSERVATIONS: PERSEUS! 85 hours of observations!! NGC1275! IC310! MAGIC Coll. (2012) FZ as corr. author! 19/03/2015! Fabio Zandanel (GRAPPA)! 6!
MAGIC OBSERVATIONS: PERSEUS! 85 hours of observations!! IC310! MAGIC Coll. (2012) FZ as corr. author! 19/03/2015! Fabio Zandanel (GRAPPA)! 7!
MAGIC OBSERVATIONS: PERSEUS! maximum cr proton acceleration efficiency! at shocks is < 40% (Pinzke & Pfrommer 2010)! OR cr propagation out of the cluster core! minimum gamma-ray! flux in the hadronic scenario! MAGIC Coll. (2012) FZ as corr. author! 19/03/2015! Fabio Zandanel (GRAPPA)! 8!
FERMI-LAT OBSERVATIONS! 60-month gamma-ray Sky > 1 GeV! Image credit: NASA/DOE/Fermi-LAT Collaboration! 9!
FERMI-LAT OBSERVATIONS! 4-year stacked analysis of 50 hiflugcs clusters! acceleration efficiency is < 21% + X CR < 1.4%! Fermi Coll. (2014)! see also Huber et al. (2013), Prokhorov & Churazov (2014),! and Griffin et al. (2014; see poster)! 10!
FERMI-LAT & RADIO RELICS! non-detections challenge the standard! picture of diffusive shock acceleration! Kang & Ryu (2013)! Vazza & Brüggen (2014)! 11!
THE COMA CLUSTER! Brown & Rudnick (2011)! Pinzke & Pfrommer (2010)! Kushnir & Waxman (2009)! Keshet et al. (2012 2014)! based on Keshet et al. (2003)! 12!
THE COMA CLUSTER! analysis of 5.25-year Fermi-LAT data! Events 100 MeV 100 GeV! 14 14 deg pixel = 0.1 deg! Residuals [%]! Preliminary FZ & Ando (2014)! 13!
THE COMA CLUSTER! analysis of 5.25-year Fermi-LAT data! Events 100 MeV 100 GeV! 14 14 deg pixel = 0.1 deg! Residuals [%]! CR-to-thermal pressure X CR < 0.6% - 2.7%! CR proton acc. efficiency < 15%! CR electron acc. efficiency < 1%! Upper limit at 0.1 F of Keshet et al.! (as also shown by Prokhorov & Churazov 2014)! FZ & Ando (2014)! 14!
THE COMA CLUSTER! Bonafede et al. (2010)! Brunetti et al. (2012)! FZ & Ando (2014)! Coma giant radio halo cannot be (uniquely)! of hadronic origin! CR proton contribution to radio emission < 60%! 15!
A NOTE ON X CR = P CR /P TH! P CR ~ P TH! flatish CR distributions! could build up significant X CR! in the outskirts but! not clear! FZ, Pfrommer & Prada (2014)! (see also Wiener, Oh & Guo 2013)! 16!
WHAT ABOUT NEUTRINOS?! Murase, Ahlers & Lacki (2013)! 17!
WHAT ABOUT NEUTRINOS?! model all galaxy clusters through their mass function! calculate radio and gamma-ray emissions! respecting both observed radio counts and gamma-ray upper limits! test different spectral indices (-1.5 to -2.4) and magnetic fields! FZ, Tamborra, Gabici & Ando (2015)! 18!
WHAT ABOUT NEUTRINOS?! FZ, Tamborra, Gabici & Ando (2015)! 19!
SUMMARY! FACTS! > 50 clusters host diffuse radio emission! no high-energy emission detected so far! CONSTRAINTS! CR-to-thermal X CR < 1% (α p = 2.1) to < 10% (α p = 2.5)! maximum CR proton acc. efficiency < 15%! CR proton / electron at odds with DSA!! giant radio halos cannot be generated only by CR protons (at least coma)! CR protons in clusters contribute! < 1 10% to EGRB fluxes! UNCERTAINITIES! CR acc. efficiency, transport properties,! spectral index + magnetic field! 20!
FUTURE PROSPECTS! we do expect CR protons to accumulate in clusters and we do expect a corresponding high-energy emission! IceCube can test the most optimistic scenarios,! but not compete with other constraints! Fermi-10 years + Cherenkov Telescope Array! see e.g. Acharya et al. (2014)! CTA artistic impression! THANKS!! 21!