Fermi bubbles their origin and possible connection to

Fermi bubbles, their origin and possible connection to cosmic rays near the Earth K. S. Cheng, D. Chernyshov, V. Dogiel, C. M. Ko

Outline • Morphology of Fermi bubbles • Discovery and modern day observations • Models of Fermi bubbles • Application to cosmic rays studies 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

50 o Dobler (2010) Su+ (2010) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Morphology of Fermi bubbles Sharp edges! < 5 o Su+ (2010) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Morphology of Fermi bubbles • Uniform brightness => edge-brightened emissivity • Almost uniform spectrum • 4 x 1037 erg/s 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, Ackermann+ (2014) July 6 -10, 2018

Important observational timestamps Bland-Hawthorn & Cohen (2003) X-Ray shell Finkbeiner (2004) WMAP “haze” Dobler (2010), Su+ (2010) Fermi bubbles Kataoka+ (2013) X-Ray shell Planck Collab. (2013) Planck “haze” Hooper & Slatyer (2013) Yang (2014) Ackermann+ (2014) Fermi bubbles 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 Pshirkov+ (2016) M 31 bubbles?

Discovery and counterparts Bland-Hawthorn & Cohen 2003, ROSAT – X-Rays 1. 5 ke. V. • X-ray shell near the position of FB • Limb brightening: no emission from the center • n=10 -2 cm-3, T = 2 ke. V 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Discovery and counterparts WMAP “Haze” 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 Finkbeiner (2004) Dobler (2012)

Discovery and counterparts Suzaku observation: Density gradient No T gradient Weak shock? Kataoka+ (2013, 2015) Yet >1000 km/s outflows: Bland-Hawthorn+ (2003), Miller+ (2013, 16), Fang+ (2014), Fox+ (2015), Bordoloi+ (2017), Sarkar+ (2017) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Discovery and counterparts Blue: gamma-rays Red and yellow: microwaves Hard spectrum: If synch, electrons ~ -2 Planck Collab. (2013) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Discovery and counterparts Powerfull activity 1 Myr ago? 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 Bland-Hawthorn+ (2013)

Models of Fermi bubbles Kompaneets (1960) Guo+ (2012) Leptonic/Hadronic jet Yang+ (2012, 2013) Barkov+ (2014) In-situ acceleration Hadronic wind Cheng+ (2011, 14, 15) Fujita+ (2013) Lacki (2014) Mersch+ (2011) Sasaki (2015) Sarkar+ (2015) Crocker+ (2011, 2015) Mou+ (2014, 2015) Zubovas+ (2012) Lifetime of electrons is short < 1 Myr => no “electron wind model” 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 Yang+ (2018)

Hadronic VS leptonic models relic IR GALPROP Strong, Moskalenko, Porter • Hadronic spectrum is harder at < 0. 1 Ge. V • Me. V telescope? Contamination! • Leptonic models REQUIRE a cut-off at ~ 300 Ge. V • Sub-Te. V detectors? Large scale structure! • HAWC, Icecube: Lunardini+ (2014), Fang+ (2017) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 vis

Hadronic VS leptonic models • Secondary electrons – soft spectrum. Additional primary electrons required (Ackermann+ 2014) • 80% of gamma-ray may be due protons (Cheng+ 2015) • Reverse shock? (Crocker+ 2015) • Spectral variations 26 th(Narayan & Slatyer, 2016) E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

In-situ acceleration “reaccelerated” power-law Fermi-LAT data Spectrum, according to GALPROP (Ackerman, 2012) 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

In-situ acceleration s ve a w cro i M a m m Ga ys a -r Galactic wind 26 th can solve the problem! (Cheng+, 2015) E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Re-acceleration of Galactic CRs E 3 f Too hard: not affected by FERMI-II acceleration Reaccelerated tail appears 3 x 1015 e. V For simplicity assume that all CRs are protons 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Fermi bubbles (reacceleration zone) Re-acceleration of Galactic CRs Reaccelerated CRs (> 3 Pe. V) Injection of CRs by SNRs (below 3 Pe. V) Galactic disk Galactic center The Earth Smooth connection at 3 Pe. V? 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018

Re-acceleration of Galactic CRs Injected by SNRs Reacc 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018 Cheng+ 2012

Conclusions • FB are one of the most interesting gamma-ray phenomena – largest gamma-ray object in the Galaxy • Nature of FB is still unknown • • Is it related to past or current activity? Is it hardonic or leptonic? Complex 3 D models are required Future observations are required • Are bubbles in M 31 real? • Giant object in the Galaxy can affect local CRs • Sings in the spectrum? 26 th E+CRS & 35 th RCRC, Barnaul/Belokurikha, July 6 -10, 2018