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

2. 26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018
Outline
Morphology of Fermi bubbles
Discovery and modern day observations
Models of Fermi bubbles
Application to cosmic rays studies
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

3. 26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018
Dobler (2010)
Su+ (2010)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

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

5. Morphology of Fermi bubbles
Uniform brightness => edge-brightened emissivity
Almost uniform spectrum
4x1037 erg/s
Ackermann+ (2014)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

6. Important observational timestamps
Bland-Hawthorn & Cohen (2003)
X-Ray shell
Finkbeiner (2004)
WMAP “haze”
Dobler (2010), Su+ (2010)
Fermi bubbles
Ackermann+ (2014)
Hooper & Slatyer (2013)
Yang (2014)
Pshirkov+ (2016)
M31 bubbles?
Planck Collab. (2013)
Planck “haze”
Kataoka+ (2013)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

7. Discovery and counterparts
Bland-Hawthorn & Cohen 2003, ROSAT – X-Rays 1.5 keV.
X-ray shell near the position of FB
Limb brightening: no emission from the center
n=10-2 cm-3, T = 2 keV
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

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

9. 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)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

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

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

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

13. Hadronic VS leptonic models
relic IR
vis
GALPROP
Strong, Moskalenko, Porter
Hadronic spectrum is harder at < 0.1 GeV
MeV telescope? Contamination!
Leptonic models REQUIRE a cut-off at ~ 300 GeV
Sub-TeV detectors? Large scale structure!
HAWC, Icecube: Lunardini+ (2014), Fang+ (2017)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

14. 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 (Narayan & Slatyer, 2016)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

15. 26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018
In-situ acceleration
“reaccelerated”
power-law
Fermi-LAT
data
Spectrum, according to GALPROP (Ackerman, 2012)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

16. 26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018
In-situ acceleration
Microwaves
Gamma-rays
Galactic wind can solve the problem! (Cheng+, 2015)
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

17. Re-acceleration of Galactic CRs
E3f
3x1015 eV
Too hard: not affected by
FERMI-II acceleration
Reaccelerated tail
appears
For simplicity assume that all CRs are protons
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018

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

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

20. 26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018
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 3D models are required
Future observations are required
Are bubbles in M31 real?
Giant object in the Galaxy can affect local CRs
Sings in the spectrum?
26th E+CRS & 35th RCRC, Barnaul/Belokurikha, July 6-10, 2018