Galactic synchrotron radiation in the context of cosmic-ray propagation models and gamma rays Elena Orlando* (Stanford University/KIPAC) and Andrew Strong (MPE, Garching) Abstract Galactic synchrotron radiation is produced by cosmic-ray electrons and positrons propagating in interstellar magnetic fields. Our present knowledge of magnetic fields, cosmic- ray electron distributions and propagation is not sufficient to distinguish various possibilities in the modeling. As a consequence the synchrotron emission complicates the component separation with Planck. Hence, any advancement in modeling, both in temperature and polarization, is important for separating the different emission components. We present our recent results in modeling Galactic synchrotron emission in the context of cosmic-ray propagation models and we show the potentiality of the relation with gamma rays seen by Fermi-LAT. Results are based on Orlando & Strong (2013) MNRAS 436,2127. The best model presented here is used for the official component separation by the Planck Collaboration. Cosmic Rays and Synchrotron Ingredients B-fields and associated observables Our knowledge of the Galactic B-field is still uncertain. Large scale (regular) Cosmic-Ray (CR) electrons (electrons+positrons) spiral in the Galactic magnetic field Radio and microwave data and small scale <100pc (random) B-field are present in our Galaxy. A large (B-field) and generate diffuse synchrotron radiation scale ordering of the B-field, which originates by stretching or compression WMAP: Radio Surveys: of the random field is also supposed to exist (anisotropic random). Disc and - Collection of ground based - Polarization maps (U, Q) halo components are observed. - Temperature maps radio surveys - 408 MHz (Haslam et al.) The following observables are used to constrain intensity and orientation of CRs! B-field the B-field components. e- e+ CR electron measurements ANISOTROPIC ISOTROPIC CR diffusion, ! Electrons REGULAR RANDOM ? RANDOM Black lines:modulation potential energy losses, 0MV (LIS), 200MV reacceleration, secondaries ! Local Interstellar spectrum (LIS) Fermi e-e+ Pamela HESS AMS01 Rotation Measures CAPRICE HEAT Polarized Synchrotron Modeling: CR electron spectral index <-> Synchrotron spectral Index - CR propagation code (GALPROP) Unpolarized Synchrotron B-field intensity and CR electron density <-> Synchrotron Intensity - CR source distribution CR electrons of energy 0.5-20 GeV <-> Synchrotron of frequencies 20 MHz-100 GHz - B-fields ORDERED Latest Improvements in modeling radio Examples of implemented B-field models Examples of modeled emissivity Examples of synchrotron emissivity for a spiral regular B-field (left) and for a spiral 3D B-field configuration: random and ordered B-field for disc and halo regular B-field plus a random B-field (right). The shape of the emissivity reflects the Spiral disc field Random field Toroidal halo field components shapes of the spiral arms of the B-field, while the diffuse component is due to the random B-field. The black circle where the emissivity is zero on the right-center of the polarization (Stokes U, Q) μG figures is where the regular B-field is parallel to the observer’s line of sight from the 8.5 observer point of view in the solar system. The Sun is at the center of that circle. free-free emission model 7.5 absorption for the lowest frequencies and the Galactic plane 6.5 orientation 8.5 kpc orientation ALL THIS INCLUDED IN GALPROP ! http://galprop.stanford.edu intensity Distance intensity Distance intensity from the from the plane (kpc) plane (kpc) First time models of total and polarized synchrotron emission in the context of CR propagation ! More info in: Orlando & Strong (2013) MNRAS 436,2127 Galactocentric radius Galactocentric radius Tracing ordered B-field: some examples Tracing total B-field: some examples Results Based on Orlando & Strong 2013 MNRAS 436,2127 and Strong, Orlando and Jaffe 2011 A&A, 534, 54 CR electron spectrum: Stokes I at 408 MHz - Break in local interstellar electron spectrum from <2 to ~3 @ few GeV WMAP P @ (Haslam et al.) 23 GHz - Injection spectrum < few GeV is harder than 1.6 B-fields - Tested the sensitivity to different formulations of the regular B-field based on the literature. Their best-fit intensity was obtained. - Confirmation of an anisotropic random component of the B-field, as assumed in previous works - Local random B-field of 4.7 - 5.3 µG Z=10 kpc Z=4 kpc Lorimer 2006 CR propagation and distribution: Sun et al. 2008, 2010 Pshirkov et al. 2011 Pshirkov et al. 2011 - Standard reacceleration models are more challenging in reproducing (ASS B-field) (BSS B-field) Case & Bhattacharya synchrotron observations than pure diffusion models (due to more Different propagation 1998 secondaries) halo size! Different CR - A flat CR source distribution in the outer Galactic plan resembles the (CR source distribution source distribution! data best Different ordered B-fields! from Strong et al. 2010) (z=4 kpc) - Preference of a halo height larger than 4 kpc in order to fit the high- B-fields are the same for all models latitude synchrotron data The multi-wavelength context Example of existing models Example of existing models with no constraints from Electrons with constraints from Electrons Black lines:modulation potential Black lines:modulation potential 0MV (LIS), 200MV Gamma rays (Fermi-LAT 5 years >1 GeV) 0MV (LIS), 200MV, 400MV,600MV Fermi e-e+ Fermi e-e+ Pamela synchrotron Pamela synchrotron HESS HESS Local Interstellar spectrum (LIS) Local Interstellar spectrum (LIS) AMS01 AMS01 Synchrotron constrains the spectrum of low-energy electrons. Their CAPRICE Low-energy electrons are affected by solar modulation, making the CAPRICE HEAT knowledge of the local interstellar spectrum (LIS) and prediction of HEAT flux should be lower than assumed above, but still in agreement gamma rays more uncertain. Moreover electron spectrum may vary with CR measurements. This affects the estimated leptonic in the Galaxy and both IC and synchrotron are tracing the same components of gamma rays. Moreover, the B-field is not very well spectrum averaged over the line of sight. Synchrotron is more known. Hence, our multi-wavelength approach helps in constraining the B-field model as well. GAMMA RAYS ≤ 80 MeV of diffuse GAMMA RAYS ~ GeV of diffuse sensitive to those electrons than gamma rays. interstellar emission is mostly of leptonic interstellar emission is mostly of origin. Electron and positron CR interact hadronic origin. Protons and Gamma rays Gamma rays with gas via bremsstrahlung and with the heavier nuclei CR interact with Synchrotron Synchrotron interstellar radiation field via inverse gas/dust producing gamma rays Compton (IC) producing gamma rays. via pion decay. Radio Radio surveys synchrotron by leptons (408 MHz) CO with Planck bremsstrahlung Inverse surveys WMAP bremsstrahlung Inverse WMAP Compton Compton π° decay 10°<|b|<45° π° decay All-sky excluded |l|<45° 10°<|b|<45° Excluded |l|<40° All-sky excluded |l|<45° Excluded |l|<40° Haslam map Credit: ESA/Planck See also Orlando et al. Fermi Symposium 2014, for the parallel work on radio and gamma-ray with Fermi-LAT The magnetic field is assumed as in Orlando & Strong 2013. Interstellar radiation field and gas The magnetic field is assumed as in Orlando & Strong 2013. Interstellar radiation field and gas (https://confluence.slac.stanford.edu/download/attachments/181539200/Orlando_Poster_Symposium2014a.pdf?api=v2 ). distribution are assumed as in Ackermann et al. 2012 distribution are assumed as in Ackermann et al. 2012 REFERENCES: Case G.L., Bhattacharya, D., ApJ, 504, 761 Pshircov, M.S. et al. 2011 ApJ, 738, 192 Lorimer, D. R., Faulkner, A. J., Lyne, A. G., et al. 2006,MNRAS, 372, 777 Strong, A.W., Orlando, E., Jaffe, T., 2011 A&A, 534, 54 Orlando, E., Strong, A. 2013 MNRAS, 436, 2127 Sun, X.H. et al., 2008 A&A, 477, 573 *E. Orlando acknowledges support via NASA Grant No. NNX13AH72G Strong, A. W. et al. 2010, ApJL, 722, L58 [email protected] .