1 / 13

Multi-Zone Modeling of Spatially Non-uniform Cosmic Ray Sources

FAA60 Barcelona, 7 November 2012. Multi-Zone Modeling of Spatially Non-uniform Cosmic Ray Sources. Armen Atoyan Concordia University, Montreal. Multi-zone modeling of nonthermal radiation of Cas A in collaboration with F. Aharonian , R. Tuffs and H. Voelk .

rhian
Download Presentation

Multi-Zone Modeling of Spatially Non-uniform Cosmic Ray Sources

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. FAA60 Barcelona, 7 November 2012 Multi-Zone Modeling of Spatially Non-uniform Cosmic Ray Sources Armen Atoyan Concordia University, Montreal

  2. Multi-zone modeling of nonthermal radiation of Cas A • in collaboration with F. Aharonian, R. Tuffs and H. Voelk. • (Paper-I: A&A 354, p.915; Paper-II A&A 355, p.211; 2000) • Basic motivation of the study (done in 1998-1999): • VHE fluxes to expect from Cas A known as a prominent source of synchrotron radiation (by that time not detected yet in -rays). • Main results : • for Cas-A : • prediction of -rayfluxes that could be expected, and what it would mean for the origin (leptonicvshadronic) • General: • Multi-zone model for CR sources that allows • (a) modification of CR energy spectra on timescales t < tloss . • (b) relaxing constrains on IC -ray fluxes from synchrotron X-rays (e.g. for Tycho).

  3. Cas A radio map Chandra X-rays 0.5-6 keV (Stage et al. 2006) Chandra -4-6 keV Likely acceleration sites:bow shocks, bright radio ring & knots in the shell, (flux variability on ~yrs scale detected from knots in radio, and recently also in X-rays) (Uchiyama & Aharonian, 2008)

  4. Single-zone approach: cannot explain synchrotron (X-rays vs synchrotron self-absorption), problems with breamsstahlung Spectra for B=100 G, 350G & 700G (Paper I)

  5. Multi-zone modeling: simplest case - two zones. Basic assumptions: (a) the source consists of compact regions with high B field (zone 1), and much larger region with lower B field (zone 2). (b) particles are accelerated (mostly) in compact zone 1, but can escape into zone 2 (by diffusion and/or convection with plasma) Equations derived for the two zone-model: • Possibility for steepening of the energy spectra in zone 1 by diffusive propagation, D(E) ~ E; hard spectra in zone 2.

  6. Energy distributions of electrons in zone 1 and zone 2 Spectral energy density Total energy distributions Spectral modifications by diffusion: possible only if the energy densities in zone 1 and zone 2 are different (!)

  7. Radiation spectra Two-zone model: B1 = 0.4mG, B2 =1.5mGEcut= 35 TeV Secular decline of radio (assuming B-field in zone 1 declines on timescales ~ 130 yr)

  8. Model predictions for -rays ICompton(target - CMB and FIR)Bremsstrahlung(ngas~ 10-15 pcc) + pp (hadronic) (Wp ~ 2 1049 ergs) TeV was later on detected (HEGRA, MAGIC, VERITAS)The spectrum is much harderthan expected for leptonic origin. Protons accelerated to ~200 TeV explain the data. Data: HEGRA 2001, VERITAS 2010

  9. Tycho SNR: type Ia Radio (NRAO) X-rays (Chundra)

  10. Two-zone model for Tycho (Atoyan & Dermer, 2012) Difference: acceleration mostly in the rim, lower B field, fast escape into zone II (no spectral modifications) Model parameters:B1 = 100G, B2 =34 GEcut= 40 TeV d = 2.8 kpc

  11. Gamma-rays: Leptonic vs Hadronic Models Ee ~ 4.6 1048 ergs Ep ~ 3 1049 (no = 0.6 pcc) Wp ~ 2 1049 ergs Leptonic: bremsstrahlung(dashed) + Compton (solid);(contribution from zone 1 only ~10%) Conclusion: neither leptonic nor hadronic origins can be excluded at this time.Detection of a cutoff at low energies could help confirm pp.

  12. Conclusions Single-zone model can miss most of the electrons which may accumulate in radio-dim regions with low B field.Multi-zone modeling of sources is need for robust predictions.

More Related