1. 1 Origin of Variability of X-ray and γ-ray Spectra on Daily Scale Radovan Milinčić Astrophysics 711 May 3 rd 2005

2. 2 Outline The case of AGN Markarian 421 and Markarian 501, Seyfert galaxy NGC 3227 and star HD 150136 The explanation for the origin of spectrum variation Alternative way of understanding the variations Consequences on exploration of characteristics of dark matter and violation of Lorentz invariance

3. 3 AGN: Markarian 421 Multi wavelength light curve recorded in 1998 Data from ASCA, EUVE and RXTE experiments RMS variability is increasing with the energy of the observed spectra. TeV γ-ray intraday variations were correlated with X-ray spectrum variations. Hardness ratio between bands is < 1. Time variability for all bands is similar and it is ~0.5 days. Also, very similar to the intraday variability in the optical light curves of flat spectrum radio quasars (FSPQs). ApJ, 542, Takahashi et al.

4. 4 Galaxy NGC 3227 Light curves and hardness ratios of 1996 November 20-22 observation. Light curves in 0.1-1.5 KeV, 1.5-3.5 KeV, 3.5-10.0 KeV and hardness ratios between them. Hardness ratio is < 1, in both cases. Time variation is the same in all bands ~0.5 days. Time (s)

5. 5 Star: HD 150136 Light curves of HD 150135 and HD 150136 in 0.5-5.0 KeV, observed in June 2002 Time variation have the same features as in 2 previous cases. Time variation ~0.5 days. astro-ph/0504559, S.L. Skinner et al.

6. 6 One Explanation for the Origin of Spectrum Variation Spectrum variation comes from light crossing through emitting region which implies that particle acceleration and cooling time scale are similar. Electron distribution in the same physical region is responsible for the emission in γ-ray and X-ray energy bands, and its rapid change in the regime where acceleration and cooling are balanced. Multiflares passing through cloud or “blob” of plasma, pass through the region where shock fronts are formed and electrons are accelerated (opening angle of the jet is 1/Γ j ).

7. 7 Other Explanation Recorded flux from Markarian 421 and Markarian 501 shows heavy absorption of TeV radiation. This indicates secondary origin of TeV γ-ray variation that doesn’t originate in the source, but is a consequence of interactions of primary γ-rays with diffuse extragalactic photons. They are formed during the development of high energy electron-photon cascades in the intergalactic medium. Absorption of X-rays from Markarian 421in intergalactic clouds of diffuse, hot gas.

8. 8 Alternative Way of Understanding the Variations All three very different stellar objects show same features in both time variability and counting rate. Shape of the variation from one minimum to another is changing itself. Relative hardness ratio is < 1 in all cases which indicates that the source of the variation may be absorption and reemission of the emitted flux.

9. 9 Is it Possible that our Galaxy Environment can Create such Spectrum Variations? Conditions that need to be satisfied in this case: a) Dynamics and dimensions of the variation in medium must be on the time scale of < 1 day. b) Compositional variation of the medium must explain changes in the observed light curve shape.

10. 10 Breathing, Growing Galaxy Dark matter that surrounds our galaxy is demanded to explain rotational features. Sky “above” galaxy is cloudy: High Velocity Clouds (HVC) and Intermediate Velocity Clouds. There is also a fountain (gas pushed out by supernovae).

11. 11 Cloudy Sky Map of neutral hydrogen galactic gas. High Velocity Clouds have speeds up to 400 km/s in the direction of galaxy. Distance from the galactic plane 15,000-30,000 light years. Chemical composition differs among clouds. Cloud complexes A and C provide the first direct evidence of infall of fresh gas. –Complex C brings ~0.1 solar mass of new material per year. –Complex A brings ~0.05 solar mass of new material per year.

12. 12 Origin of HVC Proposal 1: Source of gas is remnant halo Proposal 2: Deep intergalactic space Proposal 3: Small dwarf galaxy that Milky Way swallowed. Proposal 4: Dark matter hypothesis Chemical composition of HVC is not in agreement with the first three proposals. The forth proposal is excluded since it requires intergalactic distance to HVC.

13. 13 Galactic Fountain Provides energetically and dynamically conserved system with closed cycle of matter circulation.

14. 14 “Eating” Habits and Behavior of Black Holes Binary system with black hole of ~few star masses. (few years) Black hole in the center of spiral galaxy. (few days) GRB (few seconds)

15. 15 Flare from Galactic Center Cygnus A Black hole in our own galactic center “eats” ~1 star per year. It ejects an afterflow of that “meal” in halo above the level of the HVC (~40 kpc). Ejected material then gets gravitationally stirred, creating mini clouds. Besides highly ionized plasma the composition of the afterflow reflects somewhat distorted composition of the “eaten” star. Superheated jets of plasma (v~0.9c) in opposite directions from central black hole. Strong X-ray burst disappears after a few days.

16. 16 Impact of Dark Matter Halo on Radial Dynamics of Afterflow Simulation of temporal evolution of the gas volume density distribution. In general, the escape speed is a function of both the galactocentric distance and the height above the midplane. Normalizing the velocity field helps to determine the gas that can potentially escape the galaxy. A&A 413, 939-948 (2004), E. I. Vorobyov et al

17. 17 Observation of Extra-planar Gas in the Spiral Galaxy NGC 4559 Top left: Optical image Top right: Radio continuum Bottom left: Density contours of H1 image of extra-planar gas above galaxy. Bottom right: Velocity field of extra-planar H1 layers. Astro-ph/0504534, Barbieri et al April 25 th 2005

18. 18 Velocity and Dimensions of Mini Clouds above Milky Way Radial density profile of H1 from measurements for the galaxy NGC 4559 indicate density profile of mini clouds. Radial velocity distribution for H1 gas above galaxy plane implies mini clouds velocity. Dimensions of mini clouds from observed velocities are between 50-125 solar diameters.

19. 19 Mini Clouds Composition Figures show chemical composition of 2 stars. Difference in the observed spectra is very significant. Mini cloud composition is a function of composition of ejected material from the black hole. Change of shape of variation between neighboring variations in different spectral bands of light lines can be explained by varying chemical composition of the mini clouds.

20. 20 Implications

21. 21 Dark Matter It is known that 10-90% of dark matter consists of “dark side of our knowledge”. Gravitational coupling of mini clouds with dark matter can produce the effect of the substructure in dark matter halos. From ratio of relative variation of different spectrum bands it is possible to extract information about total cross-section for interactions of dark matter with photons.

22. 22 Violation of Lorentz Invariance Mini clouds model provides the opportunity to test a set of theoretical models predicting energy dependent light velocity. Modified relation between photon momentum and energy. The velocity becomes function of energy. The shift in shape variation for different spectral light lines from very far sources can drive constraints for violation of Lorentz invariance. This can open the questions of photon mass.

23. 23 Summary Model of mini clouds has the potential to explain temporal variation of X-ray and γ-ray spectrum as well as the variation within the spectrum shape itself. The existence of HVC may be explained by the gas from mini clouds “sinking” down to galaxy plain and being gravitationally pulled together. Dark matter interaction cross-section with photons may be constrained from the mini cloud model. From time domain shift of shape in different bands it is possible to test violation of Lorentz invariance.