X-ray radiation from the annihilation of dark matter at the galactic center

The existing and upcoming multiwavelength data from the galactic center suggest a comparative study in order to propose or rule out possible models which would explain the observations. In this paper we consider the x-ray synchrotron and the gamma-ray emission due to Kaluza-Klein dark matter and define a set of parameters for the shape of the dark matter halo which is consistent with the observations. We show that for this class of models the existing Chandra x-ray data are more restrictive than the constraints on very high energy gamma rays coming from HESS.

Figure 1

Multiwavelength luminosity of Sgr A* in the quiescent state. Observations in the radio and infrared radiation come from Refs. 37, 38, 39, 40. The Chandra data are reconstructed from Ref. 13. The HESS/MAGIC spectrum is plotted as one line since the two experiments are in agreement with each other [15, 16].

Figure 2

Expected total luminosity from the center of the Galaxy for different dark matter profiles of the form $\rho \propto r^{-\gamma }$ normalized to $0.3\mathrm{GeV}{\mathrm{cm}}^{-3}$ at the sun, for $⟨{\sigma }_{\mathrm{tot}}v⟩=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and $m_{\mathrm{dm}}=1\mathrm{TeV}$. Since the emission is diffuse, the two curves correspond to 6 arcminutes (HESS) and  arcsecond (Chandra) angular resolution. We assume a maximum density in the core due to self-annihilation (see text). The luminosity stops growing for the Chandra case when the entire region within the Chandra angular resolution is at the maximum density of dark matter.

Figure 3

Assumed magnetic field as a function of radius from the black hole. The solid line corresponds to the equipartition magnetic field of Eq. (3), whereas the red dashed line is the flux-reconnection magnetic field of Eq. (4).

Figure 4

Density profiles used in this work and presented in Table .

Figure 5

Synchrotron spectra from 1 TeV KK dark matter annihilation in the central 0.01 pc of the Galaxy assuming the three density profiles—(A), (B), (C)—described in Eq. (10). The solid lines correspond to the equipartition magnetic field of Eq. (3) and the dotted lines are the spectra with the flux-reconnection magnetic field of Eq. (4).

Figure 6

Comparison of profile (B) with Chandra data: the dot-dashed curve is an approximate fit to the data presented in 14 without the iron line. The solid curve is the signal expected from synchrotron radiation from electrons produced in dark matter annihilations assuming density profile (B). The dashed curve corresponds to the synchrotron radiation from the flat core described in the text. We assume a Chandra effective aperture of $400{\mathrm{cm}}^2$.

Figure 7

Synchrotron spectra from 10 TeV KK dark matter annihilation in the central 0.01 pc of the Galaxy assuming the three density profiles—(A), (B), (C)—described in Eq. (10). The solid lines correspond to the equipartition magnetic field of Eq. (3) and the dotted lines are the spectra with the flux-reconnection magnetic field of Eq. (4).