Proper motion of gamma-rays from microhalo sources

TL;DR

It is shown that for dark matter particle candidates that couple to photons the detection of at least one gamma-ray microhalo source with proper motion places a constraint on the couplings and mass of thedark matter particle.

Abstract

I discuss the prospects of detecting the smallest dark matter bound structures present in the Milky Way by searching for the proper motion of $γ$-ray sources in the upcoming GLAST all sky map. I show that for dark matter particle candidates that couple to photons the detection of at least one $γ$-ray microhalo source with proper motion places a constraint on the couplings and mass of the dark matter particle. For SUSY dark matter, proper motion detection implies that the mass of the particle is less than 500 GeV and the kinetic decoupling temperature is in the range of [4-100] MeV.

Figures (3)

• Figure 1: Top: The dependence of the number of visible microhalos per logarithmic mass interval to the microhalo mass and the properties of the dark matter particle. Solid lines depict the iso-number contours of microhalos which also exhibit detectable proper motion. The dashed line shows the best case scenario for SUSY CDM particle. The shaded area shows the region that is already being excluded by EGRET measurements.
• Figure 2: The angular size of microhalos as a function of microhalo mass and distance for the best case scenario of SUSY CDM. The solid line defines the distance threshold for detection. Dashed lines depict the iso-number contours of the number of microhalos per logarithmic mass interval within a volume defined by ${\cal D }$. Dot-dashed lines show the maximum distance at which a microhalo could exhibit proper motion of 1, 3, 6 & 9 arcmin. The cross-hatched area corresponds to the region where microhalos have an angular extent that should be detectable by GLAST.
• Figure 3: The dependence of the number of visible microhalos per logarithmic mass interval on the microhalo mass and redshift of formation. Solid lines as in figure \ref{['fig:figure1']}. The dashed line depicts the redshift at which microhalos form in numerical simulations DMS05METAL05DKM06.