Search

In this paper, we presented a study of temperature effects on BGO calorimeters using proton MIP's collected in the first year operation of DAMPE. By directly comparing MIP calibration constants used by DAMPE data production pipe line, we found an experimental relation between temperature and signal amplitudes of each BGO bar: a general deviation of -1.162%/$^{\circ}$C,and -0.47%/$^{\circ}$C to -1.60%/$^{\circ}$C statistically for each detector element. During 2016, DAMPE's temperature changed by about 7 degrees due to solar elevation angle and the corresponding energy scale bias is about 8%. By frequent MIP calibration operation, this kind of bias is eliminated to an acceptable value.

Milky Way-like galaxies are predicted to host a very large number of dark matter subhalos. Some massive and nearby subhalos could generate detectable gamma-rays, appearing as unidentified, spatially-extended and stable gamma-ray sources. We search for such sources in the third Fermi Large Area Telescope source List (3FGL) and report the identification of a new candidate, 3FGL J1924.8-1034. With the Fermi-LAT Pass 8 data, we find that 3FGL J1924.8-1034 is spatially-extended at a high confidence level of $5.4\sigma$, with a best-fit extension radius of $\sim0.15^{\circ}$. No significant variability has been found and its gamma-ray spectrum is well fitted by the dark matter annihilation into $b\bar{b}$ with a mass of $\sim 43$ GeV. All these facts make 3FGL J1924.8-1034 a possible dark matter subhalo candidate. However, due to the limited angular resolution, the possibility of that the spatial extension of 3FGL J1924.8-1034 is caused by the contamination from the other un-resolved point source can not be ruled out., Comment: 10 pages including 5 figures and 1 table, accepted for publication in Phys. Rev. D

N-body simulations predict that galaxies at the Milky Way scale host a large number of dark matter (DM) subhalos. Some of these subhalos, if they are massive enough or close enough to the Earth, might be detectable in $\gamma$ rays due to the DM annihilation. 3FGL J2212.5+0703, an unidentified gamma-ray source, has been suggested to be the counterpart candidate of a DM subhalo by Bertoni et al. (2015, 2016). In this work we analyze the Fermi-LAT Pass 8 data of 3FGL J2212.5+0703 to independently test the DM subhalo hypothesis of this source. In order to suppress the possible contamination from two nearby very-bright blazars, we just take into account the front-converting gamma-rays which have better angular resolutions than that of the back-converting photons. In addition to the spatial distribution analysis, we have extended the spectrum analysis down to the energies of $\sim 100$ MeV, and thoroughly examined the variability of the emission during the past 8 years. We confirm that 3FGL J2212.5+0703 is a steady and spatially-extended gamma-ray emitter at a high confidence level. The spectrum is well consistent with that expected from DM annihilation into $b\bar{b}$. The introduction of a phenomenological LogParabola spectrum just improves the fit slightly. All these results suggest that 3FGL J2212.5+0703 could be indicative of a DM subhalo., Comment: 8 pages, 4 figures. Accepted for publication in PRD