Upper limits at 95% confidence level on ⟨σv⟩ as a function of the DM mass for the τ+τ-annihilation channel, using the set of J-factors from [53] (GS set in Table 2). See Figure 2 below for more details.
Reference: S. Abdollahi et al. (The Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS Collaborations), accepted for publication in JCAP
Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive currently operating gamma-ray telescopes, namely: the satellite-borne Fermi-LAT telescope; the ground-based imaging atmospheric Cherenkov telescope arrays H.E.S.S., MAGIC, and VERITAS; and the HAWC water Cherenkov detector. Individual datasets were analyzed using a common statistical approach. Results were subsequently combined via a global joint likelihood analysis. We obtain constraints on the velocity-weighted cross section ⟨σv⟩ for DM self-annihilation as a function of the DM particle mass. This five-instrument combination allows the derivation of up to 2-3 times more constraining upper limits on ⟨σv⟩ than the individual results over a wide mass range spanning from 5 GeV to 100 TeV. Depending on the DM content modeling, the 95% confidence level observed limits reach 1.5×10−24 cm3s−1 and 3.2×10−25 cm3s−1 , respectively, in the τ +τ − annihilation channel for a DM mass of 2 TeV.
FITS files: N/A
Figures from paper (click to get full size image):
Figure 1: Illustration of a real data combination showing a comparison between TS provided by four instruments (non-solid colored lines) from the observation of the same dSph without any J-factor nuisance parameter included and their sum, i.e. the resulting combined likelihood (thin black line), for a DM particle mass of 20 TeV. The intersection of the likelihood profiles with the line TS = 2.71 indicates the 95% C.L. upper limit on ⟨σv⟩ (see text for more details). The combined likelihood (thin black line) shows a smaller value of upper limit on ⟨σv⟩ than those derived by individual instruments. We also show how the uncertainty on the J-factor affects the combined likelihood and degrades the upper limit on ⟨σv⟩ (thick black line). All likelihood profiles are normalized so that the global minimum ⟨σv⟩-hat is 0 to facilitate data handling. We note that each profile depends on the observational conditions under which a target object was observed. The sensitivity of a given instrument can be degraded and the upper limits less constraining if the observations suffer from non-optimal conditions such as a large zenith angle of observation or a short exposure time.
Figure 2: Upper limits at 95% confidence level on ⟨σv⟩ as a function of the DM mass for seven annihilation channels, using the set of J-factors from [53] (GS set in Table 2). The black solid line represents the observed combined limits obtained for the 20 dSphs included in this work, the blue dashed line is the median of the null hypothesis (H0) corresponding to the expected limits with no DM signal (⟨σv⟩ = 0), while the green and yellow bands show the 68% and 95% containment bands. Upper limits for each individual instrument are also indicated. The value of the thermal relic cross section as a function of the DM mass is given as the gray dotted-dashed line [9].
Figure 3: Same as Fig. 2, using the set of J-factors from [52, 54] (B set in Table 2).
