Dwarf galaxies represent a powerful probe of annihilating dark matter particle models, with gamma-ray data setting some of the best bounds available. A major issue in improving over existing constraints consists in the limited knowledge of the astrophysical background (mostly diffuse photons, but also unresolved sources). Perhaps more worrisome, several approaches in the literature suffer of the difficulty of assessing the systematic error due to background mis-modelling. Here we propose a data-driven method to estimate the background at the dwarf position and its uncertainty, relying on an appropriate use of the whole-sky data, via an optimisation procedure of the interpolation weights. While this article is mostly methodologically oriented, we also report the bounds based on latest Fermi-LAT data and updated information for J-factors for both isolated and stacked dwarfs. Our results are very competitive with the Fermi-LAT ones, while being derived with a more general and flexible method. We discuss the impact of profiling over the J-factor as well as over the background probability distribution function, with the latter resulting for instance crucial in drawing conclusions of compatibility with DM interpretations of the so-called Galactic Centre Excess. see ref.[7] and references therein. With little intrinsic astrophysical background emission expected [8], dSphs could be shining in gamma rays mostly in reason of their DM content, through annihilation (or decay) of WIMP particles. So far, no significant excess of gamma rays has been found from the direction of known dSphs with the Fermi-LAT, nor with TeV Cherenkov telescopes such H.E.S.S., MAGIC and VERITAS, and upper limits on the strength of the annihilation cross section as a function of the WIMP mass have been placed [9-16], now challenging vanilla WIMP scenarios for masses up to ∼ 100 GeV. The search for DM in dSphs has received a significant boost in the past few years thanks to more than twenty newly discovered objects -both "classical" and "ultra-faint" dSphs [17-23] -by wide-field optical imaging surveys such as SDSS, Pan-starrs and DES. Follow-up spectroscopic observations, which are crucial for a precise determination of the dSphs DM content and its spatial distribution, are unfortunately difficult, in particular for the ultra-faint galaxies due to their very low surface brightness and small number of stars. This implies large uncertainties in the determination of their astrophysical J-factors, i.e. the integrals along the line of sight of the DM density squared. Since the WIMP gamma-ray signal is directly proportional to this quantity, the constraints are affected correspondingly, see the discussion in ref. [24].The pipeline of the standard analysis of DM searches in Fermi-LAT dSphs is described in detail in ref. [25]. The main idea is to look for gamma-ray point-like source emission from the direction of each dSph, and then, to stack the (null-)results from the whole sample of objects in a joint likelihood, eventually accounting for uncertainties o...

We present an updated analysis of the gamma-ray flux from the directions of classical dwarf spheroidal galaxies, deriving new constraints on WIMP dark matter (DM) annihilation using a decade of Fermi-LAT data. Among the major novelties, we infer the dwarfs' J-factors by including new observations without imposing any a priori parametric profile for the DM distribution. While statistically compatible with results obtained from more conventional parameterisations, this procedure reduces the theoretical bias imposed on the data. Furthermore, we retain the full data-driven shape of the J-factors' empirical probability distributions when setting limits on DM, without imposing log-normality as is typically done. In conjunction with the data-driven J-factors, we improve on a new method for estimating the probability distribution function of the astrophysical background at the dwarf position [1], fully profiling over background uncertainties. We show that, for most “classical” dwarfs, the background systematic uncertainty dominates over the uncertainty on their J-factors. {Raw distributions of J- and D-factors (the latter being the analogous of J-factors for decaying DM) are available upon request.}

We use 15 years of γ-ray data from INTEGRAL/SPI in a refined investigation of the morphology of the Galactic bulge positron annihilation signal. Our spatial analysis confirms that the signal traces the old stellar population, revealing for the first time that it traces the boxy bulge and nuclear stellar bulge, while disfavouring the presence of additional dark matter components. Using a 3D smoothing kernel, we find that the signal is smeared out over a characteristic length scale of 150 ± 50 pc, suggesting either annihilation in situ at astrophysical sources kicked at formation or positron propagation away from sources. The former is disfavoured by its requiring kick velocities different between the Galactic nucleus (≳ 50 km s−1) and wider bulge (≲ 15 km s−1) source. Positron propagation prior to annihilation can explain the overall phenomenology of the 511 keV signal for positrons injection energies ≲ 1.4 MeV, suggesting a nucleosynthesis origin.