Gamma-ray Flux Limits Research Articles

Erratum: Gamma-ray flux limits from brown dwarfs: Implications for dark matter annihilating into long-lived mediators [Phys. Rev. D 107 , 043012 (2023)

Erratum: Gamma-ray flux limits from brown dwarfs: Implications for dark matter annihilating into long-lived mediators [Phys. Rev. D <b>107</b> , 043012 (2023)

Gamma-ray flux limits from brown dwarfs: Implications for dark matter annihilating into long-lived mediators

Brown dwarfs (BDs) are celestial objects representing the link between the least massive main-sequence stars and giant gas planets. In the first part of this article, we perform a model-independent search of a gamma-ray signal from the direction of nine nearby BDs in 13 years of \Fermi-LAT data. We find no significant excess of gamma rays, and we, therefore, set 95\% confidence level upper limits on the gamma-ray flux with a binned-likelihood approach. In the second part of the paper, we interpret these bounds within an exotic mechanism proposed for gamma-ray production in BDs: If the dark matter (DM) of the universe is constituted of particles with non-negligible couplings to the standard model, BDs may efficiently accumulate them through scatterings. DM particles eventually thermalize, and can annihilate into light, long-lived, mediators which later decay into photons outside the BD. Within this framework, we set a stacked upper limit on the DM-nucleon elastic scattering cross section at the level $\sim 10^{-38}$ cm$^{2}$ for DM masses below 10 GeV. Our limits are comparable to similar bounds from the capture of DM particles in celestial objects, but have the advantage of covering a larger portion of the parameter space in mediator decay length and DM mass. They also depend only on the local DM abundance, as opposed to the inner Galaxy profile, and are thus more robust.

Search for dark matter gamma-ray emission from the Andromeda Galaxy with the High-Altitude Water Cherenkov Observatory

The Andromeda Galaxy (M31) is a nearby (∼780 kpc) galaxy similar to our own Milky Way. Observational evidence suggests that it resides in a large halo of dark matter (DM), making it a good target for DM searches. We present a search for gamma rays from M31 using 1017 days of data from the High Altitude Water Cherenkov (HAWC) Observatory. With its wide field of view and constant monitoring, HAWC is well-suited to search for DM in extended targets like M31. No DM annihilation or decay signal was detected for DM masses from 1 to 100 TeV in the bb̄, tt̄, τ+τ−, μ+μ−, and W+W− channels. Therefore we present limits on those processes. Our limits nicely complement the existing body of DM limits from other targets and instruments. Specifically the DM decay limits from our benchmark model are the most constraining for DM masses from 25 TeV to 100 TeV in the bb̄ and tt̄ channels. In addition to DM-specific limits, we also calculate general gamma-ray flux limits for M31 in 5 energy bins from 1 TeV to 100 TeV.

Inverse Compton Gamma Rays from Dark Matter Annihilation in the Dwarf Galaxies

Dwarf spheroidal (dSph) galaxies are thought to be good candidates for dark matter search due to their high mass-to-light (M/L) ratio. One of the most favored dark matter candidates is the lightest neutralino (neutral χ particle) as predicted in the Minimal Supersymmetric Standard Model (MSSM). In this study, we model the gamma ray emission from dark matter annihilation coming from the nearby dSph galaxies Draco, Segue 1, Ursa Minor and Willman 1, taking into account the contribution from prompt photons and photons produced from inverse Compton scattering off starlight and Cosmic Microwave Background (CMB) photons by the energetic electrons and positrons from dark matter annihilation. We also compute the energy spectra of electrons and positrons from the decay of dark matter annihilation products. Gamma ray spectra and fluxes for both prompt and inverse Compton emission have been calculated for neutralino annihilation over a range of masses and found to be in agreement with the observed data. It has been found that the ultra faint dSph galaxy Segue 1 gives the largest gamma ray flux limits while the lowest gamma ray flux limits has been obtained from Ursa Minor. It is seen that for larger M/L ratio of dwarf galaxies the intensity pattern originating from e+e− pairs scattering off CMB photons is separated by larger amount from that off the starlight photons for the same neutralino mass. As the e+e− energy spectra have an exponential cut off at high energies, this may allow to discriminate some dark matter scenarios from other astrophysical sources. Finally, some more detailed study about the effect of inverse Compton scattering may help constrain the dark matter signature in the dSph galaxies.

Global study of the simplest scalar phantom dark matter model

We present a global study of the simplest scalar phantom dark matter model. The best fit parameters of the model are determined by simultaneously imposing (i) relic density constraint from WMAP, (ii) 225 live days data from direct experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the Higgs boson candidate with a mass about 125 GeV and its invisible branching ratio no larger than 40% if the decay of the Higgs boson into a pair of dark matter is kinematically allowed. The allowed parameter space is then used to predict annihilation cross sections for gamma-ray lines, event rates for three processes mono-b jet, single charged lepton and two charged leptons plus missing energies at the Large Hadron Collider, as well as to evaluate the muon anomalous magnetic dipole moment for the model.

Limits on large extra dimensions based on observations of neutron stars with the Fermi-LAT

We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) proposed by Arkani-Hamed, Dimopoulos, and Dvali. We use 11 months of data from the Fermi Large Area Telescope (Fermi-LAT) to set gamma ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein (KK) graviton production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The predicted decay of the bound KK gravitons to γγ should contribute to the flux from NSs. Considering 2 to 7 extra dimensions of the same size in the context of the HR model, we use Monte Carlo techniques to calculate the expected differential flux of gamma-rays arising from these KK gravitons, including the effects of the age of the NS, graviton orbit, and absorption of gamma-rays in the magnetosphere of the NS. We compare our Monte Carlo-based differential flux to the experimental differential flux using maximum likelihood techniques to obtain our limits on LED. Our limits are more restrictive than past EGRET-based optimistic limits that do not include these important corrections. Additionally, our limits are more stringent than LHC based limits for 3 or fewer LED, and comparable for 4 LED. We conclude that if the effective Planck scale is around a TeV, then for 2 or 3 LED the compactification topology must be more complicated than a torus.

Evidence of TeV gamma-ray emission from the nearby starburst galaxy NGC 253

Aims. The CANGAROO-II telescope observed sub-TeV gamma-ray emission from the nearby starburst galaxy NGC 253. The emission region was extended with a radial size of 0.3–0.6 degree. On the contrary, HESS could not confirm this emission and gave upper limits at the level of the CANGAROO-II flux. In order to resolve this discrepancy, we analyzed new observational results for NGC 253 by CANGAROO-III and also assessed the results by CANGAROO-II. Methods. Observation was made with three telescopes of the CANGAROO-III in October 2004. We analyzed three-fold coincidence data by the robust Fisher Discriminant method to discriminate gamma ray events from hadron events. Results. The result by the CANGAROO-III was negative. The upper limit of gamma ray flux was 5.8% Crab at 0.58 TeV for pointsource assumption. In addition, the significance of the excess flux of gamma-rays by the CANGAROO-II was lowered to less than 4 sigma after assessing treatment of malfunction of photomultiplier tubes.

Detection of diffuse TeV gamma-ray emission from the neaby starburst galaxy NGC 253

Department of Physics, Osaka City University, Osaka, Osaka 558-8585, JapanA&A 396, L1-L4(2002). A&A402, 443-455(2003)ABSTRACTContext.Aims. The CANGAROO-II telescope observed sub-TeV gamma-ray emission from the nearby starburst galaxy NGC 253. The emission regionwas extended with a radial size of 0.3-0.6 degree. On the contrary, H.E.S.S could not confirm this emission and gave upper l imits at the levelof the CANGAROO-II flux. In order to resolve this discrepancy, we analyzed new observational results for NGC 253 by CANGAROO-III andalso assessed the results by CANGAROO-II.Methods. Observation was made with three telescopes of the CANGAROO-III in October 2004. We analyzed three-fold coincidence data bythe robust Fisher Discriminant method to discriminate gamma ray events from hadron events.Results. The result by the CANGAROO-III was negative. The upper limit of gamma ray flux was 5.8% Crab at 0.58 TeV for po int-sourceassumption. In addition, the significance of the excess flux o f gamma-rays by the CANGAROO-II was lowered to less than 4 sigma afterassessing treatment of malfunction of photomultiplier tubes.Key words. gamma rays: observation – galaxies: starburst – galaxies: i ndividual: NGC 253 – galaxies: halos: cosmic rays

Particle dark matter constraints from the Draco dwarf galaxy

It is widely thought that neutralinos, the lightest supersymmetric particles, could comprise most of the dark matter. If so, then dark halos will emit radio and gamma ray signals initiated by neutralino annihilation. A particularly promising place to look for these indicators is at the center of the local group dwarf spheroidal galaxy Draco, and recent measurements of the motion of its stars have revealed it to be an even better target for dark matter detection than previously thought. We compute limits on WIMP properties for various models of Draco's dark matter halo. We find that if the halo is nearly isothermal, as the new measurements indicate, then current gamma ray flux limits prohibit much of the neutralino parameter space. If Draco has a moderate magnetic field, then current radio limits can rule out more of it. These results are appreciably stronger than other current constraints, and so acquiring more detailed data on Draco's density profile may become one of the most promising avenues for identifying dark matter.