Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays

The Cherenkov Telescope Array (CTA) is about to enter construction phase and one of its main key science projects is to perform an unbiased survey in search of extragalactic sources. We make use of both the latest blazar gamma--ray luminosity function and spectral energy distribution to derive the expected number of detectable sources for both the planned Northern and Southern arrays of the CTA observatory. We find that a shallow, wide survey of about 0.5 hour per field of view would lead to the highest number of blazar detections. Furthermore, we investigate the effect of axion-like particles and secondary gamma rays from propagating cosmic rays on the source count distribution, since these processes predict different spectral shape from standard extragalactic background light attenuation. We can generally expect more distant objects in the secondary gamma-ray scenario, while axion-like particles do not significantly alter the expected distribution. Yet, we find that, these results strongly depend on the assumed magnetic field strength during the propagation. We also provide source count predictions for the High Altitude Water Cherenkov observatory (HAWC), the Large High Altitude Air Shower Observatory (LHAASO) and a novel proposal of a hybrid detector.Comment: 16 pages, 4 figures, ApJ 2017 in pres

Constraints to dark matter annihilation from high-latitude hawc unidentified sources

The ΛCDM cosmological framework predicts the existence of thousands of subhalos in our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may outshine in gamma rays provided that the dark matter is made of weakly interacting massive particles (WIMPs), which would self-annihilate and would appear as unidentified gamma-ray sources (unIDs) in gamma-ray catalogs. Indeed, unIDs have proven to be competitive targets for dark matter searches with gamma rays. In this work, we focus on the three high-latitude (|b| ≥ 10) sources present in the 2HWC catalog of the High Altitude Water Cherenkov (HAWC) observatory with no clear associations at other wavelengths. Indeed, only one of these sources, 2HWC J1040+308, is found to be above the HAWC detection threshold when considering 760 days of data, i.e., a factor 1.5 more exposure time than in the original 2HWC catalog. Other gamma-ray instruments, such as Fermi-LAT or VERITAS at lower energies, do not detect the source. Also, this unID is reported as spatially extended, making it even more interesting in a dark matter search context. While waiting for more data that may shed further light on the nature of this source, we set competitive upper limits on the annihilation cross section by comparing this HAWC unID to expectations based on state-of-the-art N-body cosmological simulations of the Galactic subhalo population. We find these constraints to be particularly competitive for heavy WIMPs, i.e., masses above ∼25 (40) TeV in the case of the b ¯b (τ +τ −) annihilation channel, reaching velocity-averaged cross section values of 2 × 10−25 (5 × 10−25) cm3 ·s −1 . Although far from testing the thermal relic cross section value, the obtained limits are independent and nicely complementary to those from radically different DM analyses and targets, demonstrating once again the high potential of this DM search approachJ.C.-B. and M.A.S.-C. are supported by the Atracción de Talento contract no. 2016-T1/TIC-1542 granted by the Comunidad de Madrid in Spain, by the Spanish Agencia Estatal de Investigación through the grants PGC2018-095161-B-I00, IFT Centro de Excelencia Severo Ochoa SEV-2016-0597, and Red Consolider MultiDark FPA2017-90566-RED

The viability of low-mass subhaloes as targets for gamma-ray dark matter searches

In this work, we investigate the discovery potential of low-mass Galactic dark matter (DM) subhaloes for indirect searches of DM. We use data from the Via Lactea II (VL-II) N-body cosmological simulation, which resolves subhaloes down to $\mathcal{O}(10^4)$ solar masses and it is thus ideal for this purpose. First, we characterize the abundance, distribution and structural properties of the VL-II subhalo population in terms of both subhalo masses and maximum circular velocities. Then, we repopulate the original simulation with millions of subhaloes of masses down to about five orders of magnitude below the minimum VL-II subhalo mass (more than one order of magnitude in velocities). We compute subhalo DM annihilation astrophysical "J-factors" and angular sizes for the entire subhalo population, by placing the Earth at a random position but at the right galactocentric distance in the simulation. Thousands of these realizations are generated in order to obtain statistically meaningful results. We find that some nearby low-mass Galactic subhaloes, not massive enough to retain stars or gas, may indeed yield DM annihilation fluxes comparable to those expected from other, more massive and acknowledgeable DM targets like dwarf satellite galaxies. Typical angular sizes are of the order of the degree, thus subhaloes potentially appearing as extended sources in gamma-ray telescopes, depending on instrument angular resolution and sensitivity. Our work shows that low-mass Galactic subhaloes with no visible counterparts are expected to play a relevant role in current and future indirect DM search searches and should indeed be considered as excellent DM targets.Comment: 15 pages, 15 figures. Submitted to MNRAS. Comments welcome

Periodic very high energy γ -Ray Emission from LS I +61◦303 Observed with the magic telescope

The MAGIC collaboration has recently reported the discovery of γ -ray emission from the binary system LS I +61◦303 in the TeV energy region. Here we present new observational results on this source in the energy range between 300 GeV and 3 TeV. In total, 112 hr of data were taken between 2006 September and December covering four orbital cycles of this object. This large amount of data allowed us to produce an integral flux light curve covering for the first time all orbital phases of LS I +61◦303. In addition, we also obtained a differential energy spectrum for two orbital phase bins covering the phase range 0.5 < φ < 0.6 and 0.6 < φ < 0.7. The photon index in the two phase bins is consistent within the errors with an average index Γ = 2.6±0.2stat ±0.2sys. LS I +61◦303 was found to be variable at TeV energies on timescales of days. These new MAGIC measurements allowed us to search for intranight variability of the very high energy emission; however, no evidence for flux variability on timescales down to 30 min was found. To test for possible periodic structures in the light curve, we apply the formalism developed by Lomb and Scargle to the LS I +61◦303 data taken in 2005 and 2006. We found the LS I +61◦303 data set to be periodic with a period of (26.8 ± 0.2) days (with a post-trial chance probability of 10−7), close to the orbital period.Peer reviewe

Axion searches with Fermi and IACTs

Axion Like Particles (ALPs), postulated to solve the strong-CP problem, are predicted to couple with photons in the presence of magnetic fields, which may lead to a significant change in the observed spectra of gamma-ray sources such as AGNs. Here we simultaneously consider in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. We show that photon/axion mixing could explain recent puzzles regarding the observed spectra of distant gamma-ray sources as well as the recently published lower limit to the EBL intensity. We finally summarize the different signatures expected and discuss the best strategy to search for ALPs with the Fermi satellite and current Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.Comment: 4 pages, 4 figures. To appear in the proceedings of the "2nd Roma International Conference on Astroparticle Physics", Villa Mondragone, Rome, Italy, May 13-15 200

"Core group" para identificar universitários em risco para infecções sexualmente transmissíveis

OBJECTIVE: To analyze the core group for sexually transmitted infections (STI) among college students. METHODS: Cross-sectional study carried out in a convenience sample comprising 711 college students of the public university of Morelos, Mexico, between 2001 and 2003. Sociodemographic and sexual behavior information were collected using self-applied questionnaires. Herpes simplex 2 (HSV-2) infection was tested in the blood. The number of sexual partners in the last year and cocaine consumption were used as indicators to construct the dependent variable "level of STI risk" in three categories: low, medium and high risk (core group). A multinomial analysis was conducted to evaluate whether different sex behaviors were associated with the variable "level of STI risk". RESULTS: There was significant association between HSV-2 seroprevalence and the variable "level of STI risk": 13%, 5.6% and 3.8% were found in high (core group), medium and low categories, respectively. There were gender differences regarding the core group. Men started having sexual intercourse earlier, had more sex partners, higher alcohol and drug consumption, higher frequency of sex intercourse with sex workers, exchanging sex for money, occasional and concurrent partners compared to women. CONCLUSIONS: The study findings suggest existing contextual characteristics in the study population that affect their sex behavior. In Mexico, the cultural conception of sexuality is determined mainly by gender differences where men engage in higher risky sexual behavior than women.OBJETIVO: Identificar al grupo core de infecciones de transmisión sexual (ITS) en una población de estudiantes universitarios mexicanos. MÉTODOS: Se realizó un estudio transversal en una muestra por conveniencia que incluyó 711 estudiantes de una universidad pública de Morelos, México, entre 2001 y 2003. Las características sociodemográficas y de comportamiento sexual se obtuvieron mediante un cuestionario auto-aplicado. La infección por el Virus del herpes simple tipo 2 (VHS-2) se determinó en pruebas de sangre. El número de parejas sexuales durante el último año y el consumo de cocaína, fueron indicadores utilizados para construir la variable dependiente "nivel de riesgo para adquirir ITS" que tuvo tres categorías: bajo, medio y alto riesgo (grupo core). Mediante un análisis multinomial se evaluó si las características sociodemográficas y de comportamiento sexual estuvieron relacionadas con la variable dependiente. RESULTADOS: Se encontró una relación significativa entre la seroprevalencia de VHS-2 y la variable dependiente encontrando frecuencias de 13%, 5.6% y 3.8% en las categorías de alto, medio y bajo riesgo, respectivamente. Los resultados mostraron diferencias de género en la constitución del grupo core. En comparación con las mujeres, los hombres iniciaron su vida sexual a más temprana edad, reportaron mayor número de parejas sexuales, mayores niveles de consumo de alcohol y drogas, mayor frecuencia de contacto sexual con trabajadoras sexuales, intercambio de sexo por dinero, relaciones con parejas ocasionales y concurrentes. CONCLUSIONES: Los resultados sugieren que existen características contextuales que influyen en el comportamiento sexual. En México la concepción cultural de la sexualidad está conformada por diferencias marcadas entre hombres y mujeres, donde los primeros tienen un comportamiento sexual de riesgo mayor que las mujeres.OBJETIVO: Analisar o core group em estudantes universitários em risco de adquirir infecções sexualmente transmissíveis (IST). MÉTODOS: Estudo transversal com amostra de conveniência composta por 711 estudantes de universidade pública de Morelos, no México, 2001-2003. Informações sociodemográficas e de comportamento sexual foram coletadas por meio de questionário auto-aplicável. Presença de infecção por Herpes simplex 2 foi diagnosticada por exame de sangue. O número de parceiros sexuais durante o último ano anterior à pesquisa e o consumo de cocaína foram indicadores utilizados para construir a variável dependente "nível de risco para adquirir IST" e definir três categorias: baixo, médio e alto risco (core group). Foi utilizada análise multinominal para avaliar se diferentes comportamentos sexuais estavam associados à variável "nível de risco para adquirir IST". RESULTADOS: Houve associação significativa entre a soroprevalência de HSV-2 e a variável "nível de risco para adquirir IST" nas categorias de alto (13%), médio (5,6%) e baixo (3,8%) risco. Foram encontradas diferenças entre os sexos em relação ao core group. Em comparação às mulheres, os homens começaram a ter relações sexuais mais cedo, tiveram maior número de parceiras sexuais, níveis mais elevados de consumo de álcool e drogas, maior freqüência de sexo com profissionais do sexo, prática de sexo por dinheiro, parceiras ocasionais e concomitantes. CONCLUSÕES: Os resultados sugerem a existência de características contextuais da população que influenciam o comportamento sexual. No México, a concepção cultural de sexualidade é caracterizada por diferenças marcantes entre homens e mulheres, nas quais os homens têm comportamento sexual de maior risco que as mulheres

Sensitivity of the Cherenkov Telescope Array to the detection of a dark matter signal in comparison to direct detection and collider experiments

Imaging atmospheric Cherenkov telescopes (IACTs) that are sensitive to potential $\gamma$-ray signals from dark matter (DM) annihilation above $\sim50$ GeV will soon be superseded by the Cherenkov Telescope Array (CTA). CTA will have a point source sensitivity an order of magnitude better than currently operating IACTs and will cover a broad energy range between 20 GeV and 300 TeV. Using effective field theory and simplified models to calculate $\gamma$-ray spectra resulting from DM annihilation, we compare the prospects to constrain such models with CTA observations of the Galactic center with current and near-future measurements at the Large Hadron Collider (LHC) and direct detection experiments. For DM annihilations via vector or pseudoscalar couplings, CTA observations will be able to probe DM models out of reach of the LHC, and, if DM is coupled to standard fermions by a pseudoscalar particle, beyond the limits of current direct detection experiments.Comment: Accepted for publication in PRD. 20 pages, 11 figure

Constraining the dark matter contribution of γ\gamma rays in Cluster of galaxies using Fermi-LAT data

Clusters of galaxies are the largest gravitationally-bound systems in the Universe. Their dynamics are dominated by dark matter (DM), which makes them among the best targets for indirect DM searches. We analyze 12 years of data collected by the Fermi Large Area Telescope (Fermi-LAT) in the direction of 49 clusters of galaxies selected for their proximity to the Earth and their high X-ray flux, which makes them the most promising targets. We first create physically motivated models for the DM density around each cluster considering different assumptions for the substructure distribution. Then we perform a combined search for a $\gamma$-ray signal in the {\it Fermi}-LAT data between 500 MeV and 1 TeV. We find a signal of $\gamma$ rays potentially associated with DM that is at a statistical significance of $2.5\sigma-3.0\sigma$ when considering a slope for the subhalo mass distribution $\alpha=1.9$ and minimum mass of $M_{\rm{min}}=10^{-6}$ $M_{\odot}$. The best-fit DM mass and annihilation cross-sections for a $b\bar{b}$ annihilation channel are $m_{\chi}=40-60$ GeV and $\langle \sigma v \rangle = (2-4) \times 10^{-25}$ cm$^3$/s. When we consider $\alpha=2.0$ and $M_{\rm{min}}=10^{-9}$ $M_{\odot}$, the best-fit of the cross section reduces to $\langle \sigma v \rangle = (4-10) \times 10^{-26}$ cm$^3$/s. For both DM substructure models there is a tension between the values of $\langle \sigma v \rangle$ that we find and the upper limits obtained with the non-detection of a $\gamma$-ray flux from Milky Way dwarf spheroidal galaxies. This signal is thus more likely associated with $\gamma$ rays produced in the intracluster region by cosmic rays colliding with gas and photon fields.Comment: 27 Pages, 13 Figures. Accepted for publication in the PRD journa