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Longitude Latitude A recent analysis of the Fermi-LAT data by M. Su et al. [1] revealed two large spherical structures centered by our Galactic Center.

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Presentation on theme: "Longitude Latitude A recent analysis of the Fermi-LAT data by M. Su et al. [1] revealed two large spherical structures centered by our Galactic Center."— Presentation transcript:

1 Longitude Latitude A recent analysis of the Fermi-LAT data by M. Su et al. [1] revealed two large spherical structures centered by our Galactic Center and perpendicular to the galactic plane, the so called Fermi Bubbles. These structures are characterized by gamma emission with a hard and uniform spectrum and a relatively constant intensity all over the space. According to R.M. Crocker and F. Aharonian [2] the reason of the emission in region of the Fermi Bubbles can be hadronic acceleration and the proton spectrum should have almost flat E -2 shape with some cutoff (probably around 1 PeV as suggested in the paper). According to the recipe of F. Vissani [3] neutrino flux from gamma flux was estimated as: Φ υ ~ 0.4 Φ γ E 2 dΦ υ /dE=1.2*10 -7 GeV cm -2 s -1 sr -1 Cutoff for neutrino ~ 1/20 cutoff CR x υ = 50 TeV-500 TeV Shape reported by M. Su et al. was approximated according to figure on the right in galactic coordinates. The ratios are compatible with 1 in all cases inside the statistical error. There could be a systematic effect due to the different visibilities of the zones. Therefore a conservative systematic error of 3% has been considered as the average difference from 1 of the data ratios. This error was taken into account in the final analysis, where number of events in ON zone was compared to zone (average number of events). OFF/ON zones approach The Fermi Bubbles are extended but limited regions in the sky. Their sky-coverage corresponds to approximately 0.8 sr. In order to estimate the background in the Fermi Bubbles zone one can use another zone in the sky with same sky coverage and same visibility of the Fermi Bubbles (FB) zone. Such zone (OFF zone) can be defined considering a zone in the sky that corresponds to the FB zone (ON zone) after a certain shift in time. Obviously the OFF zone should not overlap with the FB zone. In galactic coordinates the OFF zone will be fixed in the sky, while in local coordinates, it will follow the FB zone as time passes. On the right plot the position of the Fermi Bubbles in local coordinates is shown at a specific time during the day (black filled region). The OFF zone (red filled region) corresponds to the Fermi Bubbles zone after a negative shift of 6 hours. The dotted lines (black for Fermi Bubbles and red for the OFF zone) show the position of the two zones in previous 2 hours. In this analysis 3 OFF zones were considered that correspond to time shift of 6, 12 and 18 hours in respect to the ON zone. Figure on the left below shows in galactic coordinates the position of the ON zone and of the 3 OFF zones together with the visibility of the ANTARES detector. ANTARES telescope The ANTARES detector [4] is large neutrino telescope that aims to detect high energy neutrinos coming from astrophysical sources. It consists of 12 lines of photomultipliers positioned at 2475 m deep in the Mediterranean sea. When a neutrino arrives close to the detector it can interact producing a high energy muon. The Cherenkov light produced by the muon in the water can be detected by the ANTARES photomultipliers. The main background is due to atmospheric muons produced by interaction of cosmic rays in the atmosphere. This background can be reduced by looking at upward going tracks. In this preliminary analysis data from with low bioluminescence conditions were used (~169 days with uncompleted detector configuration and ~419 with a detector composed of 9-12 lines). The main parameters used in this analysis are: Nlines: number of detector lines used in the fit Λ: reconstruction quality parameter (the range of Λ goes from -8 for badly reconstructed events to -4 for good ones) NHits: number of hits of the reconstructed track β: angular error of reconstructed track A preliminary cut (Λ>-6, Nhits>60, β< 1 o ) has been defined to check that number of events in 3 OFF zones are comparable. The ratios of the number of events after the preliminary cut between the OFF zones in data and Monte Carlo (MC) are presented in table below. For the final cut obtained number of events in the ON zone was compared with an average between OFF zones. The plot for Nhits distribution is presented on the right above. In total 90±5(stat) ±3 (syst) events in zone as background and 75 events in ON zone were observed. Obtained values of number of events in ON zone and were used to calculate upper limit with 90% C.L. We used a simple Feldman&Cousins limits construction with n obs =75 and b=90. Finally obtained upper limit fluxes according to the MC were estimated. The systematic error for data/MC comparison is +15% -6%. As the final upper limit flux an estimated limit plus mentioned systematic is presented. Flux upper limits from this analysis are compared with expected fluxes from the Fermi Bubbles for different cutoffs. Fluxes and table summarizing results are shown below. Current preliminary analysis due to a negative statistical fluctuation in the ON zone gives upper limits lower than it was expected by MRF. V. Kulikovskiy on behalf of the ANTARES collaboration. (INFN Genova / MSU) μ The first search for neutrino emission from the Fermi Bubbles with the ANTARES telescope Final cuts according to Model Rejection Factor with 90% C.L. were optimized using G. Feldman and R. Cousins recipe [5]. Optimization was done on OFF zones in MC to perform a blinded analysis. Precut was: Nlines> 1 β< 1 o Nhits and Λ cut were left as free parameters. Optimization was done on the 3 OFF zones in MC adding to them signal with the flux E 2 dΦ υ /dE=1.2*10 -7 GeV cm -2 s -1 sr -1 and cutoff 100 TeV. Table summarizing results and MRF for different cutoffs is presented on the right. Presented MRF flux corresponds to E 2 dΦ υ /dE=A MRF *10 -7 GeV cm -2 s -1 sr -1. It also was found that minimum MRF for different cuttoffs is lower than obtained MRFs on the table by at maximum 20%. A data/MC comparison for the final cuts is shown below. References [1] M. Su, T.R.Slatyer, D.P.Finkbeiner, arxiv: v3 [2] R.M. Crocker, F. Aharonian, Phys.Rev.Lett. 106 (2011) [3] F.L. Villante, F. Vissani, Phys. Rev. D 78 (2008) [4] The ANTARES collaboration, NIMA 656 (2011) [5] G.J. Feldman, R.D. Cousins, Phys.Rev. D 57 (1998) p [6] W.Rolke, A. Lopez, J. Conrad, F. James NIMA 551 (2005) data atm υ MC atm υ+μ MC FB υ no cutoff MC FB υ 500 TeV MC Acknowledgments. This work was done thanks to the ANTARES collaboration which has proven a possibility of undersea neutrino telescope realization. Thanks to M.Anghinolfi, H.Costantini, C.Rìviere, M.Vecchi, J.P.Ernenwein, M.Spurio, A. Kouchner, P.Coyle, F.Schüssler, R.Coniglione and J.Brunner whose help was invaluable for analysis. upper limit for 50 TeV cutoff upper limit for 100 TeV cutoff upper limit for 500 TeV cutoff upper limit for no cutoff expected flux without cutoff data atm υ MC atm υ+μ MC FB υ no cutoff MC FB υ 500 TeV MC FB υ 100 TeV MC FB υ 50 TeV MC Results after unblinding. atm υ MC atm υ+μ MC data FB υ no cutoff MC FB υ 500 TeV MC FB υ 100 TeV MC FB υ 50 TeV MC ON (75 events) (90 events) FB υ no cutoff MC FB υ 500 TeV MC FB υ 100 TeV MC FB υ 50 TeV MC atm υ MC atm υ+μ MC data Conclusions and outlook. The upper limits from this data analysis are close to the expected flux levels for some very optimistic cutoffs (no cutoff and 500 TeV cutoff). Future analysis will have more data. dotted – expected fluxes solid – 90% C.L. upper limits 50 TeV cutoff 100 TeV cutoff 500 TeV cutoff no cutoff Final flux limits according to 90% C.L. E 2 dΦ υ /dE=A upper *10 -7 GeV cm -2 s -1 sr -1 PRELIMINARY


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