Searches for astrophysical sources of neutrinos using cascade events in IceCube

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1 Searches for astrophysical sources of neutrinos using cascade events in IceCube Mike Richman TeVPA 2017 August 8, 2017 Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 1 / 18

2 The IceCube Neutrino Observatory Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 2 / 18

3 The IceCube Neutrino Observatory km deep in the South Pole glacier 5160 PMTs arranged on 86 strings 1 km 3 instrumented volume Constructed Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 3 / 18

4 Neutrino Detection interactions and detector signatures CC ν µ CC ν e / NC ν CC ν τ ν µ + N µ + X ν e + N e + X ν τ τ + X ν + N ν + X track cascade cascade (or double-bang) Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 4 / 18

5 Neutrino Detection interactions and detector signatures CC ν µ CC ν e / NC ν CC ν τ ν µ + N µ + X ν e + N e + X ν τ τ + X ν + N ν + X track cascade cascade (or double-bang) Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 4 / 18

6 Two Year Cascade Selection Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 5 / 18

7 Low Threshold Contained Events probing lower energies than HESE with an adaptive veto y[km] z[km] PE 300 PE 2200 PE PE x[km] x[km] [PRD 91, (2015)] Active volume decreases with deposited energy threshold reduced to 1 TeV Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 6 / 18

8 Observed Cascades events collected in two years of data 263 cascade events observed between 1 TeV and 1.1 PeV 10 2 Conventional ν Penetrating µ Astrophysical ν Observed Events events in 641 days E [GeV] [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 7 / 18

9 Observed Cascades events collected in two years of data 263 cascade events observed between 1 TeV and 1.1 PeV More atmospheric µ but fewer atmospheric ν from the southern sky events in 641 days sin(δ) [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 7 / 18

10 Observed Cascades events collected in two years of data 263 cascade events observed between 1 TeV and 1.1 PeV % 50% 20% More atmospheric µ but fewer atmospheric ν from the southern sky Poor angular resolution compared to tracks Sensitivity driven by low background including self-veto of atmospheric ν angular error [ ] E [GeV] [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 7 / 18

11 Sensitivity vs. Declination for two years of cascades Shown here: E 2 dn/de at 100 TeV Sensitivity has only weak direction dependence Best IceCube south sky sensitivity yet for soft spectra E 2 (E/100 TeV) γ 2 dn/de [TeV cm 2 s 1 ] South 2 Year Cascades, E 2 2 Year Cascades, E 3 7 Year Tracks, E 2 7 Year Tracks, E Day ANTARES Tracks, E 2 North sin(δ) [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 8 / 18

12 Sensitivity vs. Energy comparing selections scaled to equal livetime Shown here: scaling cascades, throughgoing tracks, and starting tracks to three years of livetime Low background gives good low-energy sensitivity for a southern source E 2 dn/de [TeV cm 2 s 1 ] Year Starting Tracks 3 Year Throughgoing Tracks 3 Year Cascades δ = 60 Enhancement at 6.3 PeV expected due to Glashow resonance E [GeV] [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 9 / 18

13 Extended Sources sensitivity for finite-sized sources Shown here: sensitivity for sources with Gaussian angular extent Poor angular resolution weak dependence on source size No dedicated extended source search with cacades Note: 7 year extended source search with tracks subject to refinement and later publication E 2 dn/de [TeV cm 2 s 1 ] Year Tracks, δ = 30 2 Year Cascades, δ = Year Cascades, δ = +0 2 Year Cascades, δ = source extension ( ) [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 10 / 18

14 Two Year Results Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 11 / 18

15 All-sky Scan and Galactic Plane results from two years of cascades All-sky scan: Hottest spot (α, δ) = (277.3, 43.4 ) Pre-trials p = 0.6% Post-trials p = 66% 24h h Galactic Plane: Simple line-source test, all-sky and South-only Post-trials p = 65% log 10 p [Submitted to ApJ (arxiv: )] Equatorial Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 12 / 18

16 Source Catalog flux constraints from two years of cascades 74 source candidates tested dn de E 2 2 Year Disc. Potential (5σ) 2 Year Sensitivity Upper Limits (90% CL) Most significant: BL Lac at (α, δ) = (330.68, ) Pre-trials p = 0.95% Post-trials p = 34% Flux constraints evaluated for E 2 and E 3 spectra E 2 dn/de [TeV cm 2 s 1 ] sin(δ) [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 13 / 18

17 Source Catalog flux constraints from two years of cascades 74 source candidates tested Most significant: BL Lac at (α, δ) = (330.68, ) Pre-trials p = 0.95% Post-trials p = 34% E 2 (E/100 TeV) dn/de [TeV cm 2 s 1 ] dn de E 3 2 Year Disc. Potential (5σ) 2 Year Sensitivity Upper Limits (90% CL) Flux constraints evaluated for E 2 and E 3 spectra sin(δ) [Submitted to ApJ (arxiv: )] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 13 / 18

18 Six Year Projections Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 14 / 18

19 Point Source Sensitivity adding four years of data with high signal acceptance IceCube Preliminary Adding data from the previous talk Competitive with tracks in the south Largest gains in the south and at low energies E 2 (E/100 TeV) γ 2 dn/de [TeV cm 2 s 1 ] South 7 Year Tracks, E 2 7 Year Tracks, E 3 6 Year Cascades, E 2 6 Year Cascades, E Day ANTARES Tracks, E 2 North sin(δ) Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 15 / 18

20 Galactic Plane Sensitivity Fermi-LAT π 0 decay model for diffuse emission Diffuse galactic emission model from π 0 decay fits +60 Fermi-LAT π 0 decay model h 0h Equatorial Flux [a.u.] [ApJ 750 (2012) 3] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 16 / 18

21 Galactic Plane Sensitivity Fermi-LAT π 0 decay model for diffuse emission Diffuse galactic emission model from π 0 decay fits +60 Fermi-LAT π 0 decay model Sensitivity: E 2 (E/100 TeV) 0.5 dn/de = Tracks: TeV/cm 2 /s [Submitted to ApJ (arxiv: )] h 0h Equatorial Signal PDF (1 reconstructed uncertainty) [a.u.] as viewed with throughgoing tracks Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 16 / 18

22 Galactic Plane Sensitivity Fermi-LAT π 0 decay model for diffuse emission Diffuse galactic emission model from π 0 decay fits +60 Fermi-LAT π 0 decay model Sensitivity: E 2 (E/100 TeV) 0.5 dn/de = Tracks: TeV/cm 2 /s [Submitted to ApJ (arxiv: )] Cascades: TeV/cm 2 /s Combined: TeV/cm 2 /s h Equatorial Signal PDF (15 reconstructed uncertainty) [a.u.] as viewed with cascades IceCube Preliminary 0h Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 16 / 18

23 Galactic Plane Sensitivity KRA-γ model for diffuse emission Modified model with hardening near galactic center +60 KRA-γ model h 0h Equatorial Flux at 100 TeV [a.u.] [ApJL 815 (2015) L25] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 17 / 18

24 Galactic Plane Sensitivity KRA-γ model for diffuse emission Modified model with hardening near galactic center +60 KRA-γ model KRA-γ (50 PeV cutoff) model sensitivity: Tracks: 0.80 model [Submitted to ApJ (arxiv: )] h 0h Equatorial Signal PDF (1 reconstructed uncertainty) [a.u.] as viewed with throughgoing tracks Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 17 / 18

25 Galactic Plane Sensitivity KRA-γ model for diffuse emission Modified model with hardening near galactic center +60 KRA-γ model KRA-γ (50 PeV cutoff) model sensitivity: Tracks: 0.80 model [Submitted to ApJ (arxiv: )] Cascades: 0.41 model Combined: 0.35 model h Equatorial Signal PDF (15 reconstructed uncertainty) [a.u.] as viewed with cascades IceCube Preliminary 0h Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 17 / 18

26 Galactic Plane Sensitivity KRA-γ model for diffuse emission Modified model with hardening near galactic center KRA-γ (50 PeV cutoff) model sensitivity: Tracks: 0.80 model [Submitted to ApJ (arxiv: )] Cascades: 0.41 model Combined: 0.35 model IceCube Preliminary Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 17 / 18

27 Outlook IceCube cascades allow enhanced southern sky sensitivity due to low background rates and the atmospheric neutrino veto. Results from two years of data were recently submitted to ApJ. Second-iteration analysis with more livetime, larger effective area, and tests of detailed galactic plane models is currently under development. Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 18 / 18

28 Backup Slides Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 19 / 18

29 Cosmic Ray Muon Background two approaches to neutrino selection Classic ν µ strategy: Earth acts as neutrino filter Well-reconstructed Northern tracks must be neutrinos North sky and ν µ only Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 20 / 18

30 Cosmic Ray Muon Background two approaches to neutrino selection Classic ν µ strategy: Earth acts as neutrino filter Well-reconstructed Northern tracks must be neutrinos Active veto to select starting events: North sky and ν µ only Reduced effective volume, but full sky and all flavor Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 20 / 18

31 High Energy Starting Events results from four years of data Search for very bright, contained events Sensitive to all flavors above 60 TeV 80(+2) events in six years [PoS(ICRC2017)981] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 21 / 18

32 High Energy Starting Events results from four years of data Search for very bright, contained events IceCube Preliminary Sensitive to all flavors above 60 TeV 80(+2) events in six years Simplified source search includes cascades and tracks hr hr Equatorial TS = 2 ln(l/l0) 12.6 [PoS(ICRC2017)981] No use of signal MC to connect to source fluxes Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 21 / 18

33 Low Threshold Contained Events results from two years of data Astrophysical excess down to 10 TeV Fit consistent with high energy search but errors are smaller Model disagreement at 30 TeV not significant (p = 5%) [PRD 91, (2015)] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 22 / 18

34 Astrophysical Muon Neutrinos results from six years of data Accept incoming tracks larger effective area Restricts search to North sky ν µ Probes higher energies Harder best fit spectrum: Φ ν (E) = Φ 0 (E/100 TeV) 2.13±0.13 Φ 0 = /GeV/cm 2 /s/sr [ApJ 833 (2016) no. 1, 3] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 23 / 18

35 Standard Point Source Analysis search for clustering with 7 years of muon tracks Standard skymap dominated by atm. ν in the North and atm. µ in the South North: p = 29% South: p = 17% h North South Equatorial 0h log 10 p [ApJ 835 (2017) no. 2, 151] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 24 / 18

36 Standard Point Source Analysis search for clustering with 7 years of muon tracks Standard skymap dominated by atm. ν in the North and atm. µ in the South North: p = 29% South: p = 17% Excess of hot spots? North: p = 25% #Points P σ Data 3σ 2σ 1σ North Expectation log 10 pmin [ApJ 835 (2017) no. 2, 151] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 24 / 18

37 Standard Point Source Analysis search for clustering with 7 years of muon tracks Standard skymap dominated by atm. ν in the North and atm. µ in the South North: p = 29% South: p = 17% Excess of hot spots? North: p = 25% South: p = 8.2% Galactic Plane ±15 : p = 26% #Points P σ Data 3σ 2σ 1σ South log 10 pmin [ApJ 835 (2017) no. 2, 151] Expectation Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 24 / 18

38 Standard Point Source Analysis search for clustering with 7 years of muon tracks Standard skymap dominated by atm. ν in the North and atm. µ in the South North: p = 29% South: p = 17% Excess of hot spots? North: p = 25% South: p = 8.2% Galactic Plane ±15 : p = 26% [ TeV cm 2 s 1 ] E ν 2 dφ deν Pre-trial (Disc. Potential) Pre-trial (Sensitivity) Post-trial Upper Limit (90%) South ANTARES (Sensitivity) Upper Limits (90%) Hotspots North sin δ [ApJ 835 (2017) no. 2, 151] Source Searches with IceCube Cascades TeVPA 17 Mike Richman (Drexel University) 24 / 18