UNASSOCIATED GAMMA-RAY SOURCES AS TARGETS FOR INDIRECT DM DETECTION - PowerPoint PPT Presentation

UNASSOCIATED GAMMA-RAY SOURCES AS TARGETS FOR INDIRECT DM DETECTION WITH FERMI-LAT J. Coronado-Blázquez M. Sánchez-Conde, A. Domínguez, M. di Mauro, E. Charles, N. Mirabal for the Fermi -LAT Collaboration Halo Substructure & Dark Matter Searches Madrid - June 2018 1

DARK MATTER (DM) SUBHALOS AS TARGETS ❑ Λ CDM cosmological model predicts lots of substructure → DM subhalos ❑ Subhalo with masses below ~ 10 7 𝑁 ⨀ do not retain gas (baryons) → no emission ❑ BUT, if they annihilate (WIMP model) → DM-induced gamma-ray emission ❑ Fermi -LAT (2008-) → We have gamma-ray source catalogs ❑ Lots of unidentified sources (unIDs) in catalogs → Some of them may be subhalos ❑ N-body cosmological simulations → What do we expect? ❑ We do not have an unequivocal signal of DM annihilation → constraints on 𝝉𝒘 , 𝒏 𝝍 2

DM ANNIHILATION IN THE WIMP MODEL 𝜐 + 𝜐 − 𝑐ത 𝑐 𝜓𝜓 → ൞ → ⋯ → 𝛿𝛿 𝐺 𝐹 > 𝐹 𝑢ℎ = 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 ∗ 𝑔 𝑞𝑞 (𝐹 > 𝐹 𝑢ℎ ) 𝑋 + 𝑋 − ? 1 ? 2 Astrophysics (Density Particle Physics (channel, profile, distance …) annihilation spectra …) 𝑒𝑂 1 𝜏𝑤 𝑔 2 𝑔 𝑞𝑞 = ෍ 𝐶 𝑔 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 = න 𝑒𝛻 න 𝜍 𝐸𝑁 𝑠 𝜇 𝑒𝜇 2 4𝜌 𝑒𝐹 2𝑛 𝜓 𝑔 𝑔 𝛦𝛻 𝑚.𝑝.𝑡 Branching ratio taken as 1 3

DM ANNIHILATION IN THE WIMP MODEL 𝜐 + 𝜐 − 𝑐ത 𝑐 𝜓𝜓 → ൞ → ⋯ → 𝛿𝛿 𝐺 𝐹 > 𝐹 𝑢ℎ = 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 ∗ 𝑔 𝑞𝑞 (𝐹 > 𝐹 𝑢ℎ ) 𝑋 + 𝑋 − ? 1 ? 2 Astrophysics (Density Particle Physics (channel, profile, distance …) annihilation spectra …) Instrument 2 · 𝐺 2 · 𝐺 𝑛 𝜓 = 𝑛 𝜓 𝑛𝑗𝑜 𝑛𝑗𝑜 𝜏𝑤 ∝ 𝑒𝑂 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 · 𝑂 𝛿 Theory 𝐹 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 · ׬ 𝑒𝐹 𝑒𝐹 𝐹 𝑢ℎ Simulations We want to probe the lowest possible 𝝉𝒘 values to rule out WIMP models 4

FIRST INGREDIENT: DM INTEGRATED SPECTRA • From Cirelli PPPC4 (PYTHIA8), including electroweak corrections • ‘Usual’ annihilation channels 𝑐ത 𝑐, 𝜐 + 𝜐 − , 𝑋 + 𝑋 − , 𝑓𝑢𝑑. • Wimp masses from 5 GeV up to 100 TeV • Parametric fit to Power Law with SuperExponential Cutoff: −Γ 𝛾 𝐹 𝑒𝑂 𝐹 − 𝐹 𝑑𝑣𝑢 𝑒𝐹 = 𝐿 · 𝑓 𝐹 0 (Later used for the minimum flux) 5

FIRST INGREDIENT: DM INTEGRATED SPECTRA • We want the integrated spectra, 𝐹 𝑒𝑂 𝑂 𝛿 = න 𝑒𝐹 𝑒𝐹 𝐹 𝑢ℎ • Dependance on the catalog energy threshold 6

SECOND INGREDIENT: J-FACTOR • We search for DM subhalos in Fermi-LAT unassociated (unIDs) sources • N-body cosmological simulations predict a number of subhalos • We could have the brightest of them already hidden among the LAT unIDs 𝐺 𝑛𝑗𝑜 2 𝜏𝑤 ∝ 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 = න 𝑒𝛻 න 𝜍 𝐸𝑁 𝑠 𝜇 𝑒𝜇 𝐾 𝑔𝑏𝑑𝑢𝑝𝑠 · 𝑂 𝛿 𝛦𝛻 𝑚.𝑝.𝑡 7

SECOND INGREDIENT: J-FACTOR • We use Via Lactea II (VL-II) simulation (0805.1244), DM only, Milky Way size, resolving subhalo masses down to ~10 5 𝑁 ⊙ • Radial distribution well described by antibiased NFW or Einasto • Subhalo mass function a power law with index close to -2 • But subhalos below the resolution limit can be very important Diemand+08 (0805.1244)

SECOND INGREDIENT: J-FACTOR A low mass subhalo close enough to the Earth can have a bigger J-factor than a further, massive subhalo

SECOND INGREDIENT: J-FACTOR • The less massive the subhalo, the nearest must be to have a relevant flux • Also, 𝐾 ∝ 𝑑 3 ∝ 𝑁 −3 ( 𝑑 ≡ concentration, bigger for lower masses)

SECOND INGREDIENT: J-FACTOR • We repopulate the original VL-II simulation in a realistic yet computationally feasible way below its mass resolution limit. • Currently a work in progress with A. Aguirre-Santaella

FERMI-LAT UNASSOCIATED SOURCES (UNIDs) Obs. Time (yr) Energy Range Total UnIDs 2FHL 6.7 50 -2000 GeV 360 48 (1508.04449) 3FHL 7 10 - 2000 GeV 1556 177 (1702.00664) 3FGL 4 0.1 – 300 GeV 3033 1010 (1501.02003) 12

UNIDs “ FILTERING ” 𝜏𝑤 ∝ 𝐾 −1 → less DM subhalo • candidates among unIDs means better constraints • Exponential rise in our constraining power below ~20% of sources in every catalog • 20% = 202 sources in 3FGL, 10 in 2FHL and 35 in 3FHL • From these numbers down, every source we remove has a big impact 13

DM SUBHALO FILTERS 1. Source associations 2. Flux variability We adopt a 3. Latitude conservative approach 4. Machine learning identification 5. Multiwavelength emission 6. Complex regions 14

SOURCE ASSOCIATIONS: OBSERVATIONAL CAMPAIGNS • Observational campaigns allowed us to remove 66 AGNs and 18 pulsars • We remove 15 additional sources found to be Millisecond Pulsars (MSPs) 15

SOURCE FLUX VARIABILITY • Apart from the official catalogs, we use FAVA (Fermi All-Sky Variability Analysis) • Does not relay on any diffuse model – just relative deviations • Some sources behave as steady on average for long periods, but can present a short flare → FAVA weekly binning important 3FHL J0500.6+1903 … but seen in flare Null variability … 16

SOURCE FLUX VARIABILITY • Note: in some cases, the flare occurs after the time period used for the catalog (e.g. 2FHL – 320 weeks, while a given source may flare in week 400) • We discard 2 2FHL, 12 3FHL and 13 3FGL sources • We also identify source “ duplicities ” : two sources that actually are the same – 2 cases confirmed 17

LATITUDE There are subhalos at low latitudes, but 1) the diffuse emission makes them very difficult to detect and 2) most of these unIDs are expected to be pulsars, which can fake DM We cut the Galactic plane ±10° , removing 14 sources in 2FHL, 70 in 3FHL, 429 in 3FGL Much less diffuse emission – Life gets easier 18

MACHINE LEARNING IDENTIFICATION • Salvetti+17 (AKA 3FGLzoo) – “4FGLzoo” on the way • Lefaucheur+Pita17 Assign probabilities to sources based on ML algorithms to derive their physical nature Applied only to the 3FGL (due to higher available statistics) – 186 rejections 2FHL & 3FHL rejections only if also present in the 3FGL (29 in 3FHL) 19

MACHINE LEARNING IDENTIFICATION • Low false positive rate: <4% (3FGLzoo), 2-4% Lefaucheur+Pita • Most of the classified sources are common to both papers, but some are not • 162 unIDs classified as AGN in the 3FGLzoo + 24 extra in Lefaucheur+Pita • Numbers refer already to the pool of unIDs that remained after the previous cuts 20

MACHINE LEARNING IDENTIFICATION • Mirabal+16 (1605.00711) applies machine learning for pulsar searches – 34 high- latitude pulsar candidates (only 3 remaining in our sample) • However, pulsars can mimic a DM signal Ackermann+12 • Therefore, this work is specially useful for us, not for rejecting unIDs but to point out VIP candidates 21

MULTIWAVELENGTH EMISSION • DM subhalos expected to Search in 5 arcmin bright only in gammas • Should they exhibit other wavelength emission (without any other kind of source within 5 - 10 arcmin, depending on the catalog) IR+Optical (WISE, Gamma (2FHL) we eliminate them 2MASS, USNO) tools.asdc.asi.it 22

MULTIWAVELENGTH EMISSION Stroh+13 SWIFT ASDC www.swift.psu.edu Total (HEASARC) /unassociated/ 2FHL 4 0 2 6 3FHL 10 2 5 17 3FGL 7 13 207 227 IR-Optic X-Ray 23

COMPLEX REGIONS • 3FGL sources flagged with “c” ( e.g. 3FGL J0342.3+3148c) • See Sec. 3.8 of 1501.02003 (3FGL paper) – Considered potential artifacts • 78, most on the Galactic plane (i.e. already excluded from our analysis before); we discard 5 high-latitude sources (only in 3FGL) 24

FAMOUS (EX-)CANDIDATES ▪ 3FGL J2212.5+0703 (Bertoni+16) – actually 2 sources ▪ 3FGL J1924.8-1034 (Xia+17) – classified as AGN by machine learning ▪ 3FGL J1119.9-2204 (Hooper+17) – seen with SWIFT ▪ 3FGL J0318.1+0252 (Hooper+17) – seen with SWIFT ▪ 3FGL J2212.5+0703 (Hooper+17) – FAVA correlation, seen with SWIFT All 3FGL (low energy) sources 25

UNIDS FILTERING RESULTS Original Result 2FHL 48 4 3FHL 177 24 3FGL 1010 16 26

THIRD INGREDIENT: LAT SENSITIVITY TO DM SUBHALOS • Minimum flux to have a 5-sigma detection over background • Normally taken as the threshold flux of the catalog • BUT, important dependance on annihilation channel, source sky position and catalog setup 27

THIRD INGREDIENT: LAT SENSITIVITY TO DM SUBHALOS • We use the fermipy analysis software to simulate sources mimicking the catalog setup (observation time, energy range, diffuse+isotropic templates …) • A putative dark matter source is simulated for each position, catalog setup, annihilation channel and DM mass • All-sky maps with this information 28

COMPARISON BETWEEN DIFFERENT DM MASSES 𝑛 𝐸𝑁 = 10 𝐻𝑓𝑊 𝑛 𝐸𝑁 = 1 𝑈𝑓𝑊 3FGL setup, 𝜐 + 𝜐 − channel 30

𝑛𝑗𝑜 vs. WIMP mass 𝐺 𝑛𝑗𝑜 vs. WIMP 𝐺 mass, all latitudes 𝑛𝑗𝑜 vs. Gal. latitude 𝐺 31

+ + = DM annihilation spectra J-factor Minimum flux 32

DARK MATTER CONSTRAINTS PRELIMINARY PRELIMINARY 33

SENSITIVITY REACH OF THE METHOD PRELIMINARY PRELIMINARY 34