dark matter annihilation in the galactic center PDF
Preview dark matter annihilation in the galactic center
DARK MATTER ANNIHILATION IN THE GALACTIC CENTER Dan Hooper – Fermilab and the University of Chicago UCLA Dark Matter Conference February 18, 2016 10 Dan Hooper – DM Annihilation in the GC Sorry if I sound like a broken record… 10 Reason 1: Overwhelming Statistical Significance and Detailed Information The Dark Matter Interpretation ! This excess consists of ~104 photons per square meter, per year (>1 GeV, within 10° of the Galactic Center) ! The spectral shape of the excess can be well fit by a dark matter Raw Mpaapr t ic le w i th a mRaesssi dinu tahle M raanpge ( xo3f ) Dar k Ma tter In T h e Galactic 7 to 12 GeV (similar to that required by CoGeNT, DAMA, and CRESST), C ent er Re gion annihilating primarily to τ+τ- (possibly among other leptons) ! The spectrum contains a (cid:2)bump-like(cid:3) feature at ~1-5 GeV ! The angular distribution of the ! Can be f it quite w ell by a simple 2 5-30 Ge V dark matter particle, in a cusped signal is well fit by a halo profile wdiitsht r ibution (γ~1.1), annihilating to bb with σv ~ 9 x 10-26 cm3/s ρ(r) ~ r -γ, with γ ~ 1.25 to 1.4 (in good agreement with expectations from simulations) ! The normalization of the signal requires the dark matter to have an annihilation cross section within a factor of a few of the value predicted for a simple thermal FIG.9: Therawgamma-raymaps(left)arnedlitche (rσesvid ~ua l3mx1ap0s-2a6ft ecrmsu3b/tsra)c tingthebest-fitGalacticdi↵usemodel, 20cm template, point sources, and isotropic template (right), in units of photons/cm2/s/sr. The right frames clearly contain a significantcentralandspatiallyextendedexcess,peakingat 1-3GeV.Resultsareshowningalacticcoordinates,andallmaps havUebeCensLmoAot heDdbMya 02.250�G1au4ssi an. ⇠ oftheGalacticPlane,whilevaluesgreat Herotohpaenro anendar eLindneont,o PnlRyDelo, nagraXteivd:1al1o1n0g.o0r0p0e6rp endiculartotheGalac- preferentially extended perpendicular to the plane. In tic Plane, but along any arbitrary orientation. Again, eachcase,theprofileslopeaveragedoverUalloCrieLntaAtio nDs Mwe 2fin0dt1ha2tt hatthequalityofthefitworsensifthethe is taken to be � =1.3 (left) and 1.2 (right). From this template is significantly elongated either along or per- figure, it is clear that the gamma-ray excess prefers to pendiculartothedirectionoftheGalacticPlane. Amild befitbyanapproximatelysphericallysy mmetricdistri- statisticalpreferenceisDfaounn Hdo,ohpoweer v- eTrh,efo Hruanmt Foorpr hDoalorkg yMatter L. Goodenough, D. Hooper, arXiv:0910.2998 bution,anddisfavorsanyaxisratiowhichdepartsfrom withanaxisratioof 1.3-1.4elongatedalonganaxisro- ⇠ FtuenImGIintp.yl9aFb:teiyg,T.mhpe1oo1irrne,atwtwshoegauanrmgceaemnsp,aepr-arraonalxdyizimemisoaatttphresiolspy(liaec2fp0ttp)%erma.onpadlcahttehwe(rirtieghshiidnt)u,aoilunmruanpiststgaaafottlfeaedrcpthsi⇠ucobt3cot5onr�aosc/rctdcoiminungn2a/tttsehe/rsescrl(b.oaecsksTUtiw-mhfieitsCileraGirgfaLrhploatrmcAeftfrieatc rhmedDenei↵sGcueMcaslweleaaamcr stloy2iacdlcesP0olo,nlat21fnoa0iuen0cnimnda significantcentralandspatiallyextendedexcess,peakingat 1-3iGneoVu.rRIensnueltrsGaarelasxhyowannainlygsaisl)a.ctWichcoiloertdhinisatmesa,yanbdeaalsltmataipss- hGaavleacbteiecnCsmenotoetrheadnbaylyasis0.2t5o�tGesatusmsioanrp.h ologies that are⇠ oftheGalacticPlane,whilevaluesgreaterthanoneare notonlyelongatedalongorperpendiculartotheGalac- preferentially extended perpendicular to the plane. In tic Plane, but along any arbitrary orientation. Again, eachcase,theprofileslopeaveragedoverallorientations wefindthatthatthequalityofthefitworsensifthethe is taken to be � =1.3 (left) and 1.2 (right). From this template is significantly elongated either along or per- figure, it is clear that the gamma-ray excess prefers to pendiculartothedirectionoftheGalacticPlane. Amild befitbyanapproximatelysphericallysy mmetricdistri- statisticalpreferenceisfound,however,foramorphology bution,anddisfavorsanyaxisratiowhi chdepartsfrom withanaxisratioof 1.3-1.4elongatedalonganaxisro- unitybymorethanapproximately20%. tated⇠35� countercl⇠ockwisefromtheGalacticPlanein galacticcoordinates(asimilarpreferencewasalsofound In Fig. 11, we generalize this approach within our inourInnerGalaxyanalysis). Whilethismaybeastatis- Galactic Center analysis to test morphologies that are Dan Hooper – DM Annihilation in the GC The Evolving Nature of the Galactic Center Debate Dan Hooper – DM Annihilation in the GC The Evolving Nature of the Galactic Center Debate UCLA 2010 There is no Galactic Center excess (“what are you smoking?”) Dan Hooper – DM Annihilation in the GC The Evolving Nature of the Galactic Center Debate UCLA 2010 There is no Galactic Center excess (“what are you smoking?”) UCLA 2012 Sure there seems to be a Galactic Center excess, but 1) Are we sure that it is spatially extended? 2) Are we mismodeling standard diffuse emission mechanisms? 3) Is there really a Galactic Center excess? Dan Hooper – DM Annihilation in the GC The Evolving Nature of the Galactic Center Debate UCLA 2010 There is no Galactic Center excess (“what are you smoking?”) UCLA 2012 Sure there seems to be a Galactic Center excess, but 1) Are we sure that it is spatially extended? 2) Are we mismodeling standard diffuse emission mechanisms? 3) Is there really a Galactic Center excess? UCLA 2014 What is generating this excess? 1) A large population of centrally located millisecond pulsars? 2) A series of recent cosmic ray outbursts? 3) Annihilating dark matter? Dan Hooper – DM Annihilation in the GC The Evolving Nature of the Galactic Center Debate UCLA 2010 There is no Galactic Center excess (“what are you smoking?”)* UCLA 2012 Sure there seems to be a Galactic Center excess, but 1) Are we sure that it is spatially extended? 2) Are we mismodeling standard diffuse emission mechanisms? 3) Is there really a Galactic Center excess? UCLA 2014 What is generating this excess? 1) A large population of centrally located millisecond pulsars? 2) A series of recent cosmic ray outbursts? 3) Annihilating dark matter? *Dave Klein was very supportive during this critical time Dan Hooper – DM Annihilation in the GC The Basic Features of the GeV Excess 7 ! Bright and highly statistically significant ! Distributed with spherical symmetry about the Galactic Center with a flux that falls as ~r -2.4, between ~0.06° and ~10° (if interpreted as annihilating dark matter, ρ ~ r -1.2 between ~10-1500 pc) DM ! The spectrum of this excess peaks at 10 10 ~1-3 GeV, and is in good agreement with that predicteFIdG .f6r: oLemft fr aame :~T3he5sp-ec5tru0m Gof teheVda rkWmaIttMer cPom ponent, extracted from a fit in our standard ROI (1� < b < 20�, | | l < 20�) for a template corresponding to a generalized NFW halo profile with an inner slope of � = 1.18 (normalized to the | | annihilating fltuox a tbanba n(gfleoofr5 �efrxomatmhe Gpallaecti)c Center). Shown for comparison (solid line) is the spectrum predicted from a 43.0 GeV darkmatterparticleannihilatingtob¯bwithacrosssectionof�v =2.25 10�26 cm3/s [(0.4GeV/cm3)/⇢local]2. Rightframe: ⇥ ⇥ as left frame, but for a full-sky ROI (b >1�), with � =1.28; shown for comparison (solid line) is the spectrum predicted from ! To normalizea 3 6t.6hGeeV odabrksmeattrevr peardtic lesaingni|hni|laatinlg wto ib¯bthwi th a cross section of �v =0.75⇥10�26 cm3/s ⇥[(0.4GeV/cm3)/⇢local]2. annihilating dark matter, a cross section of the Galactic plane; masking the region with b < 2 sistent with that extracted at higher latitudes (see Ap- � | | of σv ~ 10-26ch acnmges3th/se p riesfe rrreedqvaulueirteo d� = 1.25 in our default pendix A).7 Shown for comparison (as a solid line) is the ROI, and � = 1.29 over the whole sky. In contrast to spectrum predicted from (left panel) a 43.0 GeV dark Ref. [8], we find no significant di↵erence in the slope pre- matter particle annihilating to b¯b with a cross section ferred by the fit over the standard ROI, and by a fit only of �v = 2.25 10 26 cm3/s [(0.4GeV/cm3)/⇢ ]2, � local ⇥ ⇥ over the southern half (b < 0) of the RODI (Hwe, aGlsoofionddenoanudg(rhig h(t2p0an0e9l),a 2360.61G0e)V, DdaHrk,m Latitnerdpeanrt ic(l2e 0an1n1i-), no significant di↵erence between the fit over the full sky hilating to b¯b with a cross section of �v = 0.75 10 26 Abazajian, Kaplinghat (2012), Gordon, Macia⇥s (�2013), and the southern half of the full sky). This can be seen cm3/s [(0.4GeV/cm3)/⇢ ]2. The spectra extracted local ⇥ directly from Fig. 5, where the full-skyDanadysloaunth eernt- al (fo2r0th1is4c)o,m Cpoanleontrear,e Cinhmoolidser,a Wtelyegnoiogdearg r(e2em0e1nt4) sky fits for the same level of masking are found to favor with the predictions of the dark matter models, yielding quite similar values of � (the southern sky distribution fits of �2 =44 and 64 over the 22 error bars between 0.3 is broader than that for the full sky simply due to the and50GeV.Weemphasizethat theseuncertainties(and di↵erence in the number of photons). The best-fit values the resulting �2 values) are purely statistical, and there for gamma, from fits in the southern half of the standard are significant systematic uncertainties which are not ac- ROI and the southern half of the full sky, are 1.13 and counted for here (see the discussion in the appendices). 1.26 respectively. We also note that the spectral shape of the dark matter template is quite robust to variations in �, within the In Fig. 6, we show the spectrum of the emission cor- range where good fits are obtained (see Appendix A). related with the dark matter template in the default ROI and full-sky analysis, for their respective best-fit values of � = 1.18 and 1.28.6 We restrict to energies In Fig. 7, we plot the maps of the gamma-ray sky 50 GeV and lower to ensure numerical stability of the in four energy ranges after subtracting the best-fit dif- fit in the smaller ROI. While no significant emission is fuse model, Fermi Bubbles, and isotropic templates. In absorbed by this template at energies above 10 GeV, the 0.5-1 GeV, 1-3 GeV, and 3-10 GeV maps, the dark- ⇠ a bright and robust component is present at lower en- matter-like emission is clearly visible in the region sur- ergies, peaking near 1-3 GeV. Relative to the analy- roundingtheGalacticCenter. Muchlesscentralemission ⇠ sis of Ref. [8] (which used an incorrectly smoothed dif- is visible at 10-50 GeV, where the dark matter compo- fuse model), our spectrum is in both cases significantly nent is absent, or at least significantly less bright. harder at energies below 1 GeV, rendering it more con- FIG. 10: The raw gamma-ray maps (left) and the residual maps after subtracting the best-fit Galactic di↵use model, 20 cm template, point sources, and isotropic tFeImGp.la1t0e: (Trihgehtr)a,wingaumnimtsa-orfayphmoatopnss(/lcemft2)/asn/sdr.thTehreesirdiguhatl mfraampsesafctleerarsluybtcroancttaiinngathe best-fit Galactic di↵use model, 20 cm significantcentralandspatiallyextendedteemxcpelsast,ep,epaokiinntgsaoturc1e-s3,GaenVd.iRsoetsruolptsicarteemshpolwatnein(rgigahlat)c,ticincouonridtisnaotfeps,haontodnasl/lcmma2p/ss/sr. The right frames clearly contain a havebeensmoothedbya0.25� Gaussians.ignificantcentralan⇠dspatiallyextendedexcess,peakingat⇠1-3GeV.Resultsareshowningalacticcoordinates,andallmaps havebee7nAsmnoeoatrhleiedrbvyerasi0o.2n5�ofGtahuissswiaonr.k found this improvement only in 6 A comparison between the two ROIs with � held constant is the presence of the CTBCORE cut; we now find this hardening presented in Appendix Ai.ng to a statical preference for such a componeinndteaptetnhdeent oafsthsheoCwTnBinCOthReErigchutt.frame of Fig.2, respectively). The level of 17�. In Fig. 8, we show thinegsptoecatrsutmatiocfalthpereferennocremfaolrizsauticohnsaocfomthpeoGneanlatcatitctCheenteraasnsdhoInwnnerinGtahlaexryight frame of Fig. 2, respectively). The dark-ma⇠tter-like component, for valuleesveolfo�f =117.�2.(lIenftFig.s8ig,nwalessahreowcotmhpeastpibelcetr(useme Fofigtsh.e6andno8r)m,aallitzhaotuiognhstohfethe Galactic Center and Inner Galaxy ⇠ frame) and � = 1.3 (right frame). Sdhaorwkn-mfaotrtecro-mlikpearci-ompodneetnaitl,sfoofr tvhailsuecsomofp�ari=son1.2de(pleefntd onsitghnealpsraerceisceommopra-tible (see Figs. 6 and 8), although the son is the spectrum predicted from afr3a5m.2e5)GaenVd W� =IM1P.3 (ripghhotlofrgaymteh)a.t iSshaodwonptfeodr.compari- details of this comparison depend on the precise mor- annihilatingtob¯b. Thesolidlinerepressoenntisstthheecsopnetcrtibruum- predicted from a 35.25 GeV WIMP phology that is adopted. tion from prompt emission, whereas tahnendihoitla-dtainsghetdoab¯bn.dThesoWlidelinnoeteretphraetsetnhtestFheermcointtroioblu-gtlike determines the quality of the fit assuming a given speWcteranlostheatpheatfotrhe Fermi tool gtlike determines the dottedlinesalsoincludeanestimateftoironthferocmontprriobmutpiotnemission, whereas the dot-dashed and thedarkmattertemplate,butdoesnotqugeanlietryalolyf pthroevifidteassuming a given spectral shape for frombremsstrahlung(forthez=0.15doatntded0.l3inkepscaclsaoseisn,cludeanestimateforthecontribution a model-independent spectrum for thitshoerdoatrhkemr caottmerpote-mplate,butdoesnotgenerallyprovide frombremsstrahlung(forthez=0.15and0.3kpccases, a model-independent spectrum for this or other compo- Dan Hooper – DM Annihilation in the GC 8 10 0.5-1 GeV residual 1-3 GeV residual 20 2200 20 1122 1155 1100 10 1 10 1 0 0 c-6 88 c-6 1100 ou ou 000 n 000 66 n ts ts /cm 44 /cm 55 2 2 -10 /s/s-10 22 /s/s r r 00 00 -20 -20 --22 20 10 000 -10 -20 20 10 000 -10 -20 3-10 GeV residual 10-50 GeV residual 20 20 11..55 44 10 1 10 1 33 0-6 11..00 0-6 c c o o u u 000 22 n 000 n ts ts /c 00..55 /c m m 11 2 2 /s /s -10 /s-10 /s r r 00 00..00 -20 -20 20 10 000 -10 -20 20 10 000 -10 -20 FIG.10: Therawgamma-raymaps(left)andtheresidualmapsaftersubtractingthebest-fitGalacticdi↵usemodel,20cm FIG.7: Intensitymaps(ingalacticcoordinates)aftersubtractingthepointsourcemodelandbest-fitGalacticdi↵usetmemopdlealt,e, point sources, and isotropic template (right), in units of photons/cm2/s/sr. The right frames clearly contain a Fermi bubbles,andisotropictemplates. Templatecoe�cientsareobtainedfromthefitincludingthesethreetemplatsiegsnaifincdantcentralandspatiallyextendedexcess,peakingat 1-3GeV.Resultsareshowningalacticcoordinates,andallmaps a � = 1.3 DM-like template. Masked pixels are indicated in black. All maps have been smoothed to a common PShFaveofbe2ensmoothedbya0.25�Gaussian. ⇠ degreesfordisplay,beforemasking(thecorrespondingmaskshavenot beensmoothed;theyreflecttheactualmasksusedin theanalysis). Atenergiesbetween 0.5-10GeV(i.e.inthefirstthreeframes),thedark-matter-likeemissionDiscaleayrlylavisnible, Finkbeiner, DH, Linden, Slatyer, Rodd (2014) ⇠ aroundtheGalacticCenter. ingtoastaticalpreferenceforsuchacomponentatthe asshownintherightframeofFig.2,respectively). The level of 17�. In Fig. 8, we show the spectrum of the normalizationsoftheGalacticCenterandInnerGalaxy ⇠ dark-matter-like component, for values of � = 1.2 (left signalsarecompatible(seeFigs.6and 8),althoughthe V. THEGALACTICCENTER 10.0 GeV. Included in the fit is a model for thefGraamlaec)-and � =1.3 (right frame). Shown for compari- details of this comparison depend on the precise mor- tic di↵use emission, supplemented by a model spsaotniailslythespectrumpredictedfroma35.25GeVWIMP phologythatisadopted. tracing the observed 20 cm emission [45], a moadnenlihfoilratingtob¯b. Thesolidlinerepresentsthecontribu- In thissection, wedescribe our analysisof theFermi theisotropicgamma-raybackground,andallgammtioan-rfaryompromptemission,whereasthedot-dashedand We note that the Fermi tool gtlike determines the data from the region of the Galactic Center, defined as sources listed in the 2FGL catalog [46], as welldaostttehdelinesalsoincludeanestimateforthecontribution quality of the fit assuming a given spectral shape for |b|<5�,|l|<5�. WemakeuseofthesamePass7data two additional point sources described in Ref. [47fr]o.mWberemsstrahlung(forthez=0.15and0.3kpccases, tahmedoadrekl-imndaettpeerntdeemntplsaptee,ctbruutmdofoersnthoitsgoerneortahlelyrpcoromvpidoe- set,withQ2cutsonCTBCORE,asdescribedinthepre- allowthefluxandspectralshapeofallhigh-significance vioussection. Weperformedabinnedlikelihoodanalysis (pTS > 25) 2FGL sources located within 7� of the to this data set using the Fermi tool gtlike, dividing GalacticCentertovary. Forsomewhatmoredistantor tahnedr1e2giloongairnittohm20i0ca⇥ll2y0-0spsapcaetdiaelnbeirngsy(beaincshb0e.0tw5�ee⇥n00.0.351�6)-, lower significance sources ( =7��8� and pTS>25, Dan Hooper – DM Annihilation in the GC Sp ectrum of the Residuals 7 ! FIG. 6: Left frame: The spectrum of the dark matter component, extracted from a fit in our standard ROI (1 < b < 20 , � � | | l < 20�) for a template corresponding to a generalized NFInWnhaelorp Grofialelwaitxhyan -i nTnehr eslo pDe oMf � t=e1m.18p(nlaortmeal inzead ttoutrhaelly picks up the following spectral | | flux at an angle of 5 from the Galactic Center). Shown for comparison (solid line) is the spectrum predicted from a 43.0 GeV � dark matter particle annihilating to b¯b with a cross section osfh�va=p2e.2 5- t1h0e26 ncmo3/rsma[(l0i.z4GaetVio/cnm 3)o/⇢f th]e2. RNigFhtWfra mtee:mplate is allowed to float � local ⇥ ⇥ as left frame, but for a full-sky ROI ( b > 1 ), with � = 1.28; shown for comparison (solid line) is the spectrum predicted from � a 36.6 GeV dark matter particle anni|hi|lating to b¯b with a cirnosds seecptioennofd�ev =nt0l.y75 in1 0e2v6ecmr3y/ sen[(e0.r4gGeyV /bcmin3)/⇢ ]2. � local ⇥ ⇥ Daylan, Finkbeiner, DH, Linden, Slatyer, Rodd (2014) ! of the Galactic plane; masking the region with b < 2 sistent with that extracted at higher latitudes (see Ap- | | G� alactic Center - Various initial seeds for the dark matter spectrum, the changes the preferred value to � = 1.25 in our default pendix A).7 Shown for comparison (as a solid line) is the ROI, and � = 1.29 over the whole sky. In contrast tboestsp fiectt rsumpeprcedtricutemd f riosm th(leeftnp acnael)lcau4l3a.0teGdeV adnardk fed back into the fitting algorithm, ¯ Ref. [8], we find no significant di↵erence in the slope pre- matter particle annihilating to bb with a cross section ferred by the fit over the standard ROI, and by a fit ontlyhe pofr�ovc=e2s.2s5 is 1r0e2p6 ecma3t/esd [i(t0e.4rGaetViv/cemly3) /u⇢nti]l2 ,a best fit solution is reached. We � local ⇥ ⇥ over the southern half (b < 0) of the ROI (we also find and (right panel) a 36.6 GeV dark matter particle anni- find the final spectrum to be independent of the initial seed. no significant di↵erence between the fit over the full sky hilating to b¯b with a cross section of �v = 0.75 10 26 � ⇥ and the southern half of the full sky). This can be seen cm3/s [(0.4GeV/cm3)/⇢ ]2. The spectra extracted local ⇥ directly from Fig. 5, where the full-sky and southern- for this component are in moderately good agreement sky fits for the same level of masking are found to favor with the predictions of the dark matter models, yielding quite similar values of � (the southern sky distribution fits of �2 = 44 and 64 over the 22 error bars between 0.3 is broader than that for the full sky simply due to the and 50 GeV. We emphasize that these uncertainties (and di↵erence in the number of photons). The best-fit values the resulting �2 values) are purely statistical, and there for gamma, from fits in the southern half of the standard are significant systematic uncertainties which are not ac- ROI and the southern half of the full sky, are 1.13 and counted for here (see the discussion in the appendices). 1.26 respectively. We also note that the spectral shape of the dark matter template is quite robust to variations in �, within the In Fig. 6, we show the spectrum of the emission cor- range where good fits are obtained (see Appendix A). related with the dark matter template in the default ROI and full-sky analysis, for their respective best-fit values of � = 1.18 and 1.28.6 We restrict to energies In Fig. 7, we plot the maps of the gamma-ray sky 50 GeV and lower to ensure numerical stability of the in four energy ranges after subtracting the best-fit dif- fit in the smaller ROI. While no significant emission is fuse model, Fermi Bubbles, and isotropic templates. In absorbed by this template at energies above 10 GeV, the 0.5-1 GeV, 1-3 GeV, and 3-10 GeV maps, the dark- ⇠ a bright and robust component is present at lower en- matter-like emission is clearly visible in the region sur- ergies, peaking near 1-3 GeV. Relative to the analy- rounding the Galactic Center. Much less central emission ⇠ sis of Ref. [8] (which used an incorrectly smoothed dif- is visible at 10-50 GeV, where the dark matter compo- fuse model), our spectrum is in both cases significantly nent is absent, or at least significantly less bright. harder at energies below 1 GeV, rendering it more con- 7 An earlier version of this work found this improvement only in 6 A comparison between the two ROIs with � held constant is the presence of the CTBCORE cut; we now find this hardening presented in Appendix A. independent of the CTBCORE cut.
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