Indirect Dark Matter Search at Intermediate Mass Black Hole with the MAGIC Telescope

1. Indirect Dark Matter Search at Intermediate Mass Black Hole with the MAGIC Telescope M. Doro1(*), H.Bartko2, G.Bertone3, A.Biland4, M.Gaug5, M.Mariotti1, F.Prada6, M.Rissi4, M.Sanchez-Conde6, L.S.Stark4, F.Zandanel1on behalf of the MAGIC Collaboration# 1University of Padua- INFN, Italy 2MPI for Physics, Munich, Germany 3ETH Zurich, Switzerland 5IAC Tenerife, Spain 6IAA-CSIC Granada, Spain *michele.doro@pd.infn.it wwwmagic.mppmu.mpg.de ABSTRACTStudies of the evolution of Super Massive Black Holes expected in the centre of most galaxies predict the existence of some 100-1000 Intermediate Mass Black Holes (IMBH) also in our galaxy. Since IMBHs did not suffer major merging and baryonic accretion, they can have a very high density mini-spike DM distribution. The resulting high annihilation rate would make such objects very bright in gamma-rays. A strategy of searching for such objects as well as the scenario for future observations with the MAGIC telescope are presented. Intermediate Mass Black Holes scenario The IACT for DM searches • The orbits of stars around galactic centres allow to reconstruct the gravitational potential: a super-massive object (M≥106-9 Msun) within 10-4 pc is found to reside in the centre • Observations of high-redshift quasars suggest the existence of SMBH already when the Universe was 1Gyr old • The imaging atmospheric Cherenkov (IAC) technique is based on the detection of Cherenkov photons produced by very fast charged particles in the atmosphere, created in the so-called electromagnetic showers initiated by gamma-rays coming from the Universe • The gamma-rays trace back the place of their origin, being undeflected by cosmic magnetic field, and this constitute a viable messenger to study the deep Universe • A search for Dark Matter particles in the Universe is nowadays constrained by the large uncertainties in the flux prediction which put serious hindrances to the estimation of the observability • The second generation IAC telescopes (IACTs), and among them the MAGIC Telescope, provide low energy threshold, high flux sensitivity and good angular and energy resolution. • MAGIC, thanks to the present largest reflective dish, presents the lowest energy threshold (60 GeV at zenith) and for this reason is best suited to search for DM candidates with energy of the neutralino (>45GeV) or the Kaluza-Klein state (>400GeV) MAGIC II • Super Massive Black Holes (SMBH) are expected to form from major merging of smaller seed black holes of intermediate mass ranging from 20 to 105 Msun MAGIC I • In a recent study from Bertone, Zentner, Silk PRD 2005, simulations were performed for the evolution of such objects from very large redshift to the present. As a result, two possible scenarios emerge according to the genesis of the seed IMBHs: in the first scenario (scenario I) they resulted from collapse of zero-metallicity pop. III stars at very large redshift (z~14) directly into black-holes; in the second scenario (scenario II) IMBHs resulted from collapse of large molecular clouds with efficient hydrogen cooling and not merging: in this configuration a protogalactic disk forms with a large baryonic mass falling inward until the object becomes unstable and eventually collapse to a black-hole (up left) Stellar kinematics over a decade of years around the galactic centre (up left) Sketch of the different classed of black-holes(above left) Seed intermediate mass black-hole from Scenario I [3](above right) Sketch of collapse of molecular cloud (scenario II) [4] • A second telescope, clone of the first one, dubbed MAGIC II, is currently under construction on the MAGIC telescope site at Roque de Los Muchachos (northern hemisphere) in the Canarian island of La Palma. The stereoscopic view of two telescopes will results in an improvement of the general performance: Sensitivity increased by 100%, energy resolution by 40%, angular resolution by 30% • This major improvement will strongly push the MAGIC telescope toward an increased possibility to resolve DM sources  • In the vicinities of the IMBH, the dark matter accretes and density enhancements are formed out of the external DM profile • Starting from an initial NFW profile with index = -1, the final profile is very spiky in the inner parsec with index = -7/3 and the object is dubbed as “mini-spike”. At the very centre defined by rcut , not so far form the Schwarzchild radius, the annihilation rate is thus efficient to create the plateau of density • The dark matter annihilation, depending on the square of the density, is strongly boosted, and IMBH in the mini-spike can be brighter than the entire galactic halo for the annihilation into gamma-rays! Unidentified EGRET sources (left) The Third EGRET catalog: the unidentified sources are underlined in green colour. (right) Possible distribution of IMBHs within the galactic halo [5] Gamma ray signal from DM annihilation • Throughout this poster we will consider a CDM Universe with M=0.27, =0.73 and H0 = 71 km.s-1.Mpc-1 and the case of two possible DM candidates: the lightest neutralino within the minimal super-simmetrical extension of the Standard Model (MSSM) and the Kaluza-Klein state in multi-dimensional theories • We consider the MSSM within the mSUGRA model, where the standard partner particles bino, wino and the two Higgs boson mix into four states called neutralinos, the lightest of which is called the neutralino, to whom all SUSY particles decay in case of R-parity conservation: For the LKP particle we consider the case of the first KK excitation of the photon, namely the B(1) state, which has also decay channels to standard model particles as charged leptons (59%), quarks (35%), neutrinos (4%) and Higgs bosons(2%) • Both particles annihilate into Standard Model particles, namely quarks, other leptons and bosons W. The hadronization of such particles results in a continuum emission of gamma-rays at energies E < MDM . A direct annihilation into a pair of gammas  (E = M ) and into a couple Z (E = M- M2Z/M2) is also possible even if a second loop order channel for the neutralino case • A certain number (100-1000) of intermediate mass black holes (IMBHs) could lay in the galactic halo. The annihilating dark matter should reveal in a continuum spectrum with an exponential cut-off at the dark matter mass as underlined in the previous section. • The question is: could such objects be already observed in the past? A possible explanation - in case IMBHs exist - can be found in the 3rd EGRET catalogue where a large number (>100) of objects were observed in the HE range by the EGRET experiment on board the CGRO satellite, and are still unobserved by VHE ground based experiment • Some of these objects satisfy the conditions for being possible candidate for IMBHs: they must have a stable emission, no counterpart at other wavelengths, and a spectral index as close as possible to -1.5, which is the typical sign for quark decay of neutralino. • For the MAGIC telescope, a selection was performed inside the 3rd EGRET catalogue, with the following filters: • The source was unidentified at other wavelengths • The source was not variable (using Nolan et al 2003) • The source was at high galactic latitude to ensure suppression of possible astrophysical sources constituting background • The flux as measured by EGRET was extrapolated the VHE regime with the spectral index of a sample quark-antiquark annihilation channel. In case of flux above MAGIC sensitivity the source was tagged as possible candidate Example of spectra for DM annihilation channels for Neutralino (left and central plots) and LKP particle (right). In the leftmost plot, the typical continuous spectrum with the cut-off at the DM mass is mainly due to secondary photons from quark and gauge bosons fragmentation. In the central plot, the final state radiation from W+W- can show-up in a bump closed to the DM mass. In the rightmost plot the LKP decay mainly leptonic shows a sharper cut-off. Left and central images taken from [5], right plot from [6] MAGIC observation • During the second cycle of MAGIC scientific observation (2006-07) a candidate source from the third unidentified EGRET catalogue was observed for 25 hours. • The calculation of the flux from an IMBH is shown in the following formula [1]: where E is the energy, D is the distance of the object, v is the cross-section times the velocity, m is the DM mass, rsp is the radius of the spike, rcut is the radius of the inner region of the spike and (rsp) is the density at the spike • The source was a very strong HE emitter in the EGRET catalogue • The upper limits for the source emission are shown in green in the left panel but the analysis is still under debate due to some technical problem the telescope was suffering during the data taking • The two red lines indicate the extrapolation of the EGRET flux with a typical quarks annihilation spectrum to VHE regime, according to two values of DM mass, 300 GeV (dashed red line) and 900 GeV (solid red line) • In case the source is an IMBH, at least upper limits can then be putted on the DM mass according to the observation • From the preceding formula, the flux seems to scale with the ratio of the cross section times the velocity and the square of the mass:  ~ v / m2DM . But in the very special case of IMBH, the definition of rcut is function of the same factors (mass and cross section) rcut=rcut(v,m2DM ) and the interplay between these factors makes the dependence on the flux from the uncertainties in the particle physics smaller: • Given this particular dependence of the parameters, the fact the the objects are galactic and then close and that their spectrum should show similar shape and cut-off, the detection of such objects could be a smoking gun for DM studies, providing all the characteristics of the particle • For the third cycle of observation (2007-08) other possible candidates will consider as target to be IMBH within the third EGRET catalogue. The uncertainties given in the estimation of the position from this catalogue, of the order of less than 1 degree in the sky, is often too large for IACT observation. In this sense, new information coming from present satellite (AGILE) already orbiting in the atmosphere and GLAST, will help in the definition of new best candidates for such observation so that a complete HE-VHE spectrum will be provided. REFERENCES[1] Bertone et al., PRD 05 [2] Bertone & Merritt 2005 [3] http://www.tomabel.com [4] Koushiappas, Bullock & Dekel 2004 [5] Bertone ‘06 [6] Bergstrom et al., PRL 05a