Gamma-rays from Dark Matter Mini

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Gamma-rays from Dark Matter Mini
Gamma-rays from Dark Matter
Mini-Spikes in Andromeda
Galaxy M31
Mattia Fornasa
Dipartimento di Fisica “G. Galilei”
I.N.F.N. Padova
based on astro-ph/0703757 by M. Fornasa, M. Taoso and G.Bertone
Journal Club Seminar – Giovedì 7 giugno 2007
Introduction
Evidences for Dark Matter (DM)
• WMAP measurement ( m=0.25)
• rotation curves of galaxies
• the “bullet” cluster
Open Problems
• DM nature
• DM interactions
Detection techniques
• signals from colliders
• direct detection
• indirect detection of annihilation
products such as neutrinos, antiprotons
or gamma-rays
M. Fornasa
Chandra photo album: X-ray
image of 1E0657-558
7 Giugno 2007
Introduction
Our work is focused on indirect detection: we are looking
for gamma-rays from DM annihilation in high-density
regions in the sky
(1)
• search for a signal from the Galactic Center
• H.E.S.S. reported an excess of gamma-rays
no possible interpretation as DM annihilation
H.E.S.S. collaboration,
astro-ph/0610509
M. Fornasa
7 Giugno 2007
Introduction
• Intermediate Mass Black Holes (IMBHs)
• located in mini-halos in the Galactic smooth DM profile
• necessity to consider an extragalactic source (M31)
G. Bertone,
astro-ph/
0603148
High-energy, point-like, unknown gamma-rays
sources in a 3° region around Andromeda would be
a clear and unquestionable signal for DM annihilations
around IMBHs
M. Fornasa
7 Giugno 2007
Intermediate Mass Black Holes (IMBHs)
• mass from 20 M to 106 M
• no one actually ever “detected” an
Intermediate Mass Black Hole
G. Bertone,
astro-ph/
0603148
Evidences for IMBHs:
• Ultra Luminous X-ray
sources (ULXs)
• extrapolation of Mrelation of SMBHs to
globular clusters
• IMBHs would provide
massive seeds for the
growth of SMBHs
Miller, Colbert, astro-ph/0308402
M. Fornasa
7 Giugno 2007
Intermediate Mass Black Holes (IMBHs)
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G. Bertone,
astro-ph/
0603148
Koushiappas, Bullock, Dekel, astro-ph/0311487
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
[M /kpc 3]
Galactic halo density profile is supposed to
be a Navarro-Frenk-White (NFW):
(3)
9
10
8
10
107
106
105
104
3
10
102
G. Bertone,
astro-ph/
0603148
From a power-law density
profile, a “spike” can form with
a new slope:
10
1
10-1 -2
10
10-1
1
10
102
3
10
r [kpc]
(4)
(5)
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
Ullio, Zhao, Kamionkowski,
astro-ph/0101481
G. Bertone,
astro-ph/
0603148
From a NFW ( =-1) the final spike has
sp=-7/3
(6)
(7)
M. Fornasa
7 Giugno 2007
Spike formation at the Galactic center
Arguments against spikes formation:
• off-center black hole formation
• gravitational interaction with stars
• merger and BH binary effects
G. Bertone,
astro-ph/
0603148
Ullio, Zhao, Kamionkowski,
astro-ph/0101481
M. Fornasa
Merritt, Milosavljevic, Verde, Jimenez
astro-ph/0201376
7 Giugno 2007
IMBHs catalogue (Bertone, Zentner, Silk)
Focusing on astro-ph/0509565 by G. Bertone,
A. Zentner and J. Silk:
• initial catalogue of IMBHs
• merging tree
• selection of unmerged mini-halos
• no baryonic content and the BH lays in the center
G. Bertone,
astro-ph/
0603148
Bertone, Zentner, Silk,
Astro-ph/0509565
M. Fornasa
7 Giugno 2007
IMBHs catalogue for Andromeda
How IMBHs are characterized:
• realization ID
• Black Hole Mass [M ]
• IMBH distance from the center of the Galaxy [kpc]
• rsp [kpc]
• (rsp) [M /kpc3]
G. Bertone,
astro-ph/
0603148
Milky Way
Andromeda
Distance to
the center
8.5 kpc
784.0 kpc
Virial Mass
1.0B1012 M
6.8B1011 M
Virial Radius
205 kpc
180 kpc
Andromeda IMBHs are 65.2±14.5 per realization,
with an average mass of 1.5B105 M and
an average distance from M31 center of 32.3 kpc.
M. Fornasa
7 Giugno 2007
Annihilation Flux
(8)
G. Bertone,
astro-ph/
0603148
To compute the differential energy spectrum a particular
model of physics beyond the SM is needed:
(9)
(10)
M. Fornasa
7 Giugno 2007
Differential energy spectrum
FPS (Fornengo-Pieri-Scopel)
• MSSM is assumed and the DM candidate is the lightest
neutralino
• focused on hadronization of b quarks
• fit from simulated data, using standard package as PYTHIA
(x=E/m )
(10)
G. Bertone,
astro-ph/
0603148
a=-1.5
b=0.37
c=-16.05
d=18.01
e=-19.50
for m =1 TeV
M. Fornasa
7 Giugno 2007
Thresold effect
(11)
(12)
(Ethr=4 GeV)
G. Bertone,
astro-ph/
0603148
M. Fornasa
m = 50 GeV
5.26B10-11 cm-2s-1
m = 150 GeV
7.65B10-11 cm-2s-1
m = 300 GeV
6.92B10-11 cm-2s-1
m = 500 GeV
5.81B10-11 cm-2s-1
Ethr
m
ACTs
100 GeV
1 TeV
GLAST
4 GeV (see later)
150 GeV
7 Giugno 2007
Detection of IMBHs with ACTs
• m =1 TeV and v=3B10-26 cm3s-1
• Eth=100 GeV
• typical ACT angular resolution is 0.1°
• typical ACT effective area is 3B104 m2
• exposure time is 100 hours
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
(13)
Origin of background:
• EGRET:
(14)
• Hadronic and electronic:
(15)
(16)
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
ACT sensitivity for a 5 detection
results 1.6B10-12 cm-2s-1,
higher than the brightest bins of the previous sky map.
M. Fornasa
7 Giugno 2007
Detection of IMBHs with ACTs
Number of IMBHs over ACT sensitivity is
5.2 ± 3.1 for m =1 TeV
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
• m =150 GeV and the energy threshold is 10 MeV
• GLAST angular resolution is expected to be 3° (from 10
MeV to 500 MeV), 0.5° (from 500 MeV to 4 GeV) and 0.15°
(above 4 GeV)
• a selection is made and only high-energy photons (above
4 GeV) are considered
• extragalactic background
• hadronic and electronic backgrounds are absent
• the effective area times the exposition time is roughly
8B109 cm2s
• the resulting sensitivity for a 2 months period is
1.1B10-10cm-2s-1
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
Number of IMBHs over GLAST sensitivity is
17.1 ± 5.8 for m =150 GeV
M. Fornasa
7 Giugno 2007
Detection of IMBHs with GLAST
M. Fornasa
7 Giugno 2007
Conclusions
• fluxes from DM annihilations in mini-halos around IMBHs
that populate the Andromeda Galaxy have been computed
• detection with an ACT is very challenging, due to the
hadron background
• the scenario with GLAST is more promising, even if the
best angular resolution is achieved only after a strict selection
(very high-energy photons)
• the picture is that of isolated, point-like, bright sources
in a region 3° wide around the Andromeda center
M. Fornasa
7 Giugno 2007
Differential energy spectrum
FPS (Fornengo-Pieri-Scopel)
• MSSM is assumed and the DM candidate is a neutralino
• focused only on the main channel (hadronization of b quarks)
• fit from simulated data, using standard package as PYTHIA
(x=E/m )
• differential spectrum for leptons hadronization is
presented too (see later)
(17)
(a, b, c, d, e)=(-1.5, 0.37, -16.05, 18.01, -19.50)
(a, b, c, d, e)=(-1.31, 6.94, -4.93, -0.51, -4.53)
Kretzer Fragmentation Functions
• DM candidate is again a neutralino
• FF is the probability to have an hadron h with xQ2 from a parton
p with Q2
M. Fornasa
7 Giugno 2007
Differential energy spectrum
• focused on the photon production from a
quarks b (i.e. p=b, h= 0)
0
resulting from
(18)
• a flat spectrum for photons from pions is assumed
(19)
BBEG (Bergstrom-Bringmann-Eriksson-Gustafsson)
• differential spectrum is calculated for a DM candidate from
Universal Extra-Dimension, what is called B(1)
• contribution of primary photons from charged leptons is
no longer neglected (B(1)B(1) l+l-)
(20)
M. Fornasa
7 Giugno 2007
Differential energy spectrum
Flux from Andromeda
FPS
1.33B10-14 cm-2s-1
Kretzer FFs
9.79B10-13 cm-2s-1
BBEG
1.60B10-14 cm-2s-1
From now on, only the FPS parametrization
will be used
M. Fornasa
7 Giugno 2007
Exclusion Plot
• Solid line: all realizations with at least one
detectable IMBH
• Dashed line: 20 realizations over 200 with at
least one detectable IMBH
3
v [cm s-1]
10-24
10-25
10-26
10-27
10%
-28
10
10-29 0
M. Fornasa
200
400
600
800
1000
m [GeV]
7 Giugno 2007

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