Status of 3.5 keV line
Dmytro Iakubovskyi
Discovery Center, Niels Bohr Institute
1st Danish Astroparticle Physics Meeting,
CP3-Origins, October 6, 2016.
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Dark matter decay line
Signature of 2-body radiative decay (e.g. DM→ γ + γ,
DM→ γ + ν): monochromatic line from all DM overdensities.
Due to small (v ∼ 10−4 − 10−2 ) Doppler broadening the line is
narrow.
Line position evolves with redshift.
Flux from DM decay:
Z
Ωfov
Eγ
ρDM (~r)
S
d3~r ≈
FDM =
2
~
mDM τDM
8πm
DM τDM
4π|DL + ~r|
fov cone
DM column density
S=
Z
ρDM (r)dr
Ωfov
– integral along the line-of-sight, averaged within the instrument’s
field-of-view – slowly grows with halo mass (∼ M 0.2 ) – 0911.1774.
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
3.5 keV line
ApJ’14 [1402.2301]
PRL’14 [1402.4119]
Energy: 3.5 keV. Statistical error for line position ∼ 30 − 50 eV;
Lifetime: τDM = (2 − 20) × 1027 sec;
Possible origin: decay DM → γ + ν or DM → γ + γ.
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Subsequent works
confirmed the presence of 3.5 keV line in some objects (Boyarsky et
al., D.I. et al., Franse et al., Bulbul et al., Urban et al., Jeltema &
Profumo);
challenged its existence in other objects (Malyshev et al., Anderson
et al., Tamura et al., Sekiya et al., Hofmann et al.);
argued astrophysical origin of the line (Jeltema & Profumo, Carlson
et al., Riemer-Sørensen, Gu et al.).
See AASP’16 [1510.00358] for a detailed review.
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Line origin – radiatively decaying dark matter:
Line flux, 10-6 photons cm-2 s-1
Observations point to τDM = (6 − 8) × 1027 s [1408.2503,
1508.05186];
Apparent 2σ tension with some non-observations;
Should be careful when comparing results from different objects –
DM content in each of them is uncertain!
GC
10
Perseus
27
s
M31
0
τ DM
=
2
x1
27
=
6
28
0
x1
τ DM
s
27
0
τ DM
1
s
=
Blank-sky
8
τ DM
s
0
x1
=
.8
x1
1
0.01
0.1
Projected mass density, MSun/pc2
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Analysis of Draco dSph
The line is detected in PN camera with 2.3σ (local) and line
flux/position consistent with previous measurements;
Combination with MOS cameras decreases significance to < 2σ;
the overall signal is consistent with DM interpretation
(τDM > (7 − 9) × 1027 s).
4.5x10-6
4.0x10-6
3.5x10-6
Distant clusters (MOS)
2
PN camera flux [cts/sec/cm ]
2
Flux [cts/sec/cm ]
3.5x10-6
All clusters
(MOS)
3.0x10-6
M31
2.5x10-6
Distant clusters
(PN)
2.0x10-6
Best-fit Draco PN
1.5x10-6
GC
1.0x10-6
Distant clusters
All clusters
(MOS)
3.0x10-6
M31
2.5x10-6
2.0x10
0.0x100
= 9
2
= 4
2
= 1
∆χ
1.5x10-6
∆χ
GC
-6
1.0x10
5.0x10-7
5.0x10-7
2
∆χ
Distant clusters
(PN)
-6
Best-fit Draco MOS1+MOS2+PN
0.0x100
3.48
3.5
3.52
3.54
Line position [keV]
3.56
3.58
3.6
3.46
3.48
3.5
3.52
3.54
3.56
3.58
3.6
3.62
3.64
Line position [keV]
MNRAS’16 [1512.07217]
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Need for a microcalorimeter
Broadened line emissivity [arb. units]
160
Broadened line emissivity [arb. units]
3 x K lines, GC model 3, XMM-Newton/EPIC
1 x Ar lines, GC model 3, XMM-Newton/EPIC
1/3 x S lines, GC model 3, XMM-Newton/EPIC
1 x Cl lines, GC model 3, XMM-Newton/EPIC
180
140
120
100
80
60
40
20
0
3400
3450
3500
3550
3600
Energy [eV]
3650
3700
3750
3800
3 x K lines, GC model 3, Astro-H/SXS
1 x Ar lines, GC model 3, Astro-H/SXS
1/3 x S lines, GC model 3, Astro-H/SXS
1 x Cl lines, GC model 3, Astro-H/SXS
100
80
60
40
20
0
3400
3450
3500
3550
3600
3650
3700
3750
3800
Energy [eV]
MNRAS’15 [1507.02857]
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
A new microcalorimeter – Hitomi (Astro-H)
Launched February 17, lost March 26, 2016, much before the end
of calibration phase;
Before its loss, observed Perseus cluster core.
Hitomi vs Suzaku spectrum, Nature’16 [1607.04487].
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Hitomi spectrum of Perseus core [1607.07420]
Good news: no strong K/Cl line (claimed by Jeltema & Profumo);
Bad news: no line;
Some hints (?) of S exchange line (Gu et al. 2016).
Should there be a line in this short exposure spectrum?
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Hitomi bounds
Line in Perseus center as reported by Bulbul et al. (2014) was
“anomalously strong”. Taking at face value it was inconsistent with
all other observations.
Exclusions from Hitomi are consistent with DM signal with
τDM > (7 − 9) × 1027 s as observed from Galactic Center, M31,
stack of distant clusters and Draco dSph.
Dmytro Iakubovskyi
Status of 3.5 keV line
Discovery Center, Niels Bohr Institute
Future:
10-8
10-9
10-10
10-11
10-12
10-13
Small galaxies do not form
2
10-7
(fraction of weak interaction)
Interaction strength Sin (2θ)
Micro-X sounding rocket experiment (2017+) – large field-of-view,
large energy resolution, very small exposure – will probe Galactic
Center+Bulge region (ApJ’15 [1506.05519]);
Athena – large ESA mission (2028+), very large resolution and
collecting area (each 10×XMM-Newton) – will probe individual DM
haloes (e.g. galaxy clusters).
Too much dark matter
Excluded by previous
X-ray observations
Not enough dark matter
1
Dmytro Iakubovskyi
Status of 3.5 keV line
2
5
10
Dark matter mass MDM [keV]
30
Discovery Center, Niels Bohr Institute