The Detection of an UnexplainedEmission Line at 3.56 keV

Esra BulbulHarvard-Smithsonian Center for Astrophysics

Maxim Markevitch (NASA/GSFC), Adam Foster (CfA), Randall Smith (CfA), Mike Loewenstein (NASA/GSFC), and Scott Randall (CfA)

Line Searches in X-ray Observations of Clusters Largest

gravitationally bound aggregations of hot ICM and DM

Gas is enriched mainly via SN explosions by metals produced by stars in galaxies

Weak emission lines are now being discovered through X-ray spectroscopy

Werner et al. (2006)

2A 0335+096

Why Stacking?

73 galaxy clusters at their rest frame

Increased S/N 0.01 < z < 0.35 Smeared non-source

features, e.g. instrumental, background

XMM-Newton Stamp Images of 73 Galaxy Clusters

Background Before Stacking

Background After Stacking

Detection of An Unidentified Emission Line

Flux: 4.0 ± 0.8 x 10-6 phts cm-2 s-1

Energy: XMM - MOSFull Sample

6 Ms

with an Additional Gaussian Model…

XMM - MOSFull Sample

6 Ms

Detected in Independent PN Observations

XMM - PNFull Sample

2 Ms

Detected in Fainter 69 Clusters

XMM - PNFull Sample

1.8 Ms

Chandra ACIS-S 883 ks

Detected in Chandra Observations of the Perseus cluster

XMM-NewtonMOS

317 ks

Detected in XMM Observations of the Perseus cluster

Confirmation

Boyarsky et al. (2014a, b) detected the line independent

XMM OFFSET observations of the Perseus cluster

M31Milky Way

Energy

Nor

mal

ized

Coun

t Rat

ecn

ts/k

eV/s

cnts

/keV

/s

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keV

Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keV

Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keV

Atomic Database Estimates Ar XVII DR line at 3.62 keV

Based on Ar XVII triplet at 3.12 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keVEmission lines of strong

hydrogen- and helium-like ions

Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keVEmission lines of strong

hydrogen- and helium-like ions

Charge exchange

Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keVEmission lines of strong

hydrogen- and helium-like ions

Charge exchange Radiative recombination

continuum (RRC) feature

Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

Unlikely Astrophysical Scenarios

K XVIII line at 3.52 keVAr XVII DR line at 3.62 keVEmission lines of strong

hydrogen- and helium-like ions

Charge exchange Radiative recombination

continuum (RRC) featureAny Other Astrophysical

Explanations? Atomic Database Estimates of K XVIII line at 3.52 keV and Ar XVII

DR line at 3.62 keV

What is the origin?

Could this be a sterile neutrino decay signature?

Warm dark matter candidate sterile neutrinos decay into an active neutrino and emission line

Neutrino Properties Mass = 2Eγ

Mixing angle

Mas

s (k

eV)

The diffuse X-ray background (Boyarsky et al. 2006), cluster X-ray (Boyarsky et al. 2006b), BMW (Boyarsky et al. (2007), M31 (Watson et al. 2006), the Tremaine-Gunn bound (Bode et al. 2001), and Fornax dwarf galaxy (Strigari et al. 2006)

Sterile Neutrino vs Astrophysical Line?

Astro-HPerseus

1 Msνbar= 300 km s-1

νDM= 1300 km s-1

Sterile Neutrino Abundance

Sterile neutrinos constitutes 19% of the dark matter (Shi & ∼Fuller 1999)

may also be produced by means that do not involve oscillations, such as inflaton or Higgs decay (Kusenko 2006; Petraki & Kusenko 2008). This detection is consistent with 100% of dark matter composed of sterile neutrinos produced by these mechanisms.

If generated via split seesaw mechanism, this detection indicates that 100% of dark matter composed of sterile neutrinos (Kusenko, Takahashi, & Yanagida 2010).

If you do not want to wait for Astro-H

Alternatives for the Confirmation

Stacked Suzaku and Chandra Observations of large number of galaxy clusters – NASA/ADAP grant (PI: Bulbul)

Deep observations of dwarf spheroidal galaxiesStacked observations of more Local Group galaxies (cannot nail

it if it is a detector artifact)Deep Chandra observations of the Galactic Center

Limits from Our Detections

10-11 Mixing angle

Mas

s (k

eV)

Bright Clusters

MOS Observations of the Bright Clusters (Coma, Perseus, Ophiuchus, Centaurus)

Flux: phts cm-2 s-1

MOS Observations of the Perseus cluster

phts cm-2 s-1

MOS Observations of the Perseus cluster (core cut)

phts cm-2 s-1

not due to a dominant source in the sample, not a background or effective area feature

Δχ2 = 17.1 (1 dof)

Δχ2 = 15.7 (1 dof)