1 2014-03_cygcocoon_suzaku_jps.ppt t. mizuno et al. x-ray investigation of -ray excess in cygnus...

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2014-03_CygCocoon_Suzaku_JPS.ppt

T. Mizuno et al.

X-ray Investigation of g-ray Excess in Cygnus Region

“Cygnus Cocoon” by Suzaku( 「すざく」による白鳥座に発見さ

れたガンマ線超過の X 線探査 )

T. Tanabe, H. Takahashi (Hiroshima Univ.), K. Hayashi (ISAS/JAXA),

R. Yamazaki (AGU), I. Grenier (CEA Saclay), L. Tibaldo (SLAC)

March 29th, 2014

Tsunefumi Mizuno (Hiroshima Univ.)

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T. Mizuno et al.

Contents

• Introduction (g-ray excess “Cygnus Cocoon”)• Observations by Suzaku• Data Analysis• Discussion• Summary & Future Plan

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T. Mizuno et al.

Cygnus Cocoon (Morphology)

• GeV g-ray excess revealed by Fermi in star-forming region Cygnus-X

• Morphology follows the regions bounded by ionization fronts. No apparent spectral variations in different parts.

• Efficient confinement and/or acceleration of cosmic-rays (CRs) in the interstellar space

Excess - ( >10 )g ray map E GeV

Cygnus OB2

NGC6910

Ackermann+11

g-Cygni

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T. Mizuno et al.

Cygnus Cocoon (g-ray Spectrum)

• “Cygnus Cocoon” = GeV g-ray excess revealed by Fermi in star-forming region Cygnus-X

• Hard and Intense CRs are required to explain g-ray spectrum

HII x local CR-p

Inverse Compton from local CR-e

Milagro

LAT

• Their origin and properties to be studied by multiwavelength obs. including X-rays

Ackermann+11

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T. Mizuno et al.

Observation

• We performed Suzaku-XIS observations to investigate properties of CRs responsible for Cocoon (particle type, spectrum, etc.)

Excess - ( >10 )g ray map E GeV

region obs. date exposure [ksec](COR > 6 GV)

Source1 2012/Nov. 43.3

Source2 2013/Nov. 46.4

BG1 2012/Nov. 19.9

BG2 2012/Nov. 25.6

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T. Mizuno et al.

XIS Image (Source1)

• Count map of XIS0+3, smoothed with s=0.2 arcmin• A few sources and/or small structures were identified

and excluded to investigate the (possible) extended emission from Cygnus Cocoon

0.4-2 keV 2-10 keV

Cal Source

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Modeling of Extended Emission (1)

• Point sources and/or small structures removed• Non X-ray Background (NXB) subtracted (xisnxbgen)• The remain = Cosmic X-ray background (CXB)

+Galactic Ridge X-ray Emission (GRXE)

+possible emission from Cocoon– CXB is fixed to PL of (G=1.41, N=9.6x10-4 [c/s/cm2/keV]) based

on Kushino+02. N(H)=2x1022 [cm2] assumed– GRXE is modeled by three-temperature plasma (apec) based

on Uchiyama+09– Then examine residuals in spectrum to see if there are any

excess (=possible emission from Cocoon)

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T. Mizuno et al.

Modeling of Extended Emission (2)

• Point sources and NXB subtracted• The remain = CXB+GRXE(+possible emission from Cocoon)

– CXB is fixed to PL of Kushino+02.– GRXE is modeled with three-temperature plasma (Uchiyama+09)

co

un

t/s

/ke

V

Energy [keV]

c2

Source1 Spectrum (XIS0)

apec: Soft (~0.05 keV)

apec: Medium(~0.7 keV)

PL (CXB)apec: Hard(~5 keV)

CXB-subtracted brightness = [erg/s/cm2/sr] @2-10 keV

No apparent excess in residual, but emission from Cocoon might be hidden by models for GRXE => examine b-dependence

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Latitude Dependence of Extended Emission

• Point sources and NXB subtracted• The remain = CXB+GRXE(+possible emission from Cocoon)• CXB-subtracted brightness shows monotonous decrease as

latitude increases (as GRXE does)

bri

gh

tnes

s [1

0-7 e

rg/s

/cm

^2/

sr]

Galactic Latitude [deg]

BG1

BG2

Source1

Source2

CXB-subtracted brightness (2-10 keV)

Most of (CXB-subtracted) emission comes from GRXE

region CXB-subtracted brightness@2-10 keV [erg/s/cm2/sr]

Source1 0.59x

Source2 0.29x

BG1 0.80x

BG2 0.19x

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T. Mizuno et al.

CRs to explain Cygnus Cocoon in X-ray and g-ray

• Most of CXB-subtracted emission comes from GRXE• Conservative upper limit of X-rays from Cocoon is obtained by

subtracting brightness of BG2 (=lower limit of GRXE at source positions)

region upper limit ofX-rays from Cygnus Cocoon

Source1 0.40 x [erg/s/cm2/sr]

Source2 0.10 x [erg/s/cm2/sr]

expectation of electron scenario (synchrotron X-ray) = x [erg/s/cm2/sr]

Upper limit of X-ray emission (av. of S1 and S2) <= 40% of the expectation of electron scenario

g-ray excess is due to (1) CR protons or (2) CR electrons with cutoff at <= 50 TeV

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T. Mizuno et al.

Summary & Future Plan

• We observed Cygnus Cocoon (g-ray excess in Cygnus-X found by Fermi) by Suzaku-XIS

• Most of extended emission comes from CXB+GRXE• Conservative upper limit of X-rays from Cocoon is

<=40% of electron scenario expectation, suggesting– (1) g-ray excess is due to protons, or – (2) electrons with cutoff at <= 50 TeV

• Detailed discussion based on multiwavelength spectrum is underway

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Reference

• Ackermann+11, Science 334, 1103• Kushino+02, PASJ 54, 327• Uchiyama+09, PASJ 61, S189• Kaneda+97, ApJ 491, 638

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Backup Slides

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Latitude Dependence of Extended Emission

region Scale height

Cygnus Cocoon Source & BG

1.26±0.29 [deg]

Scutum arm(Kaneda+97)

0.64±0.10[deg]

Scale height of extended emission in Cygnus Cocoon region is ~2 larger than that of Scutum arm (l=28deg; Kaneda+97), probably due to the proximity of Cygnus-X

BG1

BG2

Source1

Source2

Galactic Latitude [deg]

bri

gh

tnes

s [1

0-7 e

rg/s

/cm

2 /sr

]

CXB-subtracted brightness

Most of extended emission can be interpreted to be from GRXE

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• Conservative upper limit of X-ray emission is <=40% of the expectation, requiring cutoff of CR electron (in electron scenario)

Simple Argument of CR Electron Cutoff

h𝜈max, sync 2000 (𝐵

10𝜇G)(

𝐸e

100TeV)2

sin 𝜃 eV

Synchrotron X-ray For B=20 μG, Ee of 50 TeV

required to produce 1 keV X-ray

In electron scenario, cutoff in <= 50 TeV is required to explain (non-detection of) X-rays

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T. Mizuno et al.

• g-ray emission = diffuse emission (ISM x Galactic CR)+point sources

• Excess is a signature of unknown high-energy objects/phenomena

g-ray Count Map

Count Map(E>10 GeV)

Galactic diffuse and known sources subtracted

g-Cygni subtracted

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• Optical from Cygnus OB2 and NGC 6910• Infrared (dust emission) measured by IRAS

Radiation Field inside Cocoon

1 meV 1 eV

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