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2014-03_CygCocoon_Suzaku_JPS.ppt X-ray Investigation of -ray Excess in Cygnus Region Cygnus Cocoon by Suzaku ( X ) March 29 th , 2014 Tsunefumi Mizuno

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2014-03_CygCocoon_Suzaku_JPS.ppt

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X-ray Investigation of -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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2014-03_CygCocoon_Suzaku_JPS.ppt

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Contents

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

  • GeV -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 -ray map (E>10 GeV)

Cygnus OB2 NGC6910

Ackermann+11

-Cygni

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Cygnus Cocoon (-ray Spectrum)

  • “Cygnus Cocoon” = GeV -ray excess revealed by

Fermi in star-forming region Cygnus-X

  • Hard and Intense CRs are required to explain -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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Observation

  • We performed Suzaku-

XIS observations to investigate properties of CRs responsible for Cocoon (particle type, spectrum, etc.)

Excess -ray map (E>10 GeV) region

  • bs. 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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XIS Image (Source1)

  • Count map of XIS0+3, smoothed with =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 (=1.41, N=9.6x10-4 [c/s/cm2/keV]) based

  • n Kushino+02. N(H)=2x1022 [cm2] assumed

– GRXE is modeled by three-temperature plasma (apec) based

  • n Uchiyama+09

– Then examine residuals in spectrum to see if there are any excess (=possible emission from Cocoon)

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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) count/s/keV Energy [keV]



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)

brightness [10-7 erg/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 0.59. x Source2 0.29. x BG1 0.80. x BG2 0.19. x

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CRs to explain Cygnus Cocoon in X-ray and -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 of X-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/cm

2/sr]

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

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

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Summary & Future Plan

  • We observed Cygnus Cocoon (-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) -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]

brightness [10-7 erg/s/cm2/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%
  • f the expectation, requiring cutoff of CR electron (in

electron scenario)

Simple Argument of CR Electron Cutoff

,~2000

  • 10 G
  • 100 TeVsin 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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  • -ray emission = diffuse emission (ISM x Galactic CR)+point sources
  • Excess is a signature of unknown high-energy objects/phenomena

-ray Count Map

Count Map (E>10 GeV)

Galactic diffuse and known sources subtracted

-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