X-ray Investigation of -ray Excess in Cygnus Region Cygnus Cocoon - PowerPoint PPT Presentation

2014-03_CygCocoon_Suzaku_JPS.ppt 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 ) March 29 th , 2014 Tsunefumi Mizuno (Hiroshima Univ.) T. Tanabe, H. Takahashi (Hiroshima Univ.), K. Hayashi (ISAS/JAXA), R. Yamazaki (AGU), I. Grenier (CEA Saclay), L. Tibaldo (SLAC) T. Mizuno et al. 1

2014-03_CygCocoon_Suzaku_JPS.ppt Contents • Introduction (  -ray excess “Cygnus Cocoon”) • Observations by Suzaku • Data Analysis • Discussion • Summary & Future Plan T. Mizuno et al. 2

2014-03_CygCocoon_Suzaku_JPS.ppt Cygnus Cocoon (Morphology) Excess  -ray map (E>10 GeV) GeV  -ray excess revealed by • Fermi in star-forming region Cygnus-X • Morphology follows the NGC6910  -Cygni regions bounded by ionization fronts. No apparent spectral variations in different parts. • Efficient confinement and/or acceleration of cosmic-rays Cygnus OB2 (CRs) in the interstellar space Ackermann+11 T. Mizuno et al. 3

2014-03_CygCocoon_Suzaku_JPS.ppt 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 LAT H II x Milagro local CR-p • Their origin and Inverse Compton from local CR-e properties to be studied by multiwavelength obs. including X-rays Ackermann+11 T. Mizuno et al. 4

2014-03_CygCocoon_Suzaku_JPS.ppt Observation Excess  -ray map (E>10 GeV) • We performed Suzaku- XIS observations to investigate properties of CRs responsible for Cocoon (particle type, spectrum, etc.) 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 T. Mizuno et al. 5

2014-03_CygCocoon_Suzaku_JPS.ppt 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 2-10 keV 0.4-2 keV Cal Source T. Mizuno et al. 6

2014-03_CygCocoon_Suzaku_JPS.ppt 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/cm 2 /keV]) based on Kushino+02. N (H)=2x10 22 [cm 2 ] 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) T. Mizuno et al. 7

2014-03_CygCocoon_Suzaku_JPS.ppt 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) Source1 Spectrum (XIS0) apec: Medium CXB-subtracted brightness = (~0.7 keV) �. �� � �� �� [erg/s/cm 2 /sr] count/s/keV @2-10 keV apec: Soft PL (CXB) (~0.05 keV) apec: Hard No apparent excess in (~5 keV) residual, but emission from Cocoon might be hidden by models for GRXE => examine b-dependence   Energy [keV] T. Mizuno et al. 8

2014-03_CygCocoon_Suzaku_JPS.ppt 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) CXB-subtracted brightness (2-10 keV) region CXB-subtracted brightness brightness [10 -7 erg/s/cm^2/sr] @2-10 keV [erg/s/cm 2 /sr] BG1 0.59 ���. ��� x �� �� Source1 Source1 0.29 ���. ��� x �� �� Source2 0.80 ���. ��� x �� �� BG1 Source2 0.19 ���. ��� x �� �� BG2 BG2 Most of (CXB-subtracted) emission comes from GRXE Galactic Latitude [deg] T. Mizuno et al. 9

2014-03_CygCocoon_Suzaku_JPS.ppt 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 expectation of electron X-rays from Cygnus Cocoon scenario (synchrotron X-ray) 0.40 x �� �� [erg/s/cm 2 /sr] Source1 = �. �� x �� �� [erg/s/cm 2 /sr] 0.10 x �� �� [erg/s/cm 2 /sr] Source2 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 T. Mizuno et al. 10

2014-03_CygCocoon_Suzaku_JPS.ppt 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 T. Mizuno et al. 11

2014-03_CygCocoon_Suzaku_JPS.ppt Reference • Ackermann+11, Science 334, 1103 • Kushino+02, PASJ 54, 327 • Uchiyama+09, PASJ 61, S189 • Kaneda+97, ApJ 491, 638 T. Mizuno et al. 12

2014-03_CygCocoon_Suzaku_JPS.ppt Backup Slides T. Mizuno et al. 13

2014-03_CygCocoon_Suzaku_JPS.ppt Latitude Dependence of Extended Emission region Scale height CXB-subtracted brightness Cygnus Cocoon 1.26±0.29 brightness [10 -7 erg/s/cm 2 /sr] Source & BG [deg] Scutum arm 0.64±0.10 (Kaneda+97) [deg] Scale height of extended BG1 emission in Cygnus Cocoon Source1 region is ~2 larger than that of Source2 Scutum arm (l=28deg; BG2 Kaneda+97), probably due to the proximity of Cygnus-X Galactic Latitude [deg] Most of extended emission can be interpreted to be from GRXE T. Mizuno et al. 14

2014-03_CygCocoon_Suzaku_JPS.ppt Simple Argument of CR Electron Cutoff • Conservative upper limit of X-ray emission is <=40% of the expectation, requiring cutoff of CR electron (in electron scenario) Synchrotron X-ray For B=20 μ G, E e of 50 TeV � � � 100 TeV� � sin � eV �� ���,���� ~2000� 10 �G� � required to produce 1 keV X-ray In electron scenario, cutoff in <= 50 TeV is required to explain (non-detection of) X-rays T. Mizuno et al. 15

2014-03_CygCocoon_Suzaku_JPS.ppt  -ray Count Map  -ray emission = diffuse emission (ISM x Galactic CR)+point sources • • Excess is a signature of unknown high-energy objects/phenomena Galactic diffuse Count Map  -Cygni and known sources (E>10 GeV) subtracted subtracted T. Mizuno et al. 16

2014-03_CygCocoon_Suzaku_JPS.ppt Radiation Field inside Cocoon • Optical from Cygnus OB2 and NGC 6910 • Infrared (dust emission) measured by IRAS 1 meV T. Mizuno et al. 1 eV 17