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Diffuse Galactic Continuum Emission with INTEGRAL/SPI A. Strong, MPE 18 Mar 2004

Diffuse Galactic Continuum Emission with INTEGRAL/SPI A. Strong, MPE 18 Mar 2004. Galactic diffuse hard X/soft gamma-rays: previously observed by RXTE, OSSE, COMPTEL, GINGA, ASCA, Chandra RXTE: 3 - 35 keV 1 o Valinia & Marshall 1998

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Diffuse Galactic Continuum Emission with INTEGRAL/SPI A. Strong, MPE 18 Mar 2004

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  1. Diffuse Galactic Continuum Emission with INTEGRAL/SPI A. Strong, MPE 18 Mar 2004

  2. Galactic diffuse hard X/soft gamma-rays: previously observed by RXTE, OSSE, COMPTEL, GINGA, ASCA, Chandra RXTE: 3 - 35 keV 1o Valinia & Marshall 1998 diffuse component |b| > 2o Revnivtsev 2003 OSSE: 50 – 500 keV 4o X 11oKinzer et al. 1999 COMPTEL: 1 – 30 MeV 2o diffuse, but sources also required to explain flux Chandra: imaging, proof of existence of diffuse component (Ebisawa 2001, Muno 2004) new:XMM:XGPS (Hands et al. 2004 astro-ph/0403304) 80% diffuse 2-10 keV (9% Galactic sources) Questions: - Point sources contribution (-> is there really diffuse emission ?) - Spectrum - Distribution Galactic diffuse continuum is major goal of INTEGRAL. Advantages of INTEGRAL: - imaging (recognize sources, diffuse emission) - large FOV and sky coverage - high spectral resolution - SPI/IBIS/JEMX

  3. Spectrum of Galactic ridge continuum pre – INTEGRAL Valinia & Marshall 2000 RXTE, OSSE Kinzer et al. 2001 OSSE Strong et al. 2000 COMPTEL Revnivtsev 2003 RXTE

  4. Galactic plane is intense source of hard X-rays/soft -rays luminosity 21038 erg s-1 origin is unclear * unresolved souces: no known source population * thermal kT~ 8 keV : too high pressure for containment in ISM * non-thermal electron bremsstrahlung, very inefficient because of ionization losses energy required ~ 1041 erg s-1, comparable to total cosmic-ray luminosity of Galaxy (including nuclei) * one possibility: in-situ acceleration of quasi-thermal“ electrons -----> (Dogiel,Inoue, Masai,Schoenfelder,Strong ApJ 581 2002)

  5. Diffuse emission analysis: long-term: imaging with e.g. maximum entropy (cf COMPTEL) but not yet enough data can anyway do spectroscopic analysis only via spatial model fitting -> model fitting approach maximum-likelihood fit to linear sum of components: * point sources * tracers of diffuse emission (COBE, HI, CO, COMPTEL ....) * instrumental background : explicit time-dependence determined in fitting. Background: template from 'empty field' observations: fixes detector ratios; background level per pointing is free. Method will work if detector background ratios ~time-independent. 12CO

  6. model fitting with spidiffit: counts = m * skymapm * SPI-response + m' background-template modelpointings components Skymap components: using HI, COinput survey maps, models Background assumed to have same form for each pointing, scaled in intensity Background template taken from OFF observations or averaging ON observations Fit: maximum likelihood Background factors 0.95 -1.05 : variation as expected. Multi-parameter statistical methods.

  7. GCDE diffuse spectral fitting 32 GCDE revolutions exposure: 3.3 106 sec energy range 18 – 1000 keV spidiffit background: time dependence free fitted components: HI+ CO + Gaussian new: 91 sources from IBIS : Lebrun et al. Nature March 18, 2004 DATA MODEL HI CO Gaussian (for e+e-)

  8. Exposure 3.3 106 sec

  9. GCDE Rev 47-123 / 18 – 68 keV maximum entropy image 4U1700-377 GRS1915+105 Sco X-1 1E1740.7-2942 649 GS1826-238 H1741-322 50 0 310 longitude

  10. 91 IBIS Sources fitted 30 0 -30 latitude 50 0 310 longitude

  11. Example of time-dependence of background determined by spidiffit

  12. GCDE spidiffit samplesource spectra 4U1700-377 1E1740.7-2942.1 H1741-322 GS1826-238

  13. GCDE Rev 47 – 123 Diffuse Sources Diffuse Including sources in the model: diffuse component remains. (although a population of weak sources cannot be excluded)

  14. GCDE Rev 47 – 123 Diffuse Kinzer et al. (1999,2001) OSSE: GC (l=b=0), VP 5+16 continuum * 0.5 positronium * 0.3 RXTE OSSE COMPTEL Positronium

  15. HI+CO Total diffuse Bulge Bulge harder, consistent with presence of positronium

  16. Sources SPI COMPTEL ridge emission COMPTEL: ridge emission 1 – 30 MeV cannot be explained completely by diffuse processes: - source component required (Strong, Moskalenko & Reimer 2000) - consistent with sum of sources from SPI ?

  17. Conclusions SPI detects apparently diffuse emission (but population of weak point sources also possible) diffuse / total ~ 0.1 consistent with new IBIS (Nature March 18) results spectrum consistent with OSSE, RXTE cf. diffuse / total = 10 2-10 keV (XMM) ?! Next step: evaluate contribution from unresolved sources

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