Centaurus A at Hard X-Rays and Soft Gamma-Rays Chandra 1-10 keV CGRO-COMPTEL 1 ± 30 MeV Fermi 100 MeV ± 100 GeV Helmut Steinle Max-Planck-Institut für extraterrestrische Physik Garching, Germany ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 1 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays Contents · Introduction · The Spectral Energy Distribution · Properties of the existing measurements in the hard X-ray / soft Gamma-ray regime · Important satellites for this energy / frequency range · Variability of the X-ray / Gamma-ray emission · Two examples of models for the Cen A Spectral Energy Distribution · Problems (features) to be considered when using the hard X-ray / soft Gamma-ray data ± the ªsoft X-ray transient problemº ± the ªSED problemº · Outlook ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 2 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Introduction In the introductory (ªsetting the stageº) section of the conference, the talks will cover all frequency ranges in which Centaurus A has been observed. The topic of this talk is the hard X-ray / soft Gamma-ray range, where the Spectral Energy Distribution (SED) shows a maximum, that in most models is contributed to the inverse Compton scattering of synchrotron photons or ambient photons. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 3 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Spectral Energy Distribution ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 4 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Spectral Energy Distribution hard X-rays / soft Gamma-rays ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 5 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Spectral Energy Distribution CGRO 50 keV 10 GeV ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 6 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Properties of the Existing Measurements in the Hard X-ray / Soft Gamma-Ray Regime In the following existing measurements in the hard X-ray (10 ± 500 keV; 1018 ± 1020 Hz) and soft Gamma-ray (500 keV ± 10 GeV; 1020 ± 1024 Hz) energy / frequency range will be discussed. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 7 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- · This frequency range is, compared to adjacent frequency ranges, poorly sampled and due to the lack of sensitive second / third generation detectors (on satellites), the spatial and temporal resolution is not at all comparable to other frequency regimes. · The lack of new detectors is due to the fact, that the interaction probability of radiation with matter in this energy range has a minimum and thus detectors with high sensitivity and good spatial resolution are extremely difficult and costly to build as they have to be very massive and due to the absorption of Gamma-rays in the Earth atmosphere, they have to be operated in space. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 8 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Comparison of the Sensitivity of Various X-ray and Gamma-ray Detectors Very few detectors exist(ed) in the 100 keV to 1 GeV range: · Sigma/Granat (1989 ± 1997) 30 keV ± 1.5 MeV · CGRO (1991 ± 2000) - BATSE 30 keV ± 1 MeV - OSSE 50 keV ± 10 MeV - COMPTEL 750 keV ± 30 MeV - EGRET 50 MeV ± 10 GeV · Integral / IBIS (2002 - ¼.) 15 keV ± ~ 1 MeV · Fermi (2008 - ¼.) (Ch. Dermer, ESA SP-382, 405-412, 1997; Fig. 1a mod.) 10 keV - >300 GeV ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 9 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The low sensitivity of the instruments results in long integration times. Although measurements can be simultaneous, the hard X-ray and Gamma-ray measurements are always orders of magnitude longer in duration than the other simultaneous observations. The detections shown often required integration times of weeks or the combination of whole observation periods of several weeks duration especially during the low emission state of Cen A which prevailed most of the time during the lifetime of Compton Gamma-ray Observatory (CGRO). The combined observation periods were most of the time separated by several weeks or months. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 10 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Comparison of the Imaging Resolution of Various X-ray and Gamma-ray Detectors Only detectors with almost no spatial resolution exist(ed) in the 100 keV to 1 GeV range: · Sigma/Granat (1989 ± 1997) 1° 1 15º on-axis · (1991 ± 2000) CGRO 1Â - BATSE ~ 1° (known sources) - OSSE 1ÂÂ 4° x 12° - COMPTEL 2° - 4° for strong sources - EGRET ~ 0.5° (@ several 100 MeV) · Integral / IBIS (2002 - ¼.) 12' (1' location) · Fermi (2008 - ¼.) Ch. Dermer, ESA SP-382, 405-412, 1997; Fig. 1b mod. 30º ± 5' ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 11 / 35 Centaurus A at Hard X-Rays and Soft Gamma-Rays ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Important Satellites for this Energy / Frequency Range (real photograph) (artists impression) (artists impression) CGRO Integral Fermi 30 keV ± 10 GeV 3 keV ± 10 MeV 10 keV ± > 300 GeV 1999 - 2000 2002 ± (active) 2008 ± (active) ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The Many Faces of Centaurus A ± Sydney, 28 June ± 3 July 2009; H. Steinle, MPE 12 / 35 Centaurus A at Hard X-Rays and Soft