Centaurus A at Hard XRays and Soft GammaRays
Chandra 110 keV CGROCOMPTEL 1 – 30 MeV Fermi 100 MeV – 100 GeV
Helmut Steinle MaxPlanckInstitut 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 XRays and Soft GammaRays Contents • Introduction • The Spectral Energy Distribution • Properties of the existing measurements in the hard Xray / soft Gammaray regime • Important satellites for this energy / frequency range • Variability of the Xray / Gammaray emission • Two examples of models for the Cen A Spectral Energy Distribution • Problems (features) to be considered when using the hard Xray / soft Gammaray data – the “soft Xray transient problem” – the “SED problem” • Outlook
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 2 / 35
Centaurus A at Hard XRays and Soft GammaRays Introduction
In the introductory (“setting the stage”) 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 Xray / soft Gammaray 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.
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Centaurus A at Hard XRays and Soft GammaRays The Spectral Energy Distribution
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Centaurus A at Hard XRays and Soft GammaRays The Spectral Energy Distribution
hard Xrays / soft Gammarays
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Centaurus A at Hard XRays and Soft GammaRays The Spectral Energy Distribution
CGRO
50 keV 10 GeV
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Centaurus A at Hard XRays and Soft GammaRays Properties of the Existing Measurements in the Hard Xray / Soft GammaRay Regime
In the following existing measurements in the
hard Xray (10 – 500 keV; 1018 – 1020 Hz)
and
soft Gammaray (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 XRays and Soft GammaRays
• 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 Gammarays in the Earth atmosphere, they have to be operated in space.
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Centaurus A at Hard XRays and Soft GammaRays Comparison of the Sensitivity of Various Xray and Gammaray 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 ….) 15 keV – ~ 1 MeV
• Fermi (2008 ….) (Ch. Dermer, ESA SP382, 405412, 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 XRays and Soft GammaRays
The low sensitivity of the instruments results in long integration times.
Although measurements can be simultaneous, the hard Xray and Gammaray 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 Gammaray 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 XRays and Soft GammaRays Comparison of the Imaging Resolution of Various Xray and Gammaray Detectors Only detectors with almost no spatial resolution exist(ed) in the 100 keV to 1 GeV range: • Sigma/Granat (1989 – 1997) 1° 1 15” onaxis • (1991 – 2000) CGRO 1´ BATSE ~ 1° (known sources) OSSE 1´´ 4° x 12° COMPTEL 2° 4° for strong sources EGRET ~ 0.5° (@ several 100 MeV) • Integral / IBIS (2002 ….) 12’ (1’ location) • Fermi (2008 ….) 30” – 5’ Ch. Dermer, ESA SP382, 405412, 1997; Fig. 1b mod. The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 11 / 35
Centaurus A at Hard XRays and Soft GammaRays 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 XRays and Soft GammaRays Compton GammaRay Observatory CGRO 30 keV – 10 GeV
Launch: April 5, 1991
Deliberate destruction: June 4, 2000
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 13 / 35
Centaurus A at Hard XRays and Soft GammaRays
The instruments of the
Compton GammaRay Observatory
operated in the energy range 30 keV (BATSE) to 10 GeV (EGRET) with OSSE and COMPTEL covering the energy range in between.
The data of this suite of hard Xray / soft Gammaray instruments are to date the only existing measurements covering simultaneously the energy range from 30 keV to 10 GeV.
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 14 / 35
Centaurus A at Hard XRays and Soft GammaRays
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 15 / 35
Centaurus A at Hard XRays and Soft GammaRays The poor spatial resolution makes it impossible to distinguish the emission components of the central region of Cen A i.e. nucleus, jet, or other radiation sources like Xray binaries.
This is the best (and only) 1 – 30 MeV map of the Centaurus A region. It is composed from all observations of the first four years of CGRO COMPTEL observations and shows an area of
40° x 40° !
The resolution is 5°.
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Centaurus A at Hard XRays and Soft GammaRays
Integral
3 keV – 10 MeV
Launch: October 17, 2002
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Centaurus A at Hard XRays and Soft GammaRays
Integral observations: (example)
IBIS/ISGRI, 43 hours rev. 587/588; August 49, 2007 15 KeV – 1 MeV (10 MeV) grid ~ 15° x 5° 15 arcmin resolution
… but the sensitivity and resolution is not sufficient to resolve anything ….
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 18 / 35
Centaurus A at Hard XRays and Soft GammaRays
Integral observations: (example)
SPI, 37.4 hours (rev. 348; August 8, 2005) 20 KeV – 9 MeV
… but the sensitivity is not sufficient to detect Cen A above 500 keV ….
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 19 / 35
Centaurus A at Hard XRays and Soft GammaRays Fermi Gammaray Space Telescope (GLAST)
20 MeV * – > 300 GeV
Launch: June 11, 2008 * The Fermi Gammaray Burst Monitor (GBM) observes the whole visible sky and operates in the energy range 10 keV – 30 MeV but has no real spatial resolution. The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 20 / 35
Centaurus A at Hard XRays and Soft GammaRays Things to come ………. see talk on Fermi (LAT) observations of Cen A by Teddy Cheung on Tuesday
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Centaurus A at Hard XRays and Soft GammaRays Back to existing data in the 50 keV to 10 GeV regime! Typical CGROOSSE observation periods of Cen A (50 keV 1 MeV) lasted one day, CGROCOMPTEL observations (0.75 – 30 MeV) typically lasted two weeks, and the EGRET (100 MeV – 1 GeV) detection of Cen A was only possible when the data of more than one observation period were analyzed. This is a summary of all existing measurements in the 10 KeV to 1 GeV energy range. They are all from CGRO.
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Centaurus A at Hard XRays and Soft GammaRays Keeping this in mind, still a significant variability of the spectra in the hard X ray / soft Gammaray data is observed. If the definition of Bond et al. based on the Xray emission below the energy range considered here (see below) is applied, the observations during the time span 1991 to 2000 have been made in two emission states:
the medium emission state (green, solid line) at the very beginning of the CGRO observations (1991; VP 12) and
the low emission state (blue, dashed line) in all following observations.
In 1995 a multiwavelength campaign covering the frequency range from radio to GeV was organized (red, only the hard Xray to Gammaray part is shown here).
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Centaurus A at Hard XRays and Soft GammaRays Variability of the Xray / Gammaray Emission
SIGMA onboard GRANAT satellite; coded aperture with angular @ 100 keV resolution of 10’15’; 35 keV – 1.3 MeV; Sigma data 1990 1994
high
intermediate
low
Bond et al. 1996 (definition of emission states)
CGRO + RXTE 1991 – 2000 1996 …
20 – 200 keV 2 – 10 keV
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 24 / 35 Centaurus A at Hard XRays and Soft GammaRays
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Centaurus A at Hard XRays and Soft GammaRays The variability in the soft Xray range (~ 10 keV) has to be used to define an emission state by which observations above 100 keV can be somehow classified. The spectra from 100 keV to 1 GeV vary between the so defined emissions states. Therefore a correlation of the emission at lower Xray energies and the MeV range is suggested.
150 keV Summary of all simultaneous measurements of Cen A with 590 keV 140 keV 16.7 MeV CGRO. (30 keV – 1 GeV)
The spectral change between the intermediate (solid line) and low state (broken line) is significantly shown in the comparison.
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 25 / 35
Centaurus A at Hard XRays and Soft GammaRays Two examples of models for the Cen A SED that show the importance of the CGRO energy range
synchrotron region inv. Compton region
CGRO
G. Ghisellini et al. A&A 432, 401410 (2005) Orellana & Romero arXiv:0902.0731v1 [astroph.HE] The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 26 / 35
Centaurus A at Hard XRays and Soft GammaRays
Problems (features) to be considered when using the hard Xray / soft Gammaray data
• Spatial resolution or the “soft Xray transient problem” in defining the emission state
• Spatial and Temporal resolution – or the “SED Problem”
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 27 / 35
Centaurus A at Hard XRays and Soft GammaRays The Soft Xray Transient Problem An Example: • The transient 1RXH J132519.8430312, = CXOU J132519.9430317; here hcs113) was almost as bright as the whole jet in 1995 (during the multiwavelength campaign). • It is only 2.5 arcmin separated from the Cen A nucleus. • The variability was confirmed by CHANDRA observations in 2000: a drop in intensity by factor 500 in six months was observed. • The transient is an ultraluminous Xray binary (close to the Eddington limit) and it is that much variable, that it could mimic strong variability of the Xray (and Gammaray) emission
of the nucleus of Cen A! The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 28 / 35 Centaurus A at Hard XRays and Soft GammaRays The Soft Xray Transient Problem (cont.)
Chandra observations have shown that many, highly variable Xray sources exist in Cen A. Their contribution to the total soft Xray luminosity and the variability observed has still to be determined. Only the high spatial resolution makes such investigations possible and the outcome will have severe consequences for variability observations of all other AGN which are too distant to be resolved.
Position of 246 Xray point sources detected by Chandra overlaid onto Chandra image in the 1 3 keV band pass a DSS image (J band) of Cen A. of the central part of Cen A. The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 29 / 35
Centaurus A at Hard XRays and Soft GammaRays The Spectral Energy Distribution Problem
• the SED is composed of data of very inhomogeneous measurements.
• the measurement characteristics
(integration time, instrument characteristics, measured area, etc.) are often not known very well; original literature is often not available.
• this results in the unanswered big questions: what was the emission state during the measurement? what was measured: nucleus
or more? The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 30 / 35
Centaurus A at Hard XRays and Soft GammaRays The SED Problem (cont.)
All measurements of the whole (optical) galaxy. However, if only the nucleus is emitting in this wavelength band …
All simultaneous measurement of the whole galaxy.
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 31 / 35
Centaurus A at Hard XRays and Soft GammaRays The SED Problem (cont.)
All observations where probably only the nucleus of Cen A was “measured” (in the fieldofview). This is assumed for Gammaray measurements!
All simultaneous measurements of the nucleus (subset of data from above).
The emission state plays a role!
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 32 / 35
Centaurus A at Hard XRays and Soft GammaRays Outlook Despite the problems, we have to live with this hard Xray / soft Gammaray data, as no other data are available and will be available in the near future. There are no accepted or proposed new generation instruments in this energy range that are currently built. Many investigations in all wavelength bands are carried out at the moment. Almost all new instruments, if they can observe Cen A, are usually pointed to this enigmatic object. A wealth of data exists already and new data are added continuously. It’s closeness can create problems (as with the Sun), but Cen A provides us with a “front seat” in the AGN theater. We can investigate this AGN in so much detail, that it can well be, that Centaurus A will become the “Rosetta Stone” of AGN science!
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Centaurus A at Hard XRays and Soft GammaRays Thank you for your attention!
Image: Capella Observatory The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 34 / 35
Centaurus A at Hard XRays and Soft GammaRays Further “Reading” (see also the poster!)
A web site, completely devoted to Centaurus A, has been set up at the MaxPlanckInstitut für extraterrestrische Physik:
http://www.mpe.mpg.de/CenA/
Contents: Facts : basic facts and a general description Observations : observations I was involved in Monitoring : Xray monitoring with RXTE (and Swift in the future) References : a complete list of references with active links Pictures : a collection of Cen A pictures in all wavelengths History : the history of Cen A observations Links : a collection of links to Cen A pages on the web
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 35 / 35
Centaurus A at Hard XRays and Soft GammaRays
X
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Centaurus A at Hard XRays and Soft GammaRays
The Many Faces of Centaurus A – Sydney, 28 June – 3 July 2009; H. Steinle, MPE 4 / 35
Radio map Cen A
Radio sky at 408 MHz Optical Appearance
40’ x 40’ 50’ x 50’ 27’ x 18’
MPG/ESO 2.2m + WFI 4 m Blanco telescope; CTIO Spitzer Space Telescope (Peng E.W. et al. AJ 124, 31443156 (2002)) (IR) Other Wavelengths
all 12’ x 12’ The Nucleus
Wide Field and Planetary Camera (WFPC2; HST)
Near Infrared Camera and MultiObject Spectrometer (NICMOS; 2.2 µm; HST) AGN Model for Cen A
10’ x 10’
12’ x 12’
Evidence for a 20 parsec disk at the nucleus of Centaurus A “disk like” structure Schreier E.J. et al. extending 2” at position angle 33° 1998, Ap.J. (Letters) 499, L143147 Dimensions
inner radio lobes 8’ x 8’
all three pictures are same scale
Xray 15’ x 8’ optical 12’ x 8’
radio 5°x 9° Cen A in the Unified AGN Scheme
• angle to lineofsight is 60° – 75°; this is like Seyfert class 2 (or Narrow Line Radio Galaxies)
• far from beeing a Blazar
• … but observed in Gammarays!
• due to closeness? The Critical Parameters
To make a consistent analysis of all Cen A data and to compare the many measurements obtained so far with theoretical models, two parameters have to be known:
• the spatial resolution (or the size of the aperture) of the instrument with which the measurement has been made and what has been measured
• the exact time (or duration) of the measurement
Not knowing the above parameters can cause severe problems as shown by the following examples. Resolution! (spatial and temporal)
The development of instruments and technologies has lead to a dramatic increase in spatial and temporal resolution:
radio
Verry Large Array; spatial resolution: 3.6” x 1.1”; 408 MHz survey; various instruments; temporal resolution: day spatial resolution: 0.85 deg; temporal resolution: n/a Resolution! (cont.)
optical
Anglo Australian Telescope; spatial resolution: 5’; Hubble Space Telescope; temporal resolution: spatial resolution: 0.5”; composite of three temporal resolution: hours 90 minute exposure pictures Resolution! (cont.)
Xray
Einstein (2 6 keV); spatial resolution: 12”; temporal resolution: 0.5 days
Chandra Space Telescope (1 – 3 keV); spatial resolution: 0.1”; temporal resolution: 0.5 days Resolution! (cont.)
Gammaray
40 deg x 40 deg ! 50 deg x 50 deg !
COMPTEL (1 – 30 MeV); INTEGRAL IBIS (15 keV – 10(?) MeV; spatial resolution: 4 deg spatial resolution: 12’ temporal resolution: weeks temporal resolution: 1.5 days