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Multi-Satellite Observation of Cen A RXTE, INTEGRAL, Suzaku, Swift Plus XMM and Chandra Richard E. Rothschild Katja Pottschmidt Alex Markowitz Valentina La Porola Craig Markwardt Jay Cummings Dan Evans Marcus Kirsch John Tomsick Tad Takahashi Kazuhiro Nakazawa Kokubun Motohide

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Instruments, Livetimes, and Rates
Instrument RXTE/PCU2 RXTE/HEXTE INTEGRAL/JEMX-1 INTEGRAL/ISGRI INTEGRAL/SPI Swift/XRT Swift/BAT Suzaku/XIS-FI Suzaku/XIS-BI Suzaku/PIN Suzaku/GSO Chandra/MEG Chandra/HEG XMM/MOS1 XMM/MOS2 XMM/PN 6/19/2006 Livetime (s) 9,472 6,073 42,080 83,160 92,453 10,086 12,165 212,304 69,018 154,000 61,562 98,342 98,342 18,900 18,911 16,664 0.557±0.009 0.583±0.009 1.77±0.02 ICWG Iceland 2006 0.0165±0.0009 0.635±0.003 0.774±0.003 2.38±0.01 2.38±0.01 6.69±0.02 2 0.232±0.001 0.327±0.002 4.51±0.005 3.84±0.007 0.471±0.004 0.908±0.013 0.127±0.004 0.662±0.008 36.3±1.9 1.27±0.04 6.59±0.01 0.0115±0.0009 Rate (0.5-2) Rate (2-10) 21.54±0.06 4.62±0.11 Rate (20-100)

RXTE "Image"

XMM PN Image

Chandra ACIS Image

Field of view and spatial resolution drastically affect what is included in "the spectrum of the nucleus of Cen A".

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2.5 keV

Energy range and energy resolution dramatically affect the modeled spectral components and thereby "the spectrum of Cen A"
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0.1

XMM & Chandra
3 0.3

10

INTEGRAL JEM-X
10 15

20

INTEGRAL ISGRI & SPI 200 Swift BAT
150

Swift XRT

0.4 Suzaku XIS

10

15 Suzaku HXD 50

100

200

3

RXTE PCA

20

RXTE HEXTE

250

2.5 keV 6/19/2006 ICWG Iceland 2006 5

Cen A Spectrum Above 2.5 keV RXTE

PCU2 n
H

HEXTE --1.83 ± 0.06 --500 ± 21 ------33/48 = 0.69

RXTE 11.2 ± 0.4 1.85 ± 0.02 390 ± 8 --6.32 ± 0.12 3.2 ± 0.8 81 100/110 = 0.91

11.2 ± 0.03 1.85 ± 0.02
0

Norm2-1 Norm20 E(Fe) F(Fe) EW
2

389 ± 9 --6.32 ± 0.12 3.2 ± 0.8 82 67/61 = 1.09

-100

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Cen A Spectrum Above 2.5 keV INTEGRAL

JEMX n
H

ISGRI ----612 ± 12 -------

SPI ----817 ± 72 -------

INTEGRAL 12.3 ± --545 ± 29 6.32 1.9 --0.7 1.9

9.3 ± 3.2 361 ± 49 --6.32 2.0 ---

Norm2-1 Norm20 E(Fe) F(Fe) EW
2 0

1.80 ± 0.12 1.97 ± 0.05 1.76 ± 0.17

1.95 ± 0.02

-100

78/63 = 1.24 21/17 = 1.23 18/18 = 1.00 123/99 = 1.25

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Cen A Above 2.5 keV Swift

XRT n
H

BAT --1.57 ± 0.18 --688 ± 54 -------

Swift 9.1 ± 0.9 1.71 ± 0.13 369 ± 20 --6.35 ± 0.05 3.0 ± 1.5 76

9.8 ± 1.1 1.83 ± 0.17
0

Norm2-1 Norm20 E(Fe) F(Fe) EW
2

384 ± 29 --6.36 ± 0.04 3.2 ± 1.5 81 59/68 = 0.87

-100

68/456= 1.22 131/125 = 1.05

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Cen A Above 2.5 keV Suzaku
XIS-BI n
H

PIN ---

GSO ---

Suzaku 10.6 ± 0.13 1.72 ± --304 ± 2 6.38 ± 0.01 2.7 ± 0.2 ---

9.8 ± 0.15

0.02 Norm2-1 Norm20 E(Fe) F(Fe) EW
2 0

1.57 ± 0.02 1.84 ± 0.03 1.97 ± 0.11 289 ± 3 --6.37 ± 0.01 2.6 ± 0.2 80 --630 ± 15 --------641 ± 48 -------

-100

168/98 = 1.71 90/75 = 1.20 26/20 = 1.31 562/195 = 2.88 XIS-FI 10.0 ± 0.1 1.68 ± 0.02
0

n

H

Norm2-1 E(Fe) F(Fe) EW
2

312 ± 2 6.37 ± 0.004 2.7 ± 0.1 81

256/98 = 2.61

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Cen A Above 2.5 keV XIS BI & FI Due to the higher energy resolution and sensitivity of the XIS telescopes, weaker features are significant. Iron edge at 7.17 ± 0.04 keV with ~ 5x10
-2 -2 -5

Another edge at 3.40 ± 0.03 keV with ~ 5x10

Emission line at 3.66 ± 0.03 keV with Flux of 5x10

cm-2s-1 or EW = 6 eV

These features and others need to be taken into account when calibrating high sensitivity instruments with good energy resolution, but they do not significantly affect continuum measurements. Including them changed the fitted power law index by <1%.

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Results from Continuum fitting above 2.5 keV RXTE/PCU2 index of 1.85 ± 0.02 defines the continuum -- Low index outliers: BAT at 1.57 ± 0.18 XIS-BI at 1.57 ± 0.02 XIS-FI at 1.68 ± 0.02 -- High index outlier: ISGRI at 1.97 ± 0.05 Suzaku/XIS defines iron line energy (6.37 ± 0.05 keV) and line flux (2.7 ± 0.1 cm-2s-1) All 4 missions agree with this within errors.

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But what about low energy absorption? Low energy telescopes and PCU2 disagree on nH but this may be a function of the power law index in which they also do not agree. Could it be the limited energy range of the telescopes? No! Fitting PCU2 in the 2.5--12 keV range yields nH = 11.6 ± 0.5 x10 = 1.88 ± 0.03 E(Fe) = 6.33 ± 0.13 keV Flux(Fe) = 2.9 ± 1.0 x10
-4 22

cm-2

cm-2s-1

Something is amiss in the telescope calibrations.

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Do Chandra and XMM also fit to a flatter power law index --- YES!!

Chandra HETG: nH = 9.9 ± 0.3 x10 = 1.57 ± 0.06 E(Fe) = 6.37 ± 0.01 keV F(Fe) = 3.1 ± 0.5 x10
-4 22

XMM cm-2 nH = 0.2 = 0.04

MOS1 8.4 ± 0.4

MOS2 8.6 ± 0.4

PN 8.6 ±

1.56 ± 0.08 1.65 ± 0.08 1.69 ±

cm-2s

-1

E(Fe) = 6.42 ± 0.02 6.38 ± 0.02 6.44 ± 0.02
ICWGF(Fe) =2006 ± 0.7 Iceland 3.4

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3.3 ± 0.7

2.5 ± 0.3 13

Cen A Below 2 keV

XMM Apec kT = 0.64±0.02 Apec Norm = 6.8±0.4 x10 Power Law = 1.01±0.04 Flux(1 keV) = 2.01±0.03 x10 Line Energy = 0.651±0.012 Line Flux = 1.5±0.5 x10 EW = 33.5
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-4 -3 -4

Suzaku 0.62±0.01 2.1±0.8x10-4 0.89±0.06 0.56±0.01 x10 0.641±0.004 0.38±0.07 x10 27.0
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Swift 0.42±0.07 12.6±4.0x10 0.84±0.44 2.1±0.5 x10 ------14
-3 -4

Cen A Below 2 keV

Results below 2 keV appear to be very calibration and systematics dependent. An Apec plus power law model can be the basis for beginning to understand the Cen A flux. Variable abundances and better energy calibration may help with the additional lines required for each instrument. Systematics associated with front or back illumination, variable contamination, instrumental lines, and sizes of extraction regions may very well dominate our detailed knowledge of emission processes below 2 keV.

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Summary of the Inter-calibration above 2.5 keV Power Law Index: RXTE/PCU2: RXTE/HEXTE: 1.85±0.02 1.83±0.06 Swift/XRT: 1.83±0.17 Suzaku/XIS-BI: 1.57±0.02 Suzaku/XIS-FI: 1.68±0.02 XMM/MOS1: XMM/MOS2: XMM/PN: 1.56±0.08 1.65±0.08 1.69±0.04

INTEGRAL/JEMX: 1.80±0.12 INTEGRAL/ISGRI: 1.97±0.05 INTEGRAL/SPI: Swift/BAT: Suzaku/PIN: Suzaku/GSO: RXTE: Swift: Suzaku:
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1.76±0.17 1.57±0.18 1.84±0.03 1.97±0.11

Chandra/HETG: 1.57±0.06 RXTE/PCU2 (2.5--10): 1.88±0.03

1.85±0.02 1.71±0.13 1.72±0.02
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INTEGRAL: 1.95±0.02

Power law index is probably 1.85 and steady.

Summary of Iron Line Measurements RXTE/PCU2: Swift/XRT: 6.32±0.12 keV 6.36±0.04 3.2 ±0.03 x 10-4 cm-2 s-1 3.2 ±0.15 2.6 ±0.02 2.7 ±0.01 3.4 ±0.07 3.3 ±0.07 2.5 ±0.03 3.1 ±0.05
-4

Suzaku/XIS-BI: 6.37±0.01 Suzaku/XIS-FI: 6.37±0.004 XMM/MOS1: XMM/MOS2: XMM/PN: 6.42 ± 0.02 6.38 ± 0.02 6.44 ± 0.02

Chandra/HETG: 6.37 ± 0.01

Line energy is most probably near 6.37 keV with a flux near 3.3 x 10

cm-2 s-1

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Summary of Using Cen A as a Calibration Source

1. 2. 3. 4. 5. 6.

Spectrum above 2.5 keV and up to at least 200 keV is an absorbed power law with an iron emission line and edge. The line of sight absorption is variable between 1 and 1.5 x 10 that must be fit for each observation.
23

cm-2, so

The power law photon index appears to be stable at 1.85±0.01 over the last decade, as seen by RXTE and BeppoSAX. While the 2-10 and 20-100 keV fluxes vary by as much as 50%, the power law index remains unchanged. The iron line energy of 6.37 may be stable, but we do not have enough high resolution measurements to know for sure. The iron line flux appears to be stable to 20% over the last decade.

BOTTOM LINE: Use the power law index for continuum calibrations with broad band instruments, but figure out why 2--10 keV measurements with focusing telescopes consistently derive indices ~ 0.2 flatter.
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