Monitoring and Light Curves

To prepare a "target of opportunity" (ToO) observation of Centaurus A in a very bright state in X-rays/gamma-rays, several instruments have been and are used to monitor the X-ray emission of Centaurus A.

Swift Monitoring @ 15 - 50 keV (2005-02-13 to present)

BAT Cen A monitor data.

(click for full resolution; plot from direct link to Swift Cen A monitoring page)

Note: as with the RXTE data, on can see that around the end of a year the data get noisier and often the count rate increases. This may be due to a similar effect as noted for the RXTE data:
Benlloch et al. (2001) mention, that: "...apparent fluctuations in the (RXTE) ASM flux at the end of each year coinciding with the closest angular separation between the sun to Cen A. This variability is due to scattering of solar X-rays off the ASM collimators onto the ASM detectors and is not due to source flux variations (Remillard, priv. comm.).".
ToO trigger theshold :
The ToO condition is met if Cen A exceeds

0.043 cts cm^-2 sec^-1

in the 15 - 50 keV energy band for more than 30 consecutive days.

Comments :
MJD 56000 = 2012-03-14
MJD 56100 = 2012-06-22
MJD 56200 = 2012-09-30
MJD 56300 = 2013-01-08
MJD 56400 = 2013-04-18

MJD - date converter

Fermi GBM Monitoring @ 12 - 300 keV in four energy bands (2008-08-12 to present)

Fermi GBM Earth Occultation Monitoring Data.
Four energy bands: 12 - 25 keV, 25 - 50 keV, 50 - 100 keV, and 100 - 300 keV.

(plot from direct link to Fermi GBM Cen A monitoring page)

From the description:
Red diamonds denote > 5-sigma statistical significance (possible detections), blue diamonds denote < -3-sigma statistical significance (usually an indication of interference or background problems). Each plot shows the long-term average as a dashed line, which is shown in pink if the long-term average statistical significance is > 10 sigma.
Comments :
MJD 54800 = 2008-11-30
MJD 55800 = 2011-08-27
MJD 56000 = 2012-03-14
MJD 56100 = 2012-06-22
MJD 56200 = 2012-09-30
MJD 56300 = 2013-01-08
MJD 56400 = 2013-04-18

MJD - date converter

Cen A X-Ray Light Curves

10 Year Vela 5b Light Curve at 1 - 12 keV (1969 - 1979)

from: J. Terrell (1986).

26 Year Light Curve at 3 - 12 keV (1969 - 1994)

Compilation from: Turner et al. (1986).

Long Term Light Curve at ∼100 keV (1968 to 1995)

Fig. 5 from: Bond et al. (1996)
This light curve overlaps with the CGRO-BATSE light curve (see below) for almost 4 years (May 1991 to end 1995) and the persistent "low state" of Cen A since 1993 is evident.

CGRO-Batse Light Curve at 20 - 200 keV (1991-04-29 to 2000-05-25)

This are all Compton Gamma-Ray Observatory (CGRO) BATSE Cen A monitoring data avaialble up to TJD 11690 (2000-05-25, the day all scientific instruments aboard CGRO were switched off prior to the deliberate destruction of the Compton Gamma-Ray Observatory by NASA).
The light curve overlaps with the RXTE-ASM light curve (see below) for almost 4.5 years (January 1996 to May 2000) and the persistent "low state" of Cen A is evident.

RXTE-ASM Light Curve at 2 - 10 keV (1996-01-05 to 2011-08-24)

This are all Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) Cen A data avaialble up to TJD 15797 (2011-08-24) about 4 months before RXTE was shut down on January 5, 2012 after a successful 16 year mission.
The light curve overlaps with the Swift-BAT light curve (see below) for almost 6.5 years May 2005 to August 2011) and the persistent "low state" of Cen A is again evident.
Note: Benlloch et al. (2001) mention, that: "...apparent fluctuations in the (RXTE) ASM flux at the end of each year coinciding with the closest angular separation between the sun to Cen A. This variability is due to scattering of solar X-rays off the ASM collimators onto the ASM detectors and is not due to source flux variations (Remillard, priv. comm.).".

Combined CGRO-BATSE (20 - 200 keV) and RXTE-ASM (2 - 10 keV) Light Curve (1991-04-29 to 2011-08-24)

Swift-BAT Light Curve at 15 - 50 keV (2005-05-13 to 2012-03-27)

This are all Swift Burst Alert Telescope (BAT) Cen A data up to TJD 15013 (2012-03-27). The Swift mission is still operating and delivering data (see "Monitoring" above).

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