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Observation Date (UT) Observation Lat

Canonical Name:Centaurus A
TeVCat Name:TeV J1325-430
Other Names:NGC 5128
Source Type:FRI
R.A.:13 25 30.3 (hh mm ss)
Dec.:-43 00 15 (dd mm ss)
Gal Long: 309.53 (deg)
Gal Lat: 19.43 (deg)
Distance: z=0.00183
Flux:0.08 (Crab Units)
Energy Threshold:250 GeV
Spectral Index:2.7
Extended:Yes
Size (X):0.04 (deg)
Size (Y):0.01 (deg)
Discovery Date:2009-03
Discovered By: H.E.S.S.
TeVCat SubCat:Default Catalog

Source Notes:

The detection of this source by H.E.S.S. was announced at the Moriond 2009 conference.
It had previously been claimed to be a TeV emitter in 1975 by Grindlay et al. (4.5 sigma).
Evidence for extension of the TeV emission from this source was reported by Sanchez et al. (2018)
making this the first extragalactic TeV source for which an extension has been reported.
These results were subsequently reported in H.E.S.S. Collaboration (2020).

Source position and its uncertainty:

The position given in TeVCat was updated on 210610 from that given in Aharonian et al. (2009) to that given in H.E.S.S. Collaboration (2020).
From H.E.S.S. Collaboration (2020):
- R.A. (J2000): 13h 25m 30.3s +/- 1.4s (stat) +/- 1.8s (sys)
- Dec. (J2000): -43d 00' 15'' +/- 15'' (stat) +/- 20'' (sys)
- "This corresponds to a slight, insignificant offset of approximately
60'' north-east from the position of the galaxy core."

From Aharonian et al. (2009):
- R.A. (J2000): 13h 25m 26.4s +/- 4.6s(stat) +/- 2.0s(syst)
- Dec. (J2000): -43d 0.7' +/- 1.1'(stat) +/- 30''(syst)

Source Extension:

From H.E.S.S. Collaboration (2020):
- The authors report "observations of Centaurus A at TeV energies that
resolve its large-scale jet."
- "To probe a possible extension at very high energy gamma-ray
energies, we selected a total of 202 hours of H.E.S.S observations of
Centaurus A between 2004 and 2016, corresponding to high-quality data
suitable for extension measurements"
- "The detection significance is 13.1 sigma at energies above 240 GeV."
- "We compare the different best-fit models by using a test statistic
(TS) value as figure of merit. In addition to the assumption of
point-like emission, we fit the data with a radially symmetric
Gaussian as well as an elliptical Gaussian model. Compared to a
point-like source, the radially symmetric Gaussian is preferred with a
TS of 6.1, and the elliptical Gaussian with TS = 19.4. The
considerable difference of the TS values implies a strong preference
for the elliptical over the radially symmetric model."
- Details of the extension measured:
... semi-major axis: 0.041 deg +/- 0.006 deg
... semi-minor axis: <0.013 deg
... ellipticity: 0.92 +0.08 -0.23
... position angle: 43.4 deg +7.7 deg -7.2 deg
... the width of the semi-major axis has a postion angle measured anticlockwise from north

From Sanchez et al. (2018):
Evidence for extension with an elliptical shape is presented:
- the Gaussian width of the semi-major axis is 0.044 +/- 0.012 deg
- the emission is point-like in the tranverse direction
- the extension is aligned with the radio jets

Distance:

From H.E.S.S. Collaboration (2018):
- "at a distance of approx. 3.8 Mpc Harris et al. (2010), Centaurus A is
the nearest active galaxy Israel (1998)"

Spectral Information:

From H.E.S.S. Collaboration (2018):
In this paper data taken betweeen 2004 and 2010 are
analysed/re-analysed. Two datasets are defined:
- Data set A was taken between April 2004 and July 2008 (these data were previously published)
- Data set B was taken between 2009 and 2010
Spectral indices:
- Data set A: 2.51 +/- 0.19 (stat) +/- 0.20 (syst)
- Data set B: 2.55 +/- 0.19 (stat) +/- 0.20 (syst)
- Combined data sets A and B: 2.52 +/- 0.13 (stat) +/- 0.20 (syst)
Normalisation constants:
- Data set A: 1.44 +/- 0.22 (stat) +0.43 (syst) -0.29(syst) e-13 cm-2 s-1 TeV-1 at E0 of 1 TeV
- Data set B: 1.50 +/- 0.22 (stat) +0.45 (syst) -0.30(syst) e-13 cm-2 s-1 TeV-1 at E0 of 1 TeV
- Combined data sets: 1.49 +/- 0.16 (stat) +0.45 (syst) -0.30(syst) e-13 cm-2 s-1 TeV-1 at E0 of 1 TeV

Flux:

From H.E.S.S. Collaboration (2018):
- "Cen A is a weak VHE source with a measured integral flux above 250 GeV
of about 0.8% of the flux of the Crab Nebula"

Source Properties:

From H.E.S.S. Collaboration (2020):
- "The physical extension of the semi-major axis of the best-fit
elliptical Gaussian exceeds 2.2 kpc, implying that a major part of the
VHE emission arises on large scales, far away from the black hole. The
derived alignment with the jet direction and the known spectral
characteristics are in line with models where the VHE emission
originates from inverse Compton (IC) upscattering of low-energy
photons by very energetic electrons accelerated along the jet"

From H.E.S.S. Collaboration (2018):
- "An updated Fermi-LAT analysis provides evidence for spectral
hardening by approximately 0.4 +/- 0.1 at gamma-ray energies above 2.8
+1.0 −0.6 GeV at a level of 4.0 sigma. The fact that the spectrum
hardens at GeV energies and extends into the VHE regime disfavour a
single-zone SSC interpretation for the overall spectral energy
distribution (SED) of the core and is suggestive of a new gamma-ray
emitting component connecting the high-energy emission above the break
energy to the one observed at VHE energies. The absence of significant
variability at both GeV and TeV energies does not yet allow
disentanglement of the physical nature of this component, though a
jet-related origin is possible and a simple two-zone SED model fit is
provided to this end"

Classification:

From Rieger & Levinson (2018):
- This source is listed as an FR-I galaxy in Figure 1.

From Aharonian et al. (2009):
- "Centaurus A (Cen A) is the nearest active galaxy (for a review see
Israel 1998). It is classified as an FR I radio galaxy; "

From Israel (1998):
- "At a distance of 3.4 Mpc, NGC 5128 (Centaurus A) is by far the
nearest active radio galaxy. It is often considered to be the
prototype Fanaroff-Riley Class I `low-luminosity' radio galaxy, and as
such it plays an important role in our understanding of a major class
of active galaxies."


Seen by: H.E.S.S.
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