12

Results on 3 southern hemisphere closest BL Lac objects:

Outline

PKS2155-304, z=0.117

PKS0548-322, z=0.069

PKS2005-489, z=0.071

Conclusions

Introduction

The Blazar Phenomenon

Unified Spectral Sequence of Blazars (Fossati et al. 98):

Phenomeological sequence according
to the Luminosity:

Correlation : sync - IC

Anti-Correlation : L-sync

Radiative losses increase with luminosity

Ghisellini et al. (02)

?

HBLs: best VHE candidates :

Very high Fx(~1 keV)/Fradio(5GHz)

High X-ray Flux (~10-11 erg s-1cm-2)

Flat X-ray spectrum

rx < 0.8, ox < 1.2

Probing blazars with VHE -rays

VHE -rays:

Monitor the most energetic electrons of the jet;
Shed light on the acceleration mechanisms at the most extreme conditions.

Absorption features in the VHE spectrum:
-> can be used to constrain the Extragalactic BackGround Light field (EBL)
in the poorly measured 0.5-20 m band;
-> needs many objects and detailed understanding of intrinsic spectra;

e.g.:

Short variability time scales (< 15’! for Mkn421) + trasparancy requirements:
-> can tightly constrain the size of emission region, , B;

Correlations between X-ray & gamma-ray emissions:
-> in some cases have shown that they are co-spatial
-> hints on the Nature of emitting particles
(same population of electrons?);

HESS : Stereo Imaging Cherenkov Telescope ~100 GeV-50 TeV

2/4 HESS Telescopes are complete with cameras

12 /h for a Crab-like source in mono-mode at zenith

First light: June 11 2002

Mirror area ~107 m2

Diameter 13 m, focal length 15 m

Camera: 960 pixels , 5° f.o.v

MPI Kernphysik, Heidelberg

Humboldt Univ. Berlin

Ruhr-Univ. Bochum

Univ. Hamburg

Landessternwarte Heidelberg

Univ. Kiel

Ecole Polytechnique, Palaiseau

Collège de France, Paris

Univ. Paris VI-VII

CEA Saclay

CESR Toulouse

LAOG Grenoble

Paris Observatory

Durham Univ.

Dublin Inst. for Adv. Studies

Charles Univ., Prag

Yerewan Physics Inst.

Univ. Potchefstroom

Univ. of Namibia, Windhoek

-ray Signal Extraction : Mono-mode

And are more irregular than -ray Images
 Cut on Moments

Std Hillas + cut on Length/Size



BC

Source

Pointing angle

Reconstructed Shower Axis

Signal obtained on Crab Nebula
~18 in 4.7 hours live-time
C. Masterson (OG 2.2)

Background CR images are isotropic
 Cut on Pointing angle 

-ray signal : ON - OFF source data

VHE emitting BL Lacs

4 firmly established VHE BL Lacs in Northern Hemisphere:
Mkn 421, Mkn 501 (z~0.03), 1ES1959+650 (z=0.047), 1ES1426+428 (z=0.129)

3rd closest BL Lac in S. hemisphere

One of the brightest BL Lacs in X-rays

Also detected by EGRET in the
GeV range (Nov 94;Vestrand et al. 95)
Hard spectrum with diff. index n=1.7

Not detected by Cangaroo during
1997 observations (Roberts et al. 99)

“Mark 6” flux 09/96-11/97 in 32.5 hr:

(>300GeV)= 4.20.75  10-11 cm-2 s-1

1 BL Lac object in Southern Hemisphere detected only by Durham Mark 6 telescope:
PKS2155-304 (z=0.116) @ E>300 GeV during 96-97 (Chadwick et al. 99)

(Whipple, Hegra, TA & CAT)

6.6 

1.2

337

1107

1444

4.7

Oct 2002

9.9 

3.1

404

625

1029

2.2 h

Jul 2002

Significance

/min

Excess

Noff

Non

Tlive (h)

PKS2155

H.E.S.S. Results : PKS2155-304, z=0.117

JULY 2002

OCT 2002

6.6 

1.2

337

1107

1444

4.7

Oct 2002

9.9 

3.1

404

625

1029

2.2 h

Jul 2002

Significance

/min

Excess

Noff

Non

Tlive (h)

PKS2155

Signal in two observation periods (alpha plots):

PKS2155-304 (continued)

PKS2155-304 dimmed in Oct 2002:
the average rate decreased from 3.1 to 1.2 /min

JULY 2002

OCT 2002

Light-curves in two observation periods (excess per observing run):

Oct

Nov

Jul

Spectrum analysis is ongoing, already indication of a very steep spectrum

PKS2005-489, z=0.071

Jul-Oct 2002

0.6 

0.13±.08

17.5

481

499

2.2 h

Jul-Oct 02

Significance

/min

Excess

Noff

Non

Tlive (h)

PKS2005

2nd closest BL Lac in S. hemisphere

Only reported in the 1st EGRET catalogue > 5Fichtel et al. 94);
hard spectrum with diff. index=2.2

Marginal GeV Source 4.1 
Lamb & Macomb 97)

Not detected by
Cangaroo (Roberts et al. 99)
nor	“Mark 6” (Chadwick 00)

“Mark 6” 3upper limit
70 hours 06/97-10/99 :

(>400GeV) < 0.79  10-11 cm-2 s-1

PKS0548-322, z=0.069

Nov-Dec 2002

0.8 

0.28±0.34

19.8

299.2

319

1.2 h

Jul-Oct 02

Significance

/min

Excess

Noff

Non

Tlive (h)

PKS2005

The closest BL Lac in S. hemisphere

Not detected by EGRET

Not detected by
Cangaroo (Roberts et al. 99) nor	“Mark 6” (Chadwick 00)

“Mark 6” 3upper limit
21.25 hours 02/96-10/99 :

(>300GeV) < 2.4  10-11 cm-2 s-1

Summary & Conclusions

Observations with the first H.E.S.S. telescope (mono-mode)

PKS2155-304 is confirmed as a new TeV source:
a clear signal at an average rate of 3 /min
with a significance level of 9.9
is detected in 2.2 hrs during July 2002.

PKS2155-304 dimmed in Oct 2002. Average rate: 1.2 /min

Spectrum analysis is ongoing, already indication of a very steep spectrum

No signal detected from PKS0548-322 and PKS2005-489 yet:	Observations are ongoing on those sources and

Other AGNs and extragalactic objects e.g. the starburst galaxy NGC253

STAY TUNED…

Présentation PowerPoint

DJANNATI

2003-09-10T18:03:02