Radio galaxy Elliptical Fanaroff-Riley type I “Misaligned” BL Lac (~ 60  ) Distance 3.5 Mpc

1. 60° Cen A Search for Gamma-rays from the Active radio galaxy Centaurus A with CANGAROO-III telescopes S. Kabuki(a), R. Enomoto(b), M. Mori(b) and CANGAROO collaborators (a) Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (b) Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan We have observed the giant radio galaxy Centaurus A (Cen A) in the TeV energy region using the CANGAROOIII stereoscopic system. The system has been in operation since 2004 and is an array of four Imaging Atmospheric Cherenkov Telescopes (IACT) with about a 100 m spacing. The observations were carried out between March and April 2004. In total 20-hour data were obtained. No statistically significant gamma-ray signal has been found above 530 GeV and we obtain an integral flux upper limit of 3.2 10-12 cm-2 sec-1 (2-level). This upper limit is less than 7 % of the gamma-ray flux from the Crab nebula. Although some groups reported detections of Cen A in the past, we give upper limits more than one-order of magnitude lower for this object. Optical image of Centaurus A (ESO/MPG 2.2-m telescope with WFI) Synchrotron self-Compton model Estimation of Flux (burst) Radio galaxy Elliptical Fanaroff-Riley type I “Misaligned” BL Lac (~ 60) Distance 3.5 Mpc Bai estimation • Double-peaked structure= synchrotron + inverse Compton(Synchrotron Self-Compton model) LBL ParameterValue  (J2000) 201.3650633  (J2000) -43.0191125 Galaxy Size 18  14 arcmin Radio Source size 8  4 degrees Distance 3.5 Mpc Apparent Magnitude 7.96 mag Total galaxy mass (41)  1011 M Outer radio lobe 250 kpc Inner radio lobe 5 kpc Inner radio jet 1.35 kpc Relativistic nuclear jet 1.65 pc Radio core 0.008 pc Dust lane radius 7 kpc CANGAROO-III HBL Bai, J.M. et al 1999 F(0.25-30TeV) = 6.410-9 erg cm-2 s-1 : Bai F(>530GeV) = 2.610-12 erg cm-2 s-1 : CANGAROO-III  ray Result of Analysis The day-by-day results of Cen A observation Radio images of Centaurus A 30 kpc ~ 0.3 Same cut as Crab ( L > 0.9 ) 2 distribution Integral Flux 2- upper limit H.E.S.S. limit (Aharonian et al, 2005) Blue : Radio jet Red : CO White : Atomic hydrogen gas Yellow : shell (32’ 32’, Charmandaris 2000) Outer lobes (408MHz) (20o20o, Haslman 1982 ) 7% Crab Flux We cannot find any sign of bursts. Outer lobes 6.9cm(4.75GHz) (5o9o, Junkes 1993) Our flux limit is 10 times lower than previous results. Multiwavelength images of Centaurus A Upper limit on density of CDM Possibility on HBL assumption Image size = 15  14 arcmin Typical AGN model 0.25o Cen A →Giant Galaxy 3.5 Mpc Gamma (TeV) X ray The annihilation rate of the CDM can be written as Radio But Cen A… Infrared / optical Far infrared IRAS 60-100m Near infrared 2MASS 1.2-2.17m . Radio VLA(6cm) 4.9GHz Mid infrared Spitzer 3.6 to 8m The accelerator measurement on the fragmentation function Gamma (MeV) One event resolution CANGAROO-III Angular resolution Synchrotron peak IC peak is limited to lower energy of such as 100 MeV. The gamma-ray flux is written X-ray Chandra 1-3 keV Visible DSS 405-645nm Ultraviolet GALEX 130-300nm Gamma Relativistic beaming effect Active Galactic Nuclei (AGN) Conclusions The gamma-ray signal was undetectable. The problem of the inclination of the jet? In this paper, we showed the result of the first stereoscopic observation of Cen A with CANGAROO-III telescopes. The observation period was from March 16 to April 19 2004 and the total observation time was 1197 min. We could not detect a TeV gamma-ray signal and the 2-upper limit was obtained to be 3.210-12 cm-2 sec-1 at energies greater than 530 GeV. This 2-upper limit corresponds to be approximately 7 %-Crab flux. This is an order of magnitude lower than past results. We derived physical parameters for an HBL model using our upper limits and multi-wavelength spectra. Assuming a volume of the emission region to be that defined by our angular resolution, we obtained a limit on the magnetic field: B > 210 G (R/12 kpc)-1. Even using a size of an order of a light year, it exceeds one Gauss, a situation which can be hardly understood. We conclude that Cen A is not classified as a normal HBL. Unified model of AGN 10% of galaxies  AGN AGN - Time variation (1000sec) - It is 100 or more times brighter than the stars of the whole galaxy. - A massive black hole (MBH) as its nuclei 10% of AGN  Jet (Blazar) Jet - Super luminal motion - Radio lobe - Hot spot - Knot Define beaming factor d = { (1-b cosq)}-1 Blazar  ~ 1/  d~~10 The flux can be written asFobs＝2+αF＝ pF. If we see Mrk501 at 60 degrees inclination like Cen A, with typical values,~5 andp~3, the flux changes by p = 1.3×10-4 . If we assume Mrk501 is at the same distance of Cen A, (F Mrk501/F CenA)2 = (z Mrk501/z Cen A)2 = (0.034/0.0008)2 = 1.8104 Thus, even if its inclination is 60 degrees like Cen A, the gamma-ray signal could be detected.