14th ISCRA, Erice July 2004 Observation of VHE gamma rays from the remnant of SN1006 with HEGRA CT1 SN1006 seen by CHANDRA Vincenzo Vitale for the HEGRA-CT1Munich Group

Outline Cosmic Rays and Super-Nova Remnants TeV gamma rays emission from SNRs The remnant of SN1006 Imaging Atmospheric Cherenkov Telescopes Data analysis (1999-2000-2001 observations) Large zenith angle observations Off-axis and Extended source observations Calibrations Results

Shock SNR Gamma rays G.Cosmic Rays VHE electrons + photons  gamma rays via Inverse Compton (synchrotron radiation) VHE nucleus + target (Inter- Stellar Matter)  π 0   Gamma rays

The remnant of SN1006 One of the brightest SN (type Ia) Age ~ 1Ky Distance 1.8 +/- 0.3 Radius 20 pc (~ 30 arcmin) Shock speed 2300 Km/sec From Roque D.L.Muchachos -> not more than 19 degrees above horizon CT1 obs. : 220h, 345K ev. @ 71-73 deg ZA

Non-thermal emissions ASCA NE SW CANGAROO Significance map 5.2 7.5 ROSAT NE and SW parts of the rim are non-thermal X rays emitters (ASCA, ROSAT) 1-20 TeV gamma rays from NE, reported by Cangaroo

Models Berezhko et al. 2002 Naito et al.1999 Theories exploit both Inverse Compton (electrons) and neutral Pion (nuclei) for the TeV gamma rays emission Evidence of acceleration of electrons up to 10-100 TeV Acceleration of nuclei not excluded

Some New Observations XMM Newton Chandra Magnetic Field SN 1006 CANGAROO significance map 6 Chandra Magnetic Field SN 1006 Berezhko et al 2003 ~ 100 μG Bamba et al. 2003 ~ 14-85 μG

Imaging Air Cherenkov Telescope Energy, flux, type and direction of primary particle from shower image Gammas and hadrons shower differ for image features and arrival direction Information extracted from images (image parameters) Monte Carlo simulations allow gamma/hadrons separation and calibration Standard candle (Crab Nebula) Gamma 1 gamma/ 300 nuclei Shara 2001

Analysis technique Different shape ==> different distributions of the image parameters Selection cuts on the image parameters

Large zenith angle observations Higher maximum detectable energy Increase of eff. collection area Transformation of images: dimensions reduction, images closer to field of view center Increasing of energy threshold (factor ~25 from 0 to 70deg ZA) Reduction of gamma/h separation power Difficulties for MC simulations

Background rejection (hadrons) Exp.Hadrons MC gamma Study of the dependence of the image parameters on the zenith angle Selection cuts with zenith angle dependence

Off-axis and Extended source observations HEGRA CT1 signal from source candidate is searched in the F.O.V. False Source Method : point- like source analysis repeated on a regular grid (according to angular resolution) Alternative method : the incoming direction of a shower lies on its axis and has distance from COG computable using MC Point-like source excess 2d distribution For HEGRA CT1 radial sigma ~ 0.12 deg =7.2’

Mrk 501 Off-axis 160 20 Excess sky map Analysis tested with a strong signal (Mrk501, 1997) off-axis, in order to simulated the SN1006 observation with exp. data. A significant bump at small Alpha (signal) Good estimate of the residual background

Effective collection area 106 m2 PI=-1 PI=-3 50 TeV Differential trigger rate (Source differential flux= A*E-PI A=10 -11 cm-2 sec -1, PI from -1 to -3 ) Effective collection area

Calibration(I): Impact Parameter Impact Parameter as linear comb.of parameters *f(Z.A.) Free parameters fixed with an optimization routine and MC

Calibration (II): Energy Energy calculated as E=L.C.(Size,Imp.Par.)*g(Z.A.) Free parameters fixed with an optimization routine and MC

Stars as position reference Sky map Map of anode currents

Results: Sky Maps An excess is found at NE part of the rim Beta Lup Kappa Can SN1006 SHELL Beta Lup Kappa Can SN1006 SHELL An excess is found at NE part of the rim

Results: signal distribution Distribution of the excess 100 -50 103 +/- 17 excess events over a background of 225 ev.

Results: Alpha parameter distributions Beta Lup Kappa Can A signal is present in the Alpha parameter distribution

Results: Integral and differential fluxes Photon Index Energy threshold TeV Flux 10-13 cm-2 s-1 Flux error -1.0 22+-2 2.40 0.39 -1.5 2.15 0.36 -2.0 18+-2 2.35 -2.5 2.21 -3.0 1.72 0.29

Conclusions (I) A large zenith angle observation (first time at >70 deg) has been successfully performed. Evidence for an excess of multi-TeV γ rays has been found. The excess sky position is consistent with NE part of the SN1006 remnant Use of bright stars as position reference (0.1deg precision) The statistical significance of the excess is 5.1 standard deviations after trials (5.6 before trials).

Conclusions (II) Energy threshold is ~(18 +/- 2) TeV. The Integral Flux from the NE part of the rim is (2.35 +/- 0.4stat +/- 0.7sys ) *10-13 ph cm-2 sec-1, phot. ind. = -2.0 The Diff. Flux (without 30% systematic error) is (0.30+/-0.15 ) *10-11(E/TeV) –(1.9+-0.2) ph cm-2 sec- 1 TeV-1 The flux upper limits for SW cap and shell-center are: 0.83 and 0.66 *10-13 ph cm-2 sec -1 (95% C.L., P.I.=-2.0)

Conclusions (III) experiment Flux at 1TeV 10-11 cm-2 sec-1 TeV-1 Photon index CANGAROO 1-20 TeV 1.1+0.4 -2.3+-0.2 CT1 18-45(60) TeV 0.3+-0.15 -1.9+-0.2 CT1 results are obtained above an energy threshold of 18TeV, the 1 TeV flux is extrapolated for comparison The maximum flux variation is in the order of (–6%)*year-1