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M ajor A tmospheric G amma-Ray I maging C herenkov Telescope International collaboration of 16 institutions from more than 10 countries, about 150 collaborators:

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The magic collaboration l.jpg

  • Major Atmospheric Gamma-RayImagingCherenkov Telescope

    • International collaboration of 16 institutions from more than 10 countries, about 150 collaborators:

    • Barcelona IFAE, Barcelona UAB, Barcelona UB, Crimean Observatory, U.C. Davis, U. Lodz, UCM Madrid, MPI Munich, INFN/ U. Padua, INFN/ U. Siena, U. Humboldt Berlin, Tuorla Observatory, Yerevan Phys. Institute, INFN/U. Udine, U. Würzburg, ETH Zürich, INR Sofia, Univ. Dortmund

The MAGIC Collaboration

  • Summary

    • Introduction:

      • MAGIC

      • Cycle I galactic targets

    • LS I +61 303

      • Previous data

      • Discovery at VHE

      • Emission models


The magic telescope l.jpg

  • MAGIC is a Imaging Air Cherenkov telescope operating in the energy range 50 GeV – 50 TeV

  • Located in the Roque de los Muchachos observatory, La Palma, Canary Island (Spain) at 28.8 N

  • Largest single-dish (17 m Ø)  lowest energy threshold

  • 576 high QE PMT camera with 3.5 Ø FOV

  • Good angular resolution~ 0.1

  • Determination of point-like sources position within 2’

  • Energy resolution 20-30%

  • Flux sensitivity: 2.5% Crab Nebula flux with 5s in 50h

  • Fast repositioning (<40s average) for GRB observation

  • Observations under moonlight possible  50% extra observation time

The MAGIC telescope


Observation cycle i l.jpg

CRAB pulsar

MAGIC

HESS J1834

  • Observations from November 2004 to May 2006

  • About 25% total observation time for Galactic targets (apart from Crab Nebula)

  • Targets include:

    • SNR:

      • Intense EGRET sources

      • HESS galactic scan sources (HESS J1834, HESS J1813)

    • PWN

    • Pulsars: limits to Crab and PSR B1957

    • Microquasars (low and high mass)

      • LS I +61 303 variable source

    • Galactic Center

    • HEGRA Unidentified TeV2032

    • Cataclysmic variable (AE Aquari)

Observation cycle I



Microquasars l.jpg

Compacts jets

Radio  IR

 X?

 gamma?

(synchrotron)

Disc

+ corona ?

X

therm +

non therm

Large scaleejection

Radio & X

gamma?

Interaction with

environment

  • Microquasars:

    • REXB displaying relativistic radio jets

    • Compact object Neutron Star or a Black Hole

    • In BH, the length and time scales are proportional to the mass, M.

    • The maximum temperature of the accretion disk is Tcol~2107M1/4

    • Laboratories of jet physics

    • Possible contributors to galactic cosmic rays

Microquasars


Spectral states l.jpg

  • X-ray and radio spectral states:

    • High/soft state steep power-law state. No radio emission.

    • Low/hard state (power-law state). Compact radio jet.

    • Intermediate and very high states  transitions. Transient radio emission.

Spectral states


Ls i 61 303 l.jpg

0.4 AU

0.7

0.5

0.3

To observer

0.9

0.2

0.1

  • LS I +61 303:

    • High Mass x-ray binary at a distance of 2 kpc

    • Optical companion is a B0 Ve star of 10.7 mag with a circumstellar disc

    • Compact object probably a neutron star

    • High eccentricity or the orbit (0.7)

    • Modulation of the emission from radio to x-rays with period 26.5 days attributed to orbital period

    • Secondary modulation of period 4 years attributed to changes in the wind flow

    • Compact jets (100 AU) resolved with radio observations  microquasar

LS I +61 303


Ls i 61 303 radio and x ray l.jpg

periastron

periastron

0.4 AU

0.7

0.5

0.3

Paredes et al. 1990

To observer

0.9

Photon index

0.2

0.1

X-ray flux

Radio flux

Greiner & Rau 2001

  • Periodic radio outbursts at phases 0.5-0.8 (close to apastron), with intensity and peak position modulated with a 4 yr period

  • X-ray outburst observed ~10 days (DF~ 0.4) before radio outbursts

  • A significant hardening of the x-ray spectrum is observed on the radio onset

LS I +61 303: radio and x-ray

3s


Ls i 61 303 radio jets l.jpg

F = 0.67-0.68

F = 0.71-0.72

Massi et al 2004

  • Double sided jets at milli-arsec scale (~200 AU) are resolved with radio interferometer MERLIN (5 GHz)

  • The jets display fast precession

LS I +61 303: radio jets

  • The projected angle changes by ~60 in 24 hours

  • The feature on the second day can be associated with the jet of the day before compatible with a velocity of 0.6c


Ls i 61 303 g rays l.jpg

Hartman et al. 1999

Massi et al. 2004

Tavani et al. 1998

  • A HE g-ray (100 MeV – 10 GeV) source detected by EGRET is marginally associated with the position of LS I +61 303.

  • The emission is variable and peaking at periastron passage (f=0.2) and f~ 0.5-0.6

LS I +61 303: g-rays

  • Interpreted as stellar photons upscattered (inverse Compton) by relativistic electrons in the jet


Ls i 61 303 at very high energies l.jpg

  • MAGIC has observed LS I +61 303 for 54 hours from November 2005 to March 2006 (6 orbital cycles)

LS I +61 303 at Very High Energies

Albert et al. 2006

  • A point-like source (E>200GeV) detected with significance of ~9s

  • Position: RA=2h40m34s, DEC=6115’ 25” [0.4’ (stat), 2’ (syst)] in agreement with LSI position  identification of g-ray source

  • The source is quiet at periastron passage and at relatively high emission level (16% Crab Nebula flux) at later phases [0.5-0.7]


Flux time variability l.jpg

  • MAGIC has observed LSI during 6 orbital cycles

  • A variable flux (probability of statistical fluctuation 310-5) detected

  • Marginal detections at phases 0.2-0.4

  • Maximum flux detected at phase 0.6-0.7 with a 16% of the Crab Nebula flux

  • Strong orbital modulation  the emission is produced by the interplay of the two objects in the binary

  • No emission at periastron, two maxima in consecutive cycles at similar phases  hint of periodicity!

Flux time variability

Albert et al. 2006


Ls i 61 303 the film l.jpg
LS I +61 303: the film

Albert et al. 2006

  • The average emission has a maximum at phase 0.6.

  • Search for intra-night flux variations (observed in radio and x-rays) yields negative result

  • Marginal detections occur at lower phases. We need more observation time at periastron passage

  • Parts of the orbit not covered due to similarities between orbital period (26.5 days) and Moon period


Contemporaneous radio observations l.jpg
Contemporaneous radio observations

Albert et al. 2006

  • We perform contemporaneous radio observations (Ryle telescope 15GHz) during the last observed orbital cycle

  • Two maxima are detected: just before periastron and higher at phase 0.7

  • TeV peak is observed one day before


Energy spectrum l.jpg
Energy spectrum

Albert et al. 2006

  • The average energy spectrum from 200 GeV to 4 TeV is well fitted by a power law with spectral index a = -2.6  0.2 (stat)  0.2 (syst)

  • The luminosity above 200 GeV is ~7 x 1033 erg s-1 (assuming a distance of 2 kpc) ~ 6 times that of mQSR LS 5039 (average)

  • It displays more luminosity at TeV energies than at x-rays


Broad band spectrum l.jpg
Broad band spectrum

Chernyakova et al. 2006

  • The absence of a spectral feature between 10 and 100 keV goes against an accretion scenario

  • Contemporaneous multiwavelength observations are needed to understand the nature of the object


Alternative emission models l.jpg

More multi-wavelength observations are needed, mainly VHE+radio

Mirabel 2006

Mirabel 2006

  • 1. Microquasar:Particles accelerated in the jet collide with stellar or synchrotron photons by inverse Compton scattering, boosting their energies to the TeV range. Similar to quasar.

    Pros: steady, double sided radio jets resolved; similar object known (LS 5039)

    Cons: No spectral cut-off from accretion disk is observed. No emission at periastron

  • 2. Binary pulsar: the g-rays are produced by the interaction of the winds of a young pulsar with that of the Be star

    Pros: spectral shape and time variability resembles that of young pulsars; similar object known PSR B1259-63

    Cons: no pulsed emission; radio jets;

Alternative emission models


Leptonic vs haroncic l.jpg

  • In the microquasar VHE+radioscenario, two alternative g-ray production mechanisms are possible:

    • Inverse Compton scattering: e + g→ e + g

      relativistic electrons from the jet with the star of synchrotron photons

    • Hadron interactions: p + p → X + p0

      └→ g g

      relativistic protons in the jet interact with non-relativistic stellar wind ions,producing gamma-rays via neutral pion decay

  • Our result seems to favor the leptonic scenario since g-rays are produced at phase 0.5-0.6 i.e far from the companion star, and there the efficiency of the leptonic process is likely higher that that of the hadronic process

  • In either case opacity seems to play a major role near periastron (e.g. by gamma-ray cascading)

  • Neutrinos are expected to be produced in a hadronic scenario (from the decay of charged pions and muons) and would be unabsorbed.

  • Differences in the spectral shape are also expected.

Leptonic vs haroncic

More g-ray data and Multi-messenger observations are needed!


Conclusions l.jpg

  • The VHE+radioMAGIC IACT has completed its first observation cycle in May 2006

  • 25% of the observation time has been devoted to Galactic objects

  • We have detected 5 TeV sources out of which a new discovery

  • The microquasar LS I +61 303 has been detected at TeV energies

    • The emission is variable

    • Possible hint of periodicity

    • The maximum of the emission happens 1/3 of the orbit away from periastron

  • New MAGIC+multi-wavelength/messenger will establish LSI nature and the mechanism of VHE g-ray production

Conclusions


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