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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
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

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

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

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

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

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

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

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

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

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

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
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
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
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
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

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

In the microquasar scenario, 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
The MAGIC 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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