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Observation of microquasars with the MAGIC telescope

Study of Cygnus X-1 binary system, with black hole and super-giant companion star, observed for gamma-ray emissions using the MAGIC telescope. Analysis includes spectral characteristics, relativistic jets, and daily signal searches.

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Observation of microquasars with the MAGIC telescope

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  1. Observation of microquasars with the MAGIC telescope Observation of Cygnus X-1 with the MAGIC telescope Javier Rico Institut de Fisica d’Altes Energies (IFAE) Barcelona, SPAIN for the MAGIC collaboration

  2. 0.2 AU 0.7 0.0 0.25 0.75 0.5 To observer Cygnus X-1 • Cygnus X-1 is binary system • The distance to the system is 2 kpc • The compact object is a black hole of M>13M☼ • The optical companion is an O9.7 super-giant with M=30M☼ and a strong stellar wind • The orbit is low-eccentric or circular with radius 0.2 AU and 5.6 days period. Modulation detected in radio and X-rays • Different phase conventions. Here T0 adopted as companion star inferior conjunction (companion between observer and black hole) • Inclination between 25 and 67 deg, 35 deg normally assumed

  3. Hard state Soft/intermediate state New probably non-thermal component emerges at 400 keV during the intermediate state (also seen by COMPTEL AT 1-10 MeV) Observations with INTEGRAL • The observed hard spectrum is well described by a model including: • Thermal comptonization at corona • Reflection on the accretion disk • The observed soft spectrum is well described by a model including: • Thermal disk • Fe line • Thermal comptonization at corona + reflection on disk

  4. Golenetskii et al. 2003 Giant outbursts • Between 1995 and 2003, 15 min to 8 hours outburst observed by Ulysses, Konus-Wind and/or BATSE • Fluxes enhanced by a factor 3 to 10 up to luminosity ~1038 erg/s (2 kpc) • Happening both in hard and soft states • No change in the spectral shape • Seems unrelated from accretion rate changes as hard/soft transitions (jet?)

  5. ~15 mas 30 AU Gallo et al. 2005 Stirling et al. 2001 Relativistic jet • Single-sided jet (microblazar?) resolved at milli-arcsec scales with VLBA in hard state. Opening angle <2°, bulk velocity is b>0.6c • 1.4 GHz obs: 5 pc (8’) diameter ring-structure of bremsstrahlung emitting ionized gas at the shock between jet and ISM. Power released by the (dark) jet is of the same order or the bolometric x-ray luminosity and 2 orders of magnitude higher than what inferred from the radio spectrum

  6. MAGIC observations • Data analized using MAGIC standard analysis. Cuts optimized for maximum sensitivity using Crab nebula observations same period and zenith angle range • Search for: • steady flux (using whole sample) • fast varying signals (day by day and below) • periodic flux (orbital folded)

  7. Search for steady emission • No significant signal is observed at any SIZE/energy cut • Upper limits at the order of 1% Crab • First limits at these energies

  8. Daily searches • 4.0s on 2006-09-25 between 20h58 and 23h41 UTC • Sample subdivided until maximum significance is reached • Correct probability by number of trials • 4.9s (4.1s after 52 trials) from 79 minutes between 22h17 23h41

  9. Signal significance and extension • Background evaluated from 5 control regions from the same observation and close nights (Off/On =22) 4.9s

  10. Source position • Source locationa = 19h58m17s, d = 35°12’8” ±1.5’ (stat) ± 2’ (syst) • Compatible with the position of Cygnus X-1 and exclude radio ring

  11. Spectrum • Spectrum unfolded of detector effects • Well fitted by power law with index -3.2±0.6 and ~10% Crab at 1 TeV

  12. Search for orbital emission • 3.8s at phase 0.9-1.0 (when the black hole is behind the star • All (97%) data correspond to the same observation night

  13. Correlation with X-rays • Correlation MAGIC- X-rays (also INTEGRAL) • MAGIC sees an excess right before the first Swift peak rise and zero flux in the decaying edge of second Swift peak • Hard x-rays could be produced at the base of the jet andg-rays further away by interaction with stellar wind • BUT… opacities are expected to be huge (10 at 1 TeV)

  14. Conclusions • With Cygnus X-1, the number of known g-ray binaries are 4, together with LS I +61 303 (MAGIC), LS 5039 and PSR B1959-63 (HESS). Paper accepted for publication at ApJL (2007-06-26) • BUT… • this is the first experimental evidence of VHE g-ray emission from a system powered by accretion • this is the first experimental evidence of VHE g-ray emission from a system containing a stellar mass black hole • the phenomenology is completely new: • short time (<1day), intense flares • probably not related to the orbital motion • hints that the emission is produced far from the compact object

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