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. 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
0.0
0.5
0.7
0.2 AU
To observer
0.25
0.75

3. Observations with INTEGRAL
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)
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. Giant outbursts
Golenetskii et al. 2003
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. Relativistic jet
Stirling et al. 2001
~15 mas
30 AU
Gallo et al. 2005
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 Month (2006) Dates Zenith [degrees] Total [hours]
Good [hours]
June 30
0.1
0.0
July
1,25,26
5-30
2.1
1.1
August
16-22
15.5
11.9
September
17-20,23,25-29
5-35
19.6
19.1
October
12-15,21-23
20-35
5.9
5.3
November
10,11,14,18,19
24-35
3.0
2.5
Total
46.2
40.0
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 location a = 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 (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 and g-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 (MAGIC), LS 5039 and PSR B (HESS). Paper accepted for publication at ApJL ( )
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