D. Galindo

Gamma rays detected from Cygnus X-1 with likely jet origin

Aims. We probe the high-energy (>60 MeV) emission from the black hole X-ray binary system, Cygnus X-1, and investigate its origin. Methods. We analyzed 7.5 yr of data by Fermi -LAT with the latest Pass 8 software version. Results. We report the detection of a signal at ~8 σ statistical significance that is spatially coincident with Cygnus X-1 and has a luminosity of 5.5 × 10 33  erg s -1 , above 60 MeV. The signal is correlated with the hard X-ray flux: the source is observed at high energies only during the hard X-ray spectral state, when the source is known to display persistent, relativistic radio-emitting jets. The energy spectrum, extending up to ~20 GeV without any sign of spectral break, is well fit by a power-law function with a photon index of 2.3 ± 0.2. There is a hint of orbital flux variability, with high-energy emission mostly coming around the superior conjunction. Conclusions. We detected GeV emission from Cygnus X-1 and probed that the emission is most likely associated with the relativistic jets. The evidence of flux orbital variability indicates the anisotropic inverse-Compton on stellar photons as the mechanism at work, thus constraining the emission region to a distance 10 11 –10 13  cm from the black hole.Aims. Probe the high-energy (>60 MeV) emission from the black hole X-ray binary system, Cygnus X-1, and investigate its origin. Methods. We analysed 7.5 yr of data by Fermi-LAT with the latest Pass 8 software version. Results. We report the detection of a signal at ∼8σ statistical significance spatially coincident with Cygnus X-1 and a luminosity above 60 MeV of 5.5×1033 erg s−1. The signal is correlated with the hard X-ray flux: the source is observed at high energies only during the hard X-ray spectral state, when the source is known to display persistent, relativistic radio emitting jets. The energy spectrum, extending up to ∼20 GeV without any sign of spectral break, is well fitted by a power-law function with a photon index of 2.3±0.2. There is a hint of orbital flux variability, with high-energy emission mostly coming around the superior conjunction. Conclusions. We detected GeV emission from Cygnus X-1 and probed that the emission is most likely associated with the relativistic jets. The evidence of flux orbital variability points to the anisotropic inverse Compton on stellar photons as the mechanism at work, thus constraining the emission region to a distance 1011 − 1013 cm from the black hole.

Gamma rays from microquasars Cygnus X-1 and Cygnus X-3

Gamma-ray observations of microquasars at high and very-high energies can provide valuable information of the acceleration processes inside the jets, the jet-environment interaction and the disk-jet coupling. Two high-mass microquasars have been deeply studied to shed light on these aspects: Cygnus X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray spectral states of black hole transients, where the radiation is dominated by non-thermal emission from the corona and jets and by thermal emission from the disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A hint of orbital flux modulation was also found, as the source is only detected in phases around the compact object superior conjunction. We conclude that the high-energy gamma-ray emission from Cygnus X-1 is most likely associated with jets and its detection allow us to constrain the production site. Moreover, we include in the discussion the final results of a MAGIC long-term campaign on Cygnus X-1 that reaches almost 100 hr of observations at different X-ray states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring activity period in radio and high-energy gamma rays, similar to the one that led to its detection in the high-energy regime in 2009. MAGIC performed comprehensive follow-up observations for a total of about 70 hr. We discuss our results in a multi-wavelength context.

Detection of high-energy gamma rays from Cygnus X-1 associated with the jets

Cygnus X1 is the prototype black hole high-mass microquasar. As a persistent and bright X-ray source is considered an optimal candidate to study the disk-jet coupling. It displays the typical soft and hard X-ray spectral states of black hole binaries where the emission is dominated by the thermal black body radiation and by non-thermal emission from the inner part of the disk and the relativistic jets, respectively. We report the detection of a 8-sigma excess, above 60 MeV, spatially coincident with Cygnus X-1 by using 7.5 yr of Fermi-LAT data and the latest Pass8 software version. The point-like signal is clearly associated to the microquasar since the emission correlates with the hard X-ray state. In addition, there is a hint of orbital flux variability with most of the emission coming around the superior conjunction. The high energy emission is most likely associated with the jets and produced via anisotropic inverse Compton scattering on the stellar photons. The subsequent constraints on the emission ...

Peculiar objects towards 3FGL J0133.3+5930: an eclipsing Be star and an active galactic nucleus

Aims. We aim to contribute to the identification of unassociated gamma-ray sources in the galactic plane in order to enlarge the currently known population of gamma-ray binaries and related systems, such as radio emitting X-ray binaries and microquasars. These objects are currently regarded as excellent test beds for the understanding of high energy phenomena in stellar systems. Methods. Potential targets of study are selected based on cross-identification of the 3rd Fermi Large Area Telescope catalogue with historical catalogues of luminous stars often found as optical counterparts in known cases. Follow-up observations and analysis of multi-wavelength archival data are later used to seek further proofs of association beyond the simple positional agreement. Results. Current results enable us to present here the case of the Fermi source 3FGL J0133.3+5930 where two peculiar objects have been discovered inside its region of uncertainty. One of them is the star TYC 3683-985-1 (LS I +59 79) whose eclipsing binary nature is reported in this work. The other one is the X-ray source SWIFT J0132.9+5932, that we found to be a likely low-power Active Galactic Nucleus at z = 0:1143 \pm 0:0002. If this second object is of blazar type, it could easily account for the observed gamma-ray photon flux. However, this is not confirmed at present, thus rendering still open the star system TYC 3683-985-1 as an alternative counterpart candidate to the Fermi source.

Tera-electron-Volt pulsed emission from the Crab detected by MAGIC

E. de Oña Wilhelmi∗1, R. Zanin2, D. Carreto Fidalgo3, D. Galindo2, D. Garrido Terrats4, W. Idec5, T. Schweizer5, W. Bednarek6, D. F. Torres1, T. Saito7, M. Gaug4, M. López3 for the MAGIC collaboration and K. Hirotani8 1Institute of Space Sciences (CSIC-IEEC) Campus UAB, Carrer de Can Magrans, s/n 08193 Barcelona Spain 2Universitat de Barcelona, ICC, IEEC-UB, E-08028 Barcelona, Spain 3Universidad Complutense, E-28040 Madrid, Spain 4Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain 5Max-Planck-Institut für Physik, D-80805 München, Germany 6University of Łódź, PL-90236 Lodz, Poland 7Kyoto University, Japan 7Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA), Taipei, P.O. Box: 23-141 Taiwan E-mail: wilhelmi@ice.csic.es, rzanin@am.ub.es, dfidalgo@gae.ucm.es,dgalindo@am.ub.es