Josep M. Paredes

Chandra Observations of the Gamma-ray Binary LSI+61303: Extended X-ray Structure?

We present a 50 ks observation of the gamma-ray binary LS I +61 303 carried out with the ACIS-I array aboard the Chandra X-Ray Observatory. This is the highest resolution X-ray observation of the source conducted so far. Possible evidence of an extended structure at a distance between 5 and 12 toward the north of LS I +61 303 has been found at a significance level of 3.2 σ. The asymmetry of the extended emission excludes an interpretation in the context of a dust-scattered halo, suggesting an intrinsic nature. On the other hand, while the obtained source flux of F0.3-10 keV = 7.1 × 10-12 ergs cm-2 s-1 and hydrogen column density NH = (0.70 ± 0.06) × 1022 cm-2 are compatible with previous results, the photon index Γ = 1.25 ± 0.09 is the hardest ever found. In light of these new results, we briefly discuss the physics behind the X-ray emission, the location of the emitter, and the possible origin of the extended emission ~0.1 pc away from LS I +61 303.

A pulsar wind nebula associated with PSR J2032+4127 as the powering source of TeV J2032+4130

The very-high-energy gamma-ray source TeV J2032+4130, in the Cygnus region, was the first source discovered of a population of extended TeV sources without low-frequency counterparts. In its field there is a pulsar, namely PSR J2032+4127, which has been detected by Fermi in gamma-rays and in radio by the Green Bank Telescope (GBT). We report on an ongoing multiwavelength campaign to search for a pulsar wind nebula associated with PSR J2032+4127 through radio and X-ray observations. Moreover, we are conducting a multi-epoch very long baseline interferometr (VLBI) campaign with the European VLBI network (EVN) in order to measure the pulsar proper motion and to find its relation with the radio nebula and the TeV extended source. All these results together, combined with a theoretical modeling of the system, enable us to propose a conceivable physical scenario in which the extended radio, X-ray and TeV emissions are accounted for.

MAGIC RESULTS ON BINARY SYSTEMS

Three X-ray binary systems have been unambiguously detected at TeV energies: LS 5039, LS I +61° +303, PSR B1259-63. Additionally, the TeV source HESS J0632+057 has been found to be a new binary system. The recent detection of the microquasar Cygnus X-3, between 100 MeV and few GeV, confirms that also this sub-class of accreting binaries displaying radio relativistic jets provides interesting candidates for very-high-energy (VHE) gamma-ray observations. The MAGIC telescopes made a significant effort to search for signals from X-ray binaries. This article will present the new results on LS I 61° +303, which show a reduction in the VHE γ-ray flux in the periodic outburst phase with respect to previous campaigns. MAGIC observed also HESS J0632 +057 in 2010 and 2011, covering an X-ray outburst reported by Swift in February 2011. These observations show significant activity in VHE gamma-rays temporally coincident with the X-ray outburst. In addition, this article will review MAGIC results on the microquasars Cygnus X-3, Cygnus X-1, and Scorpius X-1 which report constraining flux upper limits in different X-ray spectral states and as well as during flux enhancements at high energies.

CONSTRAINING THE PULSAR POWER IN GAMMA-RAY BINARIES THROUGH THERMAL X-RAY EMISSION

Gamma-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds collide producing non-thermal emission, most likely from the shocked pulsar wind. Thermal X-rays are expected from the shocked stellar wind, with a spectrum akin to the one observed in massive star binaries. The goal of this work is, through the study of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, constrain the pulsar spin-down luminosity and the stellar wind properties. A semi-analytic model is developed to compute the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries. The model results are compared with XMM-Newton observations of LS 5039, a candidate pulsar gamma-ray binary with a strong stellar wind. Exploring the range of possible values for the stellar mass-loss rate and orbital inclination, we obtain an upper limit on the pulsar spin-down luminosity of 6 × 1036 erg s-1. We conclude that, to explain the non-thermal luminosity of LS 5039 in the pulsar wind scenario, a non-thermal to spin-down luminosity ratio very close to unity may be required.

Detection of the Fermi/GBT pulsar PSR J2032+4127 with the EVN and the DiFX correlator in Bonn

We observed the Fermi/GBT pulsar PSR J2032+4127 with the EVN at 1.6 GHz in March 2010. The source has a period-averaged flux density of 0.18 mJy and a duty cycle of approximately 10% at this frequency. To obtain a good position of the source, we observed it using phase referencing with 6 EVN antennas at 1 Gbps, and we correlated the data using pulsar gating in the new DiFX correlator in Bonn. A preliminary data reduction shows that the faint pulsar was detected with a signal-to-noise ratio of 8, with an improvement of a factor of 2 thanks to the use of pulsar gating. This has provided the first accurate VLBI position of this radio pulsar. Future EVN observations will allow us to obtain an accurate proper motion of PSR J2032+4127, which will shed light to the possible association of this pulsar with the unidentified very-high-energy gamma-ray source TeV J2032+4130.