Variable Very-High-Energy Gamma-Ray Emission from the Microquasar LS I +61 303

Microquasars are binary star systems with relativistic radio-emitting jets. They are potential sources of cosmic rays and can be used to elucidate the physics of relativistic jets. We report the detection of variable gamma-ray emission above 100 gigaelectron volts from the microquasar LS I 61 + 303. Six orbital cycles were recorded. Several detections occur at a similar orbital phase, which suggests that the emission is periodic. The strongest gamma-ray emission is not observed when the two stars are closest to one another, implying a strong orbital modulation of the emission or absorption processes.

Pilomatrixoma. Review of 205 cases

Aims: To determine the incidence and clinical features of patients diagnosed with pilomatrixoma. Patients and Method: A retrospective analysis was made of 205 cases of pilomatrixoma diagnosed according to clinical and histological criteria, with an evaluation of the incidence, patient age at presentation, gender, lesion location and size, single or multiple presentation, differential diagnosis, histopathological and clinical findings and relapses. Results: Pilomatrixoma was seen to account for 1.04% of all benign skin lesions. It tended to present in pediatric patients- almost 50% corresponding to individuals under 20 years of age- with a slight male predilection (107/98). Approximately 75% of all cases presented as single lesions measuring less than 15 mm in diameter. Multiple presentations were seen in 2.43% of cases. The most frequent locations were the head and orofacial zones (particularly the parotid region), with over 50% of all cases, followed by the upper (23.9%) and lower limbs (12.7%). Only one relapse was documented following simple lesion excision. Conclusions: The frequency of pilomatrixomas was 1.04% of all benign skin lesions- the lesions being predominantly located in the maxillofacial area. Due to the benign features of this disorder, simple removal of the lesion is considered to be the treatment of choice, and is associated with a very low relapse rate.

Hints for a fast precessing relativistic radio jet in LS I + 61° 303

Here we discuss two consecutive MERLIN observations of the X-ray binary LS I +61° 303 . The first observation shows a double-sided jet extending up to about 200 AU on both sides of a central source. The jet shows a bent S-shaped structure similar to the one displayed by the well-known precessing jet of SS 433 . The precession suggested in the first MERLIN image becomes evident in the second one, showing a one-sided bent jet significantly rotated with respect to the jet of the day before. We conclude that the derived precession of the relativistic (beta=0.6) jet explains puzzling previous VLBI results. Moreover, the fact that the precession is fast could be the explanation of the never understood short term (days) variability of the associated gamma-ray source 2CG 135+01 / 3EG J0241+6103

One-sided jet at milliarcsecond scales in LS I +61˚ 303

We present Very Long Baseline Interferometry (VLBI) observations of the high mass X-ray binary LS I +61˚303, carried out with the European VLBI Network (EVN). Over the 11 hour observing run, performed ~10 days after a radio outburst, the radio source showed a constant flux density, which allowed sensitive imaging of the emission distribution. The structure in the map shows a clear extension to the southeast. Comparing our data with previous VLBI observations we interpret the extension as a collimated radio jet as found in several other X-ray binaries. Assuming that the structure is the result of an expansion that started at the onset of the outburst, we derive an apparent expansion velocity of 0:003 c, which, in the context of Doppler boosting, corresponds to an intrinsic velocity of at least 0:4 c for an ejection close to the line of sight. From the apparent velocity in all available epochs we are able to establish variations in the ejection angle which imply a precessing accretion disk. Finally we point out that LS I +61˚303, like SS 433 and Cygnus X-1, shows evidence for an emission region almostorthogonal to the relativistic jet