TY - JOUR A1 - Vieyro, Florencia L. A1 - Romero, Gustavo Esteban A1 - Bosch-Ramon, Valentin A1 - Marcote, Benito A1 - del Valle, Maria Victoria T1 - A model for the repeating FRB 121102 in the AGN scenario JF - Astronomy and astrophysics : an international weekly journal N2 - Fast radio bursts (FRBs) are transient sources of unknown origin. Recent radio and optical observations have provided strong evidence for an extragalactic origin of the phenomenon and the precise localization of the repeating FRB 121102. Observations using the Karl G. Jansky Very Large Array (VLA) and very-long-baseline interferometry (VLBI) have revealed the existence of a continuum non-thermal radio source consistent with the location of the bursts in a dwarf galaxy. All these new data rule out several models that were previously proposed, and impose stringent constraints to new models. Aims. We aim to model FRB 121102 in light of the new observational results in the active galactic nucleus (AGN) scenario. Methods. We propose a model for repeating FRBs in which a non-steady relativistic e(+)-beam, accelerated by an impulsive magneto-hydrodynamic driven mechanism, interacts with a cloud at the centre of a star-forming dwarf galaxy. The interaction generates regions of high electrostatic field called cavitons in the plasma cloud. Turbulence is also produced in the beam. These processes, plus particle isotropization, the interaction scale, and light retardation effects, provide the necessary ingredients for short-lived, bright coherent radiation bursts. Results. The mechanism studied in this work explains the general properties of FRB 121102, and may also be applied to other repetitive FRBs. Conclusions. Coherent emission from electrons and positrons accelerated in cavitons provides a plausible explanation of FRBs. KW - radio continuum: general KW - galaxies: dwarf KW - galaxies: jets KW - radiation mechanisms: non-thermal Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201730556 SN - 1432-0746 VL - 602 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - De Becker, M. A1 - del Valle, Maria Victoria A1 - Romero, G. E. A1 - Peri, C. S. A1 - Benaglia, P. T1 - X- ray study of bow shocks in runaway stars JF - Monthly notices of the Royal Astronomical Society N2 - Massive runaway stars produce bow shocks through the interaction of their winds with the interstellar medium, with the prospect for particle acceleration by the shocks. These objects are consequently candidates for non-thermal emission. Our aim is to investigate the X-ray emission from these sources. We observed with XMM-Newton a sample of five bow shock runaways, which constitutes a significant improvement of the sample of bow shock runaways studied in X-rays so far. A careful analysis of the data did not reveal any X-ray emission related to the bow shocks. However, X-ray emission from the stars is detected, in agreement with the expected thermal emission from stellar winds. On the basis of background measurements we derive conservative upper limits between 0.3 and 10 keV on the bow shocks emission. Using a simple radiation model, these limits together with radio upper limits allow us to constrain some of the main physical quantities involved in the non-thermal emission processes, such as the magnetic field strength and the amount of incident infrared photons. The reasons likely responsible for the non-detection of non-thermal radiation are discussed. Finally, using energy budget arguments, we investigate the detectability of inverse Compton X-rays in a more extended sample of catalogued runaway star bow shocks. From our analysis we conclude that a clear identification of non-thermal X-rays from massive runaway bow shocks requires one order of magnitude (or higher) sensitivity improvement with respect to present observatories. KW - acceleration of particles KW - radiation mechanisms: non-thermal KW - stars: earlytype KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx1826 SN - 0035-8711 SN - 1365-2966 VL - 471 SP - 4452 EP - 4464 PB - Oxford Univ. Press CY - Oxford ER -