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© 2015. The American Astronomical Society. The software used in this work was developed in part by the DOE-supported ASC/Alliance Center for Astrophysical Thermonuclear Flashes at the University of Chicago. HST data presented in this paper were obtained from MAST. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This work was supported by the Spanish Government under research projects AYA2011-29754-C03-01 and AYA2011-29754-C03-03. M.O. and J.F.A-C. acknowledge support by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina). Finally, we thank the referee for useful comments and suggestions., We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts a dense molecular cloud, a scenario that may be typical for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud using two-dimensional axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10^7 K, consistent with production of X-ray emission, after impacting a dense cloud. We find that jets denser than the ambient medium but less dense than the cloud produce detectable X-ray emission only at impact with the cloud. From an exploration of the model parameter space, we constrain the physical conditions (jet density and velocity and cloud density) that reproduce the intrinsic luminosity and emission measure of the X-ray source possibly associated with HH 248 well. Thus, we suggest that the extended X-ray source close to HH 248 corresponds to a jet impacting a dense cloud., National Aeronautics and Spacial Agency (NASA), EE.UU, Gobierno de España, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina), DOE-supported ASC/Alliance Center for Astrophysical Thermonuclear Flashes, University of Chicago (EE.UU), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2013. The American Astronomical Society. This work was supported by the Spanish Government (AYA2011-29754-C03-01 and AYA2011-29754-C03-03). C. S. P. was supported by the COSPAR Capacity Building Workshop Fellowship Program and the Universidad Nacional de La Plata to develop this work at the Universidad Complutense de Madrid. M. M. is supported through the ASI-INAF contract I/009/10/0. JFAC is a staff researcher of the CONICET and acknowledges support by grant PIP 2011 0100285. J.L.-S. would like to thank Drs. F. J. Carrera, P. G. Pérez González and S. Mateos for fruitful discussion on the spectral X-ray emission properties of AGN. We also acknowledges the referee of this manuscript for their suggestions and comments. Facilities: XMM-Newton (EPIC), Chandra (ACIS), Spitzer (IRAC, MIPS)., Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km s^-1, creating strong shocks when interacting with the interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated with the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated with thermal processes from the interaction of the jet with denser ambient matter and hard X-ray emission is produced by synchrotron radiation at the front shock., Ministerio de Ciencia e Innovación (MCINN), España, Agenzia Spaziale Italiana (ASI), Istituto Nazionale di Astrofisica (INAF), Universidad Nacional de La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub