Suchergebnisse

X-ray emission from young stellar objects (YSOs) is a key ingredient in understanding star formation. For the early, protostellar (Class I) phase, a very limited (and controversial) quantity of X-ray results is available to date. Within the EXTraS (Exploring the X-ray Transient and variable Sky) project, we have discovered transient X-ray emission from a source whose counterpart is ISO-Oph 85, a strongly embedded YSO in the ρ Ophiuchi star-forming region. We extract an X-ray light curve for the flaring state, and determine the spectral parameters for the flare from XMM-Newton/EPIC data with a method based upon quantile analysis. We combine photometry from infrared to millimeter wavelengths from the literature with mid-IR Spitzer and unpublished submm Herschel photometry that we analysed for this work, and we describe the resulting spectral energy distribution (SED) with a set of precomputed models. The X-ray flare of ISO-Oph 85 lasted ~2500 s and is consistent with a highly-absorbed one-component thermal model (NH = 1.0-0.5+1.2 × 1023 cm-2 and kT= 1.15-0.65+2.35 keV). The X-ray luminosity during the flare is log LX [erg/s] = 31.1+2.0-1.2; during quiescence we set an upper limit of log LX [erg/s] < 29.5. We do not detect other flares from this source. The submillimeter fluxes suggest that the object is a Class I protostar. We caution, however, that the offset between the Herschel and optical/infrared position is larger than that for other YSOs in the region, leaving some doubt on this association. To the best of our knowledge, this is the first X-ray flare from a YSO that has been recognised as a candidate Class I protostar via the analysis of its complete SED, including the submm bands that are crucial for detecting the protostellar envelope. This work shows how the analysis of the whole SED is fundamental to the classification of YSOs, and how the X-ray source detection techniques we have developed can open a new era in time-resolved analysis of the X-ray emission from stars. ; The research that led to these results has received funding from the European Union Seventh Framework Programme (FP7-SPACE-2013-1), under grant agreement n. 607452, "Exploring the X-ray Transient and variable Sky – EXTraS". ; Peer-reviewed ; Publisher Version

GRB 160821B is a short duration gamma-ray burst (GRB) detected and localized by the Neil Gehrels Swift Observatory in the outskirts of a spiral galaxy at z = 0.1613, at a projected physical offset of 16 kpc from the galaxy's center. We present X-ray, optical/nIR, and radio observations of its counterpart and model them with two distinct components of emission: a standard afterglow, arising from the interaction of the relativistic jet with the surrounding medium, and a kilonova, powered by the radioactive decay of the sub-relativistic ejecta. Broadband modelling of the afterglow data reveals a weak reverse shock propagating backward into the jet, and a likely jet-break at 3.5 d. This is consistent with a structured jet seen slightly off-axis (theta(view) similar to theta(core)) while expanding into a low-density medium (n approximate to 10(-3) cm(-3)). Analysis of the kilonova properties suggests a rapid evolution towards red colours, similar to AT2017gfo, and a low-nIR luminosity, possibly due to the presence of a long-lived neutron star. The global properties of the environment, the inferred low mass (M-ej less than or similar to 0.006 M-circle dot) and velocities (v(ej) greater than or similar to 0.05c) of lanthanide-rich ejecta are consistent with a binary neutron star merger progenitor.© 2019 The Authors. ; Partial support of the DCT was provided by Discovery Communications. LMI was built by Lowell Observatory using funds from the National Science Foundation (AST-1005313). The work is partly based on the observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. ET acknowledges financial support provided by the National Aeronautics and Space Administration through HST-GO14357, HST-GO14087, HST-GO14607, and HST-GO14850 grants from the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Incorporated. AJCT, YDH e IM acknowledge financial support from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). The development of CIRCE at GTC was supported by the University of Florida and the National Science Foundation (grant AST-0352664), in collaboration with IUCAA. RSR acknowledges support by Italian Space Agency (ASI) through the Contract no. 2015-046-R.0 and by AHEAD the European Union Horizon 2020 Programme under the AHEAD project (grant agreement no. 654215). YDH also acknowledges the support by the program of China Scholarships Council (CSC) under the grant no. 201406660015. JBG acknowledges the support of the Viera y Clavijo program funded by ACIISI and ULL. GN and AT acknowledge funding in the framework of the project ULTraS (ASI-INAF contract no. 2017-14-H.0). GR acknowledges the support of the University of Maryland through the Joint Space Science Institute Prize Postdoctoral Fellowship. ; Peer reviewed