Found 7 talks width keyword jets

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Monday December 3, 2018
Rubén Fedriani
Dublin Institute for Advanced Studies (DIAS)

Abstract

In contrast with low-mass young stellar objects (LMYSOs), very little is known about high-mass YSOs (HMYSOs). Latest results indicate that HMYSOs might be born in a similar way as LMYSOs, i.e., through disc accretion and jet ejection. HMYSOs are deeply embedded in their parent cloud and are at kpc distance, hindering direct imaging of their accretion discs. Jets then become essential to understand the physical properties of the central source. High-resolution near-IR VLT instruments allow us to study HMYSO jets down to au scales and compare them with the low-mass regime. In this talk, I will present VLT/ISAAC, SINFONI, and CRIRES results on two HMYSOs. Spectro-astrometry is used to retrieve information about the jet down to mas scales (~tens of au at kpc distance). High-resolution spectroscopy allows us to retrieve the kinematic and dynamic properties of the massive jets. Additionally, HST imaging in the [FeII] shows the jet structure close to the star. Finally, these properties are compared with low-mass jets, suggesting that the formation of HMYSOs might be a scaled-up version of their low-mass counterparts, and their properties scale with mass.


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Thursday September 10, 2015
Prof. Noah Soker
Physics Department TECHNION, Israel

Abstract

I will describe the roles of jets in several quite different astrophysical systems. These include exploding core collapse supernovae, expelling common envelopes, and heating gas in clusters of galaxies. Hot bubbles inflated by jets seem to be a key ingredient in the interaction of jets with the ambient gas. The understanding that jets can efficiently interact with the ambient gas leads to new notions, such as the jittering jets model to explode massive stars, and the grazing envelope evolution(GEE) that can replace the common envelope evolution in some cases.

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Tuesday May 19, 2015
Dr. Enrique Lopez Rodriguez
Universidad de Texas en San Antonio

Abstract

Little is known about the mid-infrared (MIR) polarization at high-angular resolution of Active Galactic Nuclei (AGN), however, the polarimetric mode of CanariCam on the 10.4-m Gran Telescopio CANARIAS has opened a new window to reveal its core. We have found a variety of results: 1) A Highly polarized synchrotron emission in the core of Cygnus A; 2) a very complex MIR polarization structures in and around the core of NGC 1068; and 3) a very low polarized core of Mrk 231. In this talk, I will present new CanariCam polarimetric results on several AGN which provide key information on our understanding of the AGN structure and jet formation.


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Thursday December 15, 2011
Dr. Miguel Ángel Aloy
University of Valencia, Spain

Abstract

Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually associated with supernovae (Woosley et al. 2006). They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium (Zhang et al. 2004). Here we report observations of the peculiar GRB 101225A (the "Christmas burst"). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to 1.6 Gpc by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium star-neutron star merger that underwent a common envelope phase expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which gets thermalized by interacting with the dense, previously ejected material and thus creating the observed black-body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy (Campana et al. 2011).


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Tuesday October 4, 2011
Dr. Ivan Agudo
Instituto Astrofisica de Andalucia, Spain

Abstract

Relativistic jets in AGN in general, and in blazars in particular, are the most energetic and among the most powerful astrophysical objects known so far. Their relativistic nature provides them the ability to emit profusely in all spectral ranges from radio wavelengths to gamma-rays, as well as abrupt variability in all time scales (from hours to years). Since the birth of gamma-ray astronomy, locating the origin of gamma-ray emission has been a fundamental problem for the knowledge of the emission processes involved. Deep and densely time sampled monitoring programs with the Fermi Gamma-ray Space Telescope and several other facilities at most of the available spectral ranges (including polarization measurements where possible) are starting to shed light for the case of blazars. After a short review of the status of the problem, some of the latest results locating the GeV emission in the jets of some blazars, at >10 parsec from the central AGN engine, will be presented together with their implications about the gamma-ray emission mechanisms involved


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Tuesday May 3, 2011
Miss Josefa Becerra
Instituto de Astrofísica de Canarias, Spain

Abstract

The MAGIC telescopes discovered very high energy (VHE, E>100 GeV) gamma-ray emission coming from the distant Flat Spectrum Radio Quasar (FSRQ) PKS 1222+21 (4C +21.35, z=0.432). It is the second most distant VHE gamma-ray source, with well measured redshift, detected until now. The detection coincides with high energy MeV/GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light, can be described by a single power law with photon index 2.72 ± 0.34 between 3 GeV and 400 GeV, consistent with gamma-ray emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region to lie outside the Broad Line Region, which would otherwise absorb the VHE gamma-rays. On the other hand, the MAGIC measurement of a doubling time of about 9 minutes indicates an extremely compact emission region, in conflict with the "far dissipation" scenario. This result challenges jet emission models in FSRQs and indicates the importance of jet sub-structures.


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Thursday November 5, 2009
Prof. Rony Keppens
Centre for Plasma-Astrophysics, K. U. Leuven, Belgium

Abstract

I will present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. In a related investigation, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. In that study, we concentrate on morphological features of the bow shock and the jet beam, for various jet Lorentz factors and magnetic field helicities. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. For the high speed jets considered, significant jet deceleration only occurs beyond distances exceeding hundred jet radii, as the axial flow can reaccelerate downstream to internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.

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