Jet emission in NGC1052 at radio, optical, and X-ray frequencies

We present a combined radio, optical, and X-ray study of the nearby LINER galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC 1052 reveal the presence of various jet-related X-ray emitting regions, a bright compact core and unresolved knots in the jet structure as well as an extended emitting region inside the galaxy well aligned with the radio synchrotron jet-emission. The spectrum of the extended X-ray emission can best be fitted with a thermal model with $kT = (0.4-0.5)$ keV, while the compact core exhibits a very flat spectrum, best approximated by an absorbed power-law with $N_{\rm H} = (0.6-0.8) \times 10^{22} {\rm cm^{-2}}$. We compare the radio structure to an optical ``structure map'' from a {\it Hubble Space Telescope} ({\it HST}) observation and find a good positional correlation between the radio jet and the optical emission cone. Bright, compact knots in the jet structure are visible in all three frequency bands whose spectrum is inconsistent with synchrotron emission.Comment: 8 pages, 5 figures (figure 2 in color), image resolution degraded wrt journal version, needs aa.cls. Accepted for publication in A&

The compact radio structure of radio-loud narrow line Seyfert 1 galaxies

We present the compact radio structure of three radio-loud narrow line Seyfert 1 galaxies from VLBA archive data at 2.3, 5 and 8.4 GHz. In RXS J16290+4007, the radio structure is mostly unresolved. The combination of compact radio structure, high brightness temperature and inverted spectrum between simultaneous 2.3 and 8.4 GHz, strongly favors jet relativistic beaming. Combining with the VLBI data at 1.6 and 8.4 GHz from literatures, we argued that RXS J16333+4718 may also harbor a relativistic jet, with resolved core-jet structure in 5 GHz. B3 1702+457 is clearly resolved with well defined jet component. The overall radio steep spectrum indicates that B3 1702+457 is likely a source optically defined as NLS1 with radio definition of compact steep spectrum sources. From these three sources, we found that radio loud NLS1s can be either intrinsically radio loud (e.g. B3 1702+457), or apparently radio loud due to jet beaming effect (e.g. RXS J16290+4007 and RXS J16333+4718).Comment: 20 pages, 3 figures, accepted for publication in The Astronomical Journa

The Radio Properties of Radio-Loud Narrow-Line Seyfert 1 Galaxies on Parsec Scales

We present the detection of compact radio structures of fourteen radio-loud narrow line Seyfert 1 (NLS1) galaxies from Very Long Baseline Array observations at 5 GHz, which were performed in 2013. While 50\% of the sources of our sample show a compact core only, the remaining 50\% exhibit a core-jet structure. The measured brightness temperatures of the cores range from $10^{8.4}$ to $10^{11.4}$ K with a median value of $10^{10.1}$ K, indicating that the radio emission is from non-thermal jets, and that, likely, most sources are not strongly beamed, then implying a lower jet speed in these radio-loud NLS1 galaxies. In combination with archival data taken at multiple frequencies, we find that seven sources show flat or even inverted radio spectra, while steep spectra are revealed in the remaining seven objects. Although all these sources are very radio-loud with $R > 100$, their jet properties are diverse, in terms of their milli-arcsecond (mas) scale (pc scale) morphology and their overall radio spectral shape. The evidence for slow jet speeds (i.e., less relativistic jets), in combination with the low kinetic/radio power, may offer an explanation for the compact VLBA radio structure in most sources. The mildly relativistic jets in these high accretion rate systems are consistent with a scenario, where jets are accelerated from the hot corona above the disk by the magnetic field and the radiation force of the accretion disk. Alternatively, a low jet bulk velocity can be explained by low spin in the Blandford-Znajek mechanism.Comment: 39 pages, 17 figures, ApJS accepte

Bi-Directional Relativistic Jets of the Radio Galaxy 1946+708: Constraints on the Hubble Constant

We present measurements of bi-directional motions in the jets of the radio galaxy 1946+708 at z=0.101. This is a Compact Symmetric Object with striking S-symmetry. Sensitive 15 GHz observations reveal a compact component at the center of symmetry with a strongly inverted spectrum, that we identify as the core. From five 4.9 GHz observations spread over 4 years we have determined the velocities of four compact jet components. If simple kinematic models can be applied then the inclination of the source and the bulk jet velocity can be directly determined for any assumed value of the Hubble constant. Conversely, the measurements already place constraints on the Hubble constant, and we show how further observations of 1946+708 can yield an increasingly accurate determination of H_0.Comment: in press at ApJ Letters, 12 page LaTex document includes 5 postscript figure

Fast TeV variability in blazars: jets in a jet

The fast TeV variability of the blazars Mrk 501 and PKS 2155--304 implies a compact emitting region that moves with a bulk Lorentz factor of Gamma_{em}~100 toward the observer. The Lorentz factor is clearly in excess of the jet Lorentz factors Gamma_j\simless 10 measured on sub-pc scales in these sources. We propose that the TeV emission originates from compact emitting regions that move relativistically {\it within} a jet of bulk Gamma_j~10. This can be physically realized in a Poynting flux-dominated jet. We show that if a large fraction of the luminosity of the jet is prone to magnetic dissipation through reconnection, then material outflowing from the reconnection regions can efficiently power the observed TeV flares through synchrotron-self-Compton emission. The model predicts simultaneous far UV/soft X-ray flares.Comment: Moderate changes to match the published version, MNRAS, 395, L29 (2009

3D simulations of microquasar jets in clumpy stellar winds

High-mass microquasars consist of a massive star and a compact object, the latter producing jets that will interact with the stellar wind. The evolution of the jets, and ultimately their radiative outcome, could depend strongly on the inhomogeneity of the wind, which calls for a detailed study. The hydrodynamics of the interaction between a jet and a clumpy wind is studied, focusing on the global wind and single clump-jet interplay. We have performed, using the code \textit{Ratpenat}, three-dimensional numerical simulations of a clumpy wind interacting with a mildly relativistic jet, and of individual clumps penetrating into a jet. For typical wind and jet velocities, filling factors of about > 0.1 are already enough for the wind to be considered as clumpy. An inhomogeneous wind makes the jet more unstable when crossing the system. Kinetic luminosities of the order 1.e37 erg/s allow the jet to reach the borders of a compact binary with an O star, as in the smooth wind case, although with a substantially higher degree of disruption. When able to enter into the jet, clumps are compressed and heated during a time of about their size divided by the sound speed in the shocked clump. Then, clumps quickly disrupt, mass-loading and slowing down the jet. We conclude that moderate wind clumpiness makes already a strong difference with the homogeneous wind case, enhancing jet disruption, mass-loading, bending, and likely energy dissipation in the form of emission. All this can have observational consequences at high-energies and also in the large scale radio jets.Comment: Accepted for publication in Astronomy & Astrophysics. The quality of the images has been reduced to fit into arXiv requirement

Jet-driven and jet-less fireballs from compact binary mergers

During a compact binary merger involving at least one neutron star, a small fraction of the gravitational energy could be liberated in such a way to accelerate a small fraction (~ 10^-6) of the neutron star mass in an isotropic or quasi-isotropic way. In presence of certain conditions, a pair-loaded fireball can form, which undergoes accelerated expansion reaching relativistic velocities. As in the standard fireball scenario, internal energy is partly transformed into kinetic energy. At the photospheric radius, the internal radiation can escape, giving rise to a pulse that lasts for a time equal to the delay time since the merger. The subsequent interaction with the interstellar medium can then convert part of the remaining kinetic energy back into radiation in a weak isotropic afterglow at all wavelengths. This scenario does not require the presence of a jet: the associated isotropic prompt and afterglow emission should be visible for all NS-NS and BH-NS mergers within 90 Mpc, independent of their inclination. The prompt emission is similar to that expected from an off-axis jet, either structured or much slower than usually assumed (Gamma ~ 10), or from the jet cocoon. The predicted afterglow emission properties can discriminate among these scenarios.Comment: 5 pages, 1 figure, revised version submitted to MNRAS Letter