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تسجيل مستخدم جديدFundamental Reference AGN Monitoring Experiment (FRAMEx) I: Jumping Out of the Plane with the VLBA
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We present the first results from the Fundamental Reference AGN Monitoring Experiment (FRAMEx), an observational campaign dedicated to understanding the physical processes that affect the apparent positions and morphologies of AGNs. In this work, we obtained simultaneous Swift X-ray Telescope (XRT) and Very Long Baseline Array (VLBA) radio observations for a snapshot campaign of 25 local AGNs that form a volume-complete sample with hard X-ray (14-195 keV) luminosities above $10^{42}$erg s$^{-1}$, out to a distance of 40 Mpc. Despite achieving an observation depth of $sim20$ $mu$Jy, we find that 16 of 25 AGNs in our sample are not detected with the VLBA on milli-arcsecond (sub-parsec) scales, and the corresponding core radio luminosity upper limits are systematically below predictions from the Fundamental Plane of black hole activity. Using archival Jansky Very Large Array (VLA) radio measurements, our sample jumps back onto the Fundamental Plane, suggesting that extended radio emission is responsible for the apparent correlation between radio emission, X-ray emission, and black hole mass. We suggest that this discrepancy is likely due to extra-nuclear radio emission produced via interactions between the AGN and host environment. We compare VLBA observations of AGNs to VLA observations of nearby Galactic black holes (GBHs) and we find a mass-independent correlation between radio and X-ray luminosities of black holes of $L_mathrm{6cm}$/$L_mathrm{2-10 keV}$ $sim$ 10$^{-6}$, in line with predictions for coronal emission, but allowing for the possibility of truly radio silent AGNs.
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The U.S. Naval Observatory (USNO), in collaboration with Paris Observatory (OP), is conducting the Fundamental Reference AGN Monitoring Experiment, or FRAMEx. FRAMEx will use USNOs and OPs in-house observing assets in the radio, infrared (IR) and vis
ible, as well as other ground- and space-based telescopes (e.g., in the X-ray) that we can access for these purposes, to observe and monitor current and candidate Reference Frame Objects (RFOs) -- consisting of Active Galactic Nuclei (AGN) -- as well as representative AGN, in order to better understand astrometric and photometric variability at multiple timescales. FRAMEx will improve the selection of RFOs as well as provide significant new data to the AGN research community. This paper describes the FRAMEx objectives, specific areas of investigation, and the initial data collection campaigns.
High magnetic fields are a distinguishing feature of neutron stars and the existence of sources (the soft gamma repeaters and the anomalous X-ray pulsars) hosting an ultra-magnetized neutron star (or magnetar) has been recognized in the past few deca
des. Magnetars are believed to be powered by magnetic energy and not by rotation, as with normal radio pulsars. Until recently, the radio quietness and magnetic fields typically above the quantum critical value (Bq~4.4x10^{13} G), were among the characterizing properties of magnetars. The recent discovery of radio pulsed emission from a few of them, and of a low dipolar magnetic field soft gamma repeater, weakened further the idea of a clean separation between normal pulsars and magnetars. In this Letter we show that radio emission from magnetars might be powered by rotational energy, similarly to what occurs in normal radio pulsars. The peculiar characteristics of magnetars radio emission should be traced in the complex magnetic geometry of these sources. Furthermore, we propose that magnetar radio activity or inactivity can be predicted from the knowledge of the stars rotational period, its time derivative and the quiescent X-ray luminosity.
The fundamental plane for black hole activity constitutes a tight correlation between jet power, X-ray luminosity, and black hole mass. Under the assumption that a Blandford-Znajek-type mechanism, which relies on black hole spin, contributes non-negl
igibly to jet production, the sufficiently small scatter in the fundamental plane shows that black hole spin differences of $mid$$Delta$a$mid sim$1 are not typical among the active galactic nuclei population. If $-$ as it seems $-$ radio loud and radio quiet objects are both faithful to the fundamental plane, models of black hole accretion in which the radio loud/radio quiet dichotomy is based on a spin dichotomy of a$sim$1/a$sim$0, respectively, are difficult to reconcile with the observations. We show how recent theoretical work based on differences in accretion flow orientation between retrograde and prograde, accommodates a small scatter in the fundamental plane for objects that do have non-negligible differences in black hole spin values. We also show that the dichotomy in spin between the most radio loud and the most radio quiet involves $mid$$Delta$a$mid approx$0. And, finally, we show how the picture that produces compatibility with the fundamental plane, also allows one to interpret other otherwise puzzling observations of jets across the mass scale including 1) the recently observed inverse relation between radio and X-rays at higher Eddington ratios in both black hole X-ray binaries as well as active galactic nuclei and 2) the apparent contradiction between jet power and black hole spin observed in X-ray hard and transitory burst states in X-ray binaries.
We present images from a long term program (MOJAVE: Monitoring of Jets in AGN with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observ
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