We present the results of the first successful observations of the Pie Town link with the Very Large Array at 74 MHz on Hercules A. The improvement in resolution from 25 to 10 arcsec resolves the ...helical- and ring-like features seen at higher frequencies. We also present new high dynamic range images of this powerful radio galaxy at 325 MHz. Our low-frequency observations confirm the multiple outburst interpretation of the spectral index differences at high frequencies. A comparison between our radio and ROSAT X-ray data does not reveal any association between the X-ray emission from the cluster and the radio lobes. There are no extra regions of radio emission at 74 MHz.
The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring ...structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.
We have made ROSAT Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) X-ray observations to study the intracluster gas surrounding the powerful radio source Hercules A. ...The cluster is luminous in X-rays (Lbol= 4.8 × 1037 W), although apparently poor in optical galaxies, and the host of the radio source is the central dominating galaxy of the cluster. The azimuthally averaged X-ray surface brightness profile is well fitted by a modified King (β) model, with core radius rc= 121 ± 10 kpc and β= 0.74 ± 0.03, but the cluster is elongated parallel to the radio source, especially on the scale of the radio lobes, and fits to individual quadrants give a core radius 50 per cent larger along the radio axis. Part of this elongation appears to be associated with enhanced X-ray emission superimposed on the outer radio lobes, which extend to just over 2rc. There are no obvious depressions in the X-ray emission coincident with the radio lobes, as expected if the relativistic plasma displaces the intracluster medium (ICM). However, we show that these depressions may be quite weak, essentially because the main part of the lobes are outside the cluster core. From the surface brightness profile for the PSPC data the X-ray emission extends out to ∼2.2-Mpc radius. In the absence of the powerful jets (which must be a transient phenomenon on cosmological time-scales), we would expect a cooling flow at the centre of the cluster; but currently it must be substantially disturbed by the expansion of the radio lobes. The PSPC spectrum reveals a cool component of the ICM with 0.5 ≲kT≲ 1 keV in addition to the ≈ 4-keV component detected by ASCA and BeppoSAX. The central cooling time could be as low as 2 Gyr if the cool component is centrally concentrated, otherwise it is around 6 Gyr. Cooling is significant on a Hubble time to a radius of about 90 kpc. The modelled central electron density of n0= 1.0 × 104 m−3 is typical for modest cooling flows. Finally, we have detected faint X-ray emission from a compact central source, with size < 15 kpc and luminosity ≈ 2 × 1036 W.
We propose the operation of floating Extensive Air Shower (EAS) detector stations in coincidence with the KM3NeT Mediterranean deep-sea neutrino telescope to determine the absolute position and ...orientation of the underwater detector and to investigate possible systematic angular errors. We evaluate the accuracy of the proposed calibration strategies using a detailed simulation of the EAS and KM3NeT detectors.
We report on a simulation study of the calibration potential offered by floating Extensive Air Shower (EAS) detector stations (HELYCON), operating in coincidence with the KM3NeT Mediterranean ...deep-sea neutrino telescope. We describe strategies in order to investigate for possible systematic errors in reconstructing the direction of energetic muons as well as to determine the absolute position of the underwater detector.
We present the usage of multi-frequency and multi-band radio, VLA, observations as well as X-ray observations in order to study the environment around two powerful radio galaxies, namely Hercules A ...and 3 C310. We study their environment both in pc- and kpc-scales. We have chosen these two radio galaxies as they present similar and unique characteristics, compared to the ones from our general knowledge about double radio galaxies associated with active galactic nuclei.
Radio Leonids at Madeira Augusto, Pedro; Gizani, Nectaria
Astronomy & geophysics : the journal of the Royal Astronomical Society,
02/2000, Letnik:
41, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Pedro Augusto and Nectaria Gizani report on an unusual way to watch a meteor storm.
Here, we report on the detection and verification of Fast Radio Burst FRB 180301, which occurred on UTC 2018 March 1 during the Breakthrough Listen observations with the Parkes telescope. ...Full-polarization voltage data of the detection were captured--a first for non-repeating FRBs--allowing for coherent de-dispersion and additional verification tests. The coherently de-dispersed dynamic spectrum of FRB 180301 shows complex, polarized frequency structure over a small fractional bandwidth. As FRB 180301 was detected close to the geosynchronous satellite band during a time of known 1-2 GHz satellite transmissions, we consider whether the burst was due to radio interference emitted or reflected from an orbiting object. Based on the preponderance of our verification tests, we find that FRB 180301 is likely of astrophysical origin, but caution that anthropogenic sources cannot conclusively be ruled out.
We have conducted a search for radio emission consistent with an artificial source targeting 1I/'Oumuamua with the Robert C. Byrd Green Bank Telescope (GBT) between 1.1 and 11.6 GHz. We searched the ...data for narrowband signals and found none. Given the close proximity to this interstellar object, we can place limits to putative transmitters with extremely low power (0.08 W).
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