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Register a new userSerendipitous discovery of a dying Giant Radio Galaxy associated with NGC 1534, using the Murchison Widefield Array
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Recent observations with the Murchison Widefield Array at 185~MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby ($z = 0.0178$) radio galaxy associated with NGC,1534. The diffuse emission presented here is the first indication that NGC,1534 is one of a rare class of objects (along with NGC,5128 and NGC,612) in which a galaxy with a prominent dust lane hosts radio emission on scales of $sim$700,kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with disks. NGC1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2,mJy,arcmin$^{-2}$. The radio lobes have one of the steepest spectral indices yet observed: $alpha=-2.1pm0.1$, and the core to lobe luminosity ratio is $<0.1$%. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as $7times10^{-7}$,Mpc$^{-3}$ and argue that normal AGN cannot spend more than 6% of their lifetime in this phase if they all go through the same cycle.
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We detail new techniques for analysing ionospheric activity, using Epoch of Reionisation (EoR) datasets obtained with the Murchison Widefield Array (MWA), calibrated by the `Real-Time System (RTS). Using the high spatial- and temporal-resolution information of the ionosphere provided by the RTS calibration solutions over 19 nights of observing, we find four distinct types of ionospheric activity, and have developed a metric to provide an `at a glance value for data quality under differing ionospheric conditions. For each ionospheric type, we analyse variations of this metric as we reduce the number of pierce points, revealing that a modest number of pierce points is required to identify the intensity of ionospheric activity; it is possible to calibrate in real-time, providing continuous information of the phase screen. We also analyse temporal correlations, determine diffractive scales, examine the relative fractions of time occupied by various types of ionospheric activity, and detail a method to reconstruct the total electron content responsible for the ionospheric data we observe. These techniques have been developed to be instrument agnostic, useful for application on LOFAR and SKA-Low.
We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the WISE source J013313.50-130330.5, an extragalactic source based on its infrared colors and consistent with a misaligned AGN-type spectrum at $zapprox 0.3$. The multi-$ u$ spectral energy distribution (SED) of the object associated to the GRG core shows a synchrotron peak at $ u approx 10^{14}$ Hz consistent with the SED of a radio galaxy blazar-like core. The angular size of the lobes are $sim 4 ^{prime}$ for the NW lobe and $sim 1.2 ^{prime}$ for the SE lobe, corresponding to projected linear distances of $sim 1078$ kpc and $sim 324$ kpc, respectively. The best-fit parameters for the SED of the GRG core and the value of jet boosting parameter $delta =2$, indicate that the GRG jet has maximum inclination $theta approx 30$ deg with respect to the line of sight, a value obtained for $delta=Gamma$, while the minimum value of $theta$ is not constrained due to the degeneracy existing with the value of Lorentz factor $Gamma$. Given the photometric redshift $z approx 0.3$, this GRG shows a core luminosity of $P_{1.4 GHz} approx 5.52 times 10^{24}$ W Hz$^{-1}$, and a luminosity $P_{1.4 GHz} approx 1.29 times 10^{25}$ W Hz$^{-1}$ for the NW lobe and $P_{1.4 GHz} approx 0.46 times 10^{25}$ W Hz$^{-1}$ for the SE lobe, consistent with the typical GRG luminosities. The radio lobes show a fractional linear polarization $approx 9 %$ consistent with typical values found in other GRG lobes.
It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky.
Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the Southern Hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21 cm emission from the epoch of reionisation in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.
We report the discovery of the first new pulsar with the Murchison Widefield Array (MWA), PSR J0036$-$1033, a long-period (0.9 s) nonrecycled pulsar with a dispersion measure (DM) of 23.1 ${rm pc,cm^{-3}}$. It was found after processing only a small fraction ($sim$1%) of data from an ongoing all-sky pulsar survey. Follow-up observations have been made with the MWA, the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes 64 m telescopes, spanning a frequency range from $sim$150 MHz to 4 GHz. The pulsar is faint, with an estimated flux density ($S$) of $sim$1 mJy at 400 MHz and a spectrum $S( u),propto, u^{-2.0 pm 0.2}$, where $ u$ is frequency. The DM-derived distance implies that it is also a low-luminosity source ($sim$ 0.1 ${rm mJy,kpc^2}$ at 1400 MHz). The analysis of archival MWA observations reveals that the pulsars mean flux density varies by up to a factor of $sim$5-6 on timescales of several weeks to months. By combining MWA and uGMRT data, the pulsar position was determined to arcsecond precision. We also report on polarization properties detected in the MWA and Parkes bands. The pulsars nondetection in previous pulsar and continuum imaging surveys, the observed high variability, and its detection in a small fraction of the survey data searched to date, all hint at a larger population of pulsars that await discovery in the southern hemisphere, with the MWA and the future low-frequency Square Kilometre Array.
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