| 1. |
- Abdo, A. A., et al.
(författare)
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Multiwavelength Monitoring of the Enigmatic Narrow-Line Seyfert 1 PMN J0948+0022 in 2009 March-July
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 707:1, s. 727-737
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Tidskriftsartikel (refereegranskat)abstract
- Following the recent discovery of γ rays from the radio-loud narrow-line Seyfert 1 galaxy PMN J0948+0022 (z = 0.5846), we started a multiwavelength campaign from radio to γ rays, which was carried out between the end of 2009 March and the beginning of July. The source displayed activity at all the observed wavelengths: a general decreasing trend from optical to γ-ray frequencies was followed by an increase of radio emission after less than two months from the peak of the γ-ray emission. The largest flux change, about a factor of about 4, occurred in the X-ray band. The smallest was at ultraviolet and near-infrared frequencies, where the rate of the detected photons dropped by a factor 1.6-1.9. At optical wavelengths, where the sampling rate was the highest, it was possible to observe day scale variability, with flux variations up to a factor of about 3. The behavior of PMN J0948+0022 observed in this campaign and the calculated power carried out by its jet in the form of protons, electrons, radiation, and magnetic field are quite similar to that of blazars, specifically of flat-spectrum radio quasars. These results confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host relativistic jets with power similar to that of average blazars.
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| 2. |
- Murphy, T., et al.
(författare)
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VAST: An ASKAP Survey for Variables and Slow Transients
- 2013
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Ingår i: Publications of the Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 30
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Tidskriftsartikel (refereegranskat)abstract
- The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae, and orphan afterglows of gamma-ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of 5 s and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.
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| 3. |
- Smirnov, O. M., et al.
(författare)
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The RATT PARROT : serendipitous discovery of a peculiarly scintillating pulsar in MeerKAT imaging observations of the Great Saturn – Jupiter Conjunction of 2020. I. Dynamic imaging and data analysis
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 528:4, s. 6517-6537
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Tidskriftsartikel (refereegranskat)abstract
- We report on a radiopolarimetric observation of the Saturn–Jupiter Great Conjunction of 2020 using the MeerKAT L-band system, initially carried out for science verification purposes, which yielded a serendipitous discovery of a pulsar. The radiation belts of Jupiter are very bright and time variable: coupled with the sensitivity of MeerKAT, this necessitated development of dynamic imaging techniques, reported on in this work. We present a deep radio ‘movie’ revealing Jupiter’s rotating magnetosphere, a radio detection of Callisto, and numerous background radio galaxies. We also detect a bright radio transient in close vicinity to Saturn, lasting approximately 45 min. Follow-up deep imaging observations confirmed this as a faint compact variable radio source, and yielded detections of pulsed emission by the commensal MeerTRAP search engine, establishing the object’s nature as a radio emitting neutron star, designated PSR J2009−2026. A further observation combining deep imaging with the PTUSE pulsar backend measured detailed dynamic spectra for the object. While qualitatively consistent with scintillation, the magnitude of the magnification events and the characteristic time–scales are odd. We are tentatively designating this object a pulsar with anomalous refraction recurring on odd time-scales (PARROT). As part of this investigation, we present a pipeline for detection of variable sources in imaging data, with dynamic spectra and light curves as the products, and compare dynamic spectra obtained from visibility data with those yielded by PTUSE. We discuss MeerKAT’s capabilities and prospects for detecting more of such transients and variables.
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