arXiv subjects

M. Wieringa

Publications and source records attributed to M. Wieringa.

9 recordsLinked to original sources

arXiv2026

Symmetric kiloparsec-scale radio knots in NGC 7213: evidence for a confined weak jet and recurrent nuclear activity

Low-luminosity active galactic nuclei (LLAGNs) often host weak radio jets whose propagation is shaped by the surrounding interstellar medium. We investigate the nearby LLAGN NGC7213 to assess its ability to launch collimated outflows beyond the nucleus and to characterise the origin and variability of newly identified radio components from parsec to kiloparsec scales. We present new MeerKAT, uGMRT, ATCA, and Australian Long Baseline Array (LBA) observations from 300 MHz to 9 GHz. We analyse the morphology and spectra of the kiloparsec-scale emission and use LBA monitoring to probe the parsec-scale core. We discover a pair of compact radio knots located symmetrically at a projected distance of ~5 kpc north and south of the nucleus. The knots have nearly identical flux densities and flat radio spectra from 300 MHz to at least 5.5 GHz, with no significant spectral or geometric asymmetry. The LBA monitoring shows that the nuclear source remains unresolved at all epochs, constraining the 8 GHz emission to sub-parsec scales, and reveals significant variability on decade-long and month-long timescales, including a flux-density increase of ~40 mJy over six months. The symmetry, spectra, and physical properties of the kiloparsec-scale knots support their interpretation as compact termination shocks of a weak or intermittent jet launched by NGC7213 and confined by the dense, disturbed interstellar medium. The unresolved, variable parsec-scale core indicates that the high-frequency radio variability originates in the innermost jet region, likely linked to a recent increase in nuclear activity. NGC7213 is therefore a nearby example of how weak jets in low-accretion AGN can produce both compact nuclear variability and symmetric kiloparsec-scale structures in complex environments.

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arXiv2023

The Co-Ordinated Radio and Infrared Survey for High-Mass Star Formation. V. The CORNISH-South Survey and Catalogue

We present the first high spatial resolution radio continuum survey of the southern Galactic plane. The CORNISH project has mapped the region defined by $295^{\circ} < l < 350^{\circ}$; $|b| < 1^{\circ}$ at 5.5-GHz, with a resolution of 2.5$^{''}$ (FWHM). As with the CORNISH-North survey, this is designed to primarily provide matching radio data to the Spitzer GLIMPSE survey region. The CORNISH-South survey achieved a root mean square noise level of $\sim$ 0.11 mJy beam$^{-1}$, using the 6A configuration of the Australia Telescope Compact Array (ATCA). In this paper, we discuss the observations, data processing and measurements of the source properties. Above a 7$σ$ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. The catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mJy. We developed a new way of measuring the integrated flux densities and angular sizes of non-Gaussian sources. The catalogue primarily provides positions, flux density measurements and angular sizes. All sources with IR counterparts at 8$μm$ have been visually classified, utilizing additional imaging data from optical, near-IR, mid-IR, far-IR and sub-millimetre galactic plane surveys. This has resulted in the detection of 524 H II regions of which 255 are ultra-compact H II regions, 287 planetary nebulae, 79 radio stars and 6 massive young stellar objects. The rest of the sources are likely to be extra-galactic. These data are particularly important in the characterization and population studies of compact ionized sources such as UCHII regions and PNe towards the Galactic mid-plane.

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arXiv2019

A year in the life of GW170817: the rise and fall of a structured jet from a binary neutron star merger

We present the results of our year-long afterglow monitoring of GW170817, the first binary neutron star (NS) merger detected by advanced LIGO and advanced Virgo. New observations with the Australian Telescope Compact Array (ATCA) and the Chandra X-ray Telescope were used to constrain its late-time behavior. The broadband emission, from radio to X-rays, is well-described by a simple power-law spectrum with index ~0.585 at all epochs. After an initial shallow rise ~t^0.9, the afterglow displayed a smooth turn-over, reaching a peak X-ray luminosity of ~5e39 erg/s at 160 d, and has now entered a phase of rapid decline ~t^(-2). The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ~22 deg from its axis. Within such model, the properties of the explosion (such as its blastwave energy E_K~2E50 erg, jet width theta_c~4 deg, and ambient density n~3E-3 cm^(-3)) fit well within the range of properties of cosmological short GRBs.

astro-ph.HE↗

arXiv2018

GRB 151027B - large-amplitude late-time radio variability

Deriving physical parameters from gamma-ray burst afterglow observations remains a challenge, even now, 20 years after the discovery of afterglows. The main reason for the lack of progress is that the peak of the synchrotron emission is in the sub-mm range, thus requiring radio observations in conjunction with X-ray/optical/near-infrared data in order to measure the corresponding spectral slopes and consequently remove the ambiguity wrt. slow vs. fast cooling and the ordering of the characteristic frequencies. We observed GRB 151027B, the 1000th Swift-detected GRB, with GROND in the optical-NIR, ALMA in the sub-millimeter, ATCA in the radio band, and combine this with public Swift-XRT X-ray data. While some observations at crucial times only return upper limits or surprising features, the fireball model is narrowly constrained by our data set, and allows us to draw a consistent picture with a fully-determined parameter set. Surprisingly, we find rapid, large-amplitude flux density variations in the radio band which are extreme not only for GRBs, but generally for any radio source. We interpret these as scintillation effects, though the extreme nature requires either the scattering screen to be at much smaller distance than usually assumed, multiple screens, or a combination of the two.

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arXiv2017

Multi-band study of RX J0838-2827 and XMM J083850.4-282759: a new asynchronous magnetic cataclysmic variable and a candidate transitional millisecond pulsar

In search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we performed a multi-wavelength campaign, in the X-ray band with Swift and XMM-Newton, performed infrared, optical (with OAGH, ESO-NTT and IAC80) and radio (ATCA) observations, as well as analysed archival hard X-ray data taken by INTEGRAL. We report on three X-ray sources consistent with the position of the Fermi-LAT source. We confirm the identification of the brightest object, RX J0838-2827, as a magnetic cataclysmic variable, that we recognize as an asynchronous system (not associated with the Fermi-LAT source). RX J0838-2827, is extremely variable in the X-ray and optical bands, and timing analysis reveals the presence of several periodicities modulating its X-ray and optical emission. The most evident modulations are interpreted as due to the binary system orbital period of ~1.64h and the white dwarf spin period of ~1.47h. A strong flux modulation at ~15h is observed at all energy bands, consistent with the beat frequency between spin and orbital periods. Optical spectra show prominent Hbeta, HeI and HeII emission lines Doppler-modulated at the orbital period and at the beat period. Therefore, RX J0838-2827, accretes through a diskless configuration and could be either a strongly asynchronous polar or a rare example of a pre-polar system in its way to reach synchronism. Among the other two X-ray sources, XMM J083850.4-282759 showed a variable X-ray emission, with a powerful flare lasting ~600s, similar to what is observed in transitional millisecond pulsars during the sub-luminous disc state: that would possibly associate this source with the Fermi-LAT source.

astro-ph.HE↗

arXiv2014

"Hiccup" accretion in the swinging pulsar IGR J18245-2452

IGR J18245-2452 is the fifteenth discovered accreting millisecond X-ray pulsar and the first source of this class showing direct evidence for transition between accretion and rotational powered emission states. These swing provided the strongest confirmation of the pulsar recycling scenario available so far. During the two XMM-Newton observations that were carried out while the source was in outburst in April 2013, IGR J18245-2452 displayed a unique and peculiar variability of its X-ray emission. In this work, we report on a detailed analysis of the XMM- Newton data and focus in particular on the timing and spectral variability of the source. IGR J18245-2452 continuously switches between lower and higher intensity states, with typical variations in flux up to a factor of about 500 in time scales as short as few seconds. These variations in the source intensity are sometimes associated to a dramatic spectral hardening, during which the power-law photon index of the source changes from Gamma=1.7 to Gamma=0.9. The pulse profiles extracted at different count rates and energies show a complex variability. These phenomena are not usually observed in accreting millisecond X-ray pulsars, at least not on such a short time scale. Fast variability was also found in the ATCA radio observations carried out for about 6 hours during the outburst at a frequency of 5.5 and 9 GHz. We interpret the variability observed from IGR J18245-2452 in terms of a "hiccup" accretion phase, during which the accretion of material from the inner boundary of the Keplerian disk is reduced by the onset of centrifugal inhibition of accretion, possibly causing the launch of strong outflows. Changes across accretion and propeller regimes have been long predicted and reproduced by MHD simulations of accreting millisecond X-ray pulsars but never observed to produce an extreme variability as that shown by IGR J18245-2452.

astro-ph.HE↗

arXiv2013

The unusual afterglow of the Gamma-Ray Burst 100621A

In order to constrain the broad-band spectral energy distribution of the afterglow of GRB 100621A, dedicated observations were performed in the optical/near-infrared with the 7-channel "Gamma-Ray Burst Optical and Near-infrared Detector" (GROND) at the 2.2m MPG/ESO telescope, in the sub-millimeter band with the large bolometer array LABOCA at APEX, and at radio frequencies with ATCA. Utilizing also Swift X-ray observations, we attempt an interpretation of the observational data within the fireball scenario. The afterglow of GRB 100621A shows a very complex temporal as well as spectral evolution. We identify three different emission components, the most spectacular one causing a sudden intensity jump about one hour after the prompt emission. The spectrum of this component is much steeper than the canonical afterglow. We interpret this component using the prescription of Vlasis et al. (2011) for a two-shell collision after the first shell has been decelerated by the circumburst medium. We use the fireball scenario to derive constraints on the microphysical parameters of the first shell. Long-term energy injection into a narrow jet seems to provide an adequate description. Another noteworthy result is the large ($A_V$ = 3.6 mag) line-of-sight host extinction of the afterglow in an otherwise extremely blue host galaxy.

astro-ph.HE↗

arXiv2001

The Nature of the Faint Radio Population

We present the results obtained so far from the optical follow-up of the ATESP sub-mJy radio survey. The ATESP results are then compared with the ones obtained from other deep radio samples and we show how the existing discrepancies about the nature of the faint radio population can be explained in terms of selection effects.

astro-ph↗

arXiv2001

HI in Abell 3128

We discuss Australia Telescope Compact Array (ATCA) HI 21cm data for the galaxy cluster A3128. Our observations are intentionally relatively shallow, and a blind search through our data cube yields (tentative) detections of only two galaxies, of which one is probably spurious. A3128 is part of the ESO Nearby Abell Cluster Survey (ENACS); redshifts are available for 193 galaxies in the A3128 region. For 148 of these galaxies the redshifts are such that the HI emission (if any) would lie within our data cube. We use the known redshifts of these galaxies to coadd their spectra and thus improve our sensitivity to HI emission. The technique is fairly successful -- the coadded spectra allow detection of an average mass content of ~ 9x10^8 Msun, almost an order of magnitude lower than for direct detection of individual objects. By dividing the total galaxy sample into subsamples we find that the gas content of late type galaxies that lie outside the X-ray emitting core of the cluster is substantially higher than that of those within the core. Even outside the X-ray emitting region the distribution of gas-rich galaxies in the cluster is not uniform, we find that gas-rich galaxies are concentrated in the east of the cluster. This is consistent with earlier analyses of the kinematics of the galaxies in A3128 which indicate the presence of subclustering. In summary we find that coadding spectra is a powerful tool for the study of HI in cluster galaxies, and suggest that this technique could be applied to substantially increase the redshift range over which such observations could be carried out.

astro-ph↗