arXiv subjects

M. P. Gawronski

Publications and source records attributed to M. P. Gawronski.

13 recordsLinked to original sources

arXiv2025

A Hyperactive FRB Pinpointed in an SMC-Like Satellite Host Galaxy

Precise localizations of fast radio bursts (FRBs) are essential for uncovering their host galaxies and immediate environments. We present the milliarcsecond-precision European VLBI Network localization of FRB 20240114A, a hyperactive repeating FRB, achieving <90x30 mas (1-sigma) accuracy. This precision places the burst 0.5 kpc from the nucleus of its low-metallicity star-forming dwarf host at a spectroscopic redshift of z = 0.130287. Our Gran Telescopio CANARIAS spectroscopic follow-up reveals that the dwarf FRB host is gravitationally bound to a more massive, star-forming spiral galaxy. This establishes the first known instance of an FRB residing in a satellite galaxy within a larger galactic system. This configuration, analogous to the Small Magellanic Cloud orbiting the Milky Way (but at a lower overall mass scale), expands the known diversity of FRB host environments and offers important insights for interpreting seemingly "hostless" or highly offset FRBs. Furthermore, our detailed dispersion measure (DM) budget analysis indicates that the dominant contribution to FRB 20240114A's DM likely originates from the foreground galaxy halos. This finding addresses the anomalously high DM observed for this FRB and underscores the significant role of intervening foreground structures in shaping observed FRB DMs, which is important for accurate FRB-based cosmological measurements. Our results highlight the importance of deep, high-resolution optical/infrared observations (e.g., with the Hubble or James Webb Space Telescopes) to fully leverage our precise radio localization and probe the immediate astrophysical birthplaces of FRB progenitors within these complex galactic systems.

astro-ph.HE↗

arXiv2024

An X-ray and radio view of the 2022 reactivation of the magnetar SGRJ1935+2154

Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of Fast Radio Bursts (FRBs). SGR J1935+2154 is one of the most active magnetars, displaying flaring events nearly every year, including outbursts as well as short and intermediate bursts. Here, we present our results on the properties of the persistent and bursting X-ray emission from SGR J1935+2154, during the initial weeks following its outburst on October 10, 2022. The source was observed with XMM-Newton and NuSTAR (quasi-)simultaneously during two epochs, separated by $\sim$5 days. The persistent emission spectrum is well described by an absorbed blackbody plus power-law model up to an energy of $\sim$25 keV. No significant changes were observed in the blackbody temperature ($kT_{\rm BB}\sim$ 0.4 keV) and emitting radius ($R_{\rm BB}\sim$ 1.9 km) between the two epochs. However, we observed a slight variation in the power-law parameters. Moreover, we detected X-ray pulsations in all the datasets and derived a spin period derivative of $\dot{P} = 5.52(5) \times 10^{-11}$ ss. This is 3.8 times larger than the value measured after the first recorded outburst in 2014. Additionally, we performed quasi-simultaneous radio observations using three 25--32-m class radio telescopes for a total of 92.5 hr to search for FRB-like radio bursts and pulsed emission. However, our analysis did not reveal any radio bursts or periodic emission.

astro-ph.HE↗

arXiv2022

X-ray burst and persistent emission properties of the magnetar SGR 1830-0645 in outburst

We report on NICER X-ray monitoring of the magnetar SGR 1830-0645 covering 223 days following its October 2020 outburst, as well as Chandra and radio observations. We present the most accurate spin ephemerides of the source so far: $ν=0.096008680(2)$~Hz, $\dotν=-6.2(1)\times10^{-14}$~Hz~s$^{-1}$, and a significant second and third frequency derivative terms indicative of non-negligible timing noise. The phase-averaged 0.8--7~keV spectrum is well fit with a double-blackbody (BB) model throughout the campaign. The BB temperatures remain constant at 0.46 and 1.2 keV. The areas and flux of each component decreased by a factor of 6, initially through a steep decay trend lasting about 46 days followed by a shallow long-term one. The pulse shape in the same energy range is initially complex, exhibiting three distinct peaks, yet with clear continuous evolution throughout the outburst towards a simpler, single-pulse shape. The rms pulsed fraction is high and increases from about 40% to 50%. We find no dependence of pulse shape or fraction on energy. These results suggest that multiple hotspots, possibly possessing temperature gradients, emerged at outburst-onset, and shrank as the outburst decayed. We detect 84 faint bursts with \nicer, having a strong preference for occurring close to the surface emission pulse maximum the first time this phenomenon is detected in such a large burst sample. This likely implies a very low altitude for the burst emission region, and a triggering mechanism connected to the surface active zone. Finally, our radio observations at several epochs and multiple frequencies reveal no evidence of pulsed or burst-like radio emission.

astro-ph.HE↗

arXiv2019

Detection statistics of the RadioAstron AGN survey

The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of $μ$as structures within their cores.

astro-ph.GA↗

arXiv2017

Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode

In September 2016, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 days with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on a hourly scale, covering six frequency ranges from 1.5 GHz to 25.6 GHz. The radio emission reached a maximum of 13.2 +/- 0.7 Jy at 7.2 GHz and 10 +/- 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: alpha steepened from 0.3 to 0.6 within 5 hours. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), VLBI observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2-hour duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core ten days before the onset of the giant flare. From the latest VLBI observation we infer that four days after the flare peak the jet emission was extended over 30 mas.

astro-ph.HE↗

arXiv2013

A 20 GHz Bright Sample for Delta > 72 deg - II. Multi-frequency Follow-up

We present follow-up observations at 5, 8 and 30 GHz of the K-band Northern Wide Survey (KNoWS) 20 GHz Bright Sample, performed with the 32-m Medicina Radio Telescope and the 32-m Torun Radio Telescope. The KNoWS sources were selected in the Northern Polar Cap (Delta > 72 deg) and have a flux density limit S(20GHz) = 115 mJy. We include NVSS 1.4 GHz measurements to derive the source radio spectra between 1.4 and 30 GHz. Based on optical identifications, 68 per cent of the sources are QSOs, and 27 per cent are radio galaxies. A redshift measurement is available for 58 per cent of the sources. The radio spectral properties of the different source populations are found to be in agreement with those of other high-frequency selected samples.

astro-ph.CO↗

arXiv2011

Emission line - radio correlation for Low Luminosity Compact sources. Evolution schemes

We present radio and optical analysis of a sample of Low Luminosity Compact (LLC) objects, selected from FIRST survey and observed with MERLIN at L-band and C-band. The main criterion used for selection was luminosity of the objects and approximately one third of the CSS sources from the new sample have a value of radio luminosity comparable to FR\,Is.The analysis of a radio properties of LLC sources show they occupy the space in radio power versus linear size diagram below the main evolutionary path of radio objects. We suggest that many of them might be short-lived objects, and their radio emission may be disrupted several times before becoming FR\,IIs. The optical analysis of the LLC sources were made based on the available SDSS images and spectra. We have classified the sources as high and low excitation galaxies (HEG and LEG, respectively). The optical and radio properties of the LLC sample are in general consistent with brighter CSSs and large-scale radio sources. However, when LLC are added to the other samples, HEG and LEG seem to follow independent, parallel evolutionary tracks. LLC and luminous CSS behave like FR\,II sources, while FR\,I seem to belong to a different group of objects, concerning ionization mechanisms. Based on our results, we propose the independent, parallel evolutionary tracks for HEG and LEG sources, evolving from GPS - CSS - FR.

astro-ph.CO↗

arXiv2011

One Centimetre Receiver Array-prototype observations of the CRATES sources at 30 GHz

Knowledge of the population of radio sources in the range ~2-200 GHz is important for understanding their effects on measurements of the Cosmic Microwave Background power spectrum. We report measurements of the 30 GHz flux densities of 605 radio sources from the Combined Radio All-sky Targeted Eight-GHz Survey (CRATES), which have been made with the One Centimetre Receiver Array prototype (OCRA-p) on the Torun 32-m telescope. The flux densities of sources that were also observed by WMAP and previous OCRA surveys are in broad agreement with those reported here, however a number of sources display intrinsic variability. We find a good correlation between the 30 GHz and Fermi gamma-ray flux densities for common sources. We examine the radio spectra of all observed sources and report a number of Gigahertz-peaked and inverted spectrum sources. These measurements will be useful for comparison to those from the Low Frequency Instrument of the Planck satellite, which will make some of its most sensitive observations in the region covered here.

astro-ph.CO↗

arXiv2010

A survey of Low Luminosity Compact sources and its implication for evolution of radio-loud AGNs. I. Radio data

We present a new sample of Compact Steep Spectrum (CSS) sources with radio luminosity below 10^26 W/Hz at 1.4 GHz called the low luminosity compact (LLC) objects. The sources have been selected from FIRST survey and observed with MERLIN at L-band and C-band. The main criterion used for selection was luminosity of the objects and approximately one third of the CSS sources from the new sample have a value of radio luminosity comparable to FRIs. About 80% of the sources have been resolved and about 30% of them have weak extended emission and disturbed structures when compared with the observations of higher luminosity CSS sources. We studied correlation between radio power and linear size, and redshift with a larger sample that included also published samples of compact objects and large scale FRIIs and FRIs. The low luminosity compact objects occupy the space in radio power versus linear size diagram below the main evolutionary path of radio objects. We suggest that many of them might be short-lived objects, and their radio emission may be disrupted several times before becoming FRIIs. We conclude that there exists a large population of short-lived low luminosity compact objects unexplored so far and part of them can be precursors of large scale FRIs.

astro-ph.CO↗

arXiv2009

30 GHz observations of sources in the VSA fields

Small angular scale (high l) studies of cosmic microwave background anisotropies require accurate knowledge of the statistical properties of extragalactic sources at cm-mm wavelengths. We have used a 30 GHz dual-beam receiver (OCRA-p) on the Torun 32-m telescope to measure the flux densities of 121 sources in VSA fields selected at 15 GHz with the Ryle Telescope. We have detected 57 sources above a limiting flux density of 5mJy, of which 31 sources have a flux density greater than 10mJy, which is our effective completeness limit. From these measurements we derive a surface density of sources above 10mJy at 30 GHz of 2.0+/-0.4 per square degree. This is consistent with the surface density obtained by Mason et al. (2009) who observed a large sample of sources selected at a much lower frequency (1.4 GHz). We have also investigated the dependence of the spectral index distribution on flux density by comparing our results with those for sources above 1 Jy selected from the WMAP 22 GHz catalogue. We conclude that the proportion of steep spectrum sources increases with decreasing flux density, qualitatively consistent with the predictions of deZotti et al. (2005). We find no evidence for an unexpected population of sources whose spectra rise towards high frequencies, which would affect our ability to interpret current high resolution CMB observations at 30 GHz and above.

astro-ph.CO↗

arXiv2009

Survey of Planetary Nebulae at 30 GHz with OCRA-p

We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources which could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high frequency spectra.

astro-ph.GA↗

arXiv2009

Double radio peak and non-thermal collimated ejecta in RS Ophiuchi following the 2006 outburst

We report MERLIN, VLA, OCRA-p, VLBA, Effelsberg and GMRT observations beginning 4.5 days after the discovery of RS Ophiuchi undergoing its 2006 recurrent nova outburst. Observations over the first 9 weeks are included, enabling us to follow spectral development throughout the three phases of the remnant development. We see dramatic brightening on days 4 to 7 at 6 GHz and an accompanying increase in other bands, particularly 1.46 GHz, consistent with transition from the initial "free expansion" phase to the adiabatic expansion phase. This is complete by day 13 when the flux density at 5 GHz is apparently declining from an unexpectedly early maximum (compared with expectations from observations of the 1985 outburst). The flux density recovered to a second peak by approximately day 40, consistent with behaviour observed in 1985. At all times the spectral index is consistent with mixed non-thermal and thermal emission. The spectral indices are consistent with a non-thermal component at lower frequencies on all dates, and the spectral index changes show that the two components are clearly variable. The estimated extent of the emission at 22 GHz on day 59 is consistent with the extended east and west features seen at 1.7 GHz with the VLBA on day 63 being entirely non-thermal. We suggest a two-component model, consisting of a decelerating shell seen in mixed thermal and non-thermal emission plus faster bipolar ejecta generating the non-thermal emission, as seen in contemporaneous VLBA observations. Our estimated ejecta mass of 4+/-2x10^{-7} M_\odot is consistent with a WD mass of 1.4 M_\odot. It may be that this ejecta mass estimate is a lower limit, in which case a lower WD mass would be consistent with the data.

astro-ph.SR↗

arXiv2005

Hybrid morphology radio sources from FIRST survey

The so-called HYbrid MOrphology Radio Sources (HYMORS) are a class of objects that appear to have a mixed Fanaroff-Riley (FR) morphology in a single object; i.e. a HYMORS has an FR I-type lobe on one side of its nucleus and an FR II-type lobe on the other side. Because of this unique feature and given that the origin of the FR morphological dichotomy is still unclear, HYMORS may possibly play a crucial role in our understanding of the FR-dichotomy. As the number of known HYMORS is quite small, we aimed to increase that number by inspecting a few areas of the sky covered by the VLA FIRST survey and by selecting 21 HYMORS candidates based on the morphology shown in the FIRST images. They were observed with the VLA in B-conf. at 4.9 GHz. Three objects from the initial sample turned out to be actual HYMORS and two others very likely to fulfill the criteria. These five were subsequently re-observed with the VLA in A-conf. at 1.4 GHz. Our results provide strong support to the findings of Gopal-Krishna & Wiita (2000), namely that there are two different kinds of jets in HYMORS; consequently, the existence of FR-dichotomy as a whole is difficult to reconcile with the class of explanations that posit fundamental differences in the central engine.

astro-ph↗