Compact objects
The discovery of fast radio bursts (FRBs) is one of the most intriguing radio astronomical discoveries of our times. FRBs are radio spikes of millisecond duration originating from cosmological distances. The nature of FRBs remains elusive, but their short duration implies a compact origin. Furthermore, FRB-like emission from the Galactic magnetar SGR 1935+2154 hints towards a neutron star origin. From the handful of FRBs that have been localized to a host galaxy, two have been associated with compact, persistent radio sources (PRSs; Chatterjee et al., 2017; Niu et al., 2022). Both display a characteristic broadband synchrotron spectra and both dwell in dwarf galaxies ($M_{\textrm{star}} \leq 10 ^{9.5} M_{\odot}$). Different models explain these PRSs as either an AGN-like source associated with a massive accreting black hole (e.g. Reines et al. 2020), or a highly energetic version of synchrotron nebulae around young neutron stars such as the Crab nebula (Michilli et al., 2018; Chatterjee et al., 2017). To improve our understanding of PRSs, it is imperative to increase the known sample size.
The experiment
In this Science Project, we perform a targeted search for PRSs using the recently published LOFAR Two-Meter Sky Survey (LoTSS) second data release (DR2) as our radio reference catalog. LoTSS DR2 comprises observations at low frequencies (~144 MHz) of the northern sky, with 4 million radio sources spanning ~5500 square degrees. A key feature of LoTSS is its astrometric accuracy of 0”.2, which is comparable to optical surveys and makes it possible to accurately cross-match source positions. Globally, we designed our search following the tell-tell signs provided by the first two known PRSs. In particular, we seek for compact radio sources coincident with dwarf galaxies having radio luminosities greater than that expected from star-formation activity alone. We show the selection process along with images of each candidate in the Figures below.
Virtual Research Environment, Data Lake and Virtual Observatory
Our code can easily be executed on the Virtual Research Environment, accessing the datasets from the Data Lake and from the Virtual Observatory, providing a simple way to reproduce results and share research activities within our team.
Where to from here?
We are planning high angular resolution follow-up observations through very long baseline interferometry to conclusively determine the compactness of these sources—a critical step towards establishing them as potential FRB hosts.
References
- Chatterjee, S., Law, C.J., Wharton, R.S., Burke-Spolaor, S., Hessels, J.W.T., Bower, G.C., Cordes, J.M., Tendulkar, S.P., Bassa, C.G., Demorest, P. and Butler, B.J., 2017. A direct localization of a fast radio burst and its host. Nature, 541(7635), pp.58-61.
- Niu, C.H., Aggarwal, K., Li, D., Zhang, X., Chatterjee, S., Tsai, C.W., Yu, W., Law, C.J., Burke-Spolaor, S., Cordes, J.M. and Zhang, Y.K., 2022. A repeating fast radio burst associated with a persistent radio source. Nature, pp.1-5.
- Reines, A.E., Condon, J.J., Darling, J. and Greene, J.E., 2020. A new sample of (wandering) massive black holes in dwarf galaxies from high-resolution radio observations. The Astrophysical Journal, 888(1), p.36.
- Michilli, D., Seymour, A., Hessels, J.W.T., Spitler, L.G., Gajjar, V., Archibald, A.M., Bower, G.C., Chatterjee, S., Cordes, J.M., Gourdji, K. and Heald, G.H., 2018. An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102. Nature, 553(7687), pp.182-185.
- Gürkan, G., Hardcastle, M.J., Smith, D.J., Best, P.N., Bourne, N., Calistro-Rivera, G., Heald, G., Jarvis, M.J., Prandoni, I., Röttgering, H.J.A. and Sabater, J., 2018. LOFAR/H-ATLAS: the low-frequency radio luminosity–star formation rate relation. Monthly Notices of the Royal Astronomical Society, 475(3), pp.3010-3028.
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