Searching for Radio Transients with Inverted Spectra in Epoch 1 of VLASS and VCSS, and Identification of a Sample of Candidate Relativistic Nuclear Transients

Abstract

For radio transients, an inverted spectrum (defined as $\alpha >0$ for a power law spectrum $S_{\nu }\propto {\nu }^{\alpha }$) constrains physical properties, which in principle can be a useful criterion for selecting specific targets of interest in a transient search. To test and develop this concept, we have searched epoch 1 of the Very Large Array Sky Survey (VLASS; 3.0 GHz) and the VLITE Commensal Sky Survey (VCSS; 340 MHz) for radio transients with inverted spectra. We discover a sample of 21 inverted-spectra transient candidates that are not associated with cataloged active galactic nuclei (AGNs). To the best of our knowledge, three of our candidates have recently been reported by others as radio transients, but none have reported transient counterparts at other wavelengths. We find that our candidates evolve slowly over years and show either highly inverted spectra or peaked spectra over $\sim$1--3 GHz. Within our sample, nine candidates are matched to optical centers of galaxies and have estimated radio spectral luminosities of $L_{3.0\mathrm{GHz}}\sim 10^{30}-10^{33}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{Hz}}^{-1}$. Based on the observed properties, we find the most plausible transient classification for our candidates to be relativistic tidal disruption events. However, it is difficult to rule out variable or transient AGNs with highly inverted spectra. Upon examining physical constraints, we confirm that mainly relativistic transients (on-axis or off-axis) with equipartition energy $E_{\mathrm{eq}}\gtrsim 10^{49}-10^{53}\mathrm{erg}$ are expected from searching VLASS and VCSS based on inverted spectra. The obtainable physical constraints, however, can be weak due to degeneracy introduced by viewing angle.

v2: updated to accepted version, DOI: 10.3847/1538-4357/add924

References in corpus (66)

• Array Programming with NumPy
• The Gaia mission
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• Active Galactic Nuclei: what's in a name?
• The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release
• The LOFAR Two-metre Sky Survey -- V. Second data release
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• The Last of FIRST: The Final Catalog and Source Identifications
• The CatWISE2020 Catalog
• The Rapid ASKAP Continuum Survey I: Design and First Results
• Science With The Australian Square Kilometre Array Pathfinder
• SkyMapper Southern Survey: Second Data Release (DR2)
• The WISE AGN Catalog
• The Dynamic Evolution of Young Extragalactic Radio Sources
• Radio Properties of Tidal Disruption Events
• The faint radio sky: radio astronomy becomes mainstream
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• A very luminous jet from the disruption of a star by a massive black hole
• The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at $z=0.27$
• A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky
• Relativistic jet feedback II: Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies
• All-purpose, all-sky photometric redshifts for the Legacy Imaging Surveys Data Release 8
• Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST
• Delayed Radio Flares from a Tidal Disruption Event
• Electrons' energy in GRB afterglows implied by radio peaks
• The variability timescales and brightness temperatures of radio flares from stars to supermassive black holes
• The Radio Luminosity-Risetime Function of Core-Collapse Supernovae
• Constraining the nature of High Frequency Peakers. I. The spectral variability
• A real-time transient detector and the Living Swift-XRT Point Source catalogue
• Are Delayed Radio Flares Common in Tidal Disruption Events? The Case of the TDE iPTF16fnl
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. IV. Continued Fading and Non-Relativistic Expansion
• A radio-emitting outflow produced by the tidal disruption event AT2020vwl
• The LOFAR LBA Sky Survey II. First data release
• MKT J170456.2-482100: the first transient discovered by MeerKAT
• Late-time observations of the relativistic tidal disruption flare candidate Swift J1112.2-8238
• Day-timescale variability in the radio light curve of the Tidal Disruption Event AT2022cmc: confirmation of a highly relativistic outflow
• High-resolution VLA Imaging of Obscured Quasars: Young Radio Jets Caught in a Dense ISM
• Resolving the decades-long transient FIRST J141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula?
• 21 new long-term variables in the GX 339-4 field: two years of MeerKAT monitoring
• Spectral Variability of Radio Sources at Low Frequencies
• Serendipitous discovery of radio flaring behaviour from a nearby M dwarf with MeerKAT
• Caltech-NRAO Stripe 82 Survey (CNSS). IV. The Birth of Radio-loud Quasar 013815+00
• A search for radio afterglows from gamma-ray bursts with the Australian Square Kilometre Array Pathfinder
• Variability and parsec-scale radio structure of candidate compact symmetric objects
• Wide-Band Spectral Variability of Peaked Spectrum Sources
• A pilot ASKAP survey for radio transients towards the Galactic Centre
• Changing-look AGNs or short-lived radio sources?
• Towards an understanding of long gamma-ray burst environments through circumstellar medium population synthesis predictions
• Radio Variable and Transient Sources on Minute Timescales in the ASKAP Pilot Surveys
• Bursts from Space: MeerKAT - The first citizen science project dedicated to commensal radio transients
• A Radio Study of Persistent Radio Sources in Nearby Dwarf Galaxies: Implications for Fast Radio Bursts
• A matched-filter approach to radio variability and transients: searching for orphan afterglows in the VAST Pilot Survey
• Transient radio emission from low-redshift galaxies at z<0.3 revealed by VLASS and FIRST surveys
• The dense and non-homogeneous circumstellar medium revealed in radio wavelengths around the Type Ib SN 2019oys
• Commensal Transient Searches in Eight Short Gamma Ray Burst Fields
• Classical Novae in the ASKAP Pilot Surveys
• High Frequency GPS sources in the AT20G Survey
• GMRT observations of extragalactic radio sources with steeply inverted spectra
• Limits on long-time-scale radio transients at 150 MHz using the TGSS ADR1 and LoTSS DR2 catalogues
• Finding radio transients with anomaly detection and active learning based on volunteer classifications
• Primary Beam Calibration for Commensal Telescopes Utilizing Offset Optics

Cited by in corpus (1)

• Radio Variability in Recently-Quenched Galaxies: The Impact of TDE or AGN Driven Outflows