GMRT observations of extragalactic radio sources with steeply inverted spectra

Abstract

We report quasi-simultaneous GMRT observations of seven extragalactic radio sources at 150, 325, 610 and 1400 MHz, in an attempt to accurately define their radio continuum spectra, particularly at frequencies below the observed spectral turnover. We had previously identified these sources as candidates for a sharply inverted integrated radio spectrum whose slope is close to, or even exceeds ${\alpha }_c$ = +2.5, the theoretical limit due to synchrotron self-absorption (SSA) in a source of incoherent synchrotron radiation arising from relativistic particles with the canonical (i.e., power-law) energy distribution. We find that four out of the seven candidates have an inverted radio spectrum with a slope close to or exceeding +2.0, while the critical spectral slope ${\alpha }_c$ is exceeded in at least one case. These sources, together with another one or two reported in very recent literature, may well be the archetypes of an extremely rare class, from the standpoint of violation of the SSA limit in compact extragalactic radio sources. However, the alternative possibility that free-free absorption is responsible for their ultra-sharp spectral turnover cannot yet be discounted.

arXiv commentAccepted for publication in MNRAS. Comments are welcome

References in corpus (11)

• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• LOFAR/H-ATLAS: A deep low-frequency survey of the Herschel-ATLAS North Galactic Pole field
• On the Evolution of and High-Energy Emission from GHz-Peaked-Spectrum Sources
• Relativistic jet feedback II: Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies
• A search for distant radio galaxies from SUMSS and NVSS: III. radio spectral energy distributions and the z-alpha correlation
• Broadband Spectral Modeling of the Extreme Gigahertz-Peaked Spectrum Radio Source PKS B0008-421
• X-ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra
• What are the megahertz peaked-spectrum sources?
• SPAM: A data reduction recipe for high-resolution, low-frequency radio-interferometric observations
• Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
• The Murchison Widefield Array Transients Survey (MWATS). A search for low frequency variability in a bright Southern hemisphere sample

Cited by in corpus (6)

• Compact steep-spectrum and peaked-spectrum radio sources
• Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST
• Radiation pressure confinement -- V. The predicted free-free absorption and emission in active galactic nuclei
• Resolved simulations of jet-ISM interaction: Implications for gas dynamics and star formation
• The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of active galactic nuclei
• Searching for Radio Transients with Inverted Spectra in Epoch 1 of VLASS and VCSS, and Identification of a Sample of Candidate Relativistic Nuclear Transients