Two Extreme Steep-Spectrum, Polarized Radio Sources Towards the Galactic Bulge

Abstract

From an on-going survey of the Galactic bulge, we have discovered a number of compact, steep spectrum radio sources. In this present study we have carried out more detailed observations for two of these sources, located 43 arcmin and 12.7 deg from the Galactic Center. Both sources have a very steep spectrum (alpha ~ -3) and are compact, with upper limits on the angular size of 1-2 arcsec. Their flux densities appear to be relatively steady on timescales of years, months, and hours, with no indications of rapid variability or transient behavior. We detect significant circularly polarized emission from both sources, but only weak or upper limits on linear polarization. Neither source has a counterpart at other wavelengths and deep, high-frequency searches fail to find pulsations. We compare their source properties with other known compact, non-thermal source populations in the bulge (e.g. X-ray binaries, magnetars, the Burper, cataclysmic variables). Our existing data support the hypothesis that they are scatter broadened millisecond or recycled pulsars, either at the bulge or along the line of sight. We also consider the possibility that they may be a new population of Galactic radio sources which share similar properties as pulsars but lack pulsations; a hypothesis that can be tested by future large-scale synoptic surveys.

12 pages, 4 figures. Submitted to MNRAS

References in corpus (25)

• The ATNF Pulsar Catalogue
• Astrophysics Source Code Library
• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• Distant Radio Galaxies and their Environments
• A Study of Multi-frequency Polarization Pulse Profiles of Millisecond Pulsars
• A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky
• A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
• The XMM-Newton serendipitous survey. X: The second source catalogue from overlapping XMM-Newton observations and its long-term variable content
• A 610-MHz survey of the ELAIS-N1 field with the Giant Metrewave Radio Telescope - Observations, data analysis and source catalogue
• An image-based search for pulsars among Fermi unassociated LAT sources
• A search for long-timescale, low-frequency radio transients
• The High Time Resolution Universe Pulsar Survey -- XVI. Discovery and timing of 40 pulsars from the southern Galactic plane
• A Faint, Steep Spectum Burst from the Radio Transient GCRT J1745-3009
• Heightened Faraday Complexity in the inner 1 kpc of the Galactic Centre
• A population of compact radio variables and transients in the radio bright zone at the Galactic center observed with the Jansky Very Large Array
• New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO-LWA
• Prospects for Discovering Pulsars in Future Continuum Surveys Using Variance Imaging
• A LOFAR search for steep-spectrum pulsars in Supernova Remnants and Pulsar Wind Nebulae
• Evolutionary Map of the Universe (EMU):Compact radio sources in the SCORPIO field towards the Galactic plane
• A GMRT 150 MHz Search for Variables and Transients in Stripe 82
• Transient Events in Archival Very Large Array Observations of the Galactic Center
• Radio Millisecond pulsars
• Reprocessing of a Green Bank 43-meter Telescope Survey of Unidentified Bright Radio Sources for Pulsars and Radio Bursts

Cited by in corpus (5)

• Discovery of ASKAP J173608.2-321635 as a Highly-Polarized Transient Point Source with the Australian SKA Pathfinder
• Searching for pulsars associated with polarised point sources using LOFAR: Initial discoveries from the TULIPP project
• Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud
• A pilot ASKAP survey for radio transients towards the Galactic Centre
• 4-8 GHz Fourier-domain Searches for Galactic Center Pulsars