Search for synchrotron emission from secondary leptons in dense cold starless cores

Abstract

We report radio continuum observations with the Australia Telescope Compact Array of two molecular clouds. The impetus for these observations is a search for synchrotron radiation by cosmic ray secondary electrons/positrons in a region of enhanced density and possibly high magnetic field. We present modelling which shows that there should be an appreciable flux of synchrotron above the more diffuse, galactic synchrotron background. The starless core G333.125-0.562 and infrared source IRAS 15596-5301 were observed at 1384 and 2368 MHz. For G333.125-0.562, we find no significant levels of radio emission from this source at either frequency, nor any appreciable polarisation: we place an upper limit on the radio continuum flux from this source of 0.5 mJy per beam at both 1384 and 2368 MHz. Due to the higher than expected flux density limits, we also obtained archival ATCA data at 8640 MHz for this cloud and place an upper limit on the flux density of 50 micro-Jy per beam. Assuming the cosmic ray spectrum is similar to that near the Sun, and given the cloud's molecular density and mass, we place an upper limit on the magnetic field of 500 micro-G. IRAS 15596-5301, with an RMS of 50 micro-Jy per beam at 1384 MHz, shows an HII region consistent with optically thin free-free emission already detected at 4800 MHz. We use the same prescription as G333 to constrain the magnetic field from this cloud to be less than 500 micro-G. We find that these values are not inconsistent with the view that magnetic field values scale with the average density of the molecular cloud.

6 pages, 5 pdf figures, accepted for publication in PASA

References in corpus (5)

• SUMSS: A Wide-Field Radio Imaging Survey of the Southern Sky. II. The Source Catalogue
• Production and propagation of cosmic-ray positrons and electrons
• Two massive star-forming regions at early evolutionary stages
• Detection of SiO emission from a massive dense cold core
• The Cosmic Ray Distribution in Sagittarius B

Cited by in corpus (9)

• Broad-band nonthermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants
• Molecular Clouds as Cosmic-Ray Barometers
• Low energy cosmic rays
• Synchrotron emission in molecular cloud cores: the SKA view
• Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
• A Self-Consistent Explanation of TeV Emissions from HESS J1640-465 and HESS J1641-463
• Observations and radiative transfer modelling of a massive dense cold core in G333
• Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations
• Prospects for Detection of Synchrotron Emission from Secondary Electrons and Positrons in Starless Cores: Application to G0.216+0.016