Low-frequency radio absorption in Tycho's supernova remnant

Abstract

Tycho's SNR is the remnant of the type Ia supernova explosion SN1572. In this work we present new low-frequency radio observations with the LOFAR Low-Band and High-Band Antennae, centred at 58 MHz and 143 MHz, and with an angular resolution of 41'' and 6'' respectively. We compare these maps to VLA maps at 327 MHz and 1420 MHz, and detect the effect of low-frequency absorption in some regions of the remnant due to the presence of free electrons along the line-of-sight. We investigate two origins for the low-frequency free-free absorption that we observe: external absorption from foreground, and internal absorption from Tycho's unshocked ejecta. The external absorption could be due to an ionised thin, diffuse cavity surrounding the SNR (although this cavity would need to be very thin to comply with the neutral fraction required to explain the remnant's optical lines), or it could be due to an over-ionised molecular shell in the vicinity of the remnant. We note that possible ionising sources are the X-ray emission from Tycho, its cosmic rays, or radiation from Tycho's progenitor. For the internal absorption, we are limited by our understanding of the spectral behaviour of the region at unabsorbed radio frequencies. However, the observations are suggestive of free-free absorption from unshocked ejecta inside Tycho's reverse shock.

Accepted in ApJ

References in corpus (10)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum
• Radio interferometric gain calibration as a complex optimization problem
• Scattered-Light Echoes from the Historical Galactic Supernovae Cassiopeia A and Tycho (SN 1572)
• A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction
• Non-linear Kalman filters for calibration in radio interferometry
• The Bubble-like Interior of the Core-Collapse Supernova Remnant Cassiopeia A
• No hot and luminous progenitor for Tycho's supernova
• Genus Statistic Applied to the X-ray Remnant of SN 1572: Clues to the Clumpy Ejecta Structure of Type Ia Supernovae

Cited by in corpus (6)

• The LOFAR Two-metre Sky Survey -- V. Second data release
• Thermal radio absorption as a tracer of the interaction of SNRs with their environments
• Rapid Deceleration of Blast Waves Witnessed in Tycho's Supernova Remnant
• Filamentary structures of ionized gas in Cygnus X
• A fresh perspective on the 3D dynamics of Tycho's supernova remnant: Ejecta asymmetries in the X-ray band
• The Crab Nebula at subarcsecond resolution with the International LOFAR Telescope