Spectral and Morphological Analysis of the Remnant of Supernova 1987A with ALMA and ATCA
Baes, Maarten; Matsuura, Mikako; Fransson, Claes; Chevalier, Roger A.; Lundqvist, Peter; Barlow, Michael J.; Meixner, Margaret; Sonneborn, George; Spyromilio, Jason; Staveley-Smith, Lister; Ng, C. -Y.; van Loon, Jacco Th.; Indebetouw, Remy; Gaensler, Bryan M.; Park, Sangwook; Zanardo, Giovanna; Manchester, Richard N.; Kamenetzky, Julia R.; Lakićević, Maša; Marcaide, Jon M.; Martí-Vidal, Ivan
Australia, Canada, United States, United Kingdom, Sweden, Belgium, Spain, Hong Kong SAR, Germany
Abstract
We present a comprehensive spectral and morphological analysis of the remnant of supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz (λ 3.2 mm to 450 μm), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component (S νvpropν-0.73) and the thermal component originating from dust grains at T ~ 22 K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localized west of the SN site, as the spectral analysis yields -0.4 <~ α <~ -0.1 across the western regions, with α ~ 0 around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position.