The remnant of supernova 1987A resolved at 3-mm wavelength

Context. The proximity of core-collapse supernova 1987A (SN 1987A) in the Large Magellanic Cloud (LMC) and its rapid evolution make it a unique case study of the development of a young supernova remnant. Aims. We aim at resolving the remnant of SN 1987A for the first time in the 3-mm band (at 94 GHz). Methods. We observed the source at 3-mm wavelength with a 750-m configuration of the Australia Telescope Compact Array (ATCA). We compared the image with a recent 3-cm image and with archival X-ray images. Results. We present a diffraction-limited image with a resolution of 0 ''.7, revealing the ring structure seen at lower frequencies and at other wavebands. The emission peaks in the eastern part of the ring. The 3-mm image bears resemblance to early X-ray images (from 1999-2000). We place an upper limit of 1 mJy (2 sigma) on any discrete source of emission in the centre (inside of the ring). The integrated flux density at 3 mm has doubled over the six years since the previous observations at 3 mm. Conclusions. At 3 mm - i.e. within the operational domain of the Atacama Large Millimeter/submillimeter Array (ALMA) - SN 1987A appears to be dominated by synchrotron radiation from the inner rim of the equatorial ring, characterised by moderately weak shocks. There is no clear sign of emission of a different nature, but the current limits do not rule out such component altogether.