NGC 3191 and the hydrogen-poor superluminous supernova SN 2017egm: 23 June 2017

On 23 May 2017, the Gaia Photometric Science Alerts programme reported the discovery of an apparent supernova, later designed SN 2017egm. It turned out to be the closest hydrogen-poor superluminous supernova (SLSN-I) ever found. We managed to capture an image of this rare explosion.

The superluminous supernova SN 2017egm and NGC 3191: 23 June 2017

The image above is the average of eleven, 120-seconds exposures, remotely taken with “Elena” (PlaneWave 17″+Paramount ME+SBIG STL-6303E) robotic unit available at Virtual Telescope. The image scale is 0.63″/pixel.

First spectroscopic follow-up suggested it could be a type II supernova, placed at more than 420 millions of light years, making it brighter than typical SNe IIP or SNe IIL.

Further investigations reserved a special surprise, as high quality spectra revealed typical features of  hydrogen-poor superluminous supernovae (SLSN-I). Considering the distance of the host galaxy, NGC 3191, this is the closest SLSN-I discovered to date, with the brightest apparent magnitude ever. Previous SLSNe-I were mainly placed in dwarf galaxies, while NGC 3139 is significantly more massive, about 1/10th the mass of the Milky Way.

From our images, we measured a magnitude of 14.4 (unfiltered, R-mags for the reference stars from UCAC-4). Assuming the distance above of 420 millions of light years, we can infer an absolute magnitude of -21.1, comparable to (and possibly brighter than ) our entire galaxy, the Milky Way.

We plan further observations of this unique target, though its position in the sky is not the best for this part of the year.

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