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Radio Observations of the Hydrogen Poor Superluminous Supernova SN 2017egm

ATel #10538; Joe Bright, Kunal Mooley, Rob Fender (University of Oxford), Assaf Horesh (The Hebrew University of Jerusalem), Rob Beswick (Jodrell Bank Centre for Astrophysics and Jodrell Bank Observatory), Therese Cantwell (The University of Manchester
on 28 Jun 2017; 14:51 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)

Subjects: Radio, Supernovae, Transient

Referred to by ATel #: 10546

We report the observations of the host galaxy of the closest hydrogen poor superluminous supernova (SLSN) SN 2017egm (Gaia17biu) at 15.5 GHz with the Arcminute Microkelvin Imager Large Array (AMI-LA). We do not detect any significant variability from the host, and conclude that we are not detecting the supernova. We also report a non-detection of SN 2017egm with eMERLIN at 5.07 GHz.

SN 2017egm was discovered by the Gaia Satellite on 2017-05-23 and was initially classified as a luminous type II supernova (ATel #10442). The classification was later revised (ATel #10498), when spectroscopic observations from the Nordic Optical Telescope revealed features associated with hydrogen poor SLSN. A possible X-ray detection of SN 2017egm was reported (ATel #10499) from Swift in the 0.3-10 keV energy band, but later observations (ATel #10531) showed no significant variability.

We triggered AMI-LA observations of SN 2017egm on 2017-06-17, shortly after its reclassification. Our 4-hour observation at 15.5 GHz (5 GHz bandwidth) reveals an unresolved source (with a clean beam major and minor axis FWHM of 58 and 30 arcseconds, respectively) at RA: 10:19:6.3, Dec: +46:27:10.8 which is consistent, within errors, with the reported optical position of SN 2017egm from Gaia (RA: 10:19:05.62, Dec: +46:27:14.08). We note, however, that archival observations of NGC 3191 from the FIRST and NVSS surveys show that the host galaxy is bright at 1.4 GHz (15.96 +/- 0.13 mJy and 12.8 +/- 0.6 mJy). Our measured flux of the source from the initial observation at 15.5 GHz is 1.8 +/- 0.1 mJy, which is consistent with the archival measurements, assuming a spectral slope of between ~-0.9 and -0.8. To check for variability we observed the source a further seven times, with the most recent observation occurring on 2017-06-26. At our 3-sigma sensitivity limit of ~150 uJy we see no significant variability in the source.

Furthermore, the source was observed on 2017-06-22 by the electronic Multi-Element Remotely-Linked Interferometer Network (eMERLIN) at a central frequency of 5.07 GHz and with a 512 MHz bandwidth. The Lovell and Pickmere telescopes were not included in the observation. The clean beam major and minor axis FWHM are 53 and 34 milliarcseconds, respectively. We do not detect a source at the position of SN 2017egm, and report a 3-sigma upper limit of ~60 uJy. This corresponds to an upper limit of ~1.2e27 erg/s/Hz at a distance of 130 Mpc. This is consistent with previously reported eMERLIN observations (ATel #10537) at 1.5 GHz.

We plan on continued monitoring of SN 2017egm with the AMI-LA and would like to thank the Mullard Radio Astronomy Observatory and the Jodrell Bank Observatory for scheduling these observations.