A tight constraint of radio luminosity of the type Ia SN 2020nvb from e-MERLIN observations
ATel #13937; J. Moldon (IAA-CSIC, Granada; JBCA, Manchester), M. Perez-Torres (IAA-CSIC, Granada), P. Lundqvist (Stockholm University), J. Bray (JBCA, Manchester)
on 12 Aug 2020; 07:38 UT
Credential Certification: Miguel A. Perez-Torres (torres@iaa.es)
Subjects: Radio, Supernovae
Referred to by ATel #: 13995
We report the non-detection at radio wavelengths of the type Ia SN 2020nvb, discovered
on 2020-07-01 13:10:34.000 at the position RA = 12:28:58.820 DEC = +03:34:22.10 in NGC
4457 (2020TNSTR2003), at a distance of 10.70 Mpc (Gavazzi et al. 1999, MNRAS, 304, 595),
and classified in ATels #13848, #13849, #13858.
We observed SN 2020nvb on July 4 with the electronic Multi-Element Radio Linked
Interferometer Network (e-MERLIN) at a central frequency of 5.1 GHz, with a bandwidth of
512 MHz, and using 6 antennas of the array. The final image has a resolution of 0.12
arcsec by 0.03 arcsec at position angle of 20 degrees. The nucleus of NGC 4457 is
clearly detected as a compact elongated source. SN 2020nvb is at an angular distance of
about 8.6 arcsecond from the host galaxy nucleus, corresponding to a projected linear
separation of about 450 pc. From Hyperleda (http://leda.univ-lyon1.fr/), the inclination
angle of the galaxy is about 35 degrees, so the deprojected linear separation is about
550 pc, thus making SN2020nvb one of the closest (to an AGN) SNe Ia ever detected. We
find no evidence of radio emission from SN 2020nvb above a 3-sigma upper limit of 54
microJy/beam in the region surrounding the optical position of the SN. We note that the
sub-arcsecond resolution of e-MERLIN is enough to completely separate the compact
nucleus from any potential compact emission at the position of SN 2020nvb, and the rest
of the diffuse galactic emission is resolved out, so no contamination from the galactic
emission affects the upper limit determination. Our flux density upper limit
corresponds to a 3-sigma upper limit to the monochromatic luminosity of 7.3E24 erg/s/Hz.
In turn, this upper limit of the luminosity sets a stringent constraint on the mass-loss
rate of the progenitor star of 2.0E-8 Msun/yr (3-sigma), for an assumed wind speed of
100 km/s and t=18 days after the explosion (corresponding to July 4th).
e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC.
