Mass-loss rate constraints from e-MERLIN observations of the Type Iax SN 2019muj

ATel #13105; M. Perez-Torres (IAA-CSIC, Granada), P. Lundqvist (Stockholm University), J. Moldon (IAA-CSIC), E. Kundu (ICRAR/Curtin University), R. Beswick (JBCA, Manchester), E. Varenius (OSO, Onsala), A. Alberdi (IAA-CSIC), S. Ryder (Macquarie University), C.-I. Bjornsson (Stockholm Univ.), C. Fransson (Stockholm Univ.).
on 13 Sep 2019; 18:07 UT
Credential Certification: Miguel A. Perez-Torres (torres@iaa.es)

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We observed the young Type Iax supernova 2019muj with the electronic Multi-Element Radio Linked Interferometer Network (e-MERLIN). SN2019muj was discovered on 7 August 2019 (UT 09:36:00) in the nearby (z=0.007035) galaxy VV 525 (Stanek et al., TNS discovery report #43337). An optical spectrum of SN2019muj on 7 August 2019 (UT 18:57:17) showed a good fit to the Type Iax SN 2005hk around a week before maximum (Hiramatsu, TNS classification report #4759). Since SN 2005hk exploded most likely 15 days before maximum (Phillips et al. 2007, PASP 119, 369), this implies that the spectrum of SN 2019muj was taken 8 days after explosion.

Our e-MERLIN observations were conducted on 11 August 2019 (centered on MJD 58706.27083 with a duration of 10h at 5.08 GHz) and 13 August 2019 (centered on MJD 58708.23265 with a duration of 9h at 1.51 GHz), when the age of the SN was of about 11 and 13 days. We observed at both frequencies using a bandwidth of 512 MHz, and centered our observations at RA = 02:26:18.490 DEC = -09:50:09.65 (J2000.0). We find no evidence of radio emission in a circular region of 5.0 arcsec of radius surrounding SN 2019muj, down to a 3-sigma upper limit of 96 and 126 microJy/beam at 5.08 and 1.51 GHz, respectively.

The corresponding upper limits in the monochromatic luminosity are 7.64E25 and 1.00E26 erg/s/Hz (3-sigma) at 5.08 and 1.51 GHz, respectively, for an assumed distance of 25.8 Mpc. Using the same radio modelling as in ATels #11324 and #12960 for SN 2018pv and SN 2019np, we place upper limits on the mass-loss rate of the supernova progenitor of 6.1E-8 and 5.6E-8 solar masses per year (3-sigma) at 5.08 and 1.51 GHz, respectively, for an assumed wind speed of 100 km/s and optically thin emission. We note that, while the assumption of optically thin emission is correct for the 5.08 GHz observations, this is not necessarily the case at 1.51 GHz, as the non-detection at this lower frequency can also be explained by optically thick synchrotron self-absorption. In this case, the implied mass-loss rate would be larger than 1.2E-7 solar masses per year. Fortunately, our 5.08 GHz e-MERLIN observations rule out such a high mass-loss rate, and so the upper limit at 1.51 GHz can only be explained by optically thin emission. These results show the importance of a combined set of frequencies, and cautions against too early observations of Type Ia SNe at low frequencies (<= 2 GHz). We thank the e-MERLIN staff for supporting our ToO program in search for radio emission from Type Ia supernovae.