Unambiguous radio detection of the tidal disruption event AT2019dsg with e-MERLIN

ATel #12960; M. Perez-Torres (IAA-CSIC, Spain), J. Moldon (JBCA, Manchester), S. Mattila (Univ. of Turku, Finland), A. Alberdi (IAA-CSIC, Spain), R. Beswick (JBCA, Manchester), S. Ryder (Macquarie Univ., Australia), E. Varenius (JBCA, Manchester), M. Fraser (Univ. College, Dublin), P. Jonker (SRON, Netherlands), E. Kankare (Univ. of Turku, Finland), E. Kool (Stockholm Univ., Sweden).
on 26 Jul 2019; 07:45 UT
Credential Certification: Miguel A. Perez-Torres (torres@iaa.es)

Tweet

We report the first detection at radio wavelengths of the nuclear transient AT2019dsg, which was discovered by the Zwicky Transient Facility on UT 2019 Apr 9 (TNS Report No. 33340) in the center of the galaxy 2MASX J20570298+1412165 (z=0.0512). AT2019dsg has been classified as a tidal disruption event (TDE), based on the spatial coincidence with the nucleus of its host galaxy and its optical properties (ATel #12751). AT2019dsg is an X-ray bright TDE (ATel #12777, ATel #12825), and 15 GHz observations on 2019 May 16.24 reported a possible radio counterpart of AT2019dsg (ATel #12798), although the quoted radio position was more than 6" off the optical one.

Here we report electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) observations of AT2019dsg at a frequency of 5.07 GHz on 2019 June 3 and 2019 June 20, which show the unambiguous detection of AT2019dsg at with e-MERLIN on 2019 June 20. The array included five antennas (Mk2, Pi, Da, De, and Cm), but not the Lovell telescope, resulting in synthesized Gaussian beams of approximately 77x32 (83x35) milliarcseconds at position angle of about 25 (28) deg on the 3rd and 20th of June, respectively. We centered our 5 GHz observations at the RA(J2000.0)= 20:57:02.97 and DEC(J2000.0)=+14:12:15.86, and imaged a 4x4 sq. arcsecond region around that position. While AT2019dsg is not detected on 2019 June 3 down to a 3-sigma level of 100 microJy, it is clearly detected on 2019 June 20 with a peak flux density of 354 +/- 23 microJy/b at the following position: RA(J2000.0)=20:57:02.96502; DEC(J2000.0)=+14:12:16.2898. The positional uncertainty is about 12 and 4 mas in RA and DEC, respectively.

The radio emission detected on 2019 June 20 corresponds to a monochromatic 5.07 GHz luminosity of (2.01 +/- 0.13)*1e28 erg/s/Hz at an age of 72 days, for an assumed luminosity distance of 228 Mpc. This value is typical of other nearby, radio loud TDEs, e.g., Arp299B-AT1 (Mattila et al. 2018, Science, 6401, 482), ASASSN-14li (Alexander et al. 2016, ApJ, 819, L25), AT2019azh (ATel #12870) at similar ages, albeit much fainter than the TDE Sw J1644+57 at z=0.35.

Further approved e-MERLIN observations are underway to trace the radio evolution of the TDE AT2019dsg. We thank the e-MERLIN staff for supporting our observing program.