ATCA radio non-detection of the TDE AT2021blz

ATel #14697; M. Perez-Torres (IAA-CSIC, Granada), S. Ryder (Macquarie University), E. Kundu (ICRAR/Curtin University), L. Marnoch (Macquarie University/CSIRO), S. Mattila (University of Turku), A. Horesh (HUIJ), T. Wevers (ESO), R. Roy (IUCAA), S. Schulze (Stockholm University), I. Mandel (Monash University), I. Arcavi (Tel Aviv University)
on 10 Jun 2021; 09:50 UT
Credential Certification: Miguel A. Perez-Torres (torres@iaa.es)

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We observed the tidal disruption event (TDE) AT 2021blz with the Australia Telescope Compact Array (ATCA) on 9 February (03:39-06:28 UT), 25 February (05:54-11:00 UT), and 31 March (01:40-03:27 UT) 2021. AT2021blz was discovered on 2021-01-31 at UTC 06:47:31.200 (JD=2459245.783) with ATLAS (2021TNSTR.312....1T), at RA = 04:32:31.252, DEC = -32:25:50.37 (J2000.0), and classified as a TDE at z=0.045 by Magee et al. (2021TNSCR.338....1M).

We simultaneously observed AT2021blz at 5.5 and 9 GHz, with 2 GHz bandwidth. We did not detect AT2021blz in any epoch, and obtained the 3-sigma upper limits quoted below. We also quote the monochromatic radio luminosity, L_freq, and the integrated radio luminosity (freq * L_freq), for a luminosity distance to AT2021blz of 199.5 Mpc.

Epoch, Freq, 3-sigma flux density upper limit, L_freq, L_freq * freq
9 February 2021, 5.5 GHz, 50 microJy/b, 2.28E27 erg/s/Hz, 1.25E37 erg/s
9 February 2021, 9.0 GHz, 70 microJy/b, 3.19E27 erg/s/Hz, 2.87E37 erg/s
25 February 2021, 5.5 GHz, 26 microJy/b, 1.18E27 erg/s/Hz, 6.50E36 erg/s
25 February 2021, 9.0 GHz, 30 microJy/b, 1.37E27 erg/s/Hz, 1.10E37 erg/s
31 March 2021, 5.5 GHz, 40 microJy/b, 1.82E27 erg/s/Hz, 1.00E37 erg/s
31 March 2021, 9.0 GHz, 50 microJy/b, 2.28E27 erg/s/Hz, 2.05E37 erg/s

Those radio non-detections up to almost 60 days after the discovery of the TDE indicate that AT2021blz is either a radio quiet TDE, which may not result in significant radio emission, or alternatively, a slowly-evolving TDE, with delayed radio emission, similar to the cases of, e.g., AT1 in Arp299B (Mattila et al. 2018, Science, 361, 482) or TDE ASASSN-15oi (Horesh et al. 2021, NatAst, 5, 491), which showed no radio emission until about six months after the discovery of the TDE. From the modelled radio light curves by Generozov et al. (MNRAS, 464, 2481), our non-detections suggest large circumnuclear gas densities (> 2000 #/cm^3) near a jet (Sedov) radius of about 1E18 cm. Further radio observations are planned to confirm which scenario is at play in this TDE.

We thank the ATNF for supporting our observations. We extend our thanks to the ATCA staff for enabling these observations. The ATCA is part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site.