ASASSN-19bt: Discovery of A Possible TDE in the TESS Field

ATel #12462; P. Cacella (DogsHeaven Observatory), Nidia Morrell (Carnegie Observatories), P. Vallely, K. Z. Stanek, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (IfA-Hawaii), T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), M. Stritzinger, S. Holmbo (Aarhus), G. Bock (Runaway Bay Observatory, M. R. Kendurkar (Prince George Astronomical Observatory), J. Brimacombe (Coral Towers Observatory)
on 1 Feb 2019; 22:07 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Patrick Vallely (vallely.7@osu.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), using data from the quadruple 14-cm "Payne-Gaposchkin" telescope in Sutherland, South Africa, we discovered a new nuclear transient source, likely either a tidal disruption event or a supernova, in the galaxy 2MASX J07001137-6602251.

ASASSN-19bt (AT 2019ahk) was discovered in images obtained on UT 2019-01-29.92 at g~18.0 mag. We do not detect (g>18.6) the object in images taken on UT 2019-01-28.12 and before. An image obtained on 2019-01-30 confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the confirmation image.

The position of ASASSN-19bt is approximately 0.9" South and 0.3" West from the center of the galaxy 2MASX J07001137-6602251 (z=0.026211, d=111 Mpc, via NED), giving an absolute g-band magnitude of approximately -17.6 (m-M=35.24, A_g=0.404). The transient lies within the Camera 4 field of the TESS Sectors 7 and 8 observations per the Web TESS Viewing Tool. Properties of the new source and photometry are summarized in the tables below:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. g mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-19bt  07:00:11.347   -66:02:25.76     2019-01-29.92      18.0          -17.6               0.95 

 
Obs. UT Date         g mag 
2019-01-28.12        >18.6 
2019-01-29.92         18.0 

This figure shows an archival 6dFGS spectrum of host 2MASX J07001137-6602251, and a follow-up spectrum of ASASSN-19bt obtained on 2019-01-31 can be seen here. While clearly bluer than the archival data, we do not observe obvious new emission lines in the follow-up spectrum. This event may be comparable to the TDE PS18kh, which did not show clear lines until it reached near maximum brightness. Additional follow-up observations are strongly encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-19xx transient names as our primary nomenclature (including supernovae, but also other classes of transients), and we encourage others to do the same. We prefer merging the names as ASASSN-19xx (AT 2019xyz) to preserve, rather than anonymize, the origin of the transient.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Villum Fonden (Denmark). For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.