ASASSN-20ls: Discovery of A Probable Low-Redshift Supernova in TESS
ATel #14018; J. Brimacombe (Coral Towers Observatory), P. Vallely, K. Z. Stanek, C. S. Kochanek, Z. Way, D. Desai, S. Bose, 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, Ping Chen (KIAA-PKU), M. Stritzinger, S. Holmbo (Aarhus)
on 16 Sep 2020; 17:34 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Patrick Vallely (vallely.7@osu.edu)
Subjects: Optical, Supernovae, Transient
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 transient source, most likely a supernova, in the galaxy ESO 194-G 021.
ASASSN-20ls (AT 2020tld) was discovered in images obtained on UT 2020-09-15.910 at g~17.0 mag. We do not detect (g>17.8) the object in images taken on UT 2020-09-11.96 and before. An image obtained on 2020-09-16 confirms the discovery of the transient. This figure shows the archival DSS image of the field (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-20ls is approximately 55.1" South and 0.9" West from the center of the galaxy ESO 194-G 021 (z=0.011201, d=43.9 Mpc, via NED), giving an absolute g-band magnitude of approximately -16.3 (m-M=33.21, A_g=0.052). The transient lies within the Camera 2 field of the ongoing TESS Sector 29 observations, per the Web TESS Viewing Tool. These observations will conclude next week, capturing the rise of ASASSN-20ls. 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-20ls 00:29:41.550 -51:32:09.46 2020-09-15.91 17.0 -16.3 55.11
Obs. UT Date g mag
2020-09-11.96 >17.8
2020-09-15.91 17.0
Follow-up observations are strongly encouraged.
ASAS-SN is currently operating at limited capacity, as some observing sites have been closed in response to the Covid-19 pandemic. While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-20xx 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-20xx (AT 2020xyz) 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.
