ASASSN-18uk: Discovery of a Raising Stellar Eruption in the TESS LMC Field

ATel #12018; J. Brimacombe (Coral Towers Observatory), 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, Australia)
on 8 Sep 2018; 18:22 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Krzysztof Stanek (stanek.32@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 "Cassius" telescope in Cerro Tololo, Chile, we discovered a ~2 mag eruption in the Large Magellanic Cloud.

ASASSN-18uk (AT 2018fxl) was discovered in images obtained on UT 2018-09-08.41 at V~15.1 mag. We also detect the object in images obtained on UT 2018-09-07.31 (V~15.4), UT 2018-09-06.31 (V~15.4), UT 2018-09-06.31 (V~15.5), UT 2018-09-05.39 (V~15.6), and UT 2018-08-30.33 (V~16.8). We do not detect (V>17.2) the object in images taken on UT 2018-08-29.33 and before, and the source has not shown significant variability in past ~4 years of ASAS-SN data. An image obtained on 2018-09-08 confirms the discovery of the transient. This figure shows the archival DSS image of the source (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-18uk is towards the Large Magellanic Cloud. Located near the South Ecliptic Pole, this transient lies within the Camera 4 field of the ongoing TESS Sector 2 observations. Properties of the new source and image-subtraction V-band photometry are summarized in the tables below:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-18uk  05:33:05.340   -69:30:31.34     2018-09-08.310      15.1 

 
Obs. UT Date         V mag 
2018-08-29.33        >17.2 
2018-09-05.39         15.6 
2018-09-06.31         15.5 
2018-09-07.31         15.4 
2018-09-08.41         15.1 

Follow-up observations are encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-18xx 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-18xx (AT 2018xyz) 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.