AstroNote 2020-182

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2020-09-22 14:38:25
Type: Object/s-Discovery/Classification
Spectroscopic classification of AT2020tkx as a nearby broad-line Ic event
Authors: S. Srivastav, S. J. Smartt, K. W. Smith, O. McBrien, J. Gillanders, P. Clark, M. Fulton, D. O'Neill, D. R. Young, M. McCollum (Queen's University Belfast), T.-W. Chen (Stockholm), J. Anderson (ESO), L. Denneau, A. Heinze, J. Tonry, H. Weiland (IfA, University of Hawaii), B. Stalder (LSST), A. Rest (STScI), D. E. Wright (University of Minnesota)
Source Group: ATLAS
Keywords: Supernova
We draw attention to the transient AT2020tkx (Gaia20ehu), a potentially unusual broad-line Ic supernova in a very faint host galaxy. Our two spectra match SN2006aj, at a pre-maximum phase, with a redshift of z ~ 0.01 (about 40 Mpc). The ATLAS lightcurve shows it may be peaking now at a relatively faint peak magnitude of M ~ -16. Further data on this peculiar explosion are encouraged.

We draw attention to the transient AT2020tkx (Gaia20ehu), discovered by Gaia on MJD 59106.49 (2020-09-14) at a magnitude of 18.47 (G-Gaia band). AT2020tkx was also detected by ATLAS and ZTF, providing a well sampled rise time. A classification spectrum was obtained from the Liverpool Telescope (Steele et al. 2004) on MJD 59110.84, and a followup LT spectrum on MJD 59113.87. 

The spectra show a blue continuum and broad features of Fe II and Si II. Gelato (Harutyunyan et al. 2008) finds a reasonable match with broad-line Ic SNe 2002ap and 2006aj at pre-maximum epochs, for an assumed redshift of 0.01. No redshift of the faint host is available, a diffuse, blue galaxy in the Pan-STARRS 3Pi images with r = 20. 

At this redshift, the line velocity inferred from Fe II is ~ 20000-25000 km/sec. The ATLAS light curve appears now to be near maximum, at a magnitude of o = 17.27 +/- 0.04 (on MJD 59114.29), implying an absolute magnitude of M ~ -16.0 (for the assumed redshift) and we observe a rise time of 11 days.  This luminosity is unusually low for a broad-line Ic event, and further spectroscopic, photometric and multi-wavelength observations are encouraged. A finder is provided to aid identification. 


Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2020tkx [Gaia20ehu]18:40:09.000+34:06:59.5418:40:09.000+34:06:59.54SN Ic-BL