DRAFT
2021-04-26 21:15:55
Type: Object/s-Discovery/Classification
Bibcode: 2021TNSAN.137....1S
Classification of ATLAS21nak (2021kgj): a possible SN 2009ip-like IIn event at 65 Mpc
Authors: S. Srivastav, S. J. Smartt, M. Fulton, K. W. Smith (Queen's University Belfast), T.-W. Chen (Stockholm), M. Huber, M. A. Tucker, B. J. Shappee, L. Denneau, A. Heinze, J. Tonry, H. Weiland (IfA, University of Hawaii), B. Stalder (LSST) A. Rest (STScI), O. McBrien, J. Gillanders, P. Clark, D. O'Neill, D. R. Young (Queen's University Belfast), K. C. Chambers, T. de Boer, J. Bulger, J. Fairlamb, C.-C. Lin, T. Lowe, E. Magnier, A. Schultz, R. J. Wainscoat, M. Willman (IfA), C. Stubbs (Harvard), D. E. Wright (University of Minnesota)
Source Group: ATLAS
Keywords: Supernova
Abstract:
We highlight photometric and spectroscopic observations of ATLAS21nak (AT2021kgj), discovered in the host galaxy NGC 4188 at z = 0.014 (65 Mpc). Spectra indicate it is a type IIn and historic detections in ATLAS and Pan-STARRS1 suggest pre-explosion outbursts starting at least ~2 years prior to discovery.

We draw attention to ATLAS21nak (2021kgj), that was discovered by ATLAS on MJD 59322.4 (Smith et al., AstroNote 2021-131). The ATLAS light curve is currently on the rise (o=16.5), and the forced photometry at the transient location indicates some excess flux in the cyan-band 10 days prior to discovery and its fast rise. Regular survey mode observations of the field in Pan-STARRS1 show activity between MJD 59288 and 59315, confirming the pre-discovery excess seen in ATLAS. Moreover, we find evidence of past activity in PS1, with outbursts around MJD 58600 and 58960.


A optical spectrum obtained with the LT/SPRAT on MJD 59325.0 shows a blue continuum with narrow emission features of H alpha, beta and gamma. The lack of broad P-Cygni features in the spectrum suggests it is similar to that of the 2012b event in SN 2009ip (e.g. Pastorello et al. 2013, ApJ, 767, 1; Mauerhan et al. 2013, MNRAS, 430, 1801). Another spectrum taken on the UH2.2m+SNIFS on MJD 59327.4 at higher resolution confirms the narrow H-Balmer lines in emission and lack of P-Cygni absorption.

The rising light curve of ATLAS21nak suggests a current absolute orange-band magnitude of M ~ -17.5.
We encourage multi-wavelength follow-up observations of this event.

This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. The SNIFS observations were performed as a part of the Spectral Classification of Astronomical Transients (SCAT) survey (Tucker et al. ATel #11444).

 

Show current TNS values
Catalog Name Reported RA Reported DEC Reported Obj-Type Reported Redshift Host Name Host Redshift Remarks TNS RA TNS DEC TNS Obj-Type TNS Redshift
TNS 2021kgj [ATLAS21nak] 12:14:07.539 -12:35:16.91 SN IIn NGC 4188 0.014347 12:14:07.543 -12:35:16.80 SN IIn 0.014347
AstroNote Publication Timestamp Title Authors
2021-131 2021-04-20 20:04:39 ATLAS21nak (AT2021kgj): discovery of a candidate SN in NGC 4188 (65 Mpc) K. W. Smith, S. Srivastav, O. McBrien, S. J. Smartt, J. Gillanders, M. Fulton, D. R. Young, L. Shingles, M. McCollum, C. Webb (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)

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