AstroNote 2021-74

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2021-02-22 18:57:28
Type: Object/s-Discovery/Classification
ATLAS21grj (AT2021dnn): discovery of a candidate supernova in NGC 0304 (65 Mpc)
Authors: S. Srivastav, K. W. Smith, 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)
Source Group: ATLAS
Keywords: Supernova
Here we report the ATLAS discovery of the transient ATLAS21grj (AT2021dnn) in galaxy NGC 0304 at magnitude o = 15.71 +/- 0.03. At a distance of 65 Mpc, the transient was discovered on MJD = 59267.23 (2021-02-22.23) with an absolute magnitude of M = -18.5 +/- 0.2. The last non-detection through forced photometry was on MJD = 59243.28. Spectroscopic classification is encouraged.

ATLAS is a twin 0.5m telescope system on Haleakala and Mauna Loa which is robotically surveying the sky above declination -40 with a cadence of 2 days (Tonry et al. 2018, PASP,130:064505). Two filters are used, cyan and orange (denoted c and o; all mags quoted are in the AB system). While carrying out the primary mission for Near Earth Objects, we search for and publicly report stationary transients to the IAU Transient Name Server.  Data processing is carried out at Queen's University which combines automated source parameter filtering, machine learning image recognition, and spatial cross-matching with astronomical catalogues (Smith et al. 2020, PASP, 132:085002). More information is on the ATLAS homepage. We are submitting AstroNotes for transients that are either within 100 Mpc, or have some other interesting feature to bring to the community's attention, such as bright nuclear transients, slowly rising or rapidly fading objects.

We report a new transient source, most likely a supernova in the galaxy NGC 0304. We discovered ATLAS21grj (AT2021dnn) on MJD 59267.23 == 2021-02-22.23, at m_o = 15.71 +/- 0.03. There was no detection by ATLAS on MJD 59243.28 == 2021-01-29.28. ATLAS21grj is offset by 5.5 arcsec south, 3.4 arcsec east from its likely host galaxy NGC 0304, which is at z = 0.017 or d = 65 Mpc (from NED), implying an absolute magnitude of M = -18.5 (assuming m-M = 34.06 and A_r = 0.12 and A_i = 0.09). A finder and forced photometry plot are attached, followup observations are encouraged.  

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. 

Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2021dnn [ATLAS21grj]00:56:06.282+24:07:31.1800:56:06.282+24:07:31.18SN Ia0.016648