Pre-explosion ASAS-SN V-Band Upper-Limits on SN 2013ej (PSN J01364816+1545310)

ATel #5237; B. J. Shappee, C. S. Kochanek, K. Z. Stanek, U. Basu, T. W-S. Holoien, J. Jencson, J. F. Beacom (Ohio State), J. L. Prieto (Princeton), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), M. Dubberley, M. Elphick, S. Foale, E. Hawkins, D. Mullens, W. Rosing, R. Ross, Z. Walker (Las Cumbres Observatory), J. Brimacombe (Coral Towers Observatory)
on 30 Jul 2013; 20:16 UT
Credential Certification: Benjamin Shappee (shappee@astronomy.ohio-state.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"; ATel #4987, #4999, #5010, #5082, #5102, #5110, #5138), using data from the double 14-cm "Brutus" telescope in Haleakala, Hawaii, we have observed the field containing M74 repeatedly over the past 50 days. Most recently we observed this field on 2013 UT July 19.54 and 23.54, 5.91 and 1.91 days before the discovery image of SN 2013ej (PSN J01364816+1545310; ATel #5228, #5229, #5230), respectively. For both of these observations our automated pipeline did not trigger on any new sources in M74 which constrains any new source to be fainter than V > 16.5 mag at these epochs.

Re-analysis of both epochs yields stronger upper-limits on the flux of any new source at the location of SN 2013ej of:

 
UT Date   Disc.     V mag limit 
2013 July 19.54     > 17.2 
2013 July 23.54     > 16.7 

These formal limits were confirmed by locating asteroids in the images with the same approximate magnitude as our limits. When combined with other early-time data these observations will help to constrain the time of explosion of SN 2013ej.