ASAS-SN Discovery of a Possible Extreme Luminosity Transient

ATel #6308; T. W.-S. Holoien, K. Z. Stanek, B. J. Shappee, C. S. Kochanek, A. B. Davis, J. Jencson, U. Basu, J. F. Beacom (Ohio State), J. L. Prieto (Universidad Diego Portales), D. Bersier (LJMU), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory)
on 11 Jul 2014; 22:07 UT
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source, possibly of extreme luminosity, coincident with the galaxy SDSS J131901.64+470057.5:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-14du  13:19:01.552   +47:00:56.7       2014-07-08.27     16.1 

ASASSN-14du was discovered in images obtained 2014 UT July 08.27 at V~16.1 mag. We also detect the object in images obtained on July 10.26 (V~16.4), July 10.27 (V~16.1), and July 11.26 (V~16.4), but we do not detect this object (V>17.5) in images taken on 2014 UT June 27.31 and before. This figure shows the ASAS-SN reference image (top-left), archival SDSS g-band image (top-right), ASAS-SN July 08 discovery image (bottom-left), and ASAS-SN July 10 confirmation image (bottom-right). The red circle is centered on the ASAS-SN position of the transient.

The ASAS-SN position of ASASSN-14du is approximately 1.0" South and 1.0" West from the core of SDSS J131901.64+470057.5, a faint (g~22.23 mag) galaxy with no spectroscopic redshift. (See the SDSS page here.) There is no variation reported at this location in CRTS or NEAT data, but there is a source with NUV~22.7 mag detected in GALEX data at these coordinates. The galaxy has a PhotoZ of z=0.186432 +/- 0.078048, which would give the transient an absolute V magnitude (before K-correction) of approx. -23.8 (m-M=39.8, A_V=0.02, Schlafly & Finkbeiner 2011) if we assume this redshift to be correct. Assuming a more modest redshift of z=0.1 gives an absolute V magnitude of approx. -22.3, meaning this transient is possibly extremely luminous even if the actual redshift of the source is significantly lower.

Follow-up observations, particularly spectroscopy, are highly encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.