[vsnet-alert 17486] ASASSN-14du (ATEL)

[Taichi Kato]

ASASSN-14du (ATEL)

   The presence of GALEX counterpart might also suggest
a high-amplitude dwarf nova.

===

ATEL #6308                                                           ATEL #6308

Title:  ASAS-SN Discovery of a Possible Extreme Luminosity Transient
Author: 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)
Queries:        tholoien at astronomy.ohio-state.edu
Posted: 11 Jul 2014; 22:07 UT
Subjects:Optical, Supernovae, Transient

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
<a href=http://www.astronomy.ohio-state.edu/~assassin/followup/asassn-14du.png>figure</a>
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 <a href=http://skyserver.sdss3.org/dr9/en
/tools/explore/obj.asp?id=1237661362370904582>here</a>.)
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 <a href=http://www.astronomy.ohio-state.edu/~assassin/index.shtml>ASAS-SN
Homepage</a> and the list of all <a href=http://www.astronomy.ohio-state.edu/~assassin/transients.html>ASAS-SN
transients</a>.