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ASAS-SN Discovery of Luminous Transient in SDSS J110840.11+340552.2

ATel #5831; J. L. Prieto (Princeton), D. Bersier (LJMU), T. W.-S. Holoien, B. J. Shappee, K. Z Stanek, C. S. Kochanek, J. Jencson, U. Basu J. F. Beacom (Ohio State), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), J. Brimacombe (Coral Towers Observatory)
on 29 Jan 2014; 19:49 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

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 in the center of SDSS J110840.11+340552.2:

Object       RA (J2000)   DEC (J2000)    Disc. UT Date   Disc. V mag  
ASASSN-14ae  11:08:39.96  +34:05:52.7     Jan. 25.51       16.96 

ASASSN-14ae was discovered in images obtained 2013 UT Jan. 25.51 at V~17 mag. The object was also detected, at approx. the same magnitude, on UT Jan. 24. The source is undetected (V>17 mag) in previous data taken at this location obtained on UT Jan. 1 and earlier. Images obtained on UT Jan 27 with the LCOGT-1m robotic telescope at McDonald observatory and with the LT-2m telescope confirm the detection of the new transient. This figure shows the ASAS-SN V-band reference image (top left), ASAS-SN V-band discovery subtraction image (top right), SDSS g-band prediscovery image (bottom left), and LT-2m g-band confirmation image (bottom right).

After our discovery, we obtained a 3ks Swift TOO observation of the transient on UT Jan 27.9. The UVOT optical/UV magnitudes of the source, measured using a r=5" aperture, were: v=16.43 +/- 0.05, b=16.70 +/- 0.04, u=15.58 +/- 0.04, uvw1=15.10 +/- 0.03, uvm2=14.76 +/- 0.02, uvw2=15.05 +/- 0.02 (uncorrected for extinction). The average coordinates of the source measured in the UVOT images are RA = 11:08:40.11, DEC = +34:05:52.4 (J2000), only 0.18" from the center of its host galaxy. This figure shows the detection of the transient in the Swift/UVOT filters. From the Swift measurements and the prediscovery imaging of the host galaxy (SDSS and 2MASS) we obtain an SED before and after discovery (see this figure) which shows that the transient is quite blue.

We also obtained an optical spectrum (range 3500-9800 Angstroms; FWHM res. 7 Angstroms) of ASASSN-14ae on UT Jan 29.2 with DIS mounted on the APO 3.5m telescope. The spectrum shows a blue continuum (Teff ~ 14500 K, fitting the blue part of the spectrum) with a broad, relatively weak P-Cygni feature consistent with H-alpha. After correcting for the redshift of the host galaxy (z=0.0436 from SDSS), we measure a velocity of -15000 km/s for the H-alpha absorption trough. A plot with the optical spectrum can be found here. The blue continuum and relatively weak H-alpha detection make this transient consistent with a young Type II supernova. Given the distance to the host galaxy (d ~ 180 Mpc) and apparent magnitude, it is a luminous event with absolute V mag -19.9 (absolute U mag approx. -21). While a young Type II SN seems the most likely interpretation, the proximity to the galactic nucleus makes a tidal capture transient a potential alternative.

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