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ASAS-SN Discovery of ASASSN-13cj, Swift follow-up and du Pont spectroscopic classifications of ASASSN-13ch and ASASSN-13cj as SN Ia

ATel #5343; J. L. Prieto (Princeton), N. Morrell (LCO), K. Z. Stanek, B. J. Shappee, C. S. Kochanek, T. W-S. Holoien, J. Jencson, U. Basu, J. F. Beacom (Ohio State), D. Grupe (Penn State), 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 Aug 2013; 03:20 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 double 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source:

Object        RA (J2000)    DEC (J2000)   Disc. UT Date    Disc. V mag    
ASASSN-13cj  16:17:11.01   +04:33:14.72    Aug. 27.27        15.3 
This transient was also detected in images obtained UT Aug. 15 (V=16.4), Aug. 21 (V=15.4) and (after discovery) Aug. 29 (V=15.3), but undetected (V > 17 mag) in images obtained Aug. 9 and earlier. After our discovery we obtained a Swift TOO observation of the transient on UT Aug. 27.7. The UVOT optical/UV magnitudes of the source, measured using a r=5" aperture, were: v=14.87 +/- 0.03, b=15.05 +/- 0.03, u=14.97 +/- 0.03, uvw1=16.56 +/- 0.07, uvm2=18.14 +/- 0.13, uvw2=17.73 +/- 0.08 (uncorrected for extinction). Since the source is located in the center of its bright host, the E/S0 galaxy SDSS J161711.04+043314.7, the Swift v-band magnitude is likely brighter than ASAS-SN V-band because of host contamination.

Follow-up spectroscopic observations were obtained on UT Aug. 30.0 by N. Morrell. We observed ASASSN-13cj (this telegram) and ASASSN-13ch (ATel #5333, #5334) with WFCCD (range 3700-9200 Angs; FWHM resolution 7 Angs) mounted on the du Pont 2.5m telescope at LCO. The spectra of both transients are of Type Ia SNe around maximum light. After cross-correlating with a library of SN spectra using SNID (Blondin & Tonry 2007) we find that they are both consistent with normal Type Ia SNe at maximum. The measured SNID redshift of ASASSN-13cj is 0.018 +/- 0.005 and we do not find any strong nebular galaxy lines to measure a secure spectroscopic redshift.

We also obtained a Swift TOO observation of ASASSN-13ch on UT Aug. 28.7. The UVOT optical/UV magnitudes of the source, measured using a r=5" aperture, were: v=15.59 +/- 0.05, b=15.59 +/- 0.03, u=15.30 +/- 0.04, and uvw1=16.79 +/- 0.07 (uncorrected for extinction). The source is undetected in uvm2 and strongly contaminated with host galaxy light in uvw2.

We thank the Swift team for scheduling our observations. For more information about the ASAS-SN project see ASAS-SN Homepage and also ASAS-SN Transients page.