Swift Observations and Spectroscopic Classification of ASASSN-14ax as a SN Ia
ATel #6143; B. J. Shappee, M. Fausnaugh, S. Villanueva, T. W-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. Jencson, U. Basu, B. Davis, J. F. Beacom (Ohio State), J. L. Prieto (Princeton), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), J. Brimacombe (Coral Towers Observatory), D. Bersier (LJMU)
on 16 May 2014; 03:43 UT
Credential Certification: Benjamin Shappee (shappee@astronomy.ohio-state.edu)
Subjects: Optical, Ultra-Violet, Supernovae
Referred to by ATel #: 6144
We have obtained a medium-resolution optical spectrum (range 4300-5700 Angstroms) of ASASSN-14ax (ATel #6133) on UT 2014 May 15.4 through a 5" slit with the CCDS spectrograph mounted on the MDM 1.3m telescope. The spectrum shows features characteristic of Type Ia SNe. We used SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) to perform cross-correlation with a library of SN spectra and find that the spectrum of ASASSN-14ax is most consistent with a normal SN Ia a few days after peak. The best-fit redshift for the supernova is z=0.029 +/- 0.004. This is marginally consistent with the PhotZ of the host galaxy of 0.058 +/- 0.026 from SDSS.
We also applied for and obtained a Swift TOO observation of the transient on UT 2014 May 14.02. The UVOT optical/UV magnitudes of the source, measured using a r=5" aperture, were: v=16.34 +/- 0.08 (stat) +/- 0.01 (sys), b=16.48 +/- 0.05 (stat) +/- 0.02 (sys), u=16.32 +/- 0.06 (stat) +/- 0.02 (sys), uvw1=17.30 +/- 0.09 (stat) +/- 0.03 (sys), uvm2=17.88 +/- 0.11 (stat) +/- 0.03 (sys), uvw2=17.82 +/- 0.09 (stat) +/- 0.03 (sys). These magnitudes are uncorrected for extinction or host galaxy contamination. Since the source is located in the center of its host, the Swift v-band magnitude is likely brighter than the reported ASAS-SN V-band (16.5) because of host contamination. We also note that the uvw2 - V color, 1.48 +/- 0.12, is significantly bluer than that of normal SNe Ia (uvw2 - V > 2.0; Figure 2 of Milne et al. 2013).
Finally, our spectra also presented narrow-line [O III] 5007 and H-beta emission redshifted by z=0.033 (consistent with our best-fit redshift). Using this redshift and the Swift v-band magnitude we estimate an absolute magnitude V mag of approx. -19.51 (m-M=35.72, A_V=0.134, Schlafly & Finkbeiner 2011).
Continued observations are encouraged.
