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Constraints on the Position of Supernova 2016adj in NGC 5128 from Keck-II NIRC2 Adaptive Optics Observations

ATel #8720; Patrick L. Kelly (UCB), David R. Ciardi (NExScI/CIT), Charles A. Beichman (NExScI/CIT), Alexei V. Filippenko (UCB), Ori D. Fox (STScI), Rahul I. Patel (NExScI/CIT), Evan Sinukoff (UH)
on 22 Feb 2016; 02:17 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Patrick Kelly (pkelly@astro.berkeley.edu)

Subjects: Infra-Red, Optical, Star, Supernovae

Referred to by ATel #: 8759

On 17 February 2016 UT, we acquired K-band images of SN 2016adj in NGC 5128 (Centaurus A) with the Near-Infrared Camera 2 (NIRC2) on the Keck-II 10-m telescope in conjunction with the adaptive optics system. After correcting exposures for astrometric distortion, we cross registered sources in the stacked 40'' x 40'' NIRC2 exposures with sources in archival Hubble Space Telescope (HST) WFC3 F814W images. The stacked NIRC2 images were acquired at an average airmass of 2.19, and the combined image has a point-spread function (PSF) with a FWHM of 0.15''.

An astrometric fit using 27 common sources yields a residual distribution with root-mean-square scatter of 0.028'' in RA and 0.029'' in Dec. We measure a position for SN 2016adj of RA = 13:25:24.118 and Dec = -43:00:57.96 (J2000) with these uncertainties in the World Coordinate System (WCS) of the drizzled image hst_11360_rc_wfc3_uvis_f814w_drz.fits available from the HST archive. Cutouts of WFC3 F814W and F160W coadded images showing the position of the supernova and uncertainties are available at http://astro.berkeley.edu/~pkelly/F814W_16adj.png and http://astro.berkeley.edu/~pkelly/F160W_16adj.png.

The constraints on the position of SN 2016adj are consistent within ~2 sigma with the coordinates of a resolved source in the F814W image having approximate coordinates RA = 13:25:24.119 and Dec = -43:00:57.90 in the same WCS. At a distance of 3.42 Mpc (Ferrarese et al. 2007, ApJ, 654, 186), the potential progenitor would have an approximate I-band absolute magnitude of -7.4 < M_I < -6.2 (Vega), given the extinction of A_V ~ 2-4 mag suggested by ATel #8657. ATel #8693 has previously claimed the possible detection of a progenitor with a similar absolute magnitude but did not report any position.