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tokens: behind the Sun. Our data include 48 epochs taken before the discovery, starting on 2003 December [upper limit from the Sloan Digital Sky Survey (SDSS) DR9 4 ] up to 2012 March. These data were taken mainly by amateur astronomers. One epoch was secured using the Ultraviolet and Optical Telescope on board the Swift satellite on 2013 September 05.65. However, only upper limits were estimated for the UVW2 (>20.9 mag) and UVW1 (>20.0 mag) bands (V egamag ). Photometric observations were preprocessed following the standard recipe in iraf 5 for CCD images (trimming, overscan, bias, and flat-field corrections). For the NIR exposures, we also applied an illumination correction and background-sky subtraction. For later epochs, multiple exposures obtained in the same night and filter were combined to improve the signal-to-noise ratio (S/N). The SN magnitudes were measured using point-spread-function (PSF) fitting with SNO o P y . 6 No template subtraction was performed since no major differences were found when comparing the photometry obtained through both PSF fitting and template subtraction. The data derived with the two methods are in agreement to within 0.1 mag. In order to calibrate the instrumental magnitudes to standard photometric systems, we used the zero-points and colour terms measured through reference SDSS stars in the field of SNhunt151. The Johnson–Cousins magnitudes of these reference stars were calculated from the Sloan magnitudes following the conversions of Chonis Gaskell ( 2008 ). For the NIR photometry, we used the Two Micron All Sky Survey (2MASS) catalogue as reference for the calibration. Once the local sequence was calibrated, we proceeded to calibrate our transient, even for non-photometric nights. Unfiltered magnitudes from amateurs were scaled to Johnson–Cousins V - or R -band magnitudes, depending on the wavelength peak efficiency of the detectors. Uncertainty estimates were obtained through artificial-star experiments. This is combined (in quadrature) with the PSF fit error returned by daophot and the propagated errors from the photometric calibration. The final calibrated SN magnitudes are listed in Tables B2 and B5 for the optical bands, and in Table B4 for the NIR range. 3.2 Space-Based Observations The SNhunt151 site was also observed by the Hubble Space Telescope ( HST ) with the Ultraviolet-Visible (UVIS; ∼ 0.04 arcsec pixel −1 ) Channel of the Wide-Field Camera 3 (WFC3) in the F 555 W and F 814 W bands. These images were taken on 2016 October 23 as part of the SN snapshot survey GO-14668 (PI: A. V. Filippenko), 1113.1 d after the V -band peak of SNhunt151's Event B (see below). A source was detected at the transient position in all images with root-mean-square uncertainties 0.01 arcsec (Fig. 1 d), through comparison with ground-based, post-discovery Copernico Telescope+AFOSC, and NOT+ALFOSC images taken on 2013 August 31 (seeing 1.16 arcsec) and 2014 August 24 (seeing 0.96 arcsec). The magnitudes of the source in