We present multi-wavelength observations of the tidal disruption event (TDE) iPTF15af, discovered by the intermediate Palomar Transient Factory (iPTF) survey at redshift z=0.07897. The optical and ultraviolet (UV) light curves of the transient show a slow decay over five months, in agreement with previous optically discovered TDEs. It also has a comparable black-body peak luminosity of Lpeak≈1.5×1044 erg/s. The inferred temperature from the optical and UV data shows a value of (3−5) ×104 K. The transient is not detected in X-rays up to LX<3×1042erg/s within the first five months after discovery. The optical spectra exhibit two distinct broad emission lines in the He II region, and at later times also Hα emission. Additionally, emission from [N III] and [O III] is detected, likely produced by the Bowen fluorescence effect. UV spectra reveal broad emission and absorption lines associated with high-ionization states of N V, C IV, Si IV, and possibly P V. These features, analogous to those of broad absorption line quasars (BAL QSOs), require an absorber with column densities NH>1023 cm−2. This optically thick gas would also explain the non-detection in soft X-rays. The profile of the absorption lines with the highest column density material at the largest velocity is opposite that of BAL QSOs. We suggest that radiation pressure generated by the TDE flare at early times could have provided the initial acceleration mechanism for this gas. Spectral UV line monitoring of future TDEs could test this proposal.
@article{arxiv.1809.07446,
title = {The Broad Absorption Line Tidal Disruption Event iPTF15af: Optical and Ultraviolet Evolution},
author = {N. Blagorodnova and S. B. Cenko and S. R. Kulkarni and I. Arcavi and J. S. Bloom and G. Duggan and A. V. Filippenko and C. Fremling and A. Horesh and G. Hosseinzadeh and E. Karamehmetoglu and A. Levan and F. J. Masci and P. E. Nugent and D. R. Pasham and S. Veilleux and R. Walters and L. Yan and W. Zheng},
journal= {arXiv preprint arXiv:1809.07446},
year = {2020}
}