Magnetar Engines in Fast Blue Optical Transients and Their Connections with SLSNe, SNe Ic-BL, and lGRBs

Abstract

We fit the multiband lightcurves of 40 fast blue optical transients (FBOTs) with the magnetar engine model. The mass of the FBOT ejecta, the initial spin period, and the polar magnetic field of the FBOT magnetars are respectively constrained to M ej = 0.11 − 0.09 + 0.22 M ⊙ , P i = 9.1 − 4.4 + 9.3 ms , and B p = 11 − 7 + 18 × 10 14 G . The wide distribution of the value of B <inf>p</inf> spreads the parameter ranges of the magnetars from superluminous supernovae (SLSNe) to broad-line Type Ic supernovae (SNe Ic-BL; some are observed to be associated with long-duration gamma-ray bursts), which are also suggested to be driven by magnetars. Combining FBOTs with the other transients, we find a strong universal anticorrelation of P i ∝ M ej − 0.41 , indicating they could share a common origin. To be specific, it is suspected that all of these transients originate from the collapse of extremely stripped stars in close binary systems, but with different progenitor masses. As a result, FBOTs distinguish themselves by their small ejecta masses with an upper limit of ∼1 M <inf>⊙</inf>, which leads to an observational separation in the rise time of the lightcurves of ∼10 days. In addition, FBOTs together with SLSNe can be separated from SNe Ic-BL by an empirical line in the M <inf>peak</inf>-t <inf>rise</inf> plane corresponding to an energy requirement of the mass of ⁵⁶Ni of ∼0.3M <inf>ej</inf>, where M <inf>peak</inf> is the peak absolute magnitude of the transients and t <inf>rise</inf> is the rise time.