Multiwavelength Analysis of Six Luminous, Fast Blue Optical Transients

Abstract: We present multiwavelength observations and analysis of six luminous fast blue optical transients (LFBOTs) discovered in Zwicky Transient Facility (ZTF) survey data. We identified these LFBOTs from their fast light-curve evolution ($t_{1/2}\leq 12$d), blue colors at peak brightness ($g-r\leq-0.5$mag), a visible host galaxy, high optical luminosity ($M_g&lt;-20$), and an X-ray or radio detection. With the exception of AT2024aehp (ZTF24abygbss), these transients exhibit peaks in their $10\,$GHz radio light curves at $t_{\text{rest}} \approx 50-100$ d, with peak radio luminosities ranging from $10<sup>{38}-10<sup>{40}$ erg s$<sup>{-1}$. Modeling the radio emission as synchrotron radiation indicates a fast ($v=0.1-0.3c$) shock in a dense ($n_e\approx10<sup>{3}-10<sup>{4}$ cm$<sup>{-3}$) medium. The X-ray emission varies by $\approx2$ orders of magnitude in luminosity ($10<sup>{42}-10<sup>{44}$ erg s$<sup>{-1}$) at $t_{\text{rest}}\sim20$d. Analysis of the host-galaxy photometry and spectroscopy for each transient shows that they are predominantly nonnuclear (a few kpc offset) with star-forming host galaxies of stellar masses $10^{{9}-10^{11}} ,M_\odot$. Unlike all other LFBOTs to date, AT2024aehp exhibited a luminous ($M&lt;-19 $mag) plateau in the optical light curve; spectra during this plateau phase showed a featureless blue continuum. The $6-15$ GHz radio emission of AT2024aehp brightened by over an order of magnitude from $t_{\text{rest}} \approx70$d to $t_{\mathrm{rest}} \approx130$d. The mostly consistent radio behavior between optically selected LFBOTs implies a similar circumburst medium, leading us to prefer a progenitor scenario in which mass is lost in a consistent way shortly prior to the terminal event, such as a massive star merging with a compact object.