MUSSES2020J: The Earliest Discovery of a Fast Blue Ultraluminous Transient at Redshift 1.063

Abstract

In this Letter, we report the discovery of an ultraluminous fast-evolving transient in rest-frame UV wavelengths, MUSSES2020J, soon after its occurrence by using the Hyper Suprime-Cam (HSC) mounted on the 8.2 m Subaru telescope. The rise time of about 5 days with an extremely high UV peak luminosity shares similarities to a handful of fast blue optical transients whose peak luminosities are comparable with the most luminous supernovae while their timescales are significantly shorter (hereafter “fast blue ultraluminous transient,” FBUT). In addition, MUSSES2020J is located near the center of a normal low-mass galaxy at a redshift of 1.063, suggesting a possible connection between the energy source of MUSSES2020J and the central part of the host galaxy. Possible physical mechanisms powering this extreme transient such as a wind-driven tidal disruption event and an interaction between supernova and circumstellar material are qualitatively discussed based on the first multiband early-phase light curve of FBUTs, although whether the scenarios can quantitatively explain the early photometric behavior of MUSSES2020J requires systematical theoretical investigations. Thanks to the ultrahigh luminosity in UV and blue optical wavelengths of these extreme transients, a promising number of FBUTs from the local to the high-z universe can be discovered through deep wide-field optical surveys in the near future.

Dust Echoes from Luminous Fast Blue Optical Transients

“…where t is measured from the onset of the explosion and L pk and t pk are the peak luminosity and peak/rise time of the transient, respectively. This rise law is roughly consistent with that measured for the extremely luminous LFBOT-like transient MUSSES2020J (Jiang et al 2022) though we caution that early dust attenuation could act to steepen the observed rise compared to the intrinsic one (we return to possible observational evidence for such early attenuation in Section 4).…”

“…A possible test of this prediction came with the discovery of the extremely luminous LFBOT candidate MUSSES2020J (Jiang et al 2022) four days prior to the optical maximum. Contrary to the naive expectation of hotter UV/optical emission at early times after the explosion while the photosphere is still compact, MUSSES2020J exhibited substantially redder colors (g − r  0) four days before optical peak, when the transient luminosity was 10 44 erg s −1 , than near the peak itself (g − r ≈ − 0.5).…”

“…Over the last few years, additional LFBOTs have been discovered, which exhibit qualitatively similar multiwavelength properties to AT2018cow, including CSS161010 (Coppejans et al 2020), AT2018lug ("Koala"; Ho et al 2020), AT2020xnd (Ho et al 2022;Bright et al 2022;Perley et al 2021), and AT2020mrf (Yao et al 2022), albeit with a wide range of X-ray luminosities and fastest ejecta speeds implied by their radio/millimeter emissions. An LFBOT-like optical/UV transient, MUSSES2020J, was recently discovered, which reached an even higher peak luminosity ∼10 46 erg s −1 with the final light-curve rise by a factor of 100 captured over just 5 days (Jiang et al 2022) though the identification of this event as an LFBOT is not certain because of the lack of multiwavelength data. To summarize the physical picture that has emerged from detailed modeling (e.g., Margutti et al 2019): AT2018cow and other LFBOTs are engine-powered explosions that generate highly aspherical ejecta spanning a wide range of velocities, propagating into a dense, radially extended preexisting CSM.…”

On the Origin of the Strong Optical Variability of Emission-line Galaxies

“…However, the required transients would be extreme SNe II events at the bright end, which could be quite rare. Overall, the above estimations imply that luminous SNe II would bring in the strong variability of our var-ELGs, while we could not rule out the contribution from faint AGN or other luminous transient events, e.g., the ultraluminous fast blue optical transient (FBOT) reported recently by Jiang et al (2022).…”

AT 2022aedm and a New Class of Luminous, Fast-cooling Transients in Elliptical Galaxies

“…A more mysterious population of fast transients has also been uncovered, with blue colors and a wide range of peak luminosities up to M < −20 mag, approaching superluminous SNe (SLSNe; Quimby et al 2011;Gal-Yam 2019). Since their identification in Pan-STARRS1 (PS1) by Drout et al (2014), such objects have been discovered in data from the Palomar Transient Factory and the Supernova Legacy Survey (Arcavi et al 2016), the Dark Energy Survey (DES; Pursiainen et al 2018), ATLAS (Prentice et al 2018), Kepler (Rest et al 2018), Hyper Suprime Cam (HSC; Tampo et al 2020;Jiang et al 2022) and ZTF (Ho et al 2023). They have been termed fast blue optical transients or rapidly evolving transients (RETs).…”