FLASH Talks: Massive X-ray flares from the coldest stars: What powers these outbursts? (Adam Burgasser) & Bumpy Declining Light Curves are Common in Hydrogen-poor Superluminous Supernovae (Griffin Hosseinzadeh)

Friday, 29 October 2021 noon — 1 p.m. MST

FLASH Talks
Adam Burgasser (UCSD) & Griffin Hosseinzadeh (UoA)
Griffin Hosseinzadeh, Steward Observatory
Bumpy Declining Light Curves are Common in Hydrogen-poor Superluminous Supernovae
Recent work has revealed that the light curves of hydrogen-poor (Type I) superluminous supernovae (SLSNe), thought to be powered by magnetar central engines, do not always follow the smooth decline predicted by a simple magnetar spin-down model. Here I will present the first systematic study of the prevalence and properties of "bumps" in the post-peak light curves of 34 SLSNe. We find that the majority (44-76%) of events cannot be explained by a smooth magnetar model alone. By fitting a simple Gaussian model to the light curve residuals, we characterize each bump with an amplitude, temperature, phase, and duration. We then explore whether the cause of these bumps is intrinsic to the supernova (e.g., a variable central engine) or extrinsic (e.g., circumstellar interaction) by investigating correlations between these bump parameters and the parameters of the underlying explosion. Both cases are plausible, requiring low-level variability in the magnetar input luminosity, small decreases in the ejecta opacity, or a thin circumstellar shell or disk. I will also describe our new photometric classification tool, Superphot, which will enable us to increase the sample size of these rare events by orders of magnitude when observations start at Vera Rubin Observatory.
 
Adam Burgasser, UCSD
Massive X-ray flares from the coldest stars: What powers these outbursts?
Magnetic emission, including flares, are common among the lowest-mass M stars, but declines sharply at the M dwarf/L dwarf transition due to a decline in photospheric ionization. Yet we are increasingly detecting some of the most energetic stellar flares from stars below the ionization threshold, including recently detected X-ray "superflares" from three distant L dwarfs. Why are these objects so active? Are they young and actively accreting? Are they interacting with unseen companions? Are these outbursts related to aurora-like radio emission detected among many brown dwarfs? We report on spectroscopic follow-up of X-ray flaring L dwarfs that suggest that these objects are surprisingly old, suggesting that magnetic emission near the hydrogen-burning limit depends on mass more than age.
 
Related publication: De Luca, Beate, Burgasser, et al. 2020, A&A 634, L13 "EXTraS discovery of an X-ray superflare from an L dwarf" https://ui.adsabs.harvard.edu/abs/2020A%26A...634L..13D/abstract

FLASH Talks are scientific talks for the staff at NOIRLab and the University of Arizona's Steward Observatory. For the Zoom link, please email Parker Fagrelius.