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Miller, A. A.

Publications and source records attributed to Miller, A. A..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The complex circumstellar environment of supernova 2023ixf

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare, followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating. Early serendipitous observations that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here, in this study, we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients

We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day < t 1/2 < 12 days, of which 28 have blue ( g – r ≲ –0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H α in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF’s SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Constraining Type Ia supernova explosions and early flux excesses with the Zwicky Transient Factory

In the new era of time-domain surveys, Type Ia supernovae are being caught sooner after explosion, which has exposed significant variation in their early light curves. Two driving factors for early-time evolution are the distribution of 56 Ni in the ejecta and the presence of flux excesses of various causes. We perform an analysis of the largest young SN Ia sample to date. We compare 115 SN Ia light curves from the Zwicky Transient Facility to the turtls model grid containing light curves of Chandrasekhar mass explosions with a range of 56 Ni masses, 56 Ni distributions, and explosion energies. We find that the majority of our observed light curves are well reproduced by Chandrasekhar mass explosion models with a preference for highly extended 56 Ni distributions. We identify six SNe Ia with an early-time flux excess in our gr-band data (four ‘blue’ and two ‘red’ flux excesses). We find an intrinsic rate of 18 ± 11 percent of early flux excesses in SNe Ia at z < 0.07, based on three detected flux excesses out of 30 (10 percent) observed SNe Ia with a simulated efficiency of 57 percent. This is comparable to rates of flux excesses in the literature but also accounts for detection efficiencies. Two of these events are mostly consistent with circumstellar material interaction, while the other four have longer lifetimes in agreement with companion interaction and 56 Ni-clump models. We find a higher frequency of flux excesses in 91T/99aa-like events (44 ± 13 percent).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq

Early observations of Type Ia supernovae (SNe Ia) provide essential clues for understanding the progenitor system that gave rise to the terminal thermonuclear explosion. Here, we present exquisite observations of SN 2019yvq, the second observed SN Ia, after iPTF 14atg, to display an early flash of emission in the ultraviolet (UV) and optical. Our analysis finds that SN 2019yvq was unusual, even when ignoring the initial flash, in that it was moderately underluminous for a SN Ia ($M_g \approx -18.5$ mag at peak) yet featured very high absorption velocities ($v \approx 15,0000$ km s -1 for Si II λ6355 at peak). We find that many of the observational features of SN 2019yvq, aside from the flash, can be explained if the explosive yield of radioactive 56 Ni is relatively low (we measure $M_{^{56}\mathrm{Ni}} = 0.31 \pm 0.05\,M_\odot$) and it and other iron-group elements are concentrated in the innermost layers of the ejecta. To explain both the UV/optical flash and peak properties of SN 2019yvq we consider four different models: interaction between the SN ejecta and a nondegenerate companion, extended clumps of 56 Ni in the outer ejecta, a double-detonation explosion, and the violent merger of two white dwarfs. Each of these models has shortcomings when compared to the observations; it is clear additional tuning is required to better match SN 2019yvq. In closing, we predict that the nebular spectra of SN 2019yvq will feature either H or He emission, if the ejecta collided with a companion, strong [Ca II] emission, if it was a double detonation, or narrow [O I] emission, if it was due to a violent merger.

79 ASTRONOMY AND ASTROPHYSICS↗