Type II supernovae (SNe) originate from the explosion of hydrogen-rich
supergiant massive stars. Their first electromagnetic signature is the shock
breakout, a short-lived phenomenon which can last from hours to days depending
on the density at shock emergence. We present 26 rising optical light curves of
SN II candidates discovered shortly after explosion by the High cadence
Transient Survey (HiTS) and derive physical parameters based on hydrodynamical
models using a Bayesian approach. We observe a steep rise of a few days in 24
out of 26 SN II candidates, indicating the systematic detection of shock
breakouts in a dense circumstellar matter consistent with a mass loss rate
$\dot{M} > 10^{-4} M_\odot yr^{-1}$ or a dense atmosphere. This implies that
the characteristic hour timescale signature of stellar envelope SBOs may be
rare in nature and could be delayed into longer-lived circumstellar material
shock breakouts in most Type II SNe.

通过高灵敏度短时变量调查发现，26 个 II 型超新星候选物在光学上有瞬时增亮现象，通过 Bayesian 方法分析其理论参数，发现在绝大多数情况下，其密致的周围环境使得主要特征的时标延迟到 longer-lived 环境中的冲击爆发。

大部份 II 型超新星中，因周围恒星物质所致的激波爆发延迟

The delay of shock breakout due to circumstellar material seen in most  Type II Supernovae

Shock breakout is the brightest radiative phenomenon in a supernova (SN) but
is difficult to be observed owing to the short duration and X-ray/ultraviolet
(UV)-peaked spectra. After the first observation from the rising phase reported
in 2008, its observability at high redshift is attracting enormous attention.
We perform multigroup radiation hydrodynamics calculations of explosions for
evolutionary presupernova models with various main-sequence masses $M_{\rm
MS}$, metallicities $Z$, and explosion energies $E$. We present multicolor
light curves of shock breakout in Type II plateau SNe, being the most frequent
core-collapse SNe, and predict apparent multicolor light curves of shock
breakout at various redshifts $z$. We derive the observable SN rate and
reachable redshift as functions of filter $x$ and limiting magnitude $m_{x,{\rm
lim}}$ by taking into account an initial mass function, cosmic star formation
history, intergalactic absorption, and host galaxy extinction. We propose a
realistic survey strategy optimized for shock breakout. For example, the
$g'$-band observable SN rate for $m_{g',{\rm lim}}=27.5$ mag is 3.3 SNe
degree$^{-2}$ day$^{-1}$ and a half of them locates at $z\geq1.2$. It is clear
that the shock breakout is a beneficial clue to probe high-$z$ core-collapse
SNe. We also establish ways to identify shock breakout and constrain SN
properties from the observations of shock breakout, brightness, time scale, and
color. We emphasize that the multicolor observations in blue optical bands with
$\sim$ hour intervals, preferably over $\geq2$ continuous nights, are essential
to efficiently detect, identify, and interpret shock breakout.

本文研究了超新星中最明亮的辐射现象 - 冲击爆发，通过多色光度学计算预测了各个红移下的冲击爆发的光度曲线，并在此基础上提出了一种针对冲击爆发优化的实际调查策略。此外，文章还阐明了利用发现的冲击爆发的亮度、时间尺度和颜色来确定超新星属性的方法，特别强调了在蓝光带中进行多色观测的重要性。