Early-phase Type Ia supernovae (SNe Ia), especially those with luminosity enhancement within the first few days of explosions ("early-excess SNe Ia"), play an irreplaceable role in addressing the ...long-standing progenitor and explosion issue of SNe Ia. In this paper, we systematically investigate 11 early-excess SNe Ia from subluminous to luminous subclasses. Eight of them are selected from 23 SNe Ia with extremely early-phase optical light curves ("golden" early-phase SNe Ia), and three of them are selected from 40 SNe Ia (including 14 golden samples) with early-phase UV/NUV light curves. We found that previously discovered early-excess SNe Ia show a clear preference for specific SN Ia subclasses. In particular, the early-excess feature shown in all six luminous (91T- and 99aa-like) SNe Ia is in conflict with the viewing angle dependence predicted by the companion-ejecta interaction scenario. Instead, such a high early-excess fraction is likely related to the explosion physics of luminous SNe Ia; i.e., a more efficient detonation happening in the progenitor of luminous SNe Ia may consequently account for the early-excess feature powered by the radiation from a 56Ni-abundant outer layer. The diversity of early-excess features shown in different SN Ia subclasses suggests multiple origins of the discovered early-excess SNe Ia, challenging their applicability as a robust progenitor indicator. Further understanding of the early-excess diversity relies not only on multiband photometry and prompt-response spectroscopy of individual early-excess SNe Ia but also on investigations of the general early-phase light-curve behavior of each SN Ia subclass, which can be realized through ongoing/forthcoming transient survey projects in the near future.
The mechanism for the blue and excessive early-phase emission reported within the first few days of several Type Ia supernovae (SNe Ia) has been suggested to be the interaction of the SN ejecta with ...either a non-degenerate companion star or circumstellar media (CSM). Recently, another mechanism has been suggested within the context of the He-detonation-triggered SN scenario (i.e., the double-detonation scenario or He-ignited violent merger), in which the radioactive isotopes in the outermost layer of the SN ejecta produce the early emission. In this paper, we investigate the properties of the excessive early-phase emission predicted by these different scenarios. The early flash in the He-detonation scenario shows behaviors different from those in the companion/CSM interaction scenarios. Especially clear diagnostics are provided once the behaviors in the UV and in the optical are combined. The spectra synthesized for the He-detonation scenario are characterized by absorptions due to He-detonation products, which develop in the decay phase. We further expect a relation between the properties of the early-phase flash and those of the maximum SN emission, in such a way that the brighter and slower initial flash is accompanied by a more substantial effect from the additional absorptions (and reddening). This relation, however, should be considered together with the maximum luminosity of the SN, since the larger luminosity suppresses the effect of the additional absorption. With these expected features, we address the possible origins of the excessive early-phase emission observed in several SNe.
The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star formation is an important clue to reveal the still unknown progenitor system of SNe Ia. Here, we report on a measurement of ...the SN Ia DTD in a delay time range of
$t_{\rm Ia} = $
0.1-8.0Gyr by using faint variable objects detected in the Subaru/XMM-Newton Deep Survey (SXDS) down to
$i'$
$\sim$
25.5. We selected 65 SN candidates showing significant spatial offset from the nuclei of the host galaxies having an old stellar population at
$z$
$\sim$
0.4-1.2, out of more than 1000 SXDS variable objects. Although spectroscopic type classification is not available for these, we quantitatively demonstrated that more than
$\sim$
80% of these should be SNe Ia. The DTD was derived using stellar age estimates of the old galaxies based on 9 band photometries from optical to mid-infrared wavelength. Combined with the observed SN Ia rate in elliptical galaxies at the local universe, the DTD in
$t_{\rm Ia}$
$\sim$
0.1-10Gyr is well described by a featureless power-law as
$f_{\rm D}$
(
$t_{\rm Ia}$
)
$\propto$
$t_{\rm Ia}^\alpha$
with
$\alpha$
$\sim$
$-$
1. The derived DTD is in excellent agreement with a generic prediction of the double-degenerate scenario, giving strong support to this scenario. In the single-degenerate (SD) scenario, although predictions by simple analytic formulations have broad DTD shapes that are similar to the observation, DTD shapes calculated by more detailed binary population synthesis tend to have strong peaks at characteristic time scales, which do not fit the observation. This result thus indicates either that the SD channel is not the major contributor to SNe Ia in an old stellar population, or that an improvement of binary population synthesis theory is required. Various sources of systematic uncertainties were examined and tested, but our main conclusions were not affected significantly.
Abstract
It has been reported that the extinction law for Type Ia supernovae (SNe Ia) may be different from the one in the Milky Way, but the intrinsic color of SNe Ia and the dust extinction are ...observationally mixed. In this study, we examine photometric properties of SNe Ia in the nearby universe (z ≲ 0.04) to investigate the SN Ia intrinsic color and the dust extinction. We focus on the Branch spectroscopic classification of 34 SNe Ia and morphological types of host galaxies. We carefully study the distribution of their peak colors on the B − V, V − R color–color diagram, as well as the color excess and absolute magnitude deviation from the stretch-color relation of the bluest SNe Ia. We find that SNe Ia which show the reddest color occur in early-type spirals and the trend holds when divided into Branch sub-types. The dust extinction becomes close to the Milky Way like extinction if we exclude some peculiar red Broad Line (BL) sub-type SNe Ia. Furthermore, two of these red BLs occur in elliptical galaxies, a less-dusty environment, suggesting intrinsic color diversity in BL sub-type SNe Ia.
Let
be a simple normal crossing (SNC) compact complex surface with trivial canonical bundle which includes triple intersections. We prove that if
is
-semistable, then there exists a family of ...smoothings in a differential geometric sense. This can be interpreted as a differential geometric analogue of the smoothability results due to Friedman, Kawamata-Namikawa, Felten-Filip-Ruddat, Chan-Leung-Ma, and others in algebraic geometry. The proof is based on an explicit construction of local smoothings around the singular locus of
, and the first author’s existence result of holomorphic volume forms on global smoothings of
. In particular, these volume forms are given as solutions of a nonlinear elliptic partial differential equation. As an application, we provide several examples of
-semistable SNC complex surfaces with trivial canonical bundle including double curves, which are smoothable to complex tori, primary Kodaira surfaces, and
surfaces. We also provide several examples of such complex surfaces including triple points, which are smoothable to
surfaces.
We present rapidly rising transients discovered by a high-cadence transient survey with the Subaru telescope and Hyper Suprime-Cam. We discovered five transients at z= 0.384-0.821, showing a rate of ...rise faster than 1 mag per day in the restframe near-ultraviolet wavelengths. The fast rate of rise and brightness are most similar to SN 2010aq and PS1-13arp, for which ultraviolet emission was detected within a few days after the shock breakout. The lower limit of the event rate of rapidly rising transients is ~9% of core-collapse supernova rates, assuming the duration of rapid rise to be 1 day. We show that the light curves of the three faint objects agree with the cooling envelope emission from the explosion of red supergiants. The other two luminous objects, however, are brighter and faster than the cooling envelope emission. We interpret these two objects to be the shock breakout from a dense wind with a mass loss rate of ~10 super(-3)M sub(middot in circle) yr super(-1), as also proposed for PS1-13arp. This mass loss rate is higher than that typically observed for red supergiants. The event rate of these luminous objects is > ~1% of the core-collapse supernova rate, and thus our study implies that more than ~1% of massive stars can experience intense mass loss a few years before the explosion.
With a booming number of Type Ia supernovae (SNe Ia) discovered within a few days of their explosions, a fraction of SNe Ia that show luminosity excess in the early phase (early-excess SNe Ia) have ...been confirmed. In this article, we report early-phase observations of seven photometrically normal SNe Ia (six early detections and one deep non detection limit) at the COSMOS field through a half-year transient survey as a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In particular, a blue light-curve excess was discovered for HSC17bmhk, a normal SN Ia with rise time longer than 18.8 days, during the first four days after the discovery. The blue early excess in optical wavelength can be explained not only by interactions with a nondegenerate companion or surrounding dense circumstellar matter but also radiation powered by radioactive decays of 56Ni at the surface of the SN ejecta. Given the growing evidence of the early-excess discoveries in normal SNe Ia that have longer rise times than the average, and a similarity in the nature of the blue excess to a luminous SN Ia subclass, we infer that early excess discovered in HSC17bmhk and other normal SNe Ia are most likely attributed to radioactive 56Ni decay at the surface of the SN ejecta. In order to successfully identify normal SNe Ia with early excess similar to that of HSC17bmhk, early UV photometries or high-cadence blue-band surveys are necessary.
Abstract We studied the optical variability of 241 BL Lacertae (BL Lacs) and 83 flat-spectrum radio quasars (FSRQs) from the 4LAC catalog using data from the Tomo-e Gozen Northern Sky Transient ...Survey, with ∼50 epochs per blazar on average. We excluded blazars whose optical variability may be underestimated due to the influence of their host galaxy based on their optical luminosity ( L O ). FSRQs with γ -ray photon index greater than 2.6 exhibit very low optical variability, and their distribution of standard deviation of repeated photometry is significantly different from that of the other FSRQs (Kolmogorov–Smirnov test p -value equal to 5 × 10 −6 ). Among a sample of blazars at any particular cosmological epoch, those with lower γ -ray luminosity ( L γ ) tend to have lower optical variability, and those FSRQs with a γ -ray photon index greater than 2.6 tend to have low L γ . We also measured the structure function of optical variability and found that the amplitude of the structure function for FSRQs is higher than previously measured and higher than that of BL Lacs at multiple time lags. Additionally, the amplitude of the structure function of FSRQs with high γ -ray photon index is significantly lower than that of FSRQs with low γ -ray photon index. The structure function of FSRQs of high γ -ray photon index shows a characteristic timescale of more than 10 days, which may be the variability timescale of the accretion disk. In summary, we infer that the optical component of FSRQs with high γ -ray photon index may be dominated by the accretion disk.
Thirteen explosion sites of Type II-P and II-L supernovae (SNe) in nearby galaxies have been observed using integral field spectroscopy, enabling both spatial and spectral study of the explosion ...sites. We used the properties of the parent stellar population of the coeval SN progenitor star to derive its metallicity and initial mass. The spectrum of the parent stellar population yields estimates of metallicity via the strong-line method and age via a comparison with simple stellar population models. These metallicity and age parameters are adopted for the progenitor star. Age, or lifetime of the star, was used to derive the initial (zero-age main sequence) mass of the star using comparisons with stellar evolution models. With this technique, we were able to determine the metallicities and initial masses of the SN progenitors in our sample. Our results indicate that some Type II SN progenitors may have been stars with masses comparable to those of SN Ib/c progenitors.
Abstract
We report the discovery of an SN 1988Z–like type IIn supernova KISS15s found in a low-mass star-forming galaxy at redshift
z
= 0.038 during the course of the Kiso Supernova Survey (KISS). ...KISS15s shows long-duration optical continuum and emission line light curves, indicating that KISS15s is powered by a continuous interaction between the expanding ejecta and dense circumstellar medium (CSM). The H
α
emission line profile can be decomposed into four Gaussians of narrow, intermediate, blueshifted intermediate, and broad velocity width components, with a full width at half maximum of ≲100, ∼2000, and ∼14,000 km s
−1
for the narrow, intermediate, and broad components, respectively. The presence of the blueshifted intermediate component, of which the line-of-sight velocity relative to the systemic velocity is about −5000 km s
−1
, suggests that the ejecta-CSM interaction region has an inhomogeneous morphology and anisotropic expansion velocity. We found that KISS15s shows increasing infrared continuum emission, which can be interpreted as hot dust thermal emission of
T
∼ 1200 K from newly formed dust in a cool, dense shell in the ejecta-CSM interaction region. The progenitor mass-loss rate, inferred from bolometric luminosity, is
, where
v
w
is the progenitor’s stellar wind velocity. This implies that the progenitor of KISS15s was a red supergiant star or a luminous blue variable that had experienced a large mass loss in the centuries before the explosion.
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