Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userType Ia Supernovae in the First Few Days: Signatures of Helium Detonation versus Interaction
44
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The mechanism for the early-phase blue and excessive emission within the first few days, reported so far for a few type Ia supernovae (SNe Ia), has been suggested to be interaction of the SN ejecta either with 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., 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 properties of the early-phase excessive emission predicted by these different scenarios. The He detonation scenario shows different behaviors in the early flash than the companion/CSM interaction scenarios. Especially clear diagnostics is provided once the behaviors in the UV and in the optical are combined. The spectra synthesized for the He detonation scenario are characterized by the absorptions due to the He detonation products, which especially 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 a way the brighter and slower initial flash is accompanied by a more substantial effect of 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 observed excessive early-phase emission for a few SNe.
rate research
Read More
The double-detonation explosion model has been considered a candidate for explaining astrophysical transients with a wide range of luminosities. In this model, a carbon-oxygen white dwarf star explodes following detonation of a surface layer of helium. One potential signature of this explosion mechanism is the presence of unburned helium in the outer ejecta, left over from the surface helium layer. In this paper we present simple approximations to estimate the optical depths of important He I lines in the ejecta of double-detonation models. We use these approximations to compute synthetic spectra, including the He I lines, for double-detonation models obtained from hydrodynamical explosion simulations. Specifically, we focus on photospheric-phase predictions for the near-infrared 10830 AA~and 2 $mu$m lines of He I. We first consider a double detonation model with a luminosity corresponding roughly to normal SNe Ia. This model has a post-explosion unburned He mass of 0.03 $M_{odot}$ and our calculations suggest that the 2 $mu$m feature is expected to be very weak but that the 10830 AA~feature may have modest opacity in the outer ejecta. Consequently, we suggest that a moderate-to-weak He I 10830 AA~feature may be expected to form in double-detonation explosions at epochs around maximum light. However, the high velocities of unburned helium predicted by the model ($sim 19,000$~km~s$^{-1}$) mean that the He I 10830 AA~feature may be confused or blended with the C I 10690~AA~line forming at lower velocities. We also present calculations for the He I 10830 AA~and 2 $mu$m lines for a lower mass (low luminosity) double detonation model, which has a post-explosion He mass of 0.077 $M_{odot}$. In this case, both the He I features we consider are strong and can provide a clear observational signature of the double-detonation mechanism.
Calculations of synthetic spectropolarimetry are one means to test multi-dimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M$_{odot}$ white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a two-dimensional double-detonation model and a three-dimensional delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels ($<$ 1 per cent) for both explosion models. Polarization in the continuum peaks at $sim$ 0.1$-$0.3 per cent and decreases after maximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si ii {lambda}6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O i {lambda}7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.
We study a sample of 16 Type Ia supernovae (SNe Ia) having both spectroscopic and photometric observations within 2 $-$ 3 days after the first light. The early $B-V$ colors of such a sample tends to show a continuous distribution. For objects with normal ejecta velocity (NV), the C~II $lambda$6580 feature is always visible in the early spectra while it is absent or very weak in the high-velocity (HV) counterpart. Moreover, the velocities of the detached high-velocity features (HVFs) of Ca~II NIR triplet (CaIR3) above the photosphere are found to be much higher in HV objects than in NV objects, with typical values exceeding 30,000 km~s$^{-1}$ at 2 $-$ 3 days. We further analyze the relation between %velocities of Si~II~$lambda$6355 at maximum, $v_{rm Si,max}$, the velocity shift of late-time [Fe~II] lines ($v_{rm [Fe~II]}$) and host galaxy mass. We find that all HV objects have redshifted $v_{rm [Fe~II]}$ while NV objects have both blue- and redshifted $v_{rm [Fe~II]}$. It is interesting to point out that the objects with redshifted $v_{rm [Fe~II]}$ are all located in massive galaxies, implying that HV and a portion of NV objects may have similar progenitor metallicities and explosion mechanisms. We propose that, with a geometric/projected effect, the He-detonation model may account for the similarity in birthplace environment and the differences seen in some SNe Ia, including $B-V$ colors, C~II feature, CaIR3 HVFs at early time and $v_{rm [Fe~II]}$ in the nebular phase. Nevertheless, some features predicted by He-detonation simulation, such as the rapidly decreasing light curve, deviate from the observations, and some NV objects with blueshifted nebular $v_{rm [Fe~II]}$ may involve other explosion mechanisms.
This work aims to study different probes of Type Ia supernova progenitors that have been suggested to be linked to the presence of circumstellar material (CSM). In particular, we have investigated, for the first time, the link between narrow blueshifted NaID absorption profiles and the presence and strength of the broad high-velocity CaII near infrared triplet absorption features seen in Type Ia supernovae around maximum light. With the probes exploring different distances from the supernova; NaID > 10$^{17}$cm, high-velocity CaII features < 10$^{15}$cm. For this, we have used a new intermediate-resolution X-shooter spectral sample of 15 Type Ia supernovae. We do not identify a link between these two probes, implying either that, one (or both) is not physically related to the presence of CSM or that the occurrence of CSM at the distance explored by one probe is not linked to its presence at the distance probed by the other. However, the previously identified statistical excess in the presence of blueshifted (over redshifted) NaID absorption is confirmed in this sample at high significance and is found to be stronger in Type Ia supernovae hosted by late-type galaxies. This excess is difficult to explain as being from an interstellar-medium origin as has been suggested by some recent modelling, as such an origin is not expected to show a bias for blueshifted absorption. However, a circumstellar origin for these features also appears unsatisfactory based on our new results given the lack of link between the two probes of CSM investigated.
Recent studies have argued that the progenitor system of type Iax supernovae must consist of a carbon-oxygen white dwarf accreting from a helium star companion. Based on existing explosion models invoking the pure deflagration of carbon-oxygen white dwarfs, we investigate the likelihood of producing spectral features due to helium in type Iax supernovae. From this scenario, we select those explosion models producing ejecta and $^{56}$Ni masses that are broadly consistent with those estimated for type Iax supernovae (0.014 - 0.478~$M_{odot}$ and $sim0.003$ - 0.183~$M_{odot}$, respectively). To this end, we present a series of models of varying luminosities ($-18.4 lesssim M_{rm{V}} lesssim -14.5$~mag) with helium abundances accounting for up to $sim$36% of the ejecta mass, and covering a range of epochs beginning a few days before B$-$band maximum to approximately two weeks after maximum. We find that the best opportunity for detecting ion{He}{i} features is at near-infrared wavelengths, and in the post-maximum spectra of the fainter members of this class. We show that the optical spectrum of SN~2007J is potentially consistent with a large helium content (a few 10$^{-2}~M_{odot}$), but argue that current models of accretion and material stripping from a companion struggle to produce compatible scenarios. We also investigate the presence of helium in all objects with near-infrared spectra. We show that SNe~2005hk, 2012Z, and 2015H contain either no helium or their helium abundances are constrained to much lower values ($lesssim$10$^{-3}~M_{odot}$). Our results demonstrate the differences in helium content among type Iax supernovae, perhaps pointing to different progenitor channels. Either SN~2007J is an outlier in terms of its progenitor system, or it is not a true member of the type Iax supernova class.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
