SN 2009E: a faint clone of SN 1987A Pastorello, A.; Pumo, M. L.; Navasardyan, H. ...
Astronomy & astrophysics,
01/2012, Letnik:
537
Journal Article
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Context.1987A-like events form a rare sub-group of hydrogen-rich core-collapse supernovae that are thought to originate from the explosion of blue supergiant stars. Although SN 1987A is the best ...known supernova, very few objects of this group have been discovered and, hence, studied. Aims. In this paper we investigate the properties of SN 2009E, which exploded in a relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest 1987A-like supernova discovered so far. We also attempt to characterize this subgroup of core-collapse supernovae with the help of the literature and present new data for a few additional objects. Methods. The lack of early-time observations from professional telescopes is compensated by frequent follow-up observations performed by a number of amateur astronomers. This allows us to reconstruct a well-sampled light curve for SN 2009E. Spectroscopic observations which started about 2 months after the supernova explosion, highlight significant differences between SN 2009E and the prototypical SN 1987A. Modelling the data of SN 2009E allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 1987A and 1998A. Results. The light curve of SN 2009E is less luminous than that of SN 1987A and the other members of this class, and the maximum light curve peak is reached at a slightly later epoch than in SN 1987A. Late-time photometric observations suggest that SN 2009E ejected about 0.04 M⊙ of 56Ni, which is the smallest 56Ni mass in our sample of 1987A-like events. Modelling the observations with a radiation hydrodynamics code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an initial radius of ~7 × 1012 cm and an ejected mass of ~19 M⊙. The photospheric spectra show a number of narrow (v ≈ 1800 km s-1) metal lines, with unusually strong Ba II lines. The nebular spectrum displays narrow emission lines of H, Na I, Ca II and O I, with the O I feature being relatively strong compared to the Ca II doublet. The overall spectroscopic evolution is reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy tail in the distribution of the 1987A-like objects in the same manner as SN 1997D and similar events represent the faint tail in the distribution of physical properties for normal type II-plateau supernovae.
We have developed a relativistic, radiation-hydrodynamics Lagrangian code, specifically tailored to simulate the evolution of the main observables (light curve and the evolution of photospheric ...velocity and temperature) in core-collapse supernova (CC-SN) events. The distinctive features of the code are an accurate treatment of radiative transfer coupled to relativistic hydrodynamics, a self-consistent treatment of the evolution of the innermost ejecta taking into account the gravitational effects of the central compact remnant, and a fully implicit Lagrangian approach to the solution of the coupled nonlinear finite difference system of equations. Our aim is to use it as a numerical tool to perform calculations of a grid of models to be compared with observations of CC-SNe. In this paper, we present some testcase simulations and a comparison with observations of SN 1987A, as well as with the results obtained with other numerical codes. We also briefly discuss the influence of the main physical parameters (ejected mass, progenitor radius, explosion energy, amount of {sup 56}Ni) on the evolution of the ejecta, and the implications of our results in connection with the possibility to 'standardize' hydrogen-rich CC-SNe for using them as candles to measure cosmological distances.
Abstract Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from ...astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g. box-shaped spectra, that would likewise very clearly point to a particle dark matter origin.
Context. Many studies on the s-process and, more specifically, on the s-process weak component have been performed so far, but a detailed scrutiny of the impact of the stellar evolution modeling ...uncertainties on the efficiency of this nucleosynthesis process is still missing. Aims. We analyze the role of convective overshooting on the production of s-nuclei in massive stars during their core He-burning phase. Methods. With the “post-processing” technique we explore the role of the convective overshooting on the production of s-nuclei in stellar models of different initial mass and metallicity (15 ≤ MZAMS/M⊙ ≤ 25; 10-4 ≤ Z ≤ 0.02), considering a range of values for the parameter f, which determines the overall efficiency of convective overshooting. Results. We find enhancements in the production of s-nuclei until a factor ~ 6 (measured as the average overproduction factor of the 6 s-only nuclear species with 60 ≲ A ≲ 90) in all our models of different initial mass and metallicity with f in the range 0.01 − 0.035 (i.e. models with overshooting) compared to the production obtained with “no-overshooting” models (i.e. models with the same initial mass and metallicity, but f = 10-5). Moreover the results indicate that the link between the overshooting parameter f and the s-process efficiency is essentially monotonic in all our models of different initial mass and metallicity. Also evident is the higher s-process efficiency when we progressively increase for a given f value both the mass of the models from 15 M⊙ to 25 M⊙ and the Z value from 10-4 to 0.02. We also briefly discuss the possible consequences of these results for some open questions linked to the s-process weak component efficiency, as well as a “rule of thumb” to evaluate the impact of the convective overshooting on the yields of a generation of stars.
Using a new s-nucleosynthesis code, coupled with the stellar evolution code Star2003, we performed simulations to study the impact of the convection treatment on the s-process during core He-burning ...in a $25\, M_{\odot}$ star (ZAMS mass) with an initial metallicity of $Z=0.02$. Particular attention was devoted to the impact of the extent of overshooting on the s-process efficiency. The results show enhancements of about a factor $2{-}3$ in s-process efficiency (measured as the average overproduction factor of the 6 s-only nuclear species with $60\la A\la 90$) with overshooting parameter values in the range $0.01{-}0.035$, compared to results obtained with the same model but without overshooting. The impact of these results on the p-process model based on type II supernovae is discussed.
Neutron induced reactions are fundamental for the nucleosynthesis of elements in the universe. Indeed, to correctly study the reactions involved in the well-known s-process in stars, which produce ...about half of the elements beyond the iron peak, it is mandatory to know the neutron abundance available in those stars. The 17O(n, a)14C reaction is one of the so-called “neutron poisons” for the pro- cess and it could play an important role in the balance of the neutron abundance. The reaction is therefore investigated in the energy range of astrophysical inter- est between 0 and 350 keV in the center of mass by applying the Trojan Horse Method to the three body reaction 2H(17O, a14C)H.
Using our new general-relativistic, radiation hydrodynamics, Lagrangian code, we computed a rather extended grid of hydrogen-rich core-collapse supernovae (CC-SNe) models and explored the potentials ...of their “standardization” as distance indicators. We discuss the properties of some calibrations previously reported in the literature, and present new correlations based on the behavior of the light curve that can be employed for calibrating hydrogen-rich CC-SNe using only photometric data.
In the last few years, some regions of the Mediterranean area have witnessed a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and ...severe extreme rainfall events, which are often exacerbated by the ever-growing urbanization. In such a context, the urban drainage systems may not be sufficient to convey the rainwater, thus increasing the risk deriving from the occurrence of such events.
We investigate the role played by initial clumping of ejecta and by efficient acceleration of cosmic rays (CRs) in determining the density structure of the post-shock region of a Type Ia supernova ...remnant (SNR) through detailed 3D MHD modeling. Our model describes the expansion of a SNR through a magnetized interstellar medium (ISM), including the initial clumping of ejecta and the effects on shock dynamics due to back-reaction of accelerated CRs. The model predictions are compared to the observations of SN 1006. We found that the back-reaction of accelerated CRs alone cannot reproduce the observed separation between the forward shock (FS) and the contact discontinuity (CD) unless the energy losses through CR acceleration and escape are very large and independent of the obliquity angle. On the contrary, the clumping of ejecta can naturally reproduce the observed small separation and the occurrence of protrusions observed in SN 1006, even without the need of accelerated CRs. We conclude that FS-CD separation is a probe of the ejecta structure at the time of explosion rather than a probe of the efficiency of CR acceleration in young SNRs.
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