arXiv subjects

N. N. Chugai

Publications and source records attributed to N. N. Chugai.

At least 55 records · Page 3Linked to original sources

arXiv2008

Progenitor mass of the type IIP supernova 2005cs

The progenitor mass of type IIP supernova can be determined from either hydrodynamic modeling of the event or pre-explosion observations. To compare these approaches, we determine parameters of the sub-luminous supernova 2005cs and estimate its progenitor mass. We compute the hydrodynamic models of the supernova to describe its light curves and expansion velocity data. We estimate a presupernova mass of 17.3 Msun, an explosion energy of 4.1x10^{50} erg, a presupernova radius of 600 Rsun, and a radioactive Ni-56 mass of 0.0082 Msun. The derived progenitor mass of SN 2005cs is 18.2 Msun, which is in-between those of low-luminosity and normal type IIP supernovae. The obtained progenitor mass of SN 2005cs is higher than derived from pre-explosion images. The masses of four type IIP supernovae estimated by means of hydrodynamic modeling are systematically higher than the average progenitor mass for the 9-25 Msun mass range. This result, if confirmed for a larger sample, would imply that a serious revision of the present-day view on the progenitors of type IIP supernovae is required.

astro-ph↗

arXiv2008

Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S

We study a possibility of detection of circumstellar absorption lines of Na I D$_{1,2}$ and Ca II H,K in spectra of type IIP supernovae at the photospheric epoch. The modelling shows that the circumstellar lines of Na I doublet will not be seen in type IIP supernovae for moderate wind density, e.g., characteristic of SN 1999em, whereas rather pronounced Ca II lines with P Cygni profile should be detectable. A similar model is used to describe Na I and Ca II circumstellar lines seen in SN 1998S, type IIL with a dense wind. We show that line intensities in this supernova are reproduced, if one assumes an ultraviolet excess, which is caused primarily by the comptonization of supernova radiation in the shock wave.

astro-ph↗

arXiv2008

Circumstellar Na I and Ca II lines of type Ia supernovae in symbiotic scenario

Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is studied for the case, when supernova explodes in a binary system with a red giant. The model suggests a spherically-symmetric wind and takes into account ionization and heating of the wind by X-rays from the shock wave and by gamma-quanta of ^{56}Ni radioactive decay. For the wind density typical of the red giant the expected optical depth of the wind in Na I lines turnes out too low (τ<0.001}) to detect the absorption. For the same wind densities the predicted optical depth of Ca II 3934 Åis sufficient for the detection (τ>0.1). I conclude that the absorption lines detected in SN 2006X cannot form in the red giant wind; they are rather related to clouds at distances larger than the dust evaporation radius (r>10^{17} cm). From the absence in SN 2006X of Ca II absorption lines not related with the similar Na I components I derive the upper limit of the mass loss rate by the wind with velocity u: \dot{M}<10^{-8}(u/10 km/s) M_{\odot} yr^{-1}.

astro-ph↗

arXiv2007

Ejecta and progenitor of the low-luminosity Type IIP supernova 2003Z

The origin of low-luminosity Type IIP supernovae is unclear: they have been proposed to originate either from massive (about 25 Msun) or low-mass (about 9 Msun) stars. We wish to determine parameters of the low-luminosity Type IIP supernova 2003Z, to estimate a mass-loss rate of the presupernova, and to recover a progenitor mass. We compute the hydrodynamic models of the supernova to describe the light curves and the observed expansion velocities. The wind density of the presupernova is estimated using a thin shell model for the interaction with circumstellar matter. We estimate an ejecta mass of 14 Msun, an explosion energy of 2.45x10^50 erg, a presupernova radius of 229 Rsun, and a radioactive Ni-56 amount of 0.0063 Msun. The upper limit of the wind density parameter in the presupernova vicinity is 10^13 g/cm, and the mass lost at the red/yellow supergiant stage is less than 0.6 Msun assuming the constant mass-loss rate. The estimated progenitor mass is in the range of 14.4-17.4 Msun. The presupernova of SN 2003Z was probably a yellow supergiant at the time of the explosion. The progenitor mass of SN 2003Z is lower than those of SN 1987A and SN 1999em, normal Type IIP supernovae, but higher than the lower limit of stars undergoing a core collapse. We propose an observational test based on the circumstellar interaction to discriminate between the massive (about 25 Msun) and moderate-mass (about 16 Msun) scenarios.

astro-ph↗

arXiv2007

Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae

We report the X-ray detection of the Type II-plateau supernova SN 2004et in the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position of the X-ray source was found to agree with the optical position within ~0.4 arcsec. Chandra also surveyed the region before the 2004 event, finding no X-ray emission at the location of the progenitor. For the post-explosion observations, a total of 202, 151, and 158 photons were detected in three pointings, each ~29 ks in length, on 2004 October 22, November 6, and December 3, respectively. The spectrum of the first observation is best fit by a thermal model with a temperature of kT=1.3 keV and a line-of-sight absorption of N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is ~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and soft counts on the first and third epochs indicates a softening over this time, although there is an insufficient number of photons to constrain the variation of temperature and absorption by spectral fitting. We model the emission as arising from the reverse shock region in the interaction between the supernova ejecta and the progenitor wind. For a Type IIP supernova with an extended progenitor, the cool shell formed at the time of shock wave breakout from the star can affect the initial evolution of the interaction shell and the absorption of radiation from the reverse shock. The observed spectral softening might be due to decreasing shell absorption. We find a pre-supernova mass loss rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is in line with expectations for a Type IIP supernova.

astro-ph↗

arXiv2006

Asymmetry of $^{56}$Ni ejecta and polarization in type IIP supernova 2004dj

I study a problem, whether the asymmetry of a $^{56}$Ni ejecta that results in the asymmetry of the H$α$ emission line at the nebular epoch of the type IIP supernova SN 2004dj is able also to account for the recently detected polarization of the supernova radiation. I developed a model of the H$α$ profile and luminosity with a nonthermal ionization and excitation taken into account adopting an asymmetric bipolar $^{56}$Ni distribution. On the background of the recovered distribution of the electron density I calculated the polarized radiation transfer. It is demonstrated that the observed polarization is reproduced at the nebular epoch around day 140 for the same parameters of the envelope and $^{56}$Ni distribution for which the luminosity and profile of H$α$ are explained.

astro-ph↗

arXiv2005

Optical observations of type IIP supernova 2004dj: Evidence for the asymmetry of $^{56}$Ni ejecta

The photometric and spectroscopic observations of nearby type IIP supernova 2004dj are presented. The $^{56}$Ni mass estimated from the light curve is $\approx0.02 M_{\odot}$. This estimate is found to be consistent with the H$α$ luminosity. SN2004dj reveals a strong asymmetry of the H$α$ emission line at the nebular epoch with the shift of the maximum of -1600 km s$^{-1}$. A similar asymmetric component is detected in H$β$, [O I] and [Ca II] lines. The line asymmetry is interpreted as a result of the asymmetry of $^{56}$Ni ejecta. The H$α$ profile and its evolution are reproduced in the model of the asymmetric bipolar $^{56}$Ni and spherical hydrogen distributions. The mass of the front $^{56}$Ni jet is comparable to the central component and twice as larger compared to the rear $^{56}$Ni jet. We note that the asymmetric bipolar structure of of $^{56}$Ni ejecta is revealed also by SN1999em, another type IIP supernova.

astro-ph↗

arXiv2005

Strong effects of time-dependent ionization in early SN 1987A

We study a time-dependent hydrogen ionization in the atmosphere of SN 1987A during the first month after the explosion. The model includes kinetics of hydrogen ionization and excitation, molecular hydrogen kinetics, and a time-dependent energy balance. The primary strong effect of the time-dependent ionization is the enhanced hydrogen ionization compared to the steady-state model. The time-dependent ionization provides a sufficient population of excited hydrogen levels to account for the observed H-alpha without invoking the external Ni-56. We find that the Ba II 6142 A line in SN 1987A can be reproduced for the LMC barium abundance. This resolves the long-standing problem of the unacceptably high barium overabundance in SN 1987A. The key missing factor that should be blamed for the "barium problem" is the time-dependent ionization. The modelling of the H-alpha profile on day 4.64 indicates the ratio of the kinetic energy to the ejected mass about 0.83 10^{50} erg/Msun.

astro-ph↗

arXiv2004

Circumstellar interaction of the type Ia supernova 2002ic

We propose a model to account for the bolometric light curve, quasi-continuum and the Ca II emission features of the peculiar type Ia supernova (SN) 2002ic, which exploded in a dense circumstellar envelope. The model suggests that the SN Ia had the maximum possible kinetic energy and that the ejecta expand in an approximately spherically symmetric (possibly clumpy) circumstellar environment. The Ca II and quasi-continuum are emitted by shocked SN ejecta that underwent deformation and fragmentation in the intershock layer. Modeling of the Ca II triplet implies that the contribution of the O I 8446 A line is about 25% of the 8500 A feature on day 234, which permits us to recover the flux in the Ca II 8579 A triplet from the flux of 8500 A blend reported by Deng et al. (2004). We use the Ca II doublet and triplet fluxes on day 234 to derive the electron temperature (~4400 K) in the Ca II line-emitting zone and the ratio of the total area of dense fragments to the area of the shell, S/S_0 ~ 100. We argue that Ca II bands and quasi-continuum originate from different zones of the shocked ejecta that reflect the abundance stratification of the supernova.

astro-ph↗

arXiv2004

On the source of the late-time infrared luminosity of SN 1998S and other type II supernovae

We present late-time near-infrared (NIR) and optical observations of the type IIn SN 1998S. The NIR photometry spans 333-1242 days after explosion, while the NIR and optical spectra cover 333-1191 days and 305-1093 days respectively. The NIR photometry extends to the M'-band (4.7 mu), making SN 1998S only the second ever supernova for which such a long IR wavelength has been detected. The shape and evolution of the H alpha and HeI 1.083 mu line profiles indicate a powerful interaction with a progenitor wind, as well as providing evidence of dust condensation within the ejecta. The latest optical spectrum suggests that the wind had been flowing for at least 430 years. The intensity and rise of the HK continuum towards longer wavelengths together with the relatively bright L' and M' magnitudes shows that the NIR emission was due to hot dust newly-formed in supernovae may provide the ejecta and/or pre-existing dust in the progenitor circumstellar medium (CSM). [ABRIDGED] Possible origins for the NIR emission are considered. Significant radioactive heating of ejecta dust is ruled out, as is shock/X-ray-precursor heating of CSM dust. More plausible sources are (a) an IR-echo from CSM dust driven by the UV/optical peak luminosity, and (b) emission from newly-condensed dust which formed within a cool, dense shell produced by the ejecta shock/CSM interaction. We argue that the evidence favours the condensing dust hypothesis, although an IR-echo is not ruled out. Within the condensing-dust scenario, the IR luminosity indicates the presence of at least 0.001 solar masses of dust in the ejecta, and probably considerably more. Finally, we show that the late-time intrinsic (K-L') evolution of type II supernovae may provide a useful tool for determining the presence or absence of a massive CSM around their progenitor stars.

astro-ph↗

arXiv2003

^{56}Ni mass in type IIP SNe: Light curves and H-alpha luminosities diagnostics

We analyse late-time observations, available photometry and spectra, of a sample of type II plateau supernovae (SNe IIP). The possibility of using H$α$ luminosity at the nebular epoch as a tracer of $^{56}$Ni mass in this class of objects is investigated, yielding a consistency with the photometry-based estimates within 20%. Interesting correlations are found and their impacts on our present understanding of the physics of core collapse SNe are discussed.

astro-ph↗

arXiv2003

Type Ia supernovae in dense circumstellar gas

We propose a simple model for the bolometric light curve of type Ia supernova exploding in a dense circumstellar (CS) envelope to describe the light curves of supernovae 2002ic and 1997cy. The modeling shows that at the radius $\sim7\times10^{15}$ cm the density of CS envelopes around both supernovae is similar. The mass of the CS envelope around SN 1997cy is close to $5 M_{\odot}$, while the characteristic time of the ejection of this envelope does not exceed 600 yr. We analyze two possible evolutionary scenarios which might lead to the explosion of type Ia supernova inside a dense CS envelope: accretion on CO white dwarf in the symbiotic binary and evolution of a single star with the initial mass of about $8 M_{\odot}$. If the conjecture about the explosion of type Ia supernova in a dense CS envelope is correct in the case of SN 2002ic and SN 1997cy then the rapid loss of the red supergiant envelope and the subsequent explosion of the CO white dwarf are synchronized by certain mechanism. This mechanism might be related to the contraction of the white dwarf as it approaches the Chandrasekhar limit. We show that formation of a (super)Chandrasekhar mass due to the merger of a CO white dwarf and CO core of a red supergiant with consequent explosion is unlikely, since it does not provide the required synchronization of the rapid mass loss and explosion.

astro-ph↗

arXiv2003

Massive circumstellar envelope around type IIn supernova SN 1995G

We model the interaction of the supernova SN 1995G with a dense circumstellar (CS) gas in a thin shell approximation. A model fit of the observed bolometric light curve combined with data on the supernova expansion velocity provides an estimate of the density of the CS shell, its mass ($\approx 1 M_{\odot}$), and age ($\approx 8$ years). It is shown that the derived CS gas density does not depend on the assumed mass of the supernova ejecta. This results from the high CS density, which ensures that the forward shock wave is essentially radiative. The derived CS density is consistent with the H$α$ luminosity and with the presence of the apparent effect of Thomson scattering in the red wing of this line. The mass of the CS envelope together with its expansion velocity indicates that the CS envelope was ejected as a result of violent energy release ($\sim 6\times10^{48}$ erg) eight years before the supernova outburst.

astro-ph↗

arXiv2003

Light curves and H$α$ luminosities as indicators of $^{56}$Ni mass in type IIP supernovae

The possibility is investigated that the H$α$ luminosity at the nebular epoch may be an additional indicator of $^{56}$Ni mass in type II supernovae with plateau (SNe IIP), on the basis of available photometry and spectra. We first derive the $^{56}$Ni mass from the $M_V$ magnitude on the radioactive tail using a standard approach. A confirmation of the correlation between $^{56}$Ni mass and plateau $M_V$ magnitude found recently by Hamuy (2003) is evident. There is strong evidence of a correlation between steepness of the $V$ light curve slope at the inflection time and the $^{56}$Ni mass. If confirmed, this relation may provide distance and extinction independent estimates of the amount of $^{56}$Ni in SNe IIP. We then apply upgraded radioactive models of H$α$ luminosity at the nebular epoch and claim that it may be a good indicator of $^{56}$Ni, if mass, energy and mixing properties vary moderately (within factor $\sim 1.4$) among SNe IIP . This method of the $^{56}$Ni mass determination from H$α$ luminosities yields results which are consistent with the photometric mass of $^{56}$Ni mass to within 20%. This result also implies that the parameters of SNe IIP events (mass, energy and mixing properties) are rather similar among the majority of SNe IIP, except for rare cases of SN II intermediate between IIP and IIL (linear), of which SN 1970G is an example.

astro-ph↗

arXiv2002

Freeze-out Effects in Hydrogen and Helium Lines of SN 1987A at the Early Photospheric Epoch

We have developed a time-dependent model of ionization, excitation and energy balance of SN 1987A atmosphere at the photospheric epoch to study early behavior of hydrogen and helium lines. The ionization freeze-out effects play a key role in producing both the strong H-alpha during nearly the first month and the He I 5876 A scattering line on day 1.76. Using an extended reaction network between hydrogen molecules and their ions demonstrates that ion-molecular processes are likely responsible for the blue peak in H-alpha profile at the Bochum event epoch.

astro-ph↗

arXiv2002

Ionization freeze-out and barium problem in supernova 1987A

We have shown that in the atmosphere of SN 1987A level populations of hydrogen are mostly controlled by an ionization freeze-out and ion-molecular processes up to 40 days. The ionization freeze-out effects are important for normal SNe II-P as well. The time dependent effects and the mutual neutralization between H^- and H^+ may result in a non-monotonic radial dependence of the Sobolev optical depth for H-alpha and then in a blue emission satellite of H-alpha observed in SN 1987A spectra at Bochum event phase. The relative abundance of molecular hydrogen about 0.0001-0.001 is high enough for the photospheric phase of SN 1987A. We emphasize that the poor knowledge of the far UV radiation field in the envelope of SN 1987A still forbids a truly reliable estimate of the Ba abundance but well-constructed and tested models may improve this situation.

astro-ph↗

arXiv2001

The origin of the high velocity circumstellar gas around SN 1998S

Modelling of high resolution Balmer line profiles in the early-time spectra of SN 1998S shows that the inferred fast (roughly 400 km/s) circumstellar (CS) gas on days 23 and 42 post-explosion is confined to a narrow, negative velocity gradient shell just above the photosphere. This gas may be identified with a slow (v < 40 km/s) progenitor wind accelerated at the ejecta-wind interface. In this scenario, the photosphere coincides with a cool dense shell formed in the reverse shock. Acceleration by radiation from the supernova or by a shock-accelerated relativistic particle precursor are both possible explanations for the observed fast CS gas. An alternative, equally plausible scenario is that the fast CS gas is accelerated within shocked clouds engulfed by the outer shock, as it propagates through the intercloud wind.

astro-ph↗

arXiv2001

Broad emission lines from opaque electron-scattering environment of SN 1998S

I propose that broad narrow-topped emission lines with full width at zero intensity >20000 km/s, seen in early-time spectra of SN 1998S, originate from a dense circumstellar gas and not from the supernova ejecta. The tremendous line width is the result of multiple scattering of the narrow line radiation on thermal electrons of the circumstellar shell with the Thomson optical depth of about 4 on 1998 March 6.

astro-ph↗