arXiv subjects

Nikolai N. Chugai

Publications and source records attributed to Nikolai N. Chugai.

14 recordsLinked to original sources

arXiv2025

PISN 2018ibb: radioactive emission of [O III] lines

Supernova 2018ibb of the PISN category related to the dynamical instability of oxygen core in a supermassive star induced by pair-creation shows at the nebular stage strong [\oiii] emission lines of an uncertain origin. I propose a simple model that demonstrates a possibility of [O III] lines emission from the supernova oxygen matter ionized and heated by the $^{56}$Co radioactive decay. The reason is pinpointed by which the [O III] line luminosity among supernovae of PISN category can vary in a broad range.

astro-ph.HE↗

arXiv2024

Superluminous supernova SN 2018ibb: Circumstellar shell and spectral effects

I explore observational effects of the cirsumstellar gas around superluminous supernova SN~2018ibb. High velocity Fe II narrow absorptions are reproduced in the model of fragmented cold dense shell. Unusual selective absorption in the emission doublet of [O I] is explained as an effect of the radiation scattering in Si II doublet lines in the supernova envelope.The strong emission of [O III] doublet at t_max + 565 days is proposed to originate from the supernova envelope, whereas its asymmetry is explained by the dust formation in the unshocked ejecta. Circumstellar interaction modeling combined with observational data suggests the cirsumstellar shell mass of about 0.14 Msun.

astro-ph.HE↗

arXiv2024

Puzzle of [Ar II] 7 mcm line broad component of SN 1987A

We explore the origin of the broad component of the [Ar II] 7 mcm line emission related to the ejecta excitation by the neutron star of SN 1987A. We argue that the line broad wings are emitted at the tmperature of $\sim300$ K. The flux excess in the red wing of [Ar II] line is reproduced by the line photons scattering off the optically thin uniform dust component with the grain size of 1 - 2 mcm and the total mass of $\mbox{(several)}\times10^{-3}\,M{\odot}$. The dusty opaque clumps containing almost all the dust of SN~1987A have a low occultation optical depth and line photon scattering on dusty clumps do not contribute noticeably in the red wing. The additional heating might be related to ionization losses of relativistic protons.

astro-ph.HE↗

arXiv2024

Study of X-ray emission from the S147 nebula by SRG/eROSITA: supernova-in-the-cavity scenario

The Simeis~147 nebula (S147), particularly well known for a spectacular net of ${\rm H}_α$-emitting filaments, is often considered one of the largest and oldest known supernova remnants in the Milky Way. Here, and in a companion paper, we present studies of X-ray emission from the S147 nebula using the data of SRG/eROSITA All-Sky Survey observations. In this paper, we argue that many inferred properties of the X-ray emitting gas are broadly consistent with a scenario of the supernova explosion in a low-density cavity, e.g. a wind-blown-bubble. This scenario assumes that a $\sim 20\,{\rm M_\odot}$ progenitor star has had small velocity with respect to the ambient ISM, so it stayed close to the center of a dense shell created during its Main Sequence evolution till the moment of the core-collapse explosion. The ejecta first propagate through the low-density cavity until they collide with the dense shell, and only then the reverse shock goes deeper into the ejecta and powers the observed X-ray emission of the nebula. The part of the remnant inside the dense shell remains non-radiative till now and, plausibly, in a state with $T_e<T_i$ and Non-Equilibrium Ionization (NEI). On the contrary, the forward shock becomes radiative immediately after entering the dense shell, and, being subject to instabilities, creates a characteristic "foamy" appearance of the nebula in ${\rm H}_α$ and radio emission.

astro-ph.HE↗

arXiv2021

Origin of postmaximum bump in luminous type Ic SN 2019stc

We address the issue of the postmaximum bump observed in the light curve of some superluminous supernovae. We rule out the popular mechanism of a circumstellar interaction suggested for the bump explanation. Instead we propose that the postmaximum bump is caused by the magnetar dipole field enhancement several months after the explosion. The modeling of SN 2019stc light curve based on the thin shell approximation implies that at the age of $\sim 90$ days the initial dipole magnetic field should be amplified by a factor of 2.8 to account for the postmaximum bump. The specific mechanism for the field amplification of the newborn magnetar on the timescale of several months has yet to be identified.

astro-ph.HE↗

arXiv2018

Type IIn SN~2010jl: probing dusty line-emitting shell

I explore signatures of a possible dust formation in the late SN~2010jl that could be imprinted in the line blueshift and the radius evolution of the dusty infrared-emitting shell. I propose a simple model that permits one to reproduce emission lines of blueshifted hydrogen and helium emission lines. The model suggests that the hydrogen emission originates primarily from shocked fragmented circumstellar clumps partially obscured by the absorbing cool dense shell and by unshocked ejecta. In the He I 1.083 $μ$m line on day 178 this component is significantly weaker compared to broad component from unshocked ejecta that is obscured by the absorprion produced by ejecta itself. Simulations of late time ($t > 400$ d) H$α$ suggest that, apart from the dust in the cool dense shell, a significant amount of dust must form in the unshocked supernova ejecta. The supernova radius predicted by the interaction model coincides with the radius of the dusty shell recovered from late time (> 460 days) infrared data, which strongly support that infrared radiation indeed originates from supernova. The ejecta dust is presumably locked in opaque blobs.

astro-ph.HE↗

arXiv2015

The spectacular evolution of Supernova 1996al over 15 years: a low energy explosion of a stripped massive star in a highly structured environment

Spectrophotometry of SN 1996al carried out throughout 15 years is presented. The early photometry suggests that SN 1996al is a Linear type-II supernova, with an absolute peak of Mv ~ -18.2 mag. Early spectra present broad, asymmetric Balmer emissions, with super-imposed narrow lines with P-Cygni profile, and He I features with asymmetric, broad emission components. The analysis of the line profiles shows that the H and He broad components form in the same region of the ejecta. By day +142, the Halpha profile dramatically changes: the narrow P-Cygni profile disappears, and the Halpha is fitted by three emission components, that will be detected over the remaining 15 yrs of the SN monitoring campaign. Instead, the He I emissions become progressively narrower and symmetric. A sudden increase in flux of all He I lines is observed between 300 and 600 days. Models show that the supernova luminosity is sustained by the interaction of low mass (~1.15 Msun) ejecta, expelled in a low kinetic energy (~ 1.6 x 10^50 erg) explosion, with highly asymmetric circumstellar medium. The detection of Halpha emission in pre-explosion archive images suggests that the progenitor was most likely a massive star (~25 Msun ZAMS) that had lost a large fraction of its hydrogen envelope before explosion, and was hence embedded in a H-rich cocoon. The low-mass ejecta and modest kinetic energy of the explosion are explained with massive fallback of material into the compact remnant, a 7-8 Msun black hole.

astro-ph.SR↗

arXiv2007

Optical Signatures of Circumstellar Interaction in Type IIP Supernovae

We propose new diagnostics for circumstellar interaction in Type IIP supernovae by the detection of high velocity (HV) absorption features in Halpha and He I 10830 A lines during the photospheric stage. To demonstrate the method, we compute the ionization and excitation of H and He in supernova ejecta taking into account time-dependent effects and X-ray irradiation. We find that the interaction with a typical red supergiant wind should result in the enhanced excitation of the outer layers of unshocked ejecta and the emergence of corresponding HV absorption, i.e. a depression in the blue absorption wing of Halpha and a pronounced absorption of He I 10830 A at a radial velocity of about -10,000 km/s. We identify HV absorption in Halpha and He I 10830 A lines of SN 1999em and in Halpha of SN 2004dj as being due to this effect. The derived mass loss rate is close to 10^{-6} Msun/yr for both supernovae, assuming a wind velocity 10 km/s. We argue that, in addition to the HV absorption formed in the unshocked ejecta, spectra of SN 2004dj and SN 1999em show a HV notch feature that is formed in the cool dense shell (CDS) modified by the Rayleigh-Taylor instability. The CDS results from both shock breakout and radiative cooling of gas that has passed through the reverse shock wave. The notch becomes dominant in the HV absorption during the late photospheric phase, ~60 d. The wind density deduced from the velocity of the CDS is consistent with the wind density found from the HV absorption produced by unshocked ejecta.

astro-ph↗

arXiv2006

Moderate Asphericity of the SN 2002ic Circumstellar Envelope

The polarization of SN 2002ic interacting with a dense circumstellar envelope is calculated in the context of the asymmetric version of a previously proposed spherical interaction model. The circumstellar envelope is taken to be oblate. The observed polarization (Wang et al. 2004) can be reproduced for an aspect ratio of 0.65-0.7 assuming inclination angles >60 degrees. This model predicts a weak sensitivity of the line profiles to the orientation, in agreement with the absence of significant variations of the line profiles among SN 2002ic-like supernovae. We propose a test for distinguishing between the binary and single star progenitor scenarios based upon the polarization distribution function for the growing sample of these events.

astro-ph↗

arXiv2005

Late Emission from the Type Ib/c SN 2001em: Overtaking the Hydrogen Envelope

The Type Ib/c supernova SN 2001em was observed to have strong radio, X-ray, and Halpha emission at an age of about 2.5 yr. Although the radio and X-ray emission have been attributed to an off-axis gamma-ray burst, we model the emission as the interaction of normal SN Ib/c ejecta with a dense, massive (3 Msun) circumstellar shell at a distance about 7 x 10^{16} cm. We investigate two models, in which the circumstellar shell has or has not been overtaken by the forward shock at the time of the X-ray observation. The circumstellar shell was presumably formed by vigorous mass loss with a rate (2-10) x 10^{-3} Msun/yr at 1000-2000 yr prior to the supernova explosion. The hydrogen envelope was completely lost, and subsequently was swept up and accelerated by the fast wind of the presupernova star up to a velocity of 30-50 km/s. Although interaction with the shell can explain most of the late emission properties of SN 2001em, we need to invoke clumping of the gas to explain the low absorption at X-ray and radio wavelengths.

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arXiv2004

The type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope

We present and analyse spectra of the Type IIn supernova 1994W obtained between 18 and 203 days after explosion. During the luminous phase (first 100 d) the line profiles are composed of three major components: (i) narrow P-Cygni lines with the absorption minima at -700 km/s; (ii) broad emission lines with BVZI ~4000 km/s; and (iii) broad, smooth wings, most apparent in H-alpha. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the supernova is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. We model the supernova deceleration and Thomson scattering wings to recover the density, radial extent and Thomson optical depth of the CS envelope during the first month. We reproduce the light curve with a hydrodynamical model and find it to be powered by a combination of internal energy leakage after the explosion of an extended pre-supernova (~10^15 cm) and luminosity from circumstellar interaction. We recover the pre-explosion kinematics of the CS envelope: it is close to homologous expansion with outer velocity ~1100 km/s and a kinematic age of ~1.5 yr. The CS envelope's high mass and kinetic energy, combined with its small age, strongly suggest that the CS envelope was explosively ejected about 1.5 yr before the supernova explosion.

astro-ph↗

arXiv2003

SN 1994W: evidence of explosive mass ejection a few years before explosion

We present and analyse spectra of the Type IIn supernova 1994W obtained between 18 and 202 days after explosion. During the first 100 days the line profiles are composed of three major components: (i) narrow P Cygni lines with absorption minima at -700 km/s; (ii) broad emission lines with BVZI ~4000 km/s; (iii) broad wings most apparent in H-alpha. These components are identified with the expanding circumstellar (CS) envelope (Sollerman, Cumming & Lundqvist 1998), shocked cool gas in the forward postshock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P Cygni lines from the supernova (SN) is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the Thomson optical depth of the CS envelope and its radial extent, 4E15 cm. The light curve, which we reproduce by a hydrodynamical model, is powered by a combination of internal energy leakage after the explosion of an extended presupernova (~1E15 cm) and luminosity from circumstellar interaction. We recover the pre-explosion kinematics of the CS envelope and find it to be close to homologous expansion with outmost velocity ~1100 km/s and a kinematic age of \~1.5 yr. The high mass and kinetic energy of the CS envelope strongly suggest that the CS envelope was explosively ejected only a few years before explosion.

astro-ph↗

arXiv1999

Probing supernovae ejecta by Halpha damping wings

It is predicted that H$α$ emission line at the early nebular epoch of type II-P supernovae may display robust observational effects of damping wings. This is illustrated by Monte-Carlo simulations. The strength of damping wing effects may be used to constrain parameters of the line-emitting zone. An anomalous redshift, width and red wing of H$α$ revealed by SN 1997D on day 150 are explained in terms of damping wing effects.

astro-ph↗

arXiv1999

The nature of SN 1997D: low-mass progenitor and weak explosion

We analyzed the spectra and light curve of the peculiar type II-P supernova 1997D to recover ejecta parameters. The optimal hydrodynamical model of SN 1997D, which meets observational constraints at the photospheric epoch, suggests a low explosion energy of about $10^{50}$ erg, ejecta mass around $6 M_{\odot}$, and presupernova radius near $85 R_{\odot}$. We confirm the previous result by Turatto et al. (\cite{tmy98}) that the ejecta contain a very low amount of radioactive $^{56}$Ni ($\approx 0.002 M_{\odot}$). Modelling the nebular spectrum supports the hydrodynamical model and permits us to estimate the mass of freshly synthesized oxygen (0.02--0.07 $M_{\odot}$). Combined with the basic results of stellar evolution theory the obtained parameters of SN 1997D imply that the progenitor was a star from the 8--12 $M_{\odot}$ mass range at the main sequence. The fact that at least some progenitors from this mass range give rise to core-collapse supernovae with a low kinetic energy ($\approx 10^{50}$ erg) and low amount of radioactive $^{56}$Ni ($\approx 0.002 M_{\odot}$) has no precedent and imposes important constraints on the explosion mechanism. We speculate that the galactic supernovae 1054 and 1181 could be attributed to SN 1997D-like events.

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