arXiv subjects

Nikolai Chugai

Publications and source records attributed to Nikolai Chugai.

At least 19 recordsLinked to original sources

arXiv2026

H\alpha\ clarifies picture of IIn supernova SN 2015da

Observational data on type IIn supernova SN 2015da are revisited to clarify some ambiguous issues of this phenomenon. The H alpha--emitting site is found to switch around day 90 from the circumstellar matter to the unshocked ejecta. This picture makes it possible to recover the expansion velocity of late time ejecta and to locate the dust formation in the inner zone of unshocked ejecta.The bolometric light curve and expansion velocities combined with modelling the circumstellar interaction imply that the supernova exploded with an energy of $\gtrsim 4\times10^{51}$ erg inside the circumstellar envelope with the mass of $\approx 14$ Msun. The recovered density of the circumstellar matter is consistent with the Thomson optical depth inferred from H alpha modelling on day 46.The observed circumstellar envelope is produced by an average mass loss rate of 0.035 Msun/yr during 400 yr before the supernova explosion.

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arXiv2025

Supernova in lost common envelope and SN 2006gy

A mechanism is proposed for synchronizing core-collapse supernova with a recent loss of a red supergiant (RSG) envelope in the common envelope regime. A perequisite for the synchronization is a moderate RSG expansion during final decade. This scenario is based on the phenomenon of preSN~II dense shell formed at the final stage of 10-20 yr as a result of powerfull mass loss. The energy deposition into the RSG envelope that powers the enormous mass loss rate is able to expand the RSG. The moderate expansion is sufficient for the close secondary component to plunge into the common envelope with a subsequent explosion of stripped helium core. Superluminous SN~2006gy is suggested to be the outcome of this scenario.

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arXiv2024

Study of X-ray emission from the S147 nebula with SRG/eROSITA: X-ray imaging, spectral characterization, and a multiwavelength picture

Simeis 147 (S147, G180.0-01.7, "Spaghetti nebula") is a supernova remnant (SNR) extensively studied across the entire electromagnetic spectrum, from radio to giga-electronvolt $γ$-rays, except in X-rays. Here, we report the first detection of significant X-ray emission from the entire SNR using data of the extended ROentgen Survey Imaging Telescope Array (eROSITA) onboard the Russian-German Spektrum Roentgen Gamma (SRG). The object is located at the Galactic anticenter, and its 3 deg size classifies it among the largest SNRs ever detected in X-rays. By employing $\sim$15 years of Fermi-LAT data, our study confirms the association of the remnant with a spatially coincident diffuse giga-electronvolt excess, namely 4FGL J0540.3+2756e or FGES J0537.6+2751. The X-ray emission is purely thermal, exhibiting strong O, Ne, and Mg lines; whereas it lacks heavier-Z elements. The emission is mainly confined to the 0.5-1.0 keV band; no significant emission is detected above 2.0 keV. Both a collisional plasma model in equilibrium and a model of nonequilibrium collisional plasma can fit the total spectrum. While the equilibrium model -- though statistically disfavored -- cannot be excluded by X-ray fitting, only the absorption column of the nonequilibrium model is consistent with expectations derived from optical extinction data. Adopting an expansion in a homogeneous medium of typical interstellar medium (ISM) density, the general SNR properties are broadly consistent with an expansion model that yields an estimated age of $\sim0.66-2\times10^{5}$ yr, that is a rather old age. The preference for an X-ray-emitting plasma in nonequilibrium, however, adds to the observational evidence that favors a substantially younger age. In a companion paper, we explore an SNR-in-cavity scenario, resulting in a much younger age that alleviates some of the inconsistencies of the old-age scenario.

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arXiv2024

Origin of broad He II 4686Å emission in early spectra of type IIP supernovae

We propose a model for the origin of the broad He II 4686A emission in the early spectrum of type II SN~2020jfo. The 4686A line is emitted presumably by dense fragments embedded into a hot gas of the forward shock wave. The fragments are produced as a result of a heavy braking of the dense low-mass shell at the ejecta boundary and a simultaneous Rayleigh-Taylor instability. The temperature of line-emitting fragments is $\approx$5$\times10^4$K. Calculations of ionization and excitation of helium and hydrogen account for the He II 4686A luminosity, the large flux ratio of He II 4686A/H$α$, and a significant optical depth of the 4686A line. We demonstrate that fragments heating by hot electrons behind the forward shock compensates cooling via the HeII 304A emission.

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arXiv2023

Discovery of a one-sided radio filament of PSR J0538+2817 in S147: escape of relativistic PWN leptons into surrounding supernova remnant?

We report the discovery of a faint radio filament near PSR J0538+2817 in the NVSS, CGPS, and the Rapid ASKAP Continuum Survey data. This pulsar is plausibly associated with the supernova that gave rise to the Spaghetti Nebula (Simeis 147). The structure is one-sided and appears to be almost aligned (within 17 degrees) with the direction of the pulsar's proper motion, but in contrast to the known cases of pulsar radio tails, it is located ahead of the pulsar. At the same time, this direction is also approximately (within 5 degrees) perpendicular to the axis of the extended non-thermal X-ray emission around the pulsar. No X-ray or optical emission is detected from the filament region, although the end point of the radio filament appears to be adjacent to a filament of H$_α$ emission. We speculate that this structure might represent a filament connecting pulsar wind nebula with the ambient interstellar medium filled with relativistic electrons escaping the pulsar nebula, i.e. a radio analogue of X-ray filaments of Guitar and Lighthouse PWNs and filaments of non-thermal radio emission in the Galactic Center.

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arXiv2023

Cosmic abundance of iron

I explore a possibility to estimate an upper limit of the current iron abundance of the barion matter. The upper limit is determined by the minimal iron abundance, at which the gamma-ray background, produced by the decay of $^{56}$Ni synthesised in the Universe to date, contradicts the observational MeV gamma-ray background. I calculate the gamma-ray background from SNe~Ia and SNe~II with the gamma-ray scattering and absorption in supernova envelope. It is shown that the model background does not contradict the observed MeV background, if the present day iron abundance of the barion matter is less than 15\% of the solar abundance.

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arXiv2022

Supernova 2009ip outbursts in 2012: From scenario to model

Spherical and aspherical models are presented for two outbursts in 2012 of supernova 2009ip. Models are based on a scenario which suggests that the August 2012 outburst is caused by the explosive shell ejection from LBV-presupernova. The model predicts an emergence of an unobserved outburst in late July 2012 related to a shock breakout and a subsequent diffusive radiative cooling of the ejected envelope. The luminosity of the first observed outburst in August 2012 was presumably powered by the central source, whereas the second, more powerful outburst in late September 2012, was caused by the ejecta interaction with the circumstellar envelope. Models provide estimates of the ejecta energy and mass along with the mass of the circumstellar shell.

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arXiv2022

Circumstellar shell and presupernova emission of SN 2020tlf

We address a phenomenon of a confined circumstellar (CS) dense shell and powerful presupernova emission of SN 2020tlf (type IIP). Modeling the \ha\ line and the circumstellar interaction implies the CS shell radius of $\sim$10$^{15}$ cm and the mass of $\sim0.2M_{\odot}$ lost during $\sim$6 yr prior to the explosion. Spectra and photometry of the supernova after the explosion do not show apparent signature of the material lost by the presupernova during its powerful luminosity. This material presumably resided in the inner zone of the CS shell. We present a hydrodynamic model of the outcome of a flash with the energy of $5\times10^{48}$ erg in the convective nuclear burning zone. The model predicts the ejection of outer layers of the presupernova ($\sim0.1M_{\odot}$) and the luminosity of $10^{40}$ erg s$^{-1}$ during several hundreds days in accord with observations. We propose the Lighthill mechanism of acoustic waves generation by the turbulence of the convective nuclear burning zone to account for the phenomenon of a compact CS shell of supernovae related to the core collapse.

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arXiv2022

Type Ibn supernova SN~2010al: Powerful mass loss half year prior to the explosion

Type Ibn supernova SN~2010al is explored to infer parameters of supernova and a circumstellar (CS) shell. The CS interaction model combined with the spectral model of 4600Å blend suggests the explosion of a WR star with the energy of $(1-1.5)\times10^{51}$ erg inside a dense confined CS shell with the mass of $\sim0.1$\msun\ and kinetic energy of $\sim 10^{48}$ erg. The confined CS shell has been formed during the last 0.4 yr prior to the core collapse.

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arXiv2021

SN 2008iy circumstellar interaction: Bright and lesser light effect

Optical photometry and spectra of the luminous type IIn supernova SN~2008iy are analysed in detail with implications for cosmic ray acceleration and the radio emission. The light curve and expansion velocities indicate ejecta with the kinetic energy of $3\times10^{51}$ erg to collide with the $\sim10$ Msun circumstellar envelope. The luminous Ha is explained as originated primarily from circumstellar clouds interacting with the forward shock. For the first time the fluorescent OI 8446A emission is used to demonstrate that the cloud fragmentation cascade spans a scale range > 2.3 dex. The narrow circumstellar Ha permitted us to estimate the acceleration efficiency of cosmic rays. The found value is close to the efficiency inferred in the same way for other two SNe~IIn, SN~1997eg and SN~2002ic. The efficiency of cosmic ray acceleration is utilized to reproduce the radio flux from SN~2008iy for the amplified magnetic field consistent with the saturated turbulent magnetic field in the diffusive shock acceleration mechanism.

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arXiv2021

Confined massive circumstellar shell in type IIL SN 2008fq

I explore a phenomenon of the circumstellar H alpha and H beta absorption lines in the spectrum of luminous type IIL SN 2008fq taken on day 6.8 after the discovery. The absorpion is identified with the radiatively accelerated preshock wind up to ~800 km/s. The required initial luminosity is attributed to the earlier circumstellar interaction with the confined dense shell of ~0.08 Msun. The modelling of similar luminous type IIL SN 1998S based on the same approach results in the comparable shell mass of ~0.1 Msun. More than 1 dex larger mass of the confined dense shell of both SNe IIL compared to that of type IIP supernovae is attributed to the larger progenitor mass of type IIL supernovae.

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arXiv2020

Early bolometric luminosity of SN 2013fs without photometry

The novel method is proposed for the reconstruction of the early bolometric light curve for supernovae IIP based on a set of spectra of H alpha emission during the first day after the shock breakout. The method exploits an effect of the radiative acceleration of the preshock circumstellar gas that is manifested in the broad H alpha wings. The efficiency of the method is demonstrated in the case of SN 2013fs with spectra taken between 6 and 10 hours after the shock breakout. The exceptional feature of this method is that it does not require the photometry, the distance, and the extinction.

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arXiv2020

Supernova Interaction with a Dense Detached Shell in SN 2001em

We carry out a comprehensive analysis of supernova \snem\ covering a period of 19 years since discovery. SN 2001em is the oldest supernova known to have undergone a metamorphosis from a stripped envelope to an interacting supernova. An early spectrum indicates it exploded as a Type Ib supernova. Later, the ejecta caught up with a dense circumstellar H-shell, ejected a few thousand years before the explosion, triggering interaction between the supernova ejecta and the dense shell, producing radio, X-ray and H$α$ emission. We use archival data with the Very Large Array in radio bands and with Chandra, XMM-NEWTON and SWIFT-XRT in X-ray bands, along with published H$α$ measurements. We combine these data with our low radio frequency observations with the Giant Metrewave Radio Telescope at two epochs covering three frequencies. While the observations missed the phase when the shock entered the dense shell, the X-rays indicate that the shock came out of the dense shell at around 1750 days. The data suggest a forward shock origin of the X-ray emission. Radio data show a spectral inversion at late epochs ($> 5000$\,d) at around 3 GHz, which mimics the properties of the central absorbed component seen in SN 1986J. A possible explanation for this component is that the progenitor of \snem\ was a massive binary system which had undergone a period of common envelope evolution. The hydrogen envelope from the \snem\ progenitor may have been lost as a result of binary interaction.

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arXiv2020

First day of type IIP supernova SN 2013fs: H$α$ from preshock accelerated gas

I explore the origin of an asymmetry of the H$α$ emission from a circumstellar (CS) shell around type IIP supernova SN 2013fs in the spectrum taken 10.3\,h after the shock breakout. A spherical model of the H$α$ emission from the CS shell that takes into account a preshock gas acceleration by the supernova radiation permits us to successfully reproduce the \ha H$α$ profile. Principal factors responsible for the H$α$ asymmetry are the high velocity of the accelerated CS preshock gas ($\sim 3000$\,km s$^{-1}$) and a low H$α$ Sobolev optical depth in a combination with an occultation of the H$α$ emission by the photosphere.

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arXiv2016

Explaining unusual line profiles of SN 2006gy

Origin of enigmatic line profiles of extremely luminous type IIn supernova SN~2006gy on day 96 is explored. Among conceivable possibilities the most preferred is the model that suggests holes in the optically thick cool dense shell (CDS). The line radiation emitted at the inner side of the opaque CDS escapes through the holes thus producing unusual line profile with the emission shifted redward. The holes could emerge as a result of a vigorous Rayleigh-Taylor instability leading to the CDS fragmentation. The model light curve with the CDS fragmentation is shown to be consistent with the SN~2006gy bolometric light curve.

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arXiv2015

X-ray and radio emission from Type IIn supernova SN 2010jl

We present all X-ray and radio observations of the Type IIn supernova SN 2010jl. The X-ray observations cover a period up to day 1500 with Chandra, XMM-Newton, NuSTAR and Swift-XRT. The Chandra observations after 2012 June, the XMM-Newton observation in 2013 November, and most of the Swift-XRT observations until 2014 December are presented for the first time. All the spectra can be fitted by an absorbed hot thermal model except for \chandra spectra on 2011 October and 2012 June when an additional component is needed. Although the origin of this component is uncertain, it is spatially coincident with the supernova and occurs when there are changes to the supernova spectrum in the energy range close to that of the extra component, indicating that the emission is related to the supernova. The X-ray light curve shows an initial plateau followed by a steep drop starting at day $\sim 300$. We attribute the drop to a decrease in the circumstellar density. The column density to the X-ray emission drops rapidly with time, showing that the absorption is in the vicinity of the supernova. We also present Very Large Array radio observations of SN 2010jl. Radio emission was detected from \sn from day 570 onwards. The radio light curves and spectra suggest that the radio luminosity was close to its maximum at the first detection. The velocity of the shocked ejecta derived assuming synchrotron self absorption is much less than that estimated from the optical and X-ray observations, suggesting that free-free absorption dominates.

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arXiv2013

A Wolf in Sheepskin: Extraordinary Supernova 2012au Veiled Behind Ordinary Radio Emission

We present extensive radio and X-ray observations of SN\, 2012au, the energetic radio luminous supernova of type Ib that may be a link between subsets of hydrogen-poor superluminous and normal core-collapse supernovae. The observations closely follow models of synchrotron emission from shock heated circum-burst medium that has a wind density profile ($ρ\propto r^{-2}$). We infer a sub-relativistic velocity for the shock wave $v \approx 0.2\,c$ and a radius of $r \approx 1.4 \times 10^{16} \rm cm$ at 25 days after the estimated date of explosion. For a constant wind velocity of 1000 km/s we determine the constant mass loss rate of the progenitor to be $\dot{M} = 3.6 \times 10^{-6} \rm M_{\odot} yr^{-1}$, consistent with the estimates from X-ray observations. We estimate the total internal energy of the radio emitting material to be $E \approx 10^{47} \rm erg$, which is intermediate to SN\,1998bw and SN\,2002ap. Evolution of the radio light curves of SN\,2012au is consistent with interaction with a smoothly distributed circum-burst medium and absence of stellar shells ejected from previous outbursts out to $r \approx 10^{17} \rm cm$ from the supernova site. Based on this we conclude that the evolution of the SN\,2012au progenitor star was relatively quiet during the final years preceding explosion. We find that the bright radio emission from SN2012au was not dissimilar from other core collapse supernovae despite it's extraordinary optical properties. We speculate that it was the nature of the explosion that led to the unusual demise of the SN2012au progenitor star.

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arXiv2012

Radio and X-ray observations of SN 2006jd: Another strongly interacting Type IIn supernova

We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope and Expanded Very Large Array; at X-ray wavelengths with {\em Chandra}, {\em XMM-Newton} and {\em Swift}-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free-free absorption by cool gas mixed into the nonthermal emitting region; external free-free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density $\sim 10^6$ cm$^{-3}$ at a radius $r\sim 2\times 10^{16}$ cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than $r^{-2}$ because of the slow evolution of the unabsorbed emission.

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