arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 271 records · Page 15Linked to original sources

arXiv2015

A call for a paradigm shift from neutrino-driven to jet-driven core-collapse supernova mechanisms

Three-dimensional (3D) simulations in recent years have shown severe difficulties producing 10^51 erg explosions of massive stars with neutrino based mechanisms while on the other hand demonstrated the large potential of mechanical effects, such as winds and jets in driving explosions. In this paper we study the typical time-scale and energy for accelerating gas by neutrinos in core-collapse supernovae (CCSNe) and find that under the most extremely favorable (and probably unrealistic) conditions, the energy of the ejected mass can reach at most 5X10^50 erg. More typical conditions yield explosion energies an order-of-magnitude below the observed 10^51 erg explosions. On the other hand, non-spherical effects with directional outflows hold promise to reach the desired explosion energy and beyond. Such directional outflows, which in some simulations are produced by numerical effects of 2D grids, can be attained by angular momentum and jet launching. Our results therefore call for a paradigm shift from neutrino-based explosions to jet-driven explosions for CCSNe.

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arXiv2014

Close stellar binary systems by grazing envelope evolution

I suggest a spiral-in process by which a stellar companion graze the envelope of a giant star while both the orbital separation and the giant radius shrink simultaneously, and a close binary system is formed. The binary system might be viewed as evolving in a constant state of `just entering a common envelope (CE) phase'. In cases where this process takes place it can be an alternative to the CE evolution where the secondary star is immerses in the giant's envelope. The grazing envelope evolution (GEE) is made possible only if the companion manages to accrete mass at a high rate and launch jets that remove the outskirts of the giant envelope, hence preventing the formation of a CE . The high accretion rate is made possible by the accretion disk that launches jets that efficiently carry the excess angular momentum and energy from the accreted mass. The orbital decay itself is caused by the gravitational interaction of the secondary star with the envelope inward to its orbit, i.e., dynamical friction (gravitational tide). Mass loss through the second Lagrangian point can carry additional angular momentum and envelope mass. The GEE lasts for tens to hundreds of years. The high accretion rate with peaks lasting months to years might lead to a bright object termed intermediate luminosity optical transient (ILOT; Red Novae; Red Transients). A bipolar nebula and/or equatorial ring are formed around the binary remnant

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arXiv2014

Constraining the double-degenerate scenario for Type Ia supernovae from merger ejected matter

We follow the mass expelled during the WD-WD merger process in a particular case of the Double-Degenerate (DD) scenario for Type Ia supernovae (SNe Ia), and find that the interaction of the SN ejecta with the resulting wind affects the early (first day) light curve in a way that may be in conflict with some SN Ia observations, if the detonation occurs shortly after the merger (i.e., $10^3~{\rm sec} \lesssim t_{\rm exp} \lesssim 1~{\rm day}$). The main source of the expelled mass is a disk-wind, or jets that are launched by the accretion disk around the more massive WD during the viscous phase of the merger. This disk-originated matter (DOM) will be shocked and heated by the SN ejecta from an explosion, leading to additional radiation in the early lightcurve. This enhanced early radiation could then be interpreted as an explosion originating from a progenitor having an inferred radius of one solar radius or more, in conflict with observations of SN 2011fe.

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arXiv2014

The fraction of type Ia supernovae exploding inside planetary nebulae (SNIPs)

Using three independent directions we estimate that the fraction of type Ia supernovae (SNe Ia) exploding inside planetary nebulae (PNe), termed SNIPs,is at least ~20%. Our three directions are as follows. (i) Taking the variable sodium absorption lines in some SN Ia to originate in a massive circumstellar matter (CSM), as has been claimed recently, we use the results of Sternberg et al. (2014) to imply that > ~20% of SN Ia occur inside a PN (or a PN descendant), hence classify them as SNIPs. (ii) We next use results that show that whenever there are hydrogen lines in SN Ia the hydrogen mass in the CSM is large (> 1 M_Sun), hence the explosion is a SNIP. We make the simplest assumption that the probability for explosion is constant in time for up to about 10^5 yrs after the merger of the core with the white dwarf (WD) in the frame of the core-degenerate scenario. This results with at least few x10 of SNe Ia that may have a SNIP origin. (iii) We examine the X-ray morphologies of 13 well-resolved close-by SN remnants (SNRs) Ia and derive a crude upper limit, according to which 10-30% of all SNRs Ia possess opposite ear-like features, which we take as evidence of SNIP origin. Our results, together with several other recent results, lead us to conclude that the two scenarios most contributing to SNe Ia are the core degenerate and the double degenerate scenarios. Together these two account for >95% of all SNe Ia.

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arXiv2014

Heating Cold Clumps by Jet-inflated Bubbles in Cooling Flow Clusters

We simulate the evolution of dense-cool clumps embedded in the intra-cluster medium (ICM) of cooling flow clusters of galaxies in response to multiple jet-activity cycles, and find that the main heating process of the clumps is mixing with the hot shocked jets' gas, the bubbles, while shocks have a limited role. We use the PLUTO hydrodynamical code in two dimensions with imposed axisymmetry, to follow the thermal evolution of the clumps. We find that the inflation process of hot bubbles, that appear as X-ray deficient cavities in observations, is accompanied by complicated induced vortices inside and around the bubbles. The vorticity induces efficient mixing of the hot bubbles' gas with the ICM and cool clumps, resulting in a substantial increase of the temperature and entropy of the clumps. For the parameters used by us heating by shocks barely competes with radiative cooling, even after 25 consecutive shocks excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary structure that can turn to observed optical filaments. We find that not all clumps are heated. Those that cool to very low temperatures will fall in and feed the central supermassive black hole (SMBH), hence closing the feedback cycle in what is termed the cold feedback mechanism.

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arXiv2014

Wave-driven stellar expansion and binary interaction in pre-supernova outbursts

We suggest that the main outcome of energy leakage carried by waves from the core to the envelope of pre-collapse massive stars is envelope expansion rather than major mass ejection. We show that the propagating waves add to the pressure in the envelope at radii smaller than the radius where the convection driven by the waves becomes supersonic, the driven radius. The extra wave pressure and wave energy dissipation lead to envelope expansion. Using the numerical code MESA we show that the envelope expansion absorbs most of the energy carried by the waves. A possible conclusion from our results is that pre-explosion outbursts (PEOs) result from a binary companion accreting mass from the extended envelope and releasing a huge amount of energy. The accreting companion is likely to expel mass in a bipolar morphology, e.g., jets and an equatorial ring.

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arXiv2014

Final common envelope ejection by migration and jets

I summarize recent analytical and numerical studies of the common envelope (CE) process and suggest to replace the commonly used alpha-prescription for the CE ejection by a prescription based on final migration and jets launched by the companion or the core of the giant stellar primary. In the migration process the core-companion binary systems is surrounded by a highly oblate (flatten) envelope, a thick circumbinary disk, formed by the large angular momentum transferred from the core-companion system to the envelope. I then show that the energy that can be released by an accreting main sequence companion can surpass the mutual gravitational energy of the core and the companion. An efficient channel to leash the accretion energy to expel the CE is through jets operating via a feedback mechanism (JFM).

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arXiv2014

First versus second generation planet formation in post common envelope binary (PCEB) planetary systems

We examine planets orbiting post-common envelope binaries (PCEBs) from the perspective of angular momentum evolution, and conclude that the planets are more likely to be first generation (FG) planets than second generation (SG) planets. FG planets were born together with the parent stars, while SG planets form later from a SG proto-planetary disk formed by mass-loss from the evolved primary star during its red giant branch (RGB) phase or asymptotic giant branch (AGB) phase. We find that in some systems the SG scenario requires that more than twenty percent of the SG proto-planetary disk mass ends in planets. Although we cannot rule out SG planet formation in these systems, this fraction of mass that ends in planets is much higher than the value commonly used in planet formation theories. On the other hand, we find that for each of the systems we can build a progenitor system composed of a main-sequence binary system orbited by the appropriate planets. This can be done if the secondary star was in a resonance with the inner planet. To account for the progenitor properties we suggest that in cases where the secondary star has a mass of ~ 0.1-0.2Msun, it was formed in the same way planets are formed, i.e., from a disk.

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arXiv2014

What sodium absorption lines tell us about type Ia supernovae

We propose that the sodium responsible for the variable NaI D absorption lines in some type Ia supernovae (SN Ia) originate mainly from dust residing at ~1 pc from the supernovae. In this Na-from-dust absorption (NaDA) model the process by which the SN Ia peak luminosity releases sodium from dust at 1 pc from the SN is similar to the processes by which solar radiation releases sodium from cometary dust when comets approach a distance of 1 AU from the Sun. The dust grains are not sublimated but rather stay intact, and release sodium by photon-stimulated desorption (PSD; or photo-sputtering). Some of the Na might start in the gas phase before the explosion. Weakening in absorption strength is caused by Na-ionizing radiation of the SN. We apply the NaDA model to SN 2006X and SN 2007le, and find it to comply better with the observed time variability of the NaI D absorption lines than the Na recombination model. The mass in the dusty shell of the NaDA model is much too high to be accounted for in the single-degenerate scenario for SN Ia. Therefore, the presence of variable NaI D lines in some SN Ia further weakens the already very problematic single-degenerate scenario for SN Ia.

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arXiv2014

Limits on core driven ILOT outbursts of asymptotic giant branch stars

We find that single-star mechanisms for Intermediate Luminosity Optical Transients (ILOTs; Red Transients; Red Novae) which are powered by energy release in the core of asymptotic giant branch (AGB) stars are likely to eject the entire envelope, and hence cannot explain ILOTs in AGB and similar stars. There are single-star and binary models for the powering of ILOTs, which are eruptive stars with peak luminosities between those of novae and supernovae. In single-star models the ejection of gas at velocities of ~500-1000 km/s and a possible bright ionizing flash, require a shock to propagate from the core outward. Using a self similar solution to follow the propagation of the shock through the envelope of two evolved stellar models, a 6Mo AGB star and an 11Mo yellow supergiant (YSG) star, we find that the shock that is required to explain the observed mass loss also ejects most of the envelope. We also show that for the event to have a strong ionizing flash the required energy expels most of the envelope. The removal of most of the envelope is in contradiction with observations. We conclude that single-star models for ILOTs of evolved giant stars encounter severe difficulties.

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arXiv2014

Triggering jet-driven explosions of core-collapse supernovae by accretion from convective regions

We find that convective regions of collapsing massive stellar cores possess sufficient stochastic angular momentum to form intermittent accretion disks around the newly born neutron star (NS) or black hole (BH), as required by the jittering-jets model for core-collapse supernova (CCSN) explosions. To reach this conclusion we derive an approximate expression for stochastic specific angular momentum in convection layers of stars, and using the mixing-length theory apply it to four stellar models at core-collapse epoch. In all models, evolved using the stellar evolution code MESA, the convective helium layer has sufficient angular momentum to form an accretion disk. The mass available for disk formation around the NS or BH is 0.1-1.2Mo; stochastic accretion of this mass can form intermittent accretion disks that launch jets powerful enough to explode the star according to the jittering-jets model. Our results imply that even if no explosion occurs after accretion of the inner ~2-5Mo of the core onto the NS or BH (the mass depends on the stellar model), accretion of outer layers of the core will eventually lead to an energetic supernova explosion.

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arXiv2014

A pre-explosion optical transient event from a white dwarf merger with a giant supernova progenitor

We examine rare evolutionary routes of binary systems where the initially more massive primary star of ~5.5-8.5Mo, forms a white dwarf (WD), while the secondary star of 4Mo < M_2,0 < M_1,0 accretes mass from the evolved primary and later terminates as a core collapse supernova (CCSN). In such a WD-NS reverse evolution a neutron star (NS) or a potential NS-progenitor massive core is formed after the WD. These SN explosions are likely to be preceded by strong interaction of the WD with the giant secondary's core, leading to an Intermediate-Luminosity Optical Transient (ILOT; Red Transient; Red Nova) event, weeks to years before the explosion. The common envelope phase of the WD and the giant ends with a merger that forms an ILOT, or an envelope ejection that leads, after a CCSN of the giant's core, to a NS-NS or WD-NS surviving binary. The WD could suffer a thermonuclear explosion, that might be observed as a Type Ia SN. Most of these CCSN and thermonuclear explosions will be peculiar. We calculate the stellar evolution of representative cases using Modules for Experiments in Stellar Astrophysics (MESA). The occurrence rate of these systems is ~3-5 percent of that of CCSNe.

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arXiv2013

Exploding Core-Collapse Supernovae by Jets-Driven Feedback Mechanism

We study the flow structure in the jittering-jets explosion model of core-collapse supernovae (CCSNe) using 2.5D hydrodynamical simulations and find that some basic requirements for explosion are met by the flow. In the jittering-jets model jets are launched by intermittent accretion disk around the newly born neutron star and in stochastic directions. They deposit their kinetic energy inside the collapsing core and induce explosion by ejecting the outer core. The accretion and launching of jets is operated by a feedback mechanism: when the jets manage to eject the core, the accretion stops. We find that even when the jets' directions are varied around the symmetry axis they inflate hot bubbles that manage to expel gas in all directions. We also find that although most of the ambient core gas is ejected outward, sufficient mass to power the jets is accreted (0.1Mo), mainly from the equatorial plane direction. This is compatible with the jittering jets explosion mechanism being a feedback mechanism.

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arXiv2013

Accelerating very fast gas in the supernova impostor sn 2009ip with jets from a stellar companion

Using hydrodynamical numerical simulations we show that high-velocity ejecta with 10,000 km/s in the outbursts of the supernova impostor SN 2009ip and similar luminous blue variable (LBV) stars can be explained by the interaction of fast jets, having velocity of 2000-3000 km/s, with a circumbinary shell (extended envelope). The density profile in the shell is very steep such that the shock wave, that is excited by the jets' interaction with the shell, accelerates to high velocities as it propagates outward. The amount of very fast ejecta is small, but sufficient to account for some absorption lines. Such an extended envelope can be formed from the binary interaction and/or the unstable phase of the LBV primary star. The jets themselves are launched by the more compact secondary star near periastron passages.

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arXiv2013

Planetary influences on photometric variation of the extreme helium subdwarf KIC10449976

We propose that the unstable 3.9days photometric periodicity of the hot subdwarf (sdO) KIC10449976 results from a tidally locked planet that is heated to 5000K by the UV radiation from the hot sdO star. Although the bolometric radiation from the planet is very small relative to that of the star, in the visible band the planet contributes 0.07% of the light, sufficient to explain the observed periodic behavior. In our proposed scenario the stochastic variations in period and light amplitude are attributed to weather on the planet. Namely, streams on the surface and thermal variations in the planet's atmosphere that are driven by the heating and by the planet rotation lead to stochastic changes in the amount of radiation emitted by the planets. We predict that a careful monitoring will reveal a gas giant planet at an orbital separation of 8.3Rsun from KIC10449976.

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arXiv2013

The explosion of supernova 2011fe in the frame of the core-degenerate scenario

We argue that the properties of the Type Ia supernova (SN Ia) SN 2011fe can be best explained within the frame of the core-degenerate (CD) scenario. In the CD scenario a white dwarf (WD) merges with the core of an asymptotic giant branch (AGB) star and forms a rapidly rotating WD, with a mass close to and above the critical mass for explosion. Rapid rotation prevents immediate collapse and/or explosion. Spinning down over a time of 0-10 Gyr brings the WD to explosion. A very long delayed explosion to post-crystallization phase, which lasts for about 2 Gyr leads to the formation of a highly carbon-enriched outer layer. This can account for the carbon-rich composition of the fastest-moving ejecta of SN 2011fe. In reaching the conclusion that the CD scenario best explains the observed properties of SN 2011fe we consider both its specific properties, like a very compact exploding object and carbon rich composition of the fastest-moving ejecta, and the general properties of SNe Ia.

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arXiv2013

Powering the Second 2012 Outburst of SN 2009ip by Repeating Binary Interaction

We propose that the major 2012 outburst of the supernova impostor SN 2009ip was powered by an extended and repeated interaction between the Luminous Blue Variable (LBV) and a more compact companion. Motivated by the recent analysis of Margutti et al. (2013) of ejected clumps and shells we consider two scenarios. In both scenarios the major 2012b outburst with total (radiated + kinetic) energy of ~5 x 10^{49} erg was powered by accretion of 2-5 solar masses onto the companion during a periastron passage (the first passage) of the binary system approximately 20 days before the observed maximum of the light curve. In the first scenario, the surviving companion scenario, the companion was not destructed and still exists in the system after the outburst. It ejected partial shells (or collimated outflows or clumps) for two consecutive periastron passages after the major one. The orbital period was reduced from ~38 days to ~25 days as a result of the mass transfer process that took place during the first periastron passage. In the second scenario, the merger scenario, some partial shells/clumps were ejected also in a second periastron passage that took place ~20 days after the first one. After this second periastron passage the companion dived too deep into the LBV envelope to launch more outflows, and merged with the LBV.

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arXiv2013

Impulsive Ejection of Gas In Bipolar Planetary Nebulae

We simulate the formation of bipolar planetary nebulae (PNe) through very short impulsive mass ejection events from binary systems, where the asymptotic giant branch (AGB) star ejects a mass shell that is accelerated by jets launched from a compact companion. The acceleration process takes place at very short distances from the binary system, such that the photon-diffusion time is long enough to prevent rapid cooling of the shocked jets' material. When the shocked jets' gas density is lower than the shell density the flow becomes Rayleigh-Taylor unstable and dense clumps are formed in the flow. At later times a PN with clumpy lobes that have a linear distance-velocity relation will be observed. This process might account for the formation of bipolar PNe with clumpy lobes, such as NGC 6302. The energy radiated during the months to years duration of such an event will appear as an intermediate-luminosity optical transient (ILOT)

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