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Non-conservative Mass Transfer in the Neutron Star Stripping Model

Nikita Kramarev, Andrey Yudin

TL;DR

This paper addresses non-conservative mass transfer in the neutron-star stripping model for NS–NS binaries, aiming to explain the 1.7 s delay between GW loss and GRB detection in GW170817–GRB170817A and related EM features. It extends the angular-momentum evolution framework to include mass loss from the system via a parameter chi, comparing fully conservative (chi=1) and fully non-conservative (chi=0) limits, with corotation and Roche-lobe constraints. The results show that allowing non-conservative transfer lengthens the stable mass-transfer phase from tenths of a second to several seconds, altering the remnant outcome and enabling a second, delayed EM signal from ejecta interaction. The findings suggest that detailed energy-balance modeling and ejecta dynamics are crucial to quantify the EM signatures and that the stripping scenario can produce double-peaked GRBs like GRB170817A and possibly GRB190425.

Abstract

The process of long-term stable mass transfer (or stripping) in a close neutron star binary system is possible at a sufficiently large initial asymmetry of the component masses. At the final stage of the evolution of such systems, the low-mass neutron star fills its Roche lobe, whereupon its mass is gradually transferred to the more massive component. At a certain point, the stability of the mass transfer is lost, causing the minimum-mass neutron star to explode. In the present stripping calculations, the effect of non-conservative mass transfer has been taken into account for the first time, resulting in an increase in the duration of stable mass transfer from a few tenths of a second to a few seconds. This allows the time delay of 1.7 s between the loss of the gravitational-wave signal and the detection of the gamma-ray burst from the multimessenger event GW170817-GRB170817A to be naturally explained. The interaction of the envelope of the exploded minimum-mass neutron star with the matter ejected during non-conservative mass transfer may explain two episodes in the light curve of this gamma-ray burst.

Non-conservative Mass Transfer in the Neutron Star Stripping Model

TL;DR

This paper addresses non-conservative mass transfer in the neutron-star stripping model for NS–NS binaries, aiming to explain the 1.7 s delay between GW loss and GRB detection in GW170817–GRB170817A and related EM features. It extends the angular-momentum evolution framework to include mass loss from the system via a parameter chi, comparing fully conservative (chi=1) and fully non-conservative (chi=0) limits, with corotation and Roche-lobe constraints. The results show that allowing non-conservative transfer lengthens the stable mass-transfer phase from tenths of a second to several seconds, altering the remnant outcome and enabling a second, delayed EM signal from ejecta interaction. The findings suggest that detailed energy-balance modeling and ejecta dynamics are crucial to quantify the EM signatures and that the stripping scenario can produce double-peaked GRBs like GRB170817A and possibly GRB190425.

Abstract

The process of long-term stable mass transfer (or stripping) in a close neutron star binary system is possible at a sufficiently large initial asymmetry of the component masses. At the final stage of the evolution of such systems, the low-mass neutron star fills its Roche lobe, whereupon its mass is gradually transferred to the more massive component. At a certain point, the stability of the mass transfer is lost, causing the minimum-mass neutron star to explode. In the present stripping calculations, the effect of non-conservative mass transfer has been taken into account for the first time, resulting in an increase in the duration of stable mass transfer from a few tenths of a second to a few seconds. This allows the time delay of 1.7 s between the loss of the gravitational-wave signal and the detection of the gamma-ray burst from the multimessenger event GW170817-GRB170817A to be naturally explained. The interaction of the envelope of the exploded minimum-mass neutron star with the matter ejected during non-conservative mass transfer may explain two episodes in the light curve of this gamma-ray burst.
Paper Structure (8 sections, 18 equations, 2 figures)

This paper contains 8 sections, 18 equations, 2 figures.

Table of Contents

  1. INTRODUCTION
  2. FORMULATION OF THE PROBLEM
  3. General Assumptions
  4. The Equation of Change in the Total Angular Momentum of the System
  5. Allowance for the Non-conservativeness
  6. The Mass Transfer Stability Criterion
  7. RESULTS OF OUR CALCULATIONS
  8. DISCUSSION AND CONCLUSIONS

Figures (2)

  • Figure 1: Evolution of the distance between the components with masses $M_1=1.7M_{\mathrm{\odot}}$ and $M_2=0.8M_{\mathrm{\odot}}$ for different mass transfer regimes. The blue solid line corresponds to the case of conservative mass transfer without accretion spin-up. The red dashed line illustrates conservative mass transfer (with spin-up). The purple dash–dotted line indicates the evolution of the distance under the assumption that all of the accreting matter is ejected from the system. For details, see the text.
  • Figure 2: Evolution of the donor mass during stable mass transfer. The designations and initial conditions are the same as those for Fig. \ref{['Fig1distance']}.