A Multi-Component Analysis Indicates a Positronic Major Flare in GRS 1915+105

TL;DR

This study applies a spectral modeling technique to analyze a major flare in GRS 1915+105, revealing multiple self-absorbed plasmoids, their magnetic nature, and energy requirements for ejection, providing new insights into the flare's physics.

Contribution

It introduces a spectral analysis method for plasmoid ejection in microquasars, determining plasma structure, composition, and energy flux independently of prior estimates.

Findings

Identified three self-absorbed components during the flare.

Determined plasmoids are electron-positron, not protonic.

Estimated energy flux for plasmoid ejection between 4.1×10^{37} and 6.1×10^{38} erg/s.

Abstract

A modeling strategy that is adapted to the study of synchrotron-self absorbed plasmoids that was developed for the quasar, Mrk 231, in Reynolds et al (2009) is applied to the microquasar GRS 1915+105. The major flare from December 1993 shows spectral evidence of three such self-absorbed components. The analysis yields an estimate of the power that is required to eject the plasmoids from the central engine that is independent of other estimates that exist in the literature for different flares. The technique has an advantage since the absorbed spectrum contains an independent constraint provided by the optical depth at each epoch of observation. The modeling procedure presented here self-consistently determines the dimensions of the radio emitting plasma from the spectral shape. Thus, structural dimensions are determined analytically that can be much smaller than interferometer beam-widths. A synthesis of the time evolution of the components allows one to address the fundamental uncertainties in previous estimates. First, the plasma is not protonic, but it is comprised of an electron-positron gas. The minimum electron energy is determined to be less than six times the electron rest mass energy. The analysis also indicates that the plasmoids are ejected from the central engine magnetically dominated. The temporal behavior is one of magnetic energy conversion to mechanical energy as the plasmoids approach equipartition. The time dependent models bound the impulsive energy flux, $Q$, required to eject the individual major flare plasmoids from the central engine to, $4.1 \times 10^{37}\mathrm{erg/s}< Q < 6.1 \times 10^{38} \mathrm {ergs/s}$.