XMM-Newton observations of the extragalactic microquasar S twenty-six and their implications for PeV cosmic rays

XMM-Newton observations of the extragalactic microquasar S twenty-six and their implications for PeV cosmic rays

The extragalactic microquasar S twenty-six has the most powerful jets observed in accreting binaries, with a kinetic luminosity of L jet approximately ten to the forty erg per second. According to the jet-disk symbiosis model, this implies that the accretion power to the stellar black hole at the core of the system should be very super-Eddington, on the order of L acc approximately equal to L jet. However, the observed X-ray flux of this system, measured by the Chandra and XMM-Newton telescopes, indicates an apparent very sub-Eddington accretion luminosity of L X approximately ten to the thirty-seven erg per second, orders of magnitude smaller than the jet power. We present here a preliminary investigation of the relationship between jet and disk power, analyze an X-ray observation of S twenty-six obtained with XMM-Newton, and propose an explanation for the emission. We also examine the acceleration and distribution of the particles to discuss the feasibility of microquasars as potential PeVatron sources, exploring their ability to produce cosmic rays with energies of about one PeV or higher.

One. Introduction

S twenty-six is a microquasar located in the galaxy NGC seven thousand seven hundred ninety-three, at a distance of three point nine megaparsecs, whose nebula has a size of approximately three hundred fifty by one hundred eighty-five parsecs. According to observations in the optical/X-ray band, it was shown that this microquasar has the most powerful jets in accreting binaries, with a mechanical luminosity of L jet approximately five times ten to the forty erg per second, and identified nonthermal X-rays produced in the core of the system. On the other hand, the radio lobe structure was resolved, and it was suggested that the radio emission from the terminal region of the jets is consistent with synchrotron radiation. X-ray hotspots approximately twenty parsecs farther out than the peak of the radio intensity in the lobes were identified, and it was argued that this emission is most likely of thermal origin.

A key parameter to characterize microquasars is the accretion rate of matter onto the compact object, which proceeds in three basic regimes, depending on the relation of the actual accretion rate to the Eddington rate. In super-Eddington regimes, the inner part of the disk launches powerful winds with mass-loss rates similar to the accretion rate. Following the jet-disk symbiosis model, the kinetic luminosity of the jet of S twenty-six estimated by implies that the accretion luminosity onto the compact object should be highly super-Eddington, of the order of L acc approximately equal to L jet. However, the observed X-ray flux from the core of the system, measured by Chandra and XMM-Newton telescopes, indicates an apparent very sub-Eddington luminosity of L X approximately ten to the thirty-seven erg per second, orders of magnitude smaller than the jet power.

In this preliminary work, we hypothesize that the compact object is a black hole of ten solar masses, accreting at super-Eddington rates, and that its actual accretion power is a few times ten to the forty erg per second (the Eddington luminosity for this black hole is approximately ten to the thirty-nine erg per second). We suggest that some energy should also be extracted from the ergosphere of the spinning black hole to provide enough power for the jet. The emission from the disk is reprocessed in the dense wind of the disk and is not observable in X-rays. We first analyze the XMM-Newton observation and then describe our theoretical model for particle acceleration and distribution. We present our results in Section four and conclude with some final remarks.