gk persei latest outburst cataclysmic variable stars

GK Persei's Latest Outburst: A Study into Cataclysmic Variable Star Systems

Introduction: GK Persei and the Swift Observatory's Role in Observing the Outburst

Chinese researchers have examined data from NASA's Swift observatory, which extensively monitored an outburst in the GK Persei cataclysmic variable system. Findings, detailed in a February 20 arXiv preprint, offer deeper insights into its nature.

Understanding Cataclysmic Variables (CVs)

Cataclysmic variables (CVs) are binary star systems where a white dwarf accretes material from a companion star. These systems undergo sudden, significant brightness increases before returning to a quiescent state. They have been identified in diverse astrophysical environments, including the Milky Way's core, the solar neighborhood, and both open and globular clusters.

Accretion Disks and Thermal Instability in CVs

In cataclysmic variables (CVs), mass transfer from the companion star typically occurs via an accretion disk surrounding the white dwarf. In certain cases, thermal instabilities within the disk trigger outbursts, classified as dwarf novae (DN), which are CVs exhibiting semi-periodic eruptions.

Polars vs. Intermediate Polars (IPs): Distinguishing CV Subclasses

Polars represent a distinct subclass of cataclysmic variables (CVs), characterized by the presence of an intensely strong magnetic field in their white dwarfs. In contrast, intermediate polars (IPs) feature a magnetic white dwarf that spins asynchronously with the system's orbital period, generating rapid oscillations corresponding its spin period.

GK Persei: A Detailed Overview

GK Persei (A 0327+43 or Nova Persei 1901) is a cataclysmic variable located approximately 1,400 light-years away. It consists of a magnetized white dwarf and a K2-type subgiant star with a mas ranging from 0.25 to 0.48 solar masses. Classified as an intermediate polar (IP), its white dwarf possesses a magnetic field strength of approximately 0.5 megagauss (MG).

The History of GK Persei's Outbursts

GK Persei experienced a classical eruption in 1901, making it the second closest nova ever recorded. The system's first documented dwarf nova (DN) outburst occurred in 1948, followed by numerous subsequent DN events, including the most recent ones in 2010, 2015, and 2018.

A Breakthrough Study of the 2010 Outburst

A research team led by Songpeng Pei from Liupanshui Normal University in China conducted an in-depth analysis of the GK Persei outburst that occurred 15 years ago. Utilizing Swift data spanning from 1.95 days post-eruption to 13.9 days before the outburst's peak, they examined the evolution of its X-ray light curves and spectra.

Advancing Our Understanding of GK persei's Intermediate Polar Nature

"Our X-ray and UV observations of the 2010 outburst have significantly advanced our understanding of this system's intermediate polar (IP) nature, especially its rare dwarf nova (DN)-like outburst behavior within a magnetic cataclysmic variable (CV) that also experiences classical nova events," the researchers stated.

Key Findings from the Study: X-ray and UV Observations

The analysis revealed that GK Persei's X-ray spectrum exhibits considerable complexity. Pei's team conducted a timing analysis, identifying at least two distinct sources of X-ray emission: one responsible for hard X-ray (2.0-10 keV) and another contributing to soft X-ray emissions (0.3-2.0 keV).

White Dwarf Spin Period and Spin Modulation in Different Energy Bands

Additionally, the study identified a white dwarf spin period of approximately 351.32 seconds within the 2-10 keV range during the 2010 outburst. Spin modulation was also observed in the softer energy band (0.3—2 keV) during the second half of the observations—an effect absent in the 2015 and 2018 outbursts—albeit with a lower amplitude compared to the 2—10 keV range.

Mass Accretion Rate Variations Across Different Outbursts

The study also revealed significant fluctuations in GK Persei's mass accretion rate across different DN outbursts. Notably, the values derived for the 2010 and 2018 outbursts were approximately an order of magnitude lower than those measured for the 2015 outburst.

Soft X-ray Emissions: Possible Origins

According to the researchers, the results indicate the GK Persei's soft X-ray emission likely originates from who distinct sources: near the magnetic poles and from a wind or surrounding circumstellar material.

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