Dissecting magnetar variability with Bayesian hierarchical models

Abstract

Neutron stars are a prime laboratory for testing physical processes under conditions of strong gravity, high density, and extreme magnetic fields. Among the zoo of neutron star phenomena, magnetars stand out for their bursting behaviour, ranging from extremely bright, rare giant flares to numerous, less energetic recurrent bursts. The exact trigger and emission mechanisms for these bursts are not known; favoured models involve either a crust fracture and subsequent energy release into the magnetosphere, or explosive reconnection of magnetic field lines. In the absence of a predictive model, understanding the physical processes responsible for magnetar burst variability is difficult. Here, we develop an empirical model that decomposes magnetar bursts into a superposition of small spike-like features with a simple functional form, where the number of model components is itself part of the inference problem. The cascades of spikes that we model might be formed by avalanches of reconnection, or crust rupture aftershocks. Using Markov Chain Monte Carlo (MCMC) sampling augmented with reversible jumps between models with different numbers of parameters, we characterise the posterior distributions of the model parameters and the number of components per burst. We relate these model parameters to physical quantities in the system, and show for the first time that the variability within a burst does not conform to predictions from ideas of self-organised criticality. We also examine how well the properties of the spikes fit the predictions of simplified cascade models for the different trigger mechanisms.

accepted for publication in The Astrophysical Journal; code available at https://bitbucket.org/dhuppenkothen/magnetron, data products at http://figshare.com/articles/SGR_J1550_5418_magnetron_data/1292424

References in corpus (10)

• 25 Years of Self-Organized Criticality: Solar and Astrophysics
• A Swift gaze into the 2006 March 29th burst forest of SGR 1900+14
• Constraints on Neutron Star Crusts From Oscillations in Giant Flares
• The Compact X-ray Source 1E 1547.0-5408 and the Radio Shell G327.24-0.13: A New Proposed Association between a Candidate Magnetar and a Candidate Supernova Remnant
• Thermoplastic waves in magnetars
• Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550 - 5418
• Hydromagnetic waves in a superfluid neutron star with strong vortex pinning
• Analytical modeling of pulse-pileup distortion using the true pulse shape; applications to Fermi-GBM
• Inference for Trans-dimensional Bayesian Models with Diffusive Nested Sampling
• Gamma-ray burst engines may have no memory

Cited by in corpus (15)

• Constraining the limiting brightness temperature and Doppler factors for the largest sample of radio bright blazars
• The Age and Structure of the Galactic Bulge from Mira Variables
• Magnetars: a short review and some sparse considerations
• The FRB 20121102A November rain in 2018 observed with the Arecibo Telescope
• Arecibo observations of a burst storm from FRB 20121102A in 2016
• A burst storm from the repeating FRB 20200120E in an M81 globular cluster
• Fast Radio Burst Trains from Magnetar Oscillations
• Searching for quasi-periodic oscillations in astrophysical transients using Gaussian processes
• A Nançay Radio Telescope study of the hyperactive repeating FRB 20220912A
• Rotational phase dependence of magnetar bursts
• DNest4: Diffusive Nested Sampling in C++ and Python
• On the use of variability time-scales as an early classifier of radio transients and variables
• Estimation of neutron star mass and radius of FRB 20240114A by identification of crustal oscillations
• Detection of Quasi-periodic Oscillations in SGR 150228213
• Identifying changing jets through their radio variability