[Paper Review] Multi-wavelength observations of the binary system PSR B1259-63/LS 2883 around the 2010-2011 periastron passage

M. Chernyakova, A. A. Abdo+15 more|arXiv (Cornell University)|Jan 7, 2014

Pulsars and Gravitational Waves Research52 references68 citations

TL;DR

This study presents multi-wavelength observations of the PSR B1259−63/LS 2883 binary system during its 2010–2011 periastron passage, revealing a GeV γ-ray flare ~30 days post-periastron with no clear counterparts in radio, X-ray, or TeV bands. The flare is linked to disk perturbations in the Be star’s circumstellar disk, inferred from Hα and Brγ line equivalent width reductions, suggesting a physical connection between disk disruption and high-energy emission.

ABSTRACT

We report on broad multi-wavelength observations of the 2010-2011 periastron passage of the gamma-ray loud binary system PSR B1259-63. High resolution interferometric radio observations establish extended radio emission trailing the position of the pulsar. Observations with the Fermi Gamma-ray Space Telescope reveal GeV gamma-ray flaring activity of the system, reaching the spin-down luminosity of the pulsar, around 30 days after periastron. There are no clear signatures of variability at radio, X-ray and TeV energies at the time of the GeV flare. Variability around periastron in the H$\alpha$ emission line, can be interpreted as the gravitational interaction between the pulsar and the circumstellar disk. The equivalent width of the H$\alpha$ grows from a few days before periastron until a few days later, and decreases again between 18 and 46 days after periastron. In near infrared we observe the similar decrease of the equivalent width of Br$\gamma$ line between the 40th and 117th day after the periastron. For the idealized disk, the variability of the H$\alpha$ line represents the variability of the mass and size of the disk. We discuss possible physical relations between the state of the disk and GeV emission under assumption that GeV flare is directly related to the decrease of the disk size.

Motivation & Objective

• To investigate the multi-wavelength behavior of PSR B1259−63 during its 2010–2011 periastron passage, particularly focusing on high-energy γ-ray flaring.
• To determine whether the observed GeV γ-ray flare has counterparts in radio, X-ray, or TeV bands.
• To examine the state of the Be star’s circumstellar disk via optical and infrared spectroscopy to assess its role in high-energy emission.
• To establish the spatial relationship between the pulsar and extended radio emission using high-resolution interferometry.
• To explore the physical link between disk state changes and the timing of the GeV flare, especially given the lack of simultaneous multi-band data at flare onset.

Proposed method

• Conducted broad-band multi-wavelength observations using Fermi-LAT for GeV γ-rays, INTEGRAL for hard X-rays, and radio interferometry with the Australian Long Baseline Array.
• Performed high-resolution radio interferometric imaging to measure the position of the pulsar relative to extended radio emission, removing cross-calibration uncertainties.
• Analyzed optical spectroscopy (Hα, He I λ6678) and near-infrared spectroscopy (Brγ) to track changes in equivalent widths over time relative to periastron.
• Compared light curves across radio, X-ray, and γ-ray bands to identify variability patterns and potential correlations with the GeV flare.
• Modeled the disk state evolution assuming gravitational interaction between the pulsar and Be star disk, linking disk size and mass variations to emission changes.
• Used time-resolved spectral analysis to assess variability in X-ray and radio flux, and to detect any pre- or post-flare anomalies.

Experimental results

Research questions

• RQ1 Does the GeV γ-ray flare observed ~30 days after periastron have detectable counterparts in radio, X-ray, or TeV bands?
• RQ2 How does the circumstellar disk of the Be star LS 2883 evolve during the pulsar's close passage, as inferred from Hα and Brγ line equivalent widths?
• RQ3 Is there a physical connection between the observed decrease in Hα and Brγ equivalent widths and the timing of the GeV flare?
• RQ4 What is the spatial morphology of the extended radio emission relative to the pulsar, and does it support a cometary tail structure?
• RQ5 Can the observed X-ray and radio light curves be explained by a stable emission mechanism, or are there subtle irregularities linked to the GeV flare?

Key findings

• A strong GeV γ-ray flare occurred ~30 days after periastron, reaching luminosities comparable to the pulsar's spin-down power, with no clear counterparts in radio, X-ray, or TeV bands.
• Extended radio emission was imaged at AU scales, showing a cometary tail morphology trailing the pulsar, with peak emission at projected distances of several tens of AU.
• The Hα line equivalent width increased before and after periastron, peaking around the time of closest approach, then decreased over 18–46 days post-periastron, indicating disk disruption.
• The Brγ line equivalent width decreased between 40 and 117 days after periastron, consistent with the Hα trend and supporting disk state changes.
• The radio and X-ray light curves showed qualitative similarity to previous periastron passages, with X-ray flux rising 20–30 days before periastron and peaking post-periastron, but no clear irregularities were detected at the flare onset.
• The first simultaneous measurement of the pulsar and extended radio emission positions within a single data set confirmed the source is located within an extended radio region of ~100 AU, resolving prior calibration uncertainties.