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Title: Light curve and SED modeling of the gamma-ray binary 1FGL J1018.6–5856: Constraints on the orbital geometry and relativistic flow

We present broadband spectral energy distributions and light curves of the gamma-ray binary 1FGL J1018.6–5856 measured in the X-ray and the gamma-ray bands. We find that the orbital modulation in the low-energy gamma-ray band is similar to that in the X-ray band, suggesting a common spectral component. However, above a GeV the orbital light curve changes significantly. We suggest that the GeV band contains significant flux from a pulsar magnetosphere, while the X-ray to TeV light curves are dominated by synchrotron and Compton emission from an intrabinary shock (IBS). We find that a simple one-zone model is inadequate to explain the IBS emission, but that beamed Synchrotron-self Compton radiation from adiabatically accelerated plasma in the shocked pulsar wind can reproduce the complex multiband light curves, including the variable X-ray spike coincident with the gamma-ray maximum. Furthermore, the model requires an inclination of ~50° and an orbital eccentricity of ~0.35, consistent with the limited constraints from existing optical observations. This picture motivates searches for pulsations from the energetic young pulsar powering the wind shock.
Authors:
 [1] ; ORCiD logo [2]
  1. Stanford Univ., Stanford, CA (United States); Chungbuk National Univ., Cheongju (Korea)
  2. Stanford Univ., Stanford, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 838; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; binaries: close; gamma rays: stars; stars: individual (1FGL J1018.6-5856); X-rays: binaries
OSTI Identifier:
1355730

An, Hongjun, and Romani, Roger W. Light curve and SED modeling of the gamma-ray binary 1FGL J1018.6–5856: Constraints on the orbital geometry and relativistic flow. United States: N. p., Web. doi:10.3847/1538-4357/aa6623.
An, Hongjun, & Romani, Roger W. Light curve and SED modeling of the gamma-ray binary 1FGL J1018.6–5856: Constraints on the orbital geometry and relativistic flow. United States. doi:10.3847/1538-4357/aa6623.
An, Hongjun, and Romani, Roger W. 2017. "Light curve and SED modeling of the gamma-ray binary 1FGL J1018.6–5856: Constraints on the orbital geometry and relativistic flow". United States. doi:10.3847/1538-4357/aa6623. https://www.osti.gov/servlets/purl/1355730.
@article{osti_1355730,
title = {Light curve and SED modeling of the gamma-ray binary 1FGL J1018.6–5856: Constraints on the orbital geometry and relativistic flow},
author = {An, Hongjun and Romani, Roger W.},
abstractNote = {We present broadband spectral energy distributions and light curves of the gamma-ray binary 1FGL J1018.6–5856 measured in the X-ray and the gamma-ray bands. We find that the orbital modulation in the low-energy gamma-ray band is similar to that in the X-ray band, suggesting a common spectral component. However, above a GeV the orbital light curve changes significantly. We suggest that the GeV band contains significant flux from a pulsar magnetosphere, while the X-ray to TeV light curves are dominated by synchrotron and Compton emission from an intrabinary shock (IBS). We find that a simple one-zone model is inadequate to explain the IBS emission, but that beamed Synchrotron-self Compton radiation from adiabatically accelerated plasma in the shocked pulsar wind can reproduce the complex multiband light curves, including the variable X-ray spike coincident with the gamma-ray maximum. Furthermore, the model requires an inclination of ~50° and an orbital eccentricity of ~0.35, consistent with the limited constraints from existing optical observations. This picture motivates searches for pulsations from the energetic young pulsar powering the wind shock.},
doi = {10.3847/1538-4357/aa6623},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 838,
place = {United States},
year = {2017},
month = {4}
}