A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae

K. L. I. Gunawardhana; K. P. S. C. Jayaratne; J. Adassuriya

doi:doi:10.11648/j.ajaa.20150303.16

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A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae

K. L. I. Gunawardhana, K. P. S. C. Jayaratne, J. Adassuriya

Published in American Journal of Astronomy and Astrophysics (Volume 3, Issue 3)

Received: 24 February 2015 Accepted: 1 May 2015 Published: 27 May 2015

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Abstract

Pulsar is a highly magnetized rotating neutron star. It continuously emits a wind of relativistic electrons and positrons. This wind creates an electron-positron-cloud around the pulsar. This cloud, which is full of relativistic electrons and positrons, is called a Pulsar Wind Nebula (PWN). As of 2014, 33 Pulsar Wind Nebulae (PWNe) have been detected in the TeV energy band. Current understanding is, these TeV photons are produced from up-scattering low-energy photons to high-energies by ultra-relativistic electrons and positrons in PWNe, which is a non-thermal process. This process is known as inverse-Compton scattering. During inverse-Compton scattering, ultra-relativistic electrons lose their energy and cool-down to low-energies. The average time that an ultra-relativistic electron takes to cool-down by inverse-Compton scattering is called the cooling time. Estimation of cooling time is important to understand how the luminosity of a PWN changes with time. This paper describes a statistical method developed for estimating the cooling time of ultra-relativistic electrons in a given PWN. This new method is a model independent technique. Cooling time was estimated as a function of two parameters: k and γ. Here k is the high-energy electron fraction in PWN at a given time and γ is the Average Bulk Lorentz Factor of electrons in the PWN. The estimated cooling time is proportional to k and inversely proportional to γ. The developed method was applied to four PWNe: MSH 15-52, HESS J1420-607, HESS J1825-137 and HESS J1837-069. The estimated cooling times vary between 1.56 kyr to 1000 kyr for MSH 15-52, 13 kyr to 8000 kyr for HESS J1420-607, 21.4 kyr to 10000 kyr for HESS J1825-137 and 22.7 kyr to 15000 kyr for HESS J1837-069.

Published in	American Journal of Astronomy and Astrophysics (Volume 3, Issue 3)
DOI	10.11648/j.ajaa.20150303.16
Page(s)	63-69
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2015. Published by Science Publishing Group

Keywords

Cooling Time, Inverse-Compton Scattering, Neutron Star, Pulsar, Pulsar Wind Nebula

References

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APA Style

K. L. I. Gunawardhana, K. P. S. C. Jayaratne, J. Adassuriya. (2015). A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. American Journal of Astronomy and Astrophysics, 3(3), 63-69. https://doi.org/10.11648/j.ajaa.20150303.16

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ACS Style

K. L. I. Gunawardhana; K. P. S. C. Jayaratne; J. Adassuriya. A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. Am. J. Astron. Astrophys. 2015, 3(3), 63-69. doi: 10.11648/j.ajaa.20150303.16

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AMA Style

K. L. I. Gunawardhana, K. P. S. C. Jayaratne, J. Adassuriya. A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. Am J Astron Astrophys. 2015;3(3):63-69. doi: 10.11648/j.ajaa.20150303.16

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@article{10.11648/j.ajaa.20150303.16,
  author = {K. L. I. Gunawardhana and K. P. S. C. Jayaratne and J. Adassuriya},
  title = {A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae},
  journal = {American Journal of Astronomy and Astrophysics},
  volume = {3},
  number = {3},
  pages = {63-69},
  doi = {10.11648/j.ajaa.20150303.16},
  url = {https://doi.org/10.11648/j.ajaa.20150303.16},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ajaa.20150303.16},
  abstract = {Pulsar is a highly magnetized rotating neutron star. It continuously emits a wind of relativistic electrons and positrons. This wind creates an electron-positron-cloud around the pulsar. This cloud, which is full of relativistic electrons and positrons, is called a Pulsar Wind Nebula (PWN). As of 2014, 33 Pulsar Wind Nebulae (PWNe) have been detected in the TeV energy band. Current understanding is, these TeV photons are produced from up-scattering low-energy photons to high-energies by ultra-relativistic electrons and positrons in PWNe, which is a non-thermal process. This process is known as inverse-Compton scattering. During inverse-Compton scattering, ultra-relativistic electrons lose their energy and cool-down to low-energies. The average time that an ultra-relativistic electron takes to cool-down by inverse-Compton scattering is called the cooling time. Estimation of cooling time is important to understand how the luminosity of a PWN changes with time. This paper describes a statistical method developed for estimating the cooling time of ultra-relativistic electrons in a given PWN. This new method is a model independent technique. Cooling time was estimated as a function of two parameters: k and γ. Here k is the high-energy electron fraction in PWN at a given time and γ is the Average Bulk Lorentz Factor of electrons in the PWN. The estimated cooling time is proportional to k and inversely proportional to γ. The developed method was applied to four PWNe: MSH 15-52, HESS J1420-607, HESS J1825-137 and HESS J1837-069. The estimated cooling times vary between 1.56 kyr to 1000 kyr for MSH 15-52, 13 kyr to 8000 kyr for HESS J1420-607, 21.4 kyr to 10000 kyr for HESS J1825-137 and 22.7 kyr to 15000 kyr for HESS J1837-069.},
 year = {2015}
}

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TY - JOUR
T1 - A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae
AU - K. L. I. Gunawardhana
AU - K. P. S. C. Jayaratne
AU - J. Adassuriya
Y1 - 2015/05/27
PY - 2015
N1 - https://doi.org/10.11648/j.ajaa.20150303.16
DO - 10.11648/j.ajaa.20150303.16
T2 - American Journal of Astronomy and Astrophysics
JF - American Journal of Astronomy and Astrophysics
JO - American Journal of Astronomy and Astrophysics
SP - 63
EP - 69
PB - Science Publishing Group
SN - 2376-4686
UR - https://doi.org/10.11648/j.ajaa.20150303.16
AB - Pulsar is a highly magnetized rotating neutron star. It continuously emits a wind of relativistic electrons and positrons. This wind creates an electron-positron-cloud around the pulsar. This cloud, which is full of relativistic electrons and positrons, is called a Pulsar Wind Nebula (PWN). As of 2014, 33 Pulsar Wind Nebulae (PWNe) have been detected in the TeV energy band. Current understanding is, these TeV photons are produced from up-scattering low-energy photons to high-energies by ultra-relativistic electrons and positrons in PWNe, which is a non-thermal process. This process is known as inverse-Compton scattering. During inverse-Compton scattering, ultra-relativistic electrons lose their energy and cool-down to low-energies. The average time that an ultra-relativistic electron takes to cool-down by inverse-Compton scattering is called the cooling time. Estimation of cooling time is important to understand how the luminosity of a PWN changes with time. This paper describes a statistical method developed for estimating the cooling time of ultra-relativistic electrons in a given PWN. This new method is a model independent technique. Cooling time was estimated as a function of two parameters: k and γ. Here k is the high-energy electron fraction in PWN at a given time and γ is the Average Bulk Lorentz Factor of electrons in the PWN. The estimated cooling time is proportional to k and inversely proportional to γ. The developed method was applied to four PWNe: MSH 15-52, HESS J1420-607, HESS J1825-137 and HESS J1837-069. The estimated cooling times vary between 1.56 kyr to 1000 kyr for MSH 15-52, 13 kyr to 8000 kyr for HESS J1420-607, 21.4 kyr to 10000 kyr for HESS J1825-137 and 22.7 kyr to 15000 kyr for HESS J1837-069.
VL - 3
IS - 3
ER -

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Author Information

K. L. I. Gunawardhana

Department of Physics, University of Colombo, Colombo-03, Sri Lanka
K. P. S. C. Jayaratne

Department of Physics, University of Colombo, Colombo-03, Sri Lanka
J. Adassuriya

Astronomy & Space Science Division, Arthur C Clarke Institute for Modern Technologies, Katubedda, Moratuwa, Sri Lanka

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APA Style

K. L. I. Gunawardhana, K. P. S. C. Jayaratne, J. Adassuriya. (2015). A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. American Journal of Astronomy and Astrophysics, 3(3), 63-69. https://doi.org/10.11648/j.ajaa.20150303.16

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ACS Style

K. L. I. Gunawardhana; K. P. S. C. Jayaratne; J. Adassuriya. A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. Am. J. Astron. Astrophys. 2015, 3(3), 63-69. doi: 10.11648/j.ajaa.20150303.16

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AMA Style

K. L. I. Gunawardhana, K. P. S. C. Jayaratne, J. Adassuriya. A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae. Am J Astron Astrophys. 2015;3(3):63-69. doi: 10.11648/j.ajaa.20150303.16

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@article{10.11648/j.ajaa.20150303.16,
  author = {K. L. I. Gunawardhana and K. P. S. C. Jayaratne and J. Adassuriya},
  title = {A Method to Estimate the Cooling Time of Ultra-Relativistic Electrons in Pulsar Wind Nebulae},
  journal = {American Journal of Astronomy and Astrophysics},
  volume = {3},
  number = {3},
  pages = {63-69},
  doi = {10.11648/j.ajaa.20150303.16},
  url = {https://doi.org/10.11648/j.ajaa.20150303.16},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ajaa.20150303.16},
  abstract = {Pulsar is a highly magnetized rotating neutron star. It continuously emits a wind of relativistic electrons and positrons. This wind creates an electron-positron-cloud around the pulsar. This cloud, which is full of relativistic electrons and positrons, is called a Pulsar Wind Nebula (PWN). As of 2014, 33 Pulsar Wind Nebulae (PWNe) have been detected in the TeV energy band. Current understanding is, these TeV photons are produced from up-scattering low-energy photons to high-energies by ultra-relativistic electrons and positrons in PWNe, which is a non-thermal process. This process is known as inverse-Compton scattering. During inverse-Compton scattering, ultra-relativistic electrons lose their energy and cool-down to low-energies. The average time that an ultra-relativistic electron takes to cool-down by inverse-Compton scattering is called the cooling time. Estimation of cooling time is important to understand how the luminosity of a PWN changes with time. This paper describes a statistical method developed for estimating the cooling time of ultra-relativistic electrons in a given PWN. This new method is a model independent technique. Cooling time was estimated as a function of two parameters: k and γ. Here k is the high-energy electron fraction in PWN at a given time and γ is the Average Bulk Lorentz Factor of electrons in the PWN. The estimated cooling time is proportional to k and inversely proportional to γ. The developed method was applied to four PWNe: MSH 15-52, HESS J1420-607, HESS J1825-137 and HESS J1837-069. The estimated cooling times vary between 1.56 kyr to 1000 kyr for MSH 15-52, 13 kyr to 8000 kyr for HESS J1420-607, 21.4 kyr to 10000 kyr for HESS J1825-137 and 22.7 kyr to 15000 kyr for HESS J1837-069.},
 year = {2015}
}

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