A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197
We report a direct measurement of the electron density turbulence parameter C _1 , enabled by 550–750 MHz baseband observations with the upgraded Giant Metrewave Radio Telescope. The parameter C _1 depends on the power-law index of the wavenumber spectrum of electron density inhomogeneities in the i...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/ade9b7 |
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| author | Visweshwar Ram Marthi Yogesh Maan |
| author_facet | Visweshwar Ram Marthi Yogesh Maan |
| author_sort | Visweshwar Ram Marthi |
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| description | We report a direct measurement of the electron density turbulence parameter C _1 , enabled by 550–750 MHz baseband observations with the upgraded Giant Metrewave Radio Telescope. The parameter C _1 depends on the power-law index of the wavenumber spectrum of electron density inhomogeneities in the ionized interstellar medium. Radio waves propagating through the inhomogeneous ionized medium suffer multipath propagation, as a result of which the pulsed emission from a neutron star undergoes scatter broadening. Consequently, interference between the delayed copies of the scatter-broadened electric field manifests as scintillation. We measure a scintillation bandwidth Δ ν _d = 149 ± 3 Hz as well as a scatter-broadening timescale τ _d = 1.22 ± 0.09 ms at 650 MHz. These two quantities are related through the uncertainty relation C _1 = 2 π Δ ν _d τ _d , using which we directly measure C _1 = 1.2 ± 0.1. We describe the methods employed to obtain these results and discuss their implications in general, as well as for the magnetar XTE J1810−197, toward which the measurements have been made. We also discuss how such effectively in situ measurements of C _1 can aid in inferring the wavenumber spectrum power-law index and hence quantitatively discriminate between the various possible scattering scenarios in the ionized medium. Finally, using the fact that C _1 ∼ 1, we nominally constrain the emission size to less than a few thousand kilometers for a screen very close to the magnetar and to within the magnetosphere for all screen distances. |
| format | Article |
| id | doaj-art-d022aa33458441fe9237478079b0012a |
| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-d022aa33458441fe9237478079b0012a2025-08-20T03:36:35ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019892L3410.3847/2041-8213/ade9b7A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197Visweshwar Ram Marthi0https://orcid.org/0000-0002-4629-314XYogesh Maan1https://orcid.org/0000-0002-0862-6062National Centre for Radio Astrophysics, Tata Institute of Fundamental Research , Post Bag 3, Ganeshkhind, Pune—411 007, IndiaNational Centre for Radio Astrophysics, Tata Institute of Fundamental Research , Post Bag 3, Ganeshkhind, Pune—411 007, IndiaWe report a direct measurement of the electron density turbulence parameter C _1 , enabled by 550–750 MHz baseband observations with the upgraded Giant Metrewave Radio Telescope. The parameter C _1 depends on the power-law index of the wavenumber spectrum of electron density inhomogeneities in the ionized interstellar medium. Radio waves propagating through the inhomogeneous ionized medium suffer multipath propagation, as a result of which the pulsed emission from a neutron star undergoes scatter broadening. Consequently, interference between the delayed copies of the scatter-broadened electric field manifests as scintillation. We measure a scintillation bandwidth Δ ν _d = 149 ± 3 Hz as well as a scatter-broadening timescale τ _d = 1.22 ± 0.09 ms at 650 MHz. These two quantities are related through the uncertainty relation C _1 = 2 π Δ ν _d τ _d , using which we directly measure C _1 = 1.2 ± 0.1. We describe the methods employed to obtain these results and discuss their implications in general, as well as for the magnetar XTE J1810−197, toward which the measurements have been made. We also discuss how such effectively in situ measurements of C _1 can aid in inferring the wavenumber spectrum power-law index and hence quantitatively discriminate between the various possible scattering scenarios in the ionized medium. Finally, using the fact that C _1 ∼ 1, we nominally constrain the emission size to less than a few thousand kilometers for a screen very close to the magnetar and to within the magnetosphere for all screen distances.https://doi.org/10.3847/2041-8213/ade9b7Radio transient sourcesInterstellar mediumInterstellar scintillation |
| spellingShingle | Visweshwar Ram Marthi Yogesh Maan A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 The Astrophysical Journal Letters Radio transient sources Interstellar medium Interstellar scintillation |
| title | A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 |
| title_full | A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 |
| title_fullStr | A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 |
| title_full_unstemmed | A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 |
| title_short | A Direct Measurement of the Electron Density Turbulence Parameter C1 and Implications for the Emission Size of Magnetar XTE J1810-197 |
| title_sort | direct measurement of the electron density turbulence parameter c1 and implications for the emission size of magnetar xte j1810 197 |
| topic | Radio transient sources Interstellar medium Interstellar scintillation |
| url | https://doi.org/10.3847/2041-8213/ade9b7 |
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