TY - JOUR

T1 - Propagation Effects in the FRB 20121102A Spectra

AU - Levkov, D. G.

AU - Panin, A. G.

AU - Tkachev, I. I.

N1 - Funding Information: We thank V. Gajjar for help, S. Sibiryakov for discussions, and the Referee for criticism. Scintillations in the FRB 20121102A spectra were studied within the framework of the RSF grant 16-12-10494. Investigation of the FRB lensing was supported by the Ministry of Science and Higher Education of the Russian Federation under the contract 075-15-2020-778 (State project Science). The rest of this paper was funded by the Foundation for the Advancement of Theoretical Physics and Mathematics, BASIS. Numerical calculations were performed on the Computational cluster of Theory Division of the Institute for Nuclear Research of the Russian Academy of Sciences. Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - We advance theoretical methods for studying propagation effects in fast radio burst (FRB) spectra. We derive their autocorrelation function in the model with diffractive lensing and strong Kolmogorov-type scintillations and analytically obtain the spectra lensed on different plasma density profiles. With these tools, we reanalyze the highest frequency 4-8 GHz data of Gajjar et al. for the repeating FRB 20121102A (FRB 121102). In the data, we discover, first, a remarkable spectral structure of almost equidistant peaks separated by 95 ± 16 MHz. We suggest that it can originate from diffractive lensing of the FRB signals on a compact gravitating object of mass 10-4 M⊙ or on a plasma underdensity near the source. Second, the spectra include erratic interstellar, presumably Milky Way scintillations. We extract their decorrelation bandwidth 3.3 ± 0.6 MHz at reference frequency 6 GHz. The third feature is a GHz-scale pattern that, as we find, linearly drifts with time and presumably represents a wideband propagation effect, e.g., GHz-scale scintillations. Fourth, many spectra are dominated by a narrow peak at 7.1 GHz. We suggest that it can be caused by propagation through a plasma lens, e.g., in the host galaxy. Fifth, separating the propagation effects, we give strong arguments that the intrinsic progenitor spectrum has a narrow GHz bandwidth and variable central frequency. This confirms expectations from the previous observations. We discuss alternative interpretations of the above spectral features.

AB - We advance theoretical methods for studying propagation effects in fast radio burst (FRB) spectra. We derive their autocorrelation function in the model with diffractive lensing and strong Kolmogorov-type scintillations and analytically obtain the spectra lensed on different plasma density profiles. With these tools, we reanalyze the highest frequency 4-8 GHz data of Gajjar et al. for the repeating FRB 20121102A (FRB 121102). In the data, we discover, first, a remarkable spectral structure of almost equidistant peaks separated by 95 ± 16 MHz. We suggest that it can originate from diffractive lensing of the FRB signals on a compact gravitating object of mass 10-4 M⊙ or on a plasma underdensity near the source. Second, the spectra include erratic interstellar, presumably Milky Way scintillations. We extract their decorrelation bandwidth 3.3 ± 0.6 MHz at reference frequency 6 GHz. The third feature is a GHz-scale pattern that, as we find, linearly drifts with time and presumably represents a wideband propagation effect, e.g., GHz-scale scintillations. Fourth, many spectra are dominated by a narrow peak at 7.1 GHz. We suggest that it can be caused by propagation through a plasma lens, e.g., in the host galaxy. Fifth, separating the propagation effects, we give strong arguments that the intrinsic progenitor spectrum has a narrow GHz bandwidth and variable central frequency. This confirms expectations from the previous observations. We discuss alternative interpretations of the above spectral features.

UR - http://www.scopus.com/inward/record.url?scp=85125864396&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/534fddac-6c64-3135-81c5-e6583bdc4c3d/

U2 - 10.3847/1538-4357/ac3250

DO - 10.3847/1538-4357/ac3250

M3 - Article

AN - SCOPUS:85125864396

VL - 925

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 109

ER -