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Peer-reviewedCC BY 4.0The Astrophysical Journal

Dual-timescale Infrared Variability in PG 1302−102: Dust Echo and Rapid Infrared Brightening

  • Zhenzhen Li1
  • Hongyan Zhou2,3
  • Bo Liu1
  • Chenwei Yang3
  • Jingbo Sun1,4
  • Liang Chen1
  • Yifei Xiong1,4
  • Lei Hao1
4 affiliations
  1. 1Chinese Academy of Sciences
  2. 2University of Science and Technology of China
  3. 3Polar Research Institute of China
  4. 4University of Chinese Academy of Sciences
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Abstract

We investigate variability on two distinct timescales in PG 1302−102 using optical and mid-infrared light curves extending through 2024. (1) The long-term optical variability has previously been interpreted as possible evidence for a subparsec binary supermassive black hole. The pre-2015 optical light curve exhibits a prominent periodogram peak near 5 yr, whereas the dominant feature shifts toward approximately 7 yr and becomes broader when observations through 2024 are included. This evolution is compatible with correlated stochastic variability and weakens the interpretation of the signal as a stable binary-orbital clock. The infrared variations lag the optical emission by 77 6 − 59 + 40 days in W1 and 90 9 − 91 + 62 days in W2. The corresponding rest-frame dust reverberation radii are approximately 0.51 and 0.60 pc, respectively. Taking into account the longer rest-frame wavelengths probed by W1 and W2 relative to the K -band measurements commonly used in previous reverberation studies, the inferred radii are consistent with the general dust size–luminosity trend of Type 1 active galactic nuclei. (2) The Wide-field Infrared Survey Explorer light curves also reveal a coherent intraday infrared brightening during the visit centered at MJD 59224. The baseline-subtracted variable flux has a color similar to that of the local baseline emission, while the rapid variability indicates a compact and distinct short-timescale mode of infrared variability in PG 1302−102.

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Cite

BibTeXRIS
BibTeX
@article{li2026dualtimescale,
  title = {{Dual-timescale Infrared Variability in PG 1302−102: Dust Echo and Rapid Infrared Brightening}},
  author = {Zhenzhen Li and Hongyan Zhou and Bo Liu and Chenwei Yang and Jingbo Sun and Liang Chen and Yifei Xiong and Lei Hao},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/ae9e2a},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9e2a},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Dual-timescale Infrared Variability in PG 1302−102: Dust Echo and Rapid Infrared Brightening
AU  - Zhenzhen Li
AU  - Hongyan Zhou
AU  - Bo Liu
AU  - Chenwei Yang
AU  - Jingbo Sun
AU  - Liang Chen
AU  - Yifei Xiong
AU  - Lei Hao
PY  - 2026
DA  - 2026/10/12
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/ae9e2a
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/ae9e2a
AB  - We investigate variability on two distinct timescales in PG 1302−102 using optical and mid-infrared light curves extending through 2024. (1) The long-term optical variability has previously been interpreted as possible evidence for a subparsec binary supermassive black hole. The pre-2015 optical light curve exhibits a prominent periodogram peak near 5 yr, whereas the dominant feature shifts toward approximately 7 yr and becomes broader when observations through 2024 are included. This evolution is compatible with correlated stochastic variability and weakens the interpretation of the signal as a stable binary-orbital clock. The infrared variations lag the optical emission by 77 6 − 59 + 40 days in W1 and 90 9 − 91 + 62 days in W2. The corresponding rest-frame dust reverberation radii are approximately 0.51 and 0.60 pc, respectively. Taking into account the longer rest-frame wavelengths probed by W1 and W2 relative to the K -band measurements commonly used in previous reverberation studies, the inferred radii are consistent with the general dust size–luminosity trend of Type 1 active galactic nuclei. (2) The Wide-field Infrared Survey Explorer light curves also reveal a coherent intraday infrared brightening during the visit centered at MJD 59224. The baseline-subtracted variable flux has a color similar to that of the local baseline emission, while the rapid variability indicates a compact and distinct short-timescale mode of infrared variability in PG 1302−102.
SN  - 0004-637X
SN  - 1538-4357
ER  -