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Constraining primordial black hole abundance with Insight-HXMT

Chen Yang, Jun-Da Pan, Xin Zhang

Abstract

Primordial black holes (PBHs) are a major candidate for dark matter and they have been extensively constrained across most mass ranges. However, PBHs in the mass range of $10^{17}$ - $10^{21}$ g remain a viable explanation for all dark matter. In this work, we use observational data from the Hard X-ray Modulation Telescope (Insight-HXMT) to refine constraints on PBHs within the mass range of $2\times10^{16}$ - $5\times10^{17}$ g. Our analysis explores three scenarios: directly using observational data, incorporating the astrophysical background model (ABM), and employing the power-law spectrum with an exponential cutoff. Our results indicate that although Insight-HXMT does not have an advantage in the first two scenarios, when considering the power-law model, its exceptional sensitivity in the hard X-ray regime and sufficiently high upper energy limit significantly strengthen the constraints on PBHs with masses greater than $10^{17}$ g compared to previous limits. Furthermore, the exclusion limit for PBHs as dark matter has reached $4\times10^{17}$ g, which is comparable to the current threshold.

Constraining primordial black hole abundance with Insight-HXMT

Abstract

Primordial black holes (PBHs) are a major candidate for dark matter and they have been extensively constrained across most mass ranges. However, PBHs in the mass range of - g remain a viable explanation for all dark matter. In this work, we use observational data from the Hard X-ray Modulation Telescope (Insight-HXMT) to refine constraints on PBHs within the mass range of - g. Our analysis explores three scenarios: directly using observational data, incorporating the astrophysical background model (ABM), and employing the power-law spectrum with an exponential cutoff. Our results indicate that although Insight-HXMT does not have an advantage in the first two scenarios, when considering the power-law model, its exceptional sensitivity in the hard X-ray regime and sufficiently high upper energy limit significantly strengthen the constraints on PBHs with masses greater than g compared to previous limits. Furthermore, the exclusion limit for PBHs as dark matter has reached g, which is comparable to the current threshold.

Paper Structure

This paper contains 9 sections, 13 equations, 2 figures.

Table of Contents

  1. Introduction
  2. The photon flux from PBH evaporation
  3. Photons generated by Hawking radiation
  4. Photons from positron annihilations
  5. Constraints with Insight-HXMT data
  6. Constraints derived directly from observational data
  7. Situation with astrophysical background
  8. Extending the energy range of the diffuse X-ray background
  9. Conclusion

Figures (2)

  • Figure 1: Various components of the total photon flux in Eq. (\ref{['eq:tf']}) for $M=10^{17}$ g and $f_{\mathrm{PBH}}=1$. The red line represents the photon flux from Galactic sources, the blue line represents the photon flux from extragalactic sources. The solid line denotes the photon flux directly emitted by Hawking radiation, while the dashed line corresponds to the photon flux produced from positron annihilation.
  • Figure 2: The constraint results in our work under three different scenarios: directly using observational data (blue solid line), incorporating the astrophysical background model (blue dashed line), and applying the power-law model fitted to the observational data (blue dotted-dashed line). These results are compared with existing constraints: magenta from Laha:2019ssq, red from Laha:2020ivk, cyan from Coogan:2020tuf, brown from Iguaz:2021irx and green from Berteaud:2022tws.