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Article Dans Une Revue Astrophys.J. Année : 2021

Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence

A.W. Shaw
  • Fonction : Auteur
R.M. Plotkin
  • Fonction : Auteur
J.C.A. Miller-Jones
  • Fonction : Auteur
J. Homan
  • Fonction : Auteur
E. Gallo
  • Fonction : Auteur
D.M. Russell
  • Fonction : Auteur
J.A. Tomsick
  • Fonction : Auteur
P. Kaaret
  • Fonction : Auteur
J. Bright
  • Fonction : Auteur

Résumé

Black hole X-ray binaries in the quiescent state (Eddington ratios typically ≲10−5) display softer X-ray spectra (photon indices Γ ∼ 2) compared to higher-luminosity black hole X-ray binaries in the hard state (Γ ∼ 1.7). However, the cause of this softening and its implications for the underlying accretion flow are still uncertain. Here, we present quasi-simultaneous X-ray and radio spectral monitoring of the black hole X-ray binary MAXI J1820+070 during the decay of its 2018 outburst and of a subsequent reflare in 2019, providing an opportunity to monitor a black hole X-ray binary as it actively transitions into quiescence. We probe 1–10 keV X-ray luminosities as low as L X ∼ 4 × 1032 erg s−1, equivalent to Eddington fractions of ∼4 × 10−7. During its decay toward quiescence, the X-ray spectrum of MAXI J1820+070 softens from Γ ∼ 1.7 to Γ ∼ 2, with the softening taking ∼30 days and completing at L X ≈ 1034 erg s−1 (≈10−5 L Edd). While the X-ray spectrum softens, the radio spectrum generally remains flat or inverted throughout the decay. We also find that MAXI J1820+070 follows a radio (L R)–X-ray luminosity correlation of the form L R ∝ L X 0.52±0.07, making it the fourth black hole system to follow the so-called “standard track” unbroken over several (in this case, four) decades in L X. Comparing the radio/X-ray spectral evolution(s) with the L R–L X plane, we find that the X-ray softening is consistent with X-rays produced by Comptonization processes in a radiatively inefficient accretion flow. We generally disfavor X-ray emission originating solely from within the jet, with the possible exception of X-rays produced via synchrotron self-Compton processes.

Dates et versions

hal-03129564 , version 1 (02-02-2021)

Identifiants

Citer

A.W. Shaw, R.M. Plotkin, J.C.A. Miller-Jones, J. Homan, E. Gallo, et al.. Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence. Astrophys.J., 2021, 907 (1), pp.34. ⟨10.3847/1538-4357/abd1de⟩. ⟨hal-03129564⟩
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