A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant - A new class of white dwarf merger remnants with X-ray emission

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Table 4.

Summary of measured and derived parameters for ZTF J2008+4449.

Origin	Parameter	Value
From Gaia DR3	Gaia ID	2082008971824158720
	Parallax	2.9149 ± 0.1349 mas
	Distance (Bailer-Jones et al. 2021)	350 ± 20 pc

From SED fitting	Radius of the white dwarf	R_WD = 4800 ± 300 km
	Temperature of the white dwarf	T_eff = 35 500 ± 300 K
	Mass of the white dwarf	M_WD = 1.12 ± 0.03 M_⊙
	Cooling age of the white dwarf	t_cool = 60 ± 10 Myr
	Extinction toward the white dwarf	E(B − V) = 0.042 ± 0.001
	Ionizing luminosity from the white dwarf	L_ion = (2.4 ± 0.1)×10⁴² s⁻¹

From SED and UV and optical spectroscopy	Average white dwarf surface magnetic field	B_p ∼ 400 − 600 MG

From light curve analysis	Spin period of the WD	P₀ = 6.55576688 ± 0.00000008 min
	Spin period of the WD	at T₀ = 59401.76 MJD_BDT
	Period derivative	Ṗ = (1.80 ± 0.09) × 10⁻¹² s/s
	Spin-down age	$P / \dot{P} = 7.0 \pm 0.4$ $P/\dot{P} = 7.0\pm0.4$ Myr
	Spin-down luminosity	L_sd ≈ 2 × 10³² erg s⁻¹

From X-rays analysis	X-ray luminosity in the	L_X = (2.3 ± 0.4)×10²⁹ erg s⁻¹
	0.25–10.0 keV band	L_X = (2.3 ± 0.4)×10²⁹ erg s⁻¹
	Power law index	Γ = 2.2 ± 0.1
	2-temperature model	$k T_{1} = 3 . 6_{- 0.7}^{+ 1.0}$ $kT_1 = 3.6^{+1.0}_{-0.7}$ keV
	2-temperature model	$k T_{2} = 0 . 23_{- 0.03}^{+ 0.04}$ $kT_2 = 0.23^{+0.04}_{-0.03}$ keV

	Ring inner radius	R_in = 20.1 ± 0.2 R_WD
	Ring outer radius	R_out = 34.9 ± 0.3 R_WD
	Ring radial thickness	δr = 14.8 ± 0.4 R_WD
From fit to the Balmer emission	System velocity	$v_{sys} = 0 . 8_{- 8.9}^{+ 9.6}$ $v_{\mathrm{sys}} = 0.8^{+9.6}_{-8.9}$ km s⁻¹
with the half-ring model	Flux in Hα	$F_{H α} = (5 . 02_{- 0.05}^{+ 0.06}) \times 10^{- 16}$ $F_{\mathrm{H\alpha}}=(5.02^{+0.06}_{-0.05})\times 10^{-16}$ erg s⁻¹ cm⁻²
	Flux in Hβ	F_Hβ = (2.8 ± 0.1)×10⁻¹⁶ erg s⁻¹ cm⁻²
	Photon ratio^a Hα/Hβ	R = 2.3 ± 0.1
	Luminosity in Hα	$L_{H α} = (5 . 02_{- 0.05}^{+ 0.06}) \times 10^{- 16}$ $L_{\mathrm{H\alpha}}=(5.02^{+0.06}_{-0.05})\times10^{-16}$ erg s⁻¹ cm⁻²

From photoionization model of the ring	Ionized density in the ring	n_e ≈ 1 × 10¹² cm⁻³
	Neutral density in the ring	n₀ ≈ 2 × 10⁷ cm⁻³
	Optical depth to Hα	τ_Hα ≈ 2
	Ring vertical thickness	H ≈ 0.1 R_WD
	Temperature in the ring	T_ring ≈ 9000 K
	Mass in the ring	M_ring ≈ 2 × 10⁻¹⁷ M_⊙

Notes.

Photon ratio includes a correction for extinction.

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