Blowouts of Nascent Wind Bubbles in Pulsar-Driven Supernovae

Abstract

Formation of a rapidly spinning, strongly magnetized neutron star (NS) may occur in various classes of core-collapse events. If the NS injects an amount of energy comparable to the explosion energy of the accompanying supernova (SN) before the SN ejecta becomes transparent, the nascent NS wind bubble can overtake the outer ejecta and undergo a blowout driven by hydrodynamic instabilities. Based on multidimensional numerical studies, we construct a minimal semi-analytic framework to follow the post-blowout dynamics and radiative evolution, map the blowout conditions by scanning the ejecta and NS parameters, and compute survey-ready multi-band light curves. For stripped-envelope SNe with an ejecta mass of $M_\mathrm{ej} \sim 10\,M_\odot$ and an explosion energy of $E_\mathrm{sn} \sim 10^{51}\,\mathrm{erg}$, blowout occurs for NSs with magnetic field strengths of $B_{\mathrm{dip}} \gtrsim 10^{13}\,\mathrm{G}$ and spin periods of $P_\mathrm{NS} \lesssim \mathrm{a\ few}\,\mathrm{ms}$. Relatively weak-field cases with $B_\mathrm{dip} \lesssim 10^{14}\,\mathrm{G}$ produce luminous double-peaked UV/optical light curves, as observed in the superluminous SN LSQ14bdq, while stronger-field cases with $B_\mathrm{dip} \gtrsim 10^{14}\,\mathrm{G}$ result in hypernovae preceded by X-ray blowout precursors. We also examine weaker and lower-mass SN explosions representing ultra-stripped SNe and accretion- or merger-induced collapse events, in which blowout is more readily achieved over a broader range of NS parameters, producing fast X-ray transients with durations of $ 10^{2\mbox{--}4}\,\mathrm{s}$ and peak luminosities of $10^{42\mbox{--}48}\,\mathrm{erg\,s^{-1}}$. Our results encourage coordinated UV, optical, and X-ray observations which constrain the formation of the most energetic NSs in the universe.

Figures (16)

• Figure 1: Schematic illustration of the blowout model and the resulting double-peaked light curve. From left to right, four evolutionary stages are shown. (i) Prior to blowout: a central engine inflates a wind bubble and drives a thin swept-up shell that expands inside the dense ejecta at $r<R_{\mathrm{tr}}$. (ii) Onset of blowout: the swept-up shell reaches the density-transition radius $R_{\mathrm{tr}}$, since the outer ejecta at $r>R_{\mathrm{tr}}$ is tenuous, the upstream ram pressure drops rapidly, and hydrodynamic instabilities broaden the shell. (iii) First peak: the thin shell is converted into a blowout admixture layer between $R_{\mathrm{in}}$ and $R_{\mathrm{out}}$, where kinetic energy flux is invariant with radius: $\rho r^{2} v^{3} \approx \mathrm{const}$. The admixture layer rapidly expands until the diffusion front $R_{\mathrm{ph}}$ penetrates into $R_{\mathrm{out}}$. Energy released by shock heating and thermal photon diffusion leakage from $R_{\mathrm{out}}$ supported the fast first peak by that. (iv) Second peak: $R_{\mathrm{ph}}$ recedes deep into the admixture layer as the ejecta become optically thin, and the release of trapped internal energy produces the second, broader peak in the light curve.
• Figure 2: Phase diagram for the occurrence of blowout in different classes of SNe. We consider representative parameters for SESNe, ultra-stripped SNe, and AIC/MIC SNe. The lines correspond to specific SN types and parameter choices, as indicated by the labels next to each curve. Upper left region of each boundary line (i.e., the region pointed to by the arrows) corresponds to pulsar parameters for which a blowout can occur under the SN condition.
• Figure 3: Post-blowout evolution of the density, expansion-velocity, and characteristic radii in a representative SESN blowout scenario. Profile curves are labeled by the time elapsed since blowout. Purple dashed lines show reference scalings $\rho\propto r^{-5}$ and $v\propto r$. At blowout, the swept-up ejecta form a thin shell and the inner profiles deviate markedly from homologous expansion. The shell then rapidly broadens, the density relaxes toward $\rho\propto r^{-5}$, and the velocity field approaches a nearly homologous profile. The right panel shows the time evolution of the inner and outer boundaries of the admixture layer, $R_{\rm in}$ and $R_{\rm out}$, together with the diffusion front $R_{\rm diff}$. For this case, $R_{\rm diff}$ lies close to $R_{\rm out}$ immediately after blowout but remains outside the dense admixture layer. Once the diffusion front penetrates into $R_{\rm out}$, the growth of its relative thickness slows, and the thickness factor $\zeta_{\rm r} = R_{\rm out}/R_{\rm in}$ asymptotes to $\simeq 20$.
• Figure 4: Bolometric luminosity (left) and graybody temperature (right) for the fiducial pulsar-driven SESN case with $M_{\rm ej}=10\,M_\odot$, $E_{\rm sn}=10^{51}\ {\rm erg}$, $B_{\rm dip}=1\times10^{14}\ {\rm G}$, and $P_{\rm NS}=2\ {\rm ms}$. In the left panel, we also show the individual contributions from shock heating at leading edge of the admixture layer ($L_{\rm sh}$), photon diffusive leakage through $R_{\rm out}$ or from $R_{\rm diff}$ ($L_{\rm diff}$), graybody emission from previously $R_{\rm diff}$-swept, optically thin ejecta ($L_{\rm thin}$), and the pulsar spin-down power ($L_{\rm sp}$). The double-peaked morphology arises from shock-powered and leakage-powered emission at early times (first peak), followed by the thermal-diffusion–dominated release of the residual internal energy (second, main peak).
• Figure 5: Multi-band observational data and fitting light curves of LSQ14bdq using our blowout model.