Charm contribution to ultrahigh-energy neutrinos from newborn magnetars

Newborn, strongly magnetized neutron stars (so-called magnetars) surrounded by their stellar or merger ejecta are expected to be sources of ultrahigh-energy neutrinos via decay of mesons produced in hadronic interactions of protons which are accelerated to ultrahigh energies by magnetic dissipation of the spindown energy. We show that not only pions and kaons but also charm hadrons, which are typically neglected due to their small production cross sections, can represent dominant contributions to neutrino fluence at ultrahigh energies, because of their short lifetimes, while the ultrahigh-energy neutrino fluence from pion and kaon production is suppressed at early times due to their significant cooling before their decay. We show that the next-generation detectors such as Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), Giant Radio Array for Neutrino Detection (GRAND) and IceCube-Gen2 have a good chance of observing neutrinos, primarily originating from charm hadrons, from nearby magnetars. We also show that neutrinos from nearby magnetar-driven merger novae could be observed in the time interval between ${10}^2\mathrm{s}$ and ${10}^3\mathrm{s}$, where the charm hadron contribution is dominant for neutrino energies above ${10}^8\mathrm{GeV}$, of relevance to next generation detectors. We also comment on potential impacts of the charm hadron contribution to the diffuse neutrino flux.

Figure 1

All-flavor neutrino light curve $E_{\nu }^2{\dot{\varphi }}_{\nu }$ at $E_{\nu }={10}^9\mathrm{GeV}$ of a magnetar at a distance of 3.5 Mpc. The charm uncertainty factor of $1/3$–3 around the central curve is given by the shaded blue region. For the case of neutrinos from pion (kaon) decay, we include an additional dashed red (black) curve to isolate the ${\nu }_{\mu }$ component from ${\pi }^{+}(K^{+})\to {\mu }^{+}{\nu }_{\mu }$ and charge conjugate, without taking into account the contributions from the muon decay. The dot-dashed vertical lines indicate the locations where decay time and cooling time are equal, based on our estimate given by Eq. (15). Here, the spin-down time is $t_{\mathrm{sd}}={10}^{3.5}\mathrm{s}$.

Figure 2

All-flavor fluence of high-energy neutrinos of a nearby magnetar at a distance of 3.5 Mpc, for different time intervals. A band in the charm spectrum in the time interval ${10}^3\mathrm{s}–1\mathrm{yr}$ is shown, spanning a factor of $1/3-3$ times the central result.

Figure 3

Neutrino fluence in the interval ${10}^2–{10}^5\mathrm{s}$ compared to the long burst sensitivities of various experiments. A band in the charm spectrum is shown, spanning a factor of $1/3-3$ times the central result. The IceCube 90% CL upper limit on the spectral fluence from GW170817 on a 14-day window [16] (dotted brown line), while the IceCube-Gen2 curve is the 90% sensitivity for an event at a similar position in the sky [16] (dotted green line). The best 90% unified CL sensitivity per energy decade for long bursts for POEMMA is given by the dashed purple line, while its the purple band is the sensitivity range over most portions of the sky [47]. The 90% CL sensitivity for GRAND 200K in the optimistic case of a source at declination $\delta =45°$ is shown by the dashed yellow line, and the yellow band is the declination-averaged sensitivity $0°<\delta <45°$ [18].

Figure 4

Left panel: contour plots where ${\dot{\varphi }}_{\nu ,\pi }+{\dot{\varphi }}_{\nu ,K}={\dot{\varphi }}_{\nu ,c}$ at the injection time $t={10}^{4.5}\mathrm{s}$. We have also marked the line where $t=t_{\mathrm{sd}}$. The lower limit in the period corresponds to the minimum spin period of a neutron star, $P_i\sim 0.6\mathrm{ms}$ [46]. The parameter space below the solid curves have ${\dot{\varphi }}_{\nu ,c}>{\dot{\varphi }}_{\nu ,\pi }+{\dot{\varphi }}_{\nu ,K}$ for a given energy. Right panel: same as left panel, but using the total fluence $\varphi$ instead of the flux $\dot{\varphi }$ at a fixed time. The parameter space to the right of the solid curves have ${\varphi }_{\nu ,c}>{\varphi }_{\nu ,\pi }+{\varphi }_{\nu ,K}$ for a given energy.

Figure 5

Neutrino fluence of a nearby neutron star merger at a distance of 3.5 Mpc, in the interval ${10}^2–{10}^3\mathrm{s}$, compared to the short burst sensitivities of various experiments. The IceCube 90% CL upper limit on the spectral fluence from GW170817 on a $\pm 500\mathrm{s}$ time window [16] is shown with a dotted brown line, while the IceCube-Gen2 curve is the 90% sensitivity for an event at a similar position in the sky [16] (dotted green line). The best 90% unified CL sensitivity per energy decade for short bursts for POEMMA is given by the dashed purple line, while its the purple band is the sensitivity range over most portions of the sky [47]. The 90% CL sensitivity for GRAND 200K in the optimistic case of a source at zenith angle $\theta =90°$ is shown by the dashed yellow line [18].

Figure 6

Left panel: magnetar-driven supernovae contributions to the all-flavor diffuse neutrino flux. The red error bars show the results of the IceCube 6-year HESE analysis, obtained by multiplying the per-flavor neutrino flux in Ref. [49] by a factor of 3. The green error bars correspond to the IceCube 6-year shower analysis [50]. The 5-year IceCube-Gen2 sensitivity is shown by the red band [16], while the 10-year GRAND200k sensitivity is shown by the yellow curve and is scaled from the 3-year sensitivity [18]. The orange curve is the IceCube nine-year 90% CL EHE diffuse flux upper limit [51]. Right panel: same as the left panel, showing instead magnetar-driven merger novae contributions to the diffuse neutrino flux.

Figure 7

As a function of $x_E=E_{D^0}/E_p$, the differential distribution of $D^0$ mesons produced in collisions of protons with $E_p$ incident of fixed target protons for $E_p={10}^{11}\mathrm{GeV}$. The four curves show the evaluation using NLO QCD, the linear and non-linear $k_T$ formulations and the sibyll result. The blue band spans a factor of $1/3-3$ times the NLO QCD result.