Suzaku and Fermi view of the supernova remnant 3C 396

ABSTRACT 3C 396 is a composite supernova remnant (SNR), consisting of a central pulsar wind nebula (PWN) and a bright shell in the west, which is known to be interacting with molecular clouds (MCs). We present a study of X-ray emission from the shell and the PWN of the SNR 3C 396 using archival Suzaku data. The spectrum of the SNR shell is clearly thermal, without a signature of a non-thermal component. The abundances of Al and Ca from the shell are slightly enhanced, which indicates the presence of metal-enriched supernova ejecta. The PWN spectra are well described by a power-law model with a photon index of ∼1.97 and a thermal component with an electron temperature of ∼0.93 keV. The analysis of about 11 yr of Fermi data revealed an 18σ detection of gamma-ray emission from the location overlapping with the position of 3C 396 / 4FGL J1903.8+0531. The spectrum of 3C 396 / 4FGL J1903.8+0531 is best fitted with a log-parabola function with parameters of α = 2.66 and β = 0.16 in the energy range of 0.2–300 GeV. The luminosity of 3C 396 / 4FGL J1903.8+0531 was found to be >1035 erg s−1 at 6.2 kpc, which rules out the inverse Compton emission model. Possible scenarios of gamma-ray emission are hadronic emission and bremsstrahlung processes, due to the fact that the SNR is expanding into dense MCs in the western and northern regions of the SNR.

Pulsar Nebulae

Recent observation with ASCA reveals that radio pulsars own X-ray diffuse nebulae around them. 11 such nebulae have been reported (Harrus, Hughes & Helfand 1996, Shibata et al. 1997, Kawai, Tamura & Shibata 1997). It is most likely that these nebulae are synchrotron nebuale powered by the pulsar wind, the outflow of relativistic particles. Kawai, Tamura and Shibata (1997) reduced an empirical law for the nebula luminosity Lx as a function of the rotation power Ėrot of the central pulsar: Lx/Ėrot = −12.3 + 0.27 log Ėrot.

Supernova Remnants with Central Pulsars

The recent discovery of a central pulsing X-ray source makes MSH 15–52 the third SNR to contain a radio pulsar surrounded by diffuse X-ray emission. The pulsar periods are all increasing with time and the consequent loss of rotational kinetic energy is enough, in each remnant, to power a synchrotron nebula with the observed luminosity and volume.After a review of the properties of the Crab Nebula it will be shown that both Vela X and MSH 15–52 have the same relationship between central pulsar and diffuse emission. Using empirical rules derived from these SNR, it is demonstrated that other plerionic remnants have similar characteristics. Two accretion-powered central sources can be distinguished from radio pulsars in SNR by the relatively high X-ray luminosity of the central source compared to that of possible synchrotron diffuse emission.

Distribution of Neutrino Fluxes from Pulsar Shells

Young pulsars apparently have a distribution of initial power outputs N (> Po−γ), with 1/2 < γ < 1 and Po ≳ 1038 ergs/sec. Assuming that ultra-high-energy (E ≳ 1015 eV) cosmic-ray nuclei are accelerated at the central pulsar, a young, dense supernova shell can be a powerful source of high-energy neutrinos. With an optical array placed in a volume of one km3 at great ocean depths, as proposed for the DUMAND detector, it is likely that ≳ 103 hadronic and electromagnetic cascades induced by neutrinos would be recorded for a stellar collapse within our Galaxy. Such supernovae occur about 8 times per century. Neutrinos from young supernova shells in the Virgo supercluster would be marginally detectable via neutrinos with N(> Po) ∝ Po−1/2, but unobservable if N(> Po) ∝ Po−1.