The short GRB 120323A had the highest flux ever detected with the Gamma-Ray Burst Monitor on board the Fermi Gamma-Ray Space Telescope. Here we study its remarkable spectral properties and their evolution using two spectral models: (1) a single emission component scenario, where the spectrum is modeled by the empirical Band function (a broken power law), and (2) a two-component scenario, where thermal (a Planck-like function) emission is observed simultaneously with a non-thermal component (a Band function). We find that the latter model fits the integrated burst spectrum significantly better than the former, and that their respective spectral parameters are dramatically different: when fit with a Band function only, the E peak of the event is unusually soft for a short gamma-ray burst (GRB; 70 keV compared to an average of 300 keV), while adding a thermal component leads to more typical short GRB values (E peak ∼ 300 keV). Our time-resolved spectral analysis produces similar results. We argue here that the two-component model is the preferred interpretation for GRB 120323A based on (1) the values and evolution of the Band function parameters of the two component scenario, which are more typical for a short GRB, and (2) the appearance in the data of a significant hardness-intensity correlation, commonly found in GRBs, when we employee two-component model fits; the correlation is non-existent in the Band-only fits. GRB 110721A, a long burst with an intense photospheric emission, exhibits the exact same behavior. We conclude that GRB 120323A has a strong photospheric emission contribution, observed for the first time in a short GRB. Magnetic dissipation models are difficult to reconcile with these results, which instead favor photospheric thermal emission and fast cooling synchrotron radiation from internal shocks. Finally, we derive a possibly universal hardness-luminosity relation in the source frame using a larger set of GRBs (L Band i = (1.59 ± 0.84) × 10 50 (E rest peak,i ) 1.33±0.07 erg s −1 ), which could be used as a possible redshift estimator for cosmology.

Gamma Ray Burst (GRB) prompt emission spectra in the keV-MeV energy range are usually considered as adequately fitted with the empirical Band function. Recent observations with the Fermi Gamma-Ray Space Telescope (Fermi) revealed deviations from the Band function, sometimes in the form of an additional black-body (BB) component, while on other occasions in the form of an additional power law (PL) component extending to high energies. In this article we investigate the possibility that the three components may be present simultaneously in the prompt emission spectra of two very bright GRBs (080916C and 090926A) observed with Fermi, and how the three components may affect the overall shape of the spectra. While the two GRBs are very different when fitted with a single Band function, they look like "twins" in the three-component scenario. Through fine-time spectroscopy down to the 100 ms time scale, we follow the evolution of the various components. We succeed in reducing the number of free parameters in the three-component model, which results in a new semi-empirical model-but with physical motivations-to be competitive with the Band function in terms of number of degrees of freedom. From this analysis using multiple components, the Band function is globally the most intense component, although the additional PL can overpower the others in sharp time structures. The Band function and the BB component are the most intense at early times and globally fade across the burst duration. The additional PL is the most intense component at late time and may be correlated with the extended high-energy emission observed thousands of seconds after the burst with Fermi/Large Area Telescope (LAT). Unexpectedly, this analysis also shows that the additional PL may be present from the very beginning of the burst, where it may even overpower the other components at low energy. We investigate the effect of the three components on the new time-resolved luminosity-hardness relation in both the observer and rest frames and show that a strong correlation exists between the flux of the non-thermal Band function and its E peak only when the three components are fitted simultaneously to the data (i.e., F NT i -E NT peak,i relation). In addition, this result points toward a universal relation between those two quantities when transposed to the central engine rest frame for all GRBs (i.e., L NT i -E rest,NT peak,i relation). We discuss theoretical implications of the three spectral components within this new empirical model. The BB component can be interpreted as the photosphere emission of a magnetized relativistic outflow. The Band component can be interpreted as synchrotron radiation in an optically thin region above the photosphere, either from internal shocks or magnetic field dissipation. The extra power law component extending to high energies likely has an inverse Compton origin of some sort, even though its extension to a much lower energy remains a mystery.

Growing evidence for shocks in nova outflows include (1) multiple velocity components in the optical spectra; (2) hard X-ray emission starting weeks to months after the outburst;(3) an early radio flare on timescales of months, in excess of that predicted from the freely expanding photo-ionized gas; and, perhaps most dramatically, (4) ∼ GeV gamma-ray emission. We present a one dimensional model for the shock interaction between the fast nova outflow and a dense external shell (DES) and its associated thermal X-ray, optical, and radio emission. The lower velocity DES could represent an earlier stage of mass loss from the white dwarf or ambient material not directly related to the thermonuclear runaway. The forward shock is radiative initially when the density of shocked gas is highest, at which times radio emission originates from the dense cooling layer immediately downstream of the shock. Our predicted radio light curve is characterized by sharper rises to maximum and later peak times at progressively lower frequencies, with a peak brightness temperature that is approximately independent of frequency. We apply our model to the recent gamma-ray producing classical nova V1324 Sco, obtaining an adequate fit to the early radio maximum for reasonable assumptions about the fast nova outflow and assuming the DES possesses a characteristic velocity ∼ 10 3 km s −1 and mass ∼ few 10 −4 M ⊙ ; the former is consistent with the velocities of narrow line absorption systems observed previously in nova spectra, while the total ejecta mass of the DES and fast outflow is consistent with that inferred independently by modeling the late radio peak as uniformly expanding photo-ionized gas. Rapid evolution of the early radio light curves require the DES to possess a steep outer density profile, which may indicate that the onset of mass loss from the white dwarf was rapid, providing indirect evidence that the DES was expelled as the result of the thermonuclear runaway event. Reprocessed X-rays from the shock absorbed by the DES at early times are found to contribute significantly to the optical/UV emission, which we speculate may be responsible for the previously unexplained 'plateaus' and secondary maxima in nova optical light curves.