Gamma-ray burst (GRB) prompt emission spectra in the keV–MeV energy range are usually considered to be 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 blackbody (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 to a single Band function, they look like “twins” in the three-component scenario. Through fine-time spectroscopy down to the 100 ms timescale, 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

Is light a particle with zero mass? Short answer: Yes—but with an important nuance. Light is made of particles called photons, and each photon has zero rest mass. However, that doesn’t mean it has no energy or physical effects. 🔹 What “zero mass” actually means Photons have zero rest mass → they cannot be at rest. Because of this, they must always move at the speed of light (c ≈ 3 × 10⁸ m/s). This is a direct consequence of special relativity. 🔹 But photons still carry energy and momentum Even without mass, light still behaves like something “real”: Energy: E=hνE = h\nuE=hν Momentum: p=Ecp = \frac{E}{c}p=cE So photons can: Push objects (radiation pressure) Transfer energy (e.g., solar panels) Interact with matter 🔹 Wave–particle duality Light is not just a particle or a wave—it’s both. This is described by wave-particle duality: Acts like a wave (interference, diffraction) Acts like a particle (photons hitting detectors) 🔹 Why zero mass matters Because photons have zero rest mass: They always travel at c They follow spacetime paths (affected by gravity → gravitational lensing) They are described by quantum electrodynamics 🧠 Key takeaway Light is made of particles (photons), and those particles have zero rest mass—but still carry energy, momentum, and physical influence. If you want to go deeper, I can connect this to your earlier cosmology work—like how zero-mass photons still contribute to entropy and early-universe dynamics. Now when we photon cannot be at rest,is it at res

Blackbody Radiation 4.3 BLACKBODY RADIATION All objects continually emit and absorb electromagnetic radiation. The emitted radiation is given the special name blackbody radiation. The spectrum of the radiation emitted by an object is continuous. The temperature of the object determines the wavelength at which the spectrum is maximum and the total energy output per unit time. 4.3.1 Introduction 4.3.2 Examples of Blackbody Radiation 4.3.3 The Spectrum of Blackbody Radiation 4.3.4 Blackbody Emissions and Temperature 4.3.5 Absorptivity and Emissivity 4.3.7 Key Points about Radiant Energy and Blackbody Radiation 4.3.1 Introduction All material objects emit electromagnetic radiation; the distribution of photon energies and fluxes emitted depend primarily on the object's temperature. This phenomenon is known as blackbody radiation . Because the amount of radiation, and its spectrum depends on the temperature, it is sometimes called thermal radiation , or heat radiation . The object in question can be large (stars and planets), small (single molecules), solid, liquid, or gaseous. Blackbody radiation is a familiar phenomenon: When the temperature of an object (such as a piece of metal) is increased, it begins to glow reddish-orange, and, as the temperature is further increased, its glow becomes progressively whiter. As the temperature is further increased, the glow takes on a bluish cast, however, at such high temperature, the glow is usually so intense that it is painful to look at, and even harmful to the eyes (which is why welders use dark goggles when working). Even when an object is cool, and we do not see a glow at all, the object is constantly emitting radiation that is mostly in the infrared region. Night vision equipment detects this infrared radiation, and electronically converts the image detected in the infrared to a visible image. Blackbody radiation is continually removing energy from an object, thereby causing it to cool. This is the reason that the Earth's su