Observations Of Transient Events Research Articles

Monte Carlo Radiation Transport for Astrophysical Transients Powered by Circumstellar Interaction

In this paper, we introduce SuperLite, an open-source Monte Carlo radiation transport code designed to produce synthetic spectra for astrophysical transient phenomena affected by circumstellar interaction. SuperLite utilizes Monte Carlo methods for semi-implicit, semirelativistic radiation transport in high-velocity shocked outflows, employing multigroup structured opacity calculations. The code enables rapid post-processing of hydrodynamic profiles to generate high-quality spectra that can be compared with observations of transient events, including superluminous supernovae, pulsational pair-instability supernovae, and other peculiar transients. We present the methods employed in SuperLite and compare the code’s performance to that of other radiative transport codes, such as SuperNu and CMFGEN. We show that SuperLite has successfully passed standard Monte Carlo radiation transport tests and can reproduce spectra of typical supernovae of Type Ia, Type IIP, and Type IIn.

Gammas and Charged Particles Identification in Lateral and Additional Apertures of GAMMA-400

The GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) will be a new generation satellite gamma-observatory. The gamma-ray telescope GAMMA-400 consists of the anticoincidence system (top and lateral sections—ACtop and AClat), the converter-tracker (C), the time-of-flight system TOF (two sections S1 and S2), the position-sensitive and electromagnetic calorimeters (CC1 and CC2), the scintillation detectors of the calorimeter (S3 and S4) and lateral anticoincidence detectors of the calorimeter LD. Two apertures used for observation of transient events do not require the best angular resolution as for the gamma-ray bursts and solar flares from both upper and lateral directions. Additional aperture allows the particle registering from upper direction, which do not interact with converter-tracker and do not form a TOF signal. The lateral aperture allows registering of γ-quanta in perpendicular direction with respect to main axis of GAMMA-400 due to CC2, LD, S3, and S4. The thickness of CC2 in this direction is ∼44 X0 and this allows detection of gammas, electrons and positrons with energies up to 10 TeV. The results of calculation of the fractal dimension of temporal profiles of additional aperture prototype of GAMMA-400 during its calibration using secondary positron beam of the synchrotron C-25P “PAKHRA” of Lebedev Physical Institute confirm the absence of any correlation between the AC and CC1 characteristics and correspondence of additional aperture background to Poisson statistics or Erlang one with shape parameter up to 10.

Single-shot compressed ultrafast photography at one hundred billion frames per second.

The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 10(5) frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 10(7) frames per second. Despite these sensors' widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10(11) frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an x-y-t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescent--such as fluorescent or bioluminescent--objects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUP's capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical research.