Narrow Results

The recent observations by Fermi large area telescope (Fermi-LAT) showed that in addition to the radio galaxies and blazars, Narrow-Line Seyfert 1 (NLSy1) galaxies are also $\gamma$-rays emitters. NLSy1 are AGNs with optical spectral properties similar to those of Seyfert 1 galaxies, except for having narrow Balmer lines and strong optical lines. They also exhibit strong X-ray variability, steep X-ray spectra and relatively high luminosity. The multiwavelength emission properties of 1H 0323+342, SBS 0846+513 and PMN J0948+0022 are discussed, using the $\gamma$-ray data from the last 8.8 years Fermi-LAT observations as well as available Swift(UVOT/XRT) data. It is shown that one-zone synchrotron/synchrotron self-Compton (SSC) model can satisfactorily reproduce their observed broadband spectra.

The decay of bromine-76 was studied using high resolution HpGe detectors in singles and coincidence mode. Bromine-76 was produced via two reactions: ⁷⁵As(α,3n)⁷⁶Br and ⁷⁶Se(p,n)⁷⁶Br. The results of these experiments verified the previously reported levels of ⁷⁶Se. In addition to the previously described transitions and levels, 37 new γ-rays and 15 new energy levels were found for the first time.

The decay of ⁷²As has been investigated by means of γ-ray spectroscopy. The ⁷²As nuclei were produced through the ⁷²Ge(p, n)⁷²As reaction. The Compton-suppressed spectrometer and high-purity Ge detectors have been used in singles and in coincidence modes respectively to study γ-rays in the β⁺+EC decay of ⁷²As to ⁷²Ge. 79 γ-rays, among which 3 were observed for the first time, were reported. A decay scheme of ⁷²As including 1 new level is proposed that accommodates 77 of these transitions. Tentative spin and parity assignments are suggested for a number of levels according to the log ft values and γ-branching ratios.

The γ-ray spectra of ¹⁸⁸Re decay have been studied by using a Compton-suppressed spectrometer and a three parameters γ-γ-T list coincidence system. Experimental data analysis demonstrated that six γ-rays at 557, 810, 1463, 1867, 1936 and 2022 keV and three levels at 1443, 1936 and 2022 keV are confirmed again. Seven new γ-rays at 309.60±0.04, 826.90±0.02, 979.29±0.08, 1103.7±0.4, 1828.2±0.1, 1842.5±0.2 and 1982.5±0.2 keV have been identified, three new levels at 309.60, 1828.2 and 1982.5 keV are assigned. The β^- decay branching ratio is deduced. In addition, in order to study this γ-unstable nucleus, shape calculations using the Hartree–Fock–Bogoliubov-like formalism were carried out for positive-parity states in ¹⁸⁸Os. The TRS plots reveal that, as the spin increases up the band, the triaxiality parameter γ changes.

We explored $\gamma$-ray mean lifetimes of transitions $2^{+}\to 0^{+}$ state suggested by earlier researchers such as Grodzins [Phys. Lett. 2 (1962)], Bohr and Mettelson [Mat. Fys. Medd. Dan. Vid. Selsk 27 (1953) 1], Wang’s formula [Chin. J. Phys. 18 (1980) 151], and best global fit formulae [Phys. Rev. C 37 (1988) 805], equations accessible in the literature for nuclei ranging from ${}^{128}$Ce to ${}^{252}$Fm. Also, as compared to other equations accessible in the literature, the standard deviation observed utilizing Grodzins formula with regard to experiments was lower. We also forecasted $\gamma$-ray mean lifetimes of transitions $2^{+}\to 0^{+}$ state and $B(E2)$-values for nuclei ranging from ${}^{122}$Ce to ${}^{256}$Fm. Around 136 even–even nuclei’s mean lifetimes and $B(E2)$-values are predicted which are helpful in the Coulomb fission process.

The decay of bromine-76 is studied by means of γ-ray spectroscopy. Bromine-76 is produced via two reactions: ⁷⁵As(α, 3n)⁷⁶Br and ⁷⁶Se(p, n)⁷⁶Br. The results of these experiments verify the previously reported levels of ⁷⁶Se. In addition to the previously described transitions and levels, 37 new γ-rays and 15 new energy levels are found for the first time. In addition, in order to study the deformation of ⁷⁶Se which lies in transitional region between strongly deformed and spherical nuclei, we calculate the total Routhian surfaces (TRS) of positive-parity states by cranking shell model formalism.

The Large Area Telescope on the Fermi γ-ray Space Telescope provides unprecedented sensitivity for all-sky monitoring of γ-ray activity. It has detected a few Galactic sources, including 2 γ-ray binaries and a microquasar. In addition, it is an adequate telescope to detect other transient sources. The observatory scans the entire sky every three hours and allows a general search for flaring activity on daily timescales. This search is conducted automatically as part of the ground processing of the data and allows a fast response to transient events, typically less than a day. Most of the outbursts detected are spatially associated with known blazars, but in several cases during the first years of observations, γ-ray flares occurring near the Galactic plane did not reveal any initially compelling counterparts. This prompted follow-up observations in X-ray, optical, and radio to attempt to identify the origin of the emission and probe the possible existence of a class of transient γ-ray sources in the Galaxy. Here we report on these LAT events and the results of the multiwavelength counterpart searches.

A γ-ray diffraction property of a silicon single crystal was studied in the Laue geometry using 1.33 MeV and 1.17 MeV γ-ray of ⁶⁰Co. The thickness was chosen to maximize the reflectivity of (440) lattice plane in γ-ray energy ranges of 1 to 2 MeV. We measured diffracted γ-rays from the crystal by an NaI scintillator. A measured diffraction intensity of 1.33 MeV γ-rays was 18 counts/sec by using 3.0 TBq a ⁶⁰Coγ-ray radiation system. The measured intensity is 30% lower than an expected value.

In 1998-2011, the BL Lacertae blazar was active in various bands, including TeV energies. During the growth of activity in the gamma band, the spectrum of the object became flat, with the spectral index decreasing. This effect is associated with the conversion mechanism of particle acceleration in the BL Lacertae jet.