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Objective. Monolithic crystal detectors are increasingly being applied in positron emission tomography (PET) devices owing to their excellent depth-of-interaction (DOI) resolution capabilities and high detection efficiency. In this study, we constructed and evaluated a dual-ended readout monolithic crystal detector based on a multiplexing method. Approach. We employed two 12 × 12 silicon photomultiplier (SiPM) arrays for readout, and the signals from the 12 × 12 array were merged into 12 X and 12 Y channels using channel multiplexing. In 2D reconstruction, three methods based on the centre of gravity (COG) were compared, and the concept of thresholds was introduced. Furthermore, a light convolutional neural network (CNN) was employed for testing. To enhance depth localization resolution, we proposed a method by utilizing the mutual information from both ends of the SiPMs. The source width and collimation effect were simulated using GEANT4, and the intrinsic spatial resolution was separated from the measured values. Main results. At an operational voltage of 29 V for the SiPM, an energy resolution of approximately 12.5 % was achieved. By subtracting a 0.8 % threshold from the total energy in every channel, a 2D spatial resolution of approximately 0.90 mm full width at half maximum (FWHM) can be obtained. Furthermore, a higher level of resolution, approximately 0.80 mm FWHM, was achieved using a CNN, with some alleviation of edge effects. With the proposed DOI method, a significant 1.36 mm FWHM average DOI resolution can be achieved. Additionally, it was found that polishing and black coating on the crystal surface yielded smaller edge effects compared to a rough surface with a black coating. Significance. The introduction of a threshold in COG method and a dual-ended readout scheme can lead to excellent spatial resolution for monolithic crystal detectors, which can help to develop PET systems with both high sensitivity and high spatial resolution. [ABSTRACT FROM AUTHOR]

For blazars, its radio emissions are composed of two components. In the high energy bands, Tera-electronvolts (TeV; 1012electronvolts) emissions were detected from some blazars. Does the TeV emission also consist of two components? To investigate the TeV emission component, we compiled a sample of 51 TeV blazars with available radio core dominance parameters and applied a two-component (the beamed and the unbeamed) model to study the composition of blazar TeV emission. We obtained the core-dominance parameter at the TeV band through applying a relativistic beaming model, and found that the average TeV core-dominance parameter is log R TeV BL = 〈 3.12 ± 2.83 〉 for 46 BL Lacs, and that is log R TeV FSRQ = 〈 4.80 ± 1.76 〉 for 5 FSRQs, which shows an indication that the core dominance parameter in BL Lacs is smaller than that in FSRQs. For the three subclasses of BL Lacsâ€"high synchrotron peaked BL Lacs(HBLs), intermediate synchrotron peaked BL Lacs(IBLs) and low synchrotron peaked(LBLs), log R TeV HBL is smaller than log R TeV IBL and log R TeV LBL . Our results suggest that the blazar TeV emission from the core is thousands times stronger than from the extended region and the TeV emission is more core-dominated for the lower synchrotron peaked sources. In addition, a significant correlation between the TeV core-dominance parameter ( log R TeV ) and the radio one ( log R radio ) log R TeV = (2.56 ± 0.08) log R radio + 0.99 , is obtained suggesting that the TeV emission is beamed and the TeV core-dominance parameter is an indicator of beaming effect at the TeV bands, and that the TeV emission has stronger beaming effect than the radio emission. [ABSTRACT FROM AUTHOR]

In a two-component model, the total observed emissions are the sum of two contributions, namely a beamed one and an unbeamed one. The observed beamed emissions from a relativistic jet are strongly boosted due to the beaming effect while the observed unbeamed emissions are the same as that in the co-moving frame. In the X-ay band, it is hard to separate the beamed and the unbeamed emissions from observations. However, it is interesting to investigate the X-ray emissions applying the two-component model as in Kembhavi (Mon. Not. R. Astron. Soc. 264:683, 1993). In this work, a sample of 397 blazars with available X-ray data and radio core-dominance parameters are compiled and the method proposed by Kembhavi et al is adopted to separate the two components in the X-ray emissions, then we also discuss the difference between BL Lac objects and FSRQs. Our results show that: (1) The beamed emissions dominate the X-ray emissions. (2) The averaged X-ray core-dominance parameter in BL Lacertae objects is greater than that in FSRQs. (3) A correlation between X-ray spectral index and X-ray core-dominance parameter is obtained, which supports the unified scheme of BL Lac objects, FR type I galaxies and FR type II with galaxy morphology, FSRQs unified with FR type two quasars. [ABSTRACT FROM AUTHOR]

The origin of jets is one of the most important issues concerning active galactic nuclei, yet it has remained obscure. In this work, we made use of information from emission lines, spectral energy distributions, and Fermiâ€"LAT Îł -ray emission to construct a blazar sample that contains 667 sources. We note that jet power originations are different for BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs). The correlation between jet power P jet and the normalized disk luminosity L Disk/ L Edd shows a slope of âˆ'1.77 for BL Lacs and a slope of 1.16 for FSRQs. The results seem to suggest that BL Lac jets are powered by extracting black hole (BH) rotation energy, while FSRQ jets are mostly powered by accretion disks. Meanwhile, we find the accretion ratio M ̇ / M ̇ Edd increases with the normalized Îł -ray luminosity. Based on this, we propose a dividing line, log (L BLR / L Edd) = 0.25 log (L Îł / L Edd) âˆ' 2.23 , to separate FSRQs and BL Lacs in the diagram of L BLR/ L Edd against L Îł / L Edd using a machine-learning method; the method gives an accuracy of 84.5%. In addition, we propose an empirical formula, M BH / M ☉ ≃ L Îł 0.65 / 21.46 , to estimate BH mass based on a strong correlation between Îł -ray luminosity and BH mass. Strong Îł -ray emission is typical in blazars, and the emission is always boosted by a Doppler-beaming effect. In this work, we generate a new method to estimate a lower limit of Doppler factor δ and give δ BL Lac = 7.94 and δ FSRQ = 11.55. [ABSTRACT FROM AUTHOR]