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Register a new userA Simple BATSE Measure of GRB Duty Cycle
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We introduce a definition of gamma-ray burst (GRB) duty cycle that describes the GRBs efficiency as an emitter; it is the GRBs average flux relative to the peak flux. This GRB duty cycle is easily described in terms of measured BATSE parameters; it is essentially fluence divided by the quantity peak flux times duration. Since fluence and duration are two of the three defining characteristics of the GRB classes identified by statistical clustering techniques (the other is spectral hardness), duty cycle is a potentially valuable probe for studying properties of these classes.
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We propose a scenario for a periodic filling and emptying of the accretion disc of GRS 1915+105, by computing the mass transfer rate from the donor and comparing it with the observed accretion rate. The binary parameters found by Greiner et al. (2001) predict evolutionary expansion of the donor along the giant branch with a conservative mass transfer rate (1 - 2)E-8 solar masses per year. This reservoir can support the present accretion with a duty cycle 0.05 - 0.1 (the active time as a fraction of the total life time). The viscosity time scale at the circularization radius (15 solar radii from the primary 14 solar mass black hole) is identified as the recurrent quiescent time during which a new disc is formed once consumed by the BH. For small viscosity (alpha = 0.001) it equals to 300 - 400 years. The microquasar phase, with the duty cycle, will last around 10 million years ending with a long period black hole + white dwarf system.
We prove that every pair of exponential polynomials with imaginary frequencies generates a Poisson-type formula.
Revised upper limits on gamma-ray burst repetition rates are found using the BATSE 3B and 4B catalogs. A statistical repetition model is assumed in which sources burst at a mean rate but in which BATSE observes bursts randomly from each source.
Radio loud Active Galactic Nuclei are episodic in nature, cycling through periods of activity and quiescence. In this work we investigate the duty cycle of the radio galaxy B2~0258+35, which was previously suggested to be a restarted radio galaxy based on its morphology. The radio source consists of a pair of kpc-scale jets embedded in two large-scale lobes (~240 kpc) with relaxed shape and very low surface brightness, which resemble remnants of a past AGN activity. We have combined new LOFAR data at 145 MHz and new SRT data at 6600 MHz with available WSRT data at 1400 MHz to investigate the spectral properties of the outer lobes and derive their age. Interestingly, the spectrum of both the outer Northern and Southern lobes is not ultra-steep as expected for an old ageing plasma with spectral index values equal to $rm alpha_{1400}^{145}=0.48pm0.11$ and $rm alpha_{6600}^{1400}=0.69pm0.20$ in the outer Northern lobe, and $rm alpha_{1400}^{145}=0.73pm0.07$ in the outer Southern lobe. Moreover, despite the wide frequency coverage available for the outer Northern lobe (145-6600~MHz), we do not identify a significant spectral curvature (SPC$simeq$0.2$pm0.2$). While mechanisms such as in-situ particle reacceleration, mixing or compression can temporarily play a role in preventing the spectrum from steepening, in no case seem the outer lobes to be compatible with being very old remnants of past activity as previously suggested (with age $gtrsim$ 80 Myr). We conclude that either the large-scale lobes are still fuelled by the nuclear engine or the jets have switched off no more than a few tens of Myr ago. Our study shows the importance of combining morphological and spectral properties to reliably classify the evolutionary stage of low surface brightness, diffuse emission that low frequency observations are revealing around a growing number of radio sources.
We study systems with finite number of states $A_i$ ($i=1,..., n$), which obey the first order kinetics (master equation) without detailed balance. For any nonzero complex eigenvalue $lambda$ we prove the inequality $frac{|Im lambda |}{|Re lambda |} leq cotfrac{pi}{n}$. This bound is sharp and it becomes an equality for an eigenvalue of a simple irreversible cycle $A_1 to A_2 to... to A_n to A_1$ with equal rate constants of all transitions. Therefore, the simple cycle with the equal rate constants has the slowest decay of the oscillations among all first order kinetic systems with the same number of states.
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