اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLooking for the underlying cause of black hole X-ray variability in GRMHD simulations
245
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a log-normal distribution of flux and a linear rms-flux relation, which indicate that the underlying variability process is stochastic in nature. It is also thought to be intrinsic to accretion. This variability has been modelled as inward propagating fluctuations of mass accretion rate, although the physical process driving the fluctuations remains puzzling. In this work, we analyse five exceptionally long duration general relativistic magnetohydrodynamic (GRMHD) simulations of optically thin, geometrically thick, black hole accretion flows to look for hints of propagating fluctuations in the simulation data. We find that the accretion profiles from these simulations do show evidence for inward propagating fluctuations below the viscous frequency by featuring strong radial coherence and positive time lags when comparing smaller to larger radii, although these time lags are generally shorter than the viscous time-scale and frequency independent. Our simulations also support the notion that the fluctuations in $dot{M}$ build up in a multiplicative manner, as the simulations exhibit linear rms-mass flux relations, as well as log-normal distributions of their mass fluxes. When combining the mass fluxes from the simulations with an assumed emissivity profile, we additionally find broad agreement with observed power spectra and time lags, including a recovery of the frequency dependency of the time lags.
قيم البحث
اقرأ أيضاً
We present global radiation GRMHD simulations of strongly magnetized accretion onto a spinning, stellar mass black hole at sub-Eddington rates. Using a frequency-dependent Monte Carlo procedure for Compton scattering, we self-consistently evolve a tw
o-temperature description of the ion-electron fluid and its radiation field. For an Eddington ratio $L/L_{rm Edd} gtrsim 10^{-3}$, the emergent spectrum forms an apparent power law shape from thermal Comptonization up to a cutoff at $simeq 100$ keV, characteristic of that seen in the hard spectral states of black hole X-ray binary systems. At these luminosities, the radiative efficiency is high ($approx 24%$) and results in a denser midplane region where magnetic fields are dynamically important. For $L/L_{rm Edd} sim 10^{-2}$, our hot accretion flow appears to undergo thermal runaway and collapse. Our simulations demonstrate that hot accretion flows can be radiatively efficient and provide an estimate of their maximum luminosity.
We present the results of long-term monitoring of the X-ray emission from the ultraluminous X-ray source XMMUJ122939.9+075333 in the extragalactic globular cluster RZ2109. The combination of the high X-ray luminosity, short term X-ray variability, X-
ray spectrum, and optical emission suggest that this system is likely an accreting black hole in a globular cluster. To study the long-term behavior of the X-ray emission from this source, we analyze both new and archival Chandra and XMM-Newton observations, covering 16 years from 2000 to 2016. For all of these observations, we fit extracted spectra of RZ2109 with xspec models. The spectra are all dominated by a soft component, which is very soft with typical fit temperatures of T $simeq$ 0.15 keV. The resulting X-ray fluxes show strong variability on short and long timescales. We also find that the X-ray spectrum often shows no significant change even with luminosity changes as large as a factor of five.
In the past decades, the phenomenology of fast time variations of high-energy flux from black-hole binaries has increased, thanks to the availability of more and more sophisticated space observatories, and a complex picture has emerged. Recently, mod
els have been developed to interpret the observed signals in terms of fundamental frequencies connected to General Relativity, which has opened a promising way to measure the prediction of GR in the strong-field regime. I review the current standpoint both from the observational and theoretical side and show that these systems are the most promising laboratories for testing GR and the observations available today suggest that the next observational facilities can lead to a breakthrough in the field.
A calibration is made for the correlation between the X-ray Variability Amplitude (XVA) and Black Hole (BH) mass. The correlation for 21 reverberation-mapped Active Galactic Nuclei (AGN) appears very tight, with an intrinsic dispersion of 0.20 dex. T
he intrinsic dispersion of 0.27 dex can be obtained if BH masses are estimated from the stellar velocity dispersions. We further test the uncertainties of mass estimates from XVAs for objects which have been observed multiple times with good enough data quality. The results show that the XVAs derived from multiple observations change by a factor of 3. This means that BH mass uncertainty from a single observation is slightly worse than either reverberation-mapping or stellar velocity dispersion measurements; however BH mass estimates with X-ray data only can be more accurate if the mean XVA value from more observations is used. Applying this relation, the BH mass of RE J1034+396 is found to be $4^{+3}_{-2} times 10^6$ $M_{odot}$. The high end of the mass range follows the relationship between the 2$f_0$ frequencies of high-frequency QPO and the BH masses derived from the Galactic X-ray binaries. We also calculate the high-frequency constant $C= 2.37 M_odot$ Hz$^{-1}$ from 21 reverberation-mapped AGN. As suggested by Gierlinski et al., $M_{rm BH}=C/C_{rm M}$, where $C_{rm M}$ is the high-frequency variability derived from XVA. Given the similar shape of power-law dominated X-ray spectra in ULXs and AGN, this can be applied to BH mass estimates of ULXs. We discuss the observed QPO frequencies and BH mass estimates in the Ultra-Luminous X-ray source M82 X-1 and NGC 5408 X-1 and favor ULXs as intermediate mass BH systems (abridged).
The broad iron spectral features are often seen in X-ray spectra of Active Galactic Nuclei (AGN) and black-hole binaries (BHB). These features may be explained either by the relativistic disc reflection scenario or the partial covering scenario: It i
s hardly possible to determine which model is valid from time-averaged spectral analysis. Thus, X-ray spectral variability has been investigated to constrain spectral models. To that end, it is crucial to study iron structure of BHBs in detail at short time-scales, which is, for the first time, made possible with the Parallel-sum clocking (P-sum) mode of XIS detectors on board Suzaku. This observational mode has a time-resolution of 7.8~ms as well as a CCD energy-resolution. We have carried out systematic calibration of the P-sum mode, and investigated spectral variability of the BHB GRS 1915+105. Consequently, we found that the spectral variability of GRS 1915+105 does not show iron features at sub-seconds. This is totally different from variability of AGN such as 1H0707--495, where the variation amplitude significantly drops at the iron K-energy band. This difference can be naturally explained in the framework of the partial covering scenario.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
