اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNLS1 galaxies and estimation of their central black hole masses from the X-ray excess variance method
170
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Black hole mass determination in active galaxies is a key issue in understanding various luminosity states. In the present paper we try to generalise the mass determination method based on the X-ray excess variance, successfully used for typical broad line Seyfert 1 galaxies (BLS1) to Narrow Line Seyfert 1 (NLS1) galaxies. NLS1 galaxies differ from BLS1 with respect to several properties. They are generally more variable in 2-10 keV energy band so the natural expectation is the need to use a different scaling coefficient between the mass and the variance in these two types of sources. However, we find that such a simple approach is not enough. Although for majority of the 21 NLS1 galaxies in our sample a single scaling coefficient (larger by a factor 20) provided us with a satisfactory method of mass determination, in a small subset of NLS1 galaxies this approach failed. Variability of those objects appeared to be at the intermediate level between NLS1 and BLS1 galaxies. These exceptional NLS1 galaxies have much harder soft X-ray spectra than majority of NLS1 galaxies. We thus postulate that the division of Seyfert 1 galaxies into BLS1 and NLS1 according to the widths of the Hbeta line is less generic than according to the soft X-ray slope.
قيم البحث
اقرأ أيضاً
We estimate black hole masses in Narrow Line Seyfert 1 (NLS1) galaxies at the basis of their X-ray excess variance. We apply the standard approach appropriate for Broad Line Seyfert 1 (BLS1) galaxies. In general, we find that the obtained masses are
by a factor sim 20 too small to agree with values obtained from other methods (reverberation, stellar dispersion). However, a small subset of our NLS1 objects does not require that multiplication, or the correction factor is less than 4. We find that this subset have a soft X-ray photon index, Gamma_{0.1-2.4 keV}, smaller than 2. We thus postulate that this subclass of NLS1 actually belongs to BLS1.
Values of black hole masses are frequently determined with the help of the reverberation method. This method requires a specific geometrical factor related to the distribution of the orbits of the Broad Line Region clouds. Onken et al. determined the
value f^2= 1.37+/-0.45 from the black hole mass - dispersion relation. In this paper we determine this factor using an independent mass determination from the X-ray variance method for a number of Seyfert 1 galaxies and comparing them with the reverberation results by Peterson et al. We obtain mean value f^2 = 1.12 +/- 0.54, consistent with Onken et al. Both values are larger than the value 0.75 corresponding to a spherical geometry. It indicates that most probably all values of the black hole masses obtained with the use of the Kaspi et al. formulae should be multiplied by a factor of sim 1.7. This also shows that the Broad Line Region is rather flat, and hints for a dependence of the factor f^2 on a source inclination seem to be present in the data.
We review briefly direct and indirect methods of measuring the masses of black holes in galactic nuclei, and then focus attention on supermassive black holes in active nuclei, with special attention to results from reverberation mapping and their lim
itations. We find that the intrinsic scatter in the relationship between the AGN luminosity and the broad-line region size is very small, ~0.11 dex, comparable to the uncertainties in the better reverberation measurements. We also find that the relationship between reverberation-based black hole masses and host-galaxy bulge luminosities also seems to have surprisingly little intrinsic scatter, ~0.17 dex. We note, however, that there are still potential systematics that could affect the overall mass calibration at the level of a factor of a few.
We discuss two methods to estimate black hole (BH) masses using X-ray data only: from the X-ray variability amplitude and from the photon index Gamma. The first method is based on the anti-correlation between BH mass and X-ray variability amplitude.
Using a sample of AGN with BH masses from reverberation mapping, we show that this method shows small intrinsic scatter. The second method is based on the correlation between Gamma and both the Eddington ratio L_{bol}/L_{Edd} and the bolometric correction L_{bol}/L_{2-10keV}.
Several investigations of the X-ray variability of active galactic nuclei (AGN) using the normalised excess variance (${sigma^2_{rm NXS}}$) parameter have shown that variability has a strong anti-correlation with black hole mass ($M_{rm BH}$) and X-r
ay luminosity ($L_{rm X}$). In this study we confirm these previous correlations and find no evidence of a redshift evolution. Using observations from XMM-Newton, we determine the ${sigma^2_{rm NXS}}$ and $L_{rm X}$ for a sample of 1091 AGN drawn from the XMM-Newton Cluster Survey (XCS) - making this the largest study of X-ray spectral properties of AGNs. We created light-curves in three time-scales; 10 ks, 20 ks and 40 ks and used these to derive scaling relations between ${sigma^2_{rm NXS}}$, $L_{rm X}$ (2.0-10 keV range) and literature estimates of $M_{rm BH}$ from reverberation mapping. We confirm the anti-correlation between $M_{rm BH}$ and ${sigma^2_{rm NXS}}$ and find a positive correlation between $M_{rm BH}$ and $L_{rm X}$. The use of ${sigma^2_{rm NXS}}$ is practical only for pointed observations where the observation time is tens of kiloseconds. For much shorter observations one cannot accurately quantify variability to estimate $M_{rm BH}$. Here we describe a method to derive $L_{rm X}$ from short duration observations and used these results as an estimate for $M_{rm BH}$. We find that it is possible to estimate $L_{rm X}$ from observations of just a few hundred seconds and that when correlated with $M_{rm BH}$, the relation is statistically similar to the relation of $M_{rm BH}$-$L_{rm X}$ derived from a spectroscopic analysis of full XMM observations. This method may be particularly useful to the eROSITA mission, an all-sky survey, which will detect $>$10$^{6}$ AGN.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
