J/ApJ/698/895 Variations in QSOs optical flux (Kelly+, 2009)
Are the variations in quasar optical flux driven by thermal fluctuations?
Kelly B.C., Bechtold J., Siemiginowska A.
<Astrophys. J., 698, 895-910 (2009)>
=2009ApJ...698..895K 2009ApJ...698..895K
ADC_Keywords: QSOs ; Active gal. nuclei ; Models
Keywords: accretion, accretion disks - galaxies: active -
methods: data analysis - quasars: general
Abstract:
We analyze a sample of optical light curves, compiled from the
literature, for 100 quasars, 70 of which have black hole mass
estimates. Our sample is the largest and broadest used yet for
modeling quasar variability. The sources in our sample have z<2.8,
1042≲λLλ(5100Å)≲1046, and
106≲MBH/M☉≲1010. We model the light curves as a
continuous time stochastic process, providing a natural means of
estimating the characteristic timescale and amplitude of quasar
variations. We employ a Bayesian approach to estimate the
characteristic timescale and amplitude of flux variations; our
approach is not affected by biases introduced from discrete sampling
effects.
Description:
Our sample consists of 55 AGNs from the MACHO survey (Geha et al.
2003AJ....125....1G 2003AJ....125....1G), 37 Palomar Green (PG) quasars from the sample of
Giveon et al. (1999MNRAS.306..637G 1999MNRAS.306..637G), and eight Seyfert galaxies from
the AGN Watch database (http://www.astronomy.ohio-state.edu/~agnwatch/).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 48 109 Quasars analyzed in this work (table from
erratum 2011, ApJ, 732, 128)
table2.dat 50 109 Results from CAR(1) process fits to quasar light
curves (table from erratum 2011, ApJ, 732, 128)
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See also:
J/ApJS/185/156 : The Lick AGN monitoring project (Walsh+, 2009)
J/ApJ/625/78 : QSOs properties (Hao+, 2005)
J/A+A/369/57 : Monitoring Mkn 279 in BVRI and Hβ fluxes (Santos-Lleo+,
2001)
J/ApJ/269/352 : Quasar evolution (Schmidt+, 1983)
http://www.astronomy.ohio-state.edu/~agnwatch/ : AGN Watch Website
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 10 F4.1 s RAs Second of Right Ascension (J2000)
12 A1 --- DE- Sign of the Declination (J2000)
13- 14 I2 deg DEd Degree of Declination (J2000)
16- 17 I2 arcmin DEm Arcminute of Declination (J2000)
19- 22 F4.1 arcsec DEs Arcsecond of Declination (J2000)
24- 28 F5.3 --- z Redshift
30- 34 F5.2 [10-7W] logL5100 Log of monochromatic luminosity at 5100Å
36- 40 F5.2 [Msun] logMBH ? Log of Blackhole mass
42- 45 F4.2 [Msun] e_logMBH ? The 1σ error in logMBH
47- 48 I2 --- Ref Optical light curve reference (1)
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Note (1): Reference as follows:
1 = Giveon et al. (1999MNRAS.306..637G 1999MNRAS.306..637G);
2 = Geha et al. (2003AJ....125....1G 2003AJ....125....1G);
3 = Stirpe et al. (1994ApJ...425..609S 1994ApJ...425..609S);
4 = Peterson et al. (2000ApJ...542..161P 2000ApJ...542..161P);
5 = Kaspi et al. (1996ApJ...470..336K 1996ApJ...470..336K);
6 = Santos-Lleo et al. (2001, Cat. J/A+A/369/57);
7 = Peterson et al. (2002ApJ...581..197P 2002ApJ...581..197P);
8 = Carone et al. (1996ApJ...471..737C 1996ApJ...471..737C);
9 = Shemmer et al. (2001ApJ...561..162S 2001ApJ...561..162S; <[SRB2001] N> in Simbad);
10 = Collier et al. (1998ApJ...500..162C 1998ApJ...500..162C).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 10 F4.1 s RAs Second of Right Ascension (J2000)
12 A1 --- DE- Sign of the Declination (J2000)
13- 14 I2 deg DEd Degree of Declination (J2000)
16- 17 I2 arcmin DEm Arcminute of Declination (J2000)
19- 22 F4.1 arcsec DEs Arcsecond of Declination (J2000)
24- 27 F4.2 [d] logtau ? Log of characteristic time scale τ
of the quasar lightcurve (1)
29 A1 --- f_logtau [c] poor fit (2)
31- 34 F4.2 [d] e_logtau ? Lower 95% confidence interval in logtau
36- 39 F4.2 [d] E_logtau ? Upper 95% confidence interval in logtau
41- 45 F5.2 [---] logsig ? Log of standard deviation in the input
process to Equation 1 (1)
47- 50 F4.2 [---] e_logsig ? The error in logsigma
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Note (1): In this work, we model quasar light curves as a continuous time
first-order autoregressive process (CAR(1)). The CAR(1) process is
described by the following stochastic differential equation (e.g.,
Brockwell & Davis 2002, Introduction to Time Series and Forecasting,
2nd ed. (New York: Springer)):
dX(t)=-(1/τ)X(t)dt+σ(dtε(t))0.5+bdt, τ,σ,t>0
Here, τ is called the "relaxation time" of the process X(t), and
ε(t) is a white noise process with zero mean and variance
equal to 1. Within the context of this work, X(t) is the quasar flux.
The relaxation time, τ, can be interpreted as the time required
for the time series to become roughly uncorrelated, and σ can be
interpreted as describing the variability of the time series on
timescales short compared to τ. The standard deviation of quasar
flux variations on time scales of 1 day is expected to be equal to
σ. See section 3 for further details.
Note (2):
c = The CAR(1) process provided a poor fit to these lightcurves, and
the data was not used in our regression analysis.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 09-Jun-2011