J/ApJ/880/32 Optical/γ-ray flares for Fermi-LAT blazars (Liodakis+, 2019)
Probing blazar emission processes with optical/gamma-ray flare correlations.
Liodakis I., Romani R.W., Filippenko A.V., Kocevski D., Zheng W.
<Astrophys. J., 880, 32 (2019)>
=2019ApJ...880...32L 2019ApJ...880...32L
ADC_Keywords: BL Lac objects; QSOs; Active gal. nuclei; Redshifts; Optical;
Gamma rays
Keywords: galaxies: active ; galaxies: jets ; relativistic processes
Abstract:
Even with several thousand Fermi-Large Area Telescope (LAT) blazar
detections, the γ-ray emission mechanism is poorly understood.
We explore correlated optical/γ-ray flux variations for 178
Fermi-LAT blazars regularly monitored by the Katzman Automatic Imaging
Telescope, the Small and Moderate Aperture Research Telescope System,
and the Steward Observatory. Out of the 178 sources, 121 show a
measurable (>1σ) discrete correlation function peak. Using the
derived time lags and Bayesian block light-curve decompositions, we
measure the fraction of common and orphan flares between the two
bands. After accounting for sampling and sensitivity limitations we
quantify for the first time the true orphan flare rates of optical and
γ-ray flares: 54.5% of optical and 20% of γ-ray flares are
orphan events. Both the intraband temporal relation and the small
orphan γ-ray flare fraction point toward leptonic processes as
the likely mechanisms for the high-energy emission. Motivated to
discriminate between synchrotron self-Compton (SSC) and
external-Compton dominance in individual sources, we use the flux-flux
variations to determine the slope m of the log fopt-log fγ
dependence. The slope distribution suggests a bimodal population with
high and intermediate synchrotron peak objects showing larger m than
low synchrotron peak objects. We find that m is naturally decreased
through pollution from the orphan (typically optical) flares and
develop a method to statistically recover, given the sources' measured
orphan flare rate, the intrinsic m. While source classes show
composite behavior, the majority of BL Lac objects favor m=2,
indicating an SSC origin for the γ-rays. No preference for
either m is found in flat spectrum radio quasars.
Description:
We begin our sample selection with the sources observed by the Katzman
Automatic Imaging Telescope (KAIT). KAIT has been observing a total of
152 sources (white-light observations roughly corresponding to the R
band) that were detected at high significance (>10σ) by
Fermi-LAT during the first year of operations (Abdo+ 2010, J/ApJS/188/405)
since 2008. To increase our sample and improve our statistics we
included sources observed by the Steward Observatory 2.3m Bok
Telescope (19 sources; see Smith+, 2009arXiv0912.3621S 2009arXiv0912.3621S) and the Small
and Moderate Aperture Research Telescope System (SMARTS, 31 sources;
see Bonning+ 2012ApJ...756...13B 2012ApJ...756...13B) monitoring programs. The optical
observations cover the time period between 2008 and 2017.
Our final sample consists of 178 γ-ray-detected sources (80
LSPs, 27 ISPs, 35 HSPs, and 36 sources without SED peak information).
Based on optical spectra, 107 sources have been classified as BL Lac
objects, 64 as FSRQs, 4 as radio galaxies, and 3 are as yet
unclassified.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 97 178 The discrete correlation function (DCF) and
flux-flux correlation results for the sources
in our sample
lcs/* . 157 Individual KAIT light curve files in ASCII format
from http://herculesii.astro.berkeley.edu/kait/agn/
(2021-jan-26)
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See also:
II/5 : UBV Photometry of Bright Stars (Johnson+ 1966)
VII/274 : The Roma BZCAT - 5th edition (Massaro+, 2015)
J/A+A/445/441 : SED of BL Lacertae objects (Nieppola+, 2006)
J/A+A/488/867 : Synchrotron peak frequency of 135 AGN (Nieppola+, 2008)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJS/188/405 : Fermi-LAT first source catalog (1FGL) (Abdo+, 2010)
J/ApJS/218/23 : Fermi LAT third source catalog (3FGL) (Acero+, 2015)
J/ApJ/813/51 : γ-ray to IR study of CTA 102 (Casadio+, 2015)
J/ApJ/810/L9 : 1.5Jy MOJAVE AGN sample and 3FGL data (Lister+, 2015)
J/other/AstBu/70.264 : Sample of 877 blazars (Mingaliev+, 2015)
J/MNRAS/467/4565 : Bimodal radio variability in OVRO blazars (Liodakis+, 2017)
J/ApJ/866/137 : Bright blazars variability brightness temp. (Liodakis+, 2018)
http://herculesii.astro.berkeley.edu/kait/agn/ : KAIT Fermi AGN monitoring
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Name Name (1)
18- 18 A1 --- Class Class (2)
20- 22 A3 --- SED Spectral energy distribution class (3)
24- 28 F5.3 --- z [0.0/2.2]? Redshift
30- 36 F7.2 d tau [-106/86.3]? Derived time lag
38- 42 F5.2 d e_tau [0.26/19.7]? Uncertainty in tau
44- 44 A1 --- l_DCF Limit flag on DCF
46- 49 F4.2 --- DCF [1.0/3.5]? DCF peak significance
51- 55 F5.2 --- m [-0.22/3.12]? Slope of the optical-gamma ray
log-log correlation
57- 60 F4.2 --- e_m [0.02/1.6]? Uncertainty in m
62- 66 F5.2 --- rho [-0.14/0.9]? Spearman's test correlation
coefficient
68- 75 E8.2 --- p [0/0.97]? Probability associated
with the Spearman test
76 A1 --- f_p [i] i: probabilities <1E-56 have been set
to zero by CDS
78- 85 E8.2 --- p1 [0/0.98]? Probability of association with m=1,
intrinsic linear slope
87- 94 E8.2 --- p2 [0/0.99]? Probability of association with m=2,
intrinsic quadratic slope
96- 97 A2 --- LC [lc] LC: KAIT light curve available;
column added by CDS
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Note (1): Names are either as listed in the KAIT website:
http://herculesii.astro.berkeley.edu/kait/agn/ or at their respective
observatories' websites.
Note (2): The optical classification is taken from Simbad and NED.
B = BL Lac objects (107 occurrences),
F = Flat spectrum radio quasars (FSRQs; 64 occurrences),
G = radio galaxies (4 occurrences).
Note (3): The SED classification is from Nieppola+ (2006, J/A+A/445/441 and
2008, J/A+A/488/867); Abdo+ (2010, J/ApJ/716/30);
Cohen+ (2014ApJ...797..137C 2014ApJ...797..137C); Lister+ (2015, J/ApJ/810/L9);
Mingaliev+ (2015, J/other/AstBu/70.264); Angelakis+ (2016MNRAS.463.3365A 2016MNRAS.463.3365A)
and references therein. Class as follows:
LSP = low synchrotron peak (80 occurrences)
HSP = high synchrotron peak (35 occurrences)
ISP = intermediate synchrotron peak (27 occurrences)
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History:
From electronic version of the journal for Table 1
Light curves downloaded at: http://herculesii.astro.berkeley.edu/kait/agn/
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Jan-2021