J/MNRAS/519/6349 The gamma/optical flares of 4FGL-DR3 blazars (De Jaeger+, 2023)
Optical/γ-ray blazar flare correlations understanding the high-energy
emission process using ASAS-SN and Fermi light curves.
De Jaeger T., Shappee B.J., Kochanek C.S., Hinkle J.T., Garrappa S.,
Liodakis I., Franckowiak A., Stanek K.Z., Beacom J.F., Prieto J.L.
<Mon. Not. R. Astron. Soc. 519, 6349-6380 (2023)>
=2023MNRAS.519.6349D 2023MNRAS.519.6349D (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Active gal. nuclei ; QSOs ; Spectroscopy ; Photometry ;
Gamma rays ; Optical ; Radio sources ; Positional data ;
Redshifts ; GRB
Keywords: relativistic processes - galaxies: active - galaxies: jets
Abstract:
Using blazar light curves from the optical All-Sky Automated Survey
for Supernovae (ASAS-SN) and the γ-ray Fermi-LAT telescope, we
performed the most extensive statistical correlation study between
both bands, using a sample of 1180 blazars. This is almost an order of
magnitude larger than other recent studies. Blazars represent more
than 98 per cent of the AGNs detected by Fermi- LAT and are the
brightest γ-ray sources in the extragalactic sky. They are
essential for studying the physical properties of astrophysical jets
from central black holes. However, their γ-ray flare mechanism
is not fully understood. Multiwavelength correlations help constrain
the dominant mechanisms of blazar variability. We search for temporal
relationships between optical and γ-ray bands. Using a Bayesian
Block Decomposition, we detect 1414 optical and 510 γ-ray
flares, we find a strong correlation between both bands. Among all the
flares, we find 321 correlated flares from 133 blazars, and derive an
average rest-frame time delay of only 1.1-8.5+7.1 d, with no
difference between the flat-spectrum radio quasars, BL Lacertae-like
objects or low, intermediate, and high-synchrotron peaked blazar
classes. Our time-delay limit rules out the hadronic
proton-synchrotron model as the driver for non-orphan flares and
suggests a leptonic single-zone model. Limiting our search to
well-defined light curves and removing 976 potential but unclear
'orphan' flares, we find 191 (13 per cent) and 115 (22 per cent) clear
'orphan' optical and γ-ray flares. The presence of 'orphan'
flares in both bands challenges the standard one-zone blazar flare
leptonic model and suggests multizone synchrotron sites or a hadronic
model for some blazars.
Description:
In this work, we investigate the question of the high-energy emission
process by looking for optical/γ-ray flare correlations for 1180
blazar light curves from the Fermi-LAT Collaboration data base
(Abdollahi et al. 2022ApJS..260...53A 2022ApJS..260...53A, Cat. IX/67). This sample
represents the most extensive and homogeneous statistical study of
blazar flares. We selected all the sources from the 12-yr Fermi-LAT
point source (4FGL-DR3 with a variability index greater than 24.725.
This leads to a sample of 1695 sources. Then, we remove all sources
with any non-zero entry in the analysis flags column indicating that
they are affected by systematic errors. Finally, we select only the
blazars and blazar candidates, the sources classified as FSRQ, BL Lac,
or blazar candidates of uncertain type (BCU), with light curves in the
Fermi LAT. This leads to a final sample of 1180 sources consisting of
503 FSRQs, 437 BL Lacs, and 240 BCU (814 LSP, 123 ISP, and 127 HSP)
sources.
The γ-ray light curves were obtained from the LAT Light Curve
Repository website. A full description of the data reduction is found
on the Fermi-LAT Light Curve Repository website and in Abdollahi et
al. (2022ApJS..260...53A 2022ApJS..260...53A, Cat. IX/67). The optical V and g light
curves come from ASAS-SN which is ideal for searching for blazar flare
correlations. Those two unique features allow us to do the most
extensive statistical study of blazar flares to date with minimal
selection biased, as we observe all the blazars independently of their
properties or localization. Next, explained in section 3 and 4 we
exploit these light curves to find time correlations between flares in
gamma and optical lights. The tablea1.dat provides astrometric,
physical and flares properties of our 1180 4FGL-DR3 selected blazars.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 99 1180 Relevant informations and properties of our
blazars sample
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See also:
J/MNRAS/480/5517 : Multiwavelength cross-correlations in blazars
(Liodakis+, 2018)
J/MNRAS/439/690 : Optical/γ-ray variability in blazars (Hovatta+, 2014)
J/ApJ/893/L20 : Proton synchrotron gamma-rays in blazars (Liodakis+, 2020)
J/ApJ/880/32 : Optical/γ-ray flares for Fermi-LAT blazars
(Liodakis+, 2019)
J/ApJ/866/137 : Bright blazars variability brightness temp. (Liodakis+,2018)
J/ApJ/864/84 : Swift follow-up obs. of the TXS 0506+056 blazar
(Keivani+, 2018)
J/ApJ/789/135 : Gamma-ray bright blazars spectrophotometry
(Williamson+, 2014)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJS/247/33 : The Fermi LAT fourth source catalog (4FGL)
(Abdollahi+, 2020)
J/ApJS/218/23 : Fermi LAT third source catalog (3FGL) (Acero+, 2015)
J/ApJS/183/46 : Fermi/LAT bright gamma-ray source list (0FGL) (Abdo+, 2009)
II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)
IX/67 : Incremental Fermi LAT 4th source cat. (4FGL-DR3)
(Fermi-LAT col., 2022)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- 4FGL 4FGL-DR3 name identifier from Abdollahi et
al. 2022ApJS..260...53A 2022ApJS..260...53A, Cat. IX/67
(4FGL_Name)
14- 23 F10.6 deg RAdeg Right ascension (J2000) (RA)
25- 34 F10.6 deg DEdeg Declination (J2000) (Dec)
36- 63 A28 --- Associated Source name to the γ-ray emissions
linked to Simbad database (Association)
65- 70 A6 --- Class Source class type (Class) (1)
72- 74 A3 --- SED Spectral energy distribution class type
(SED_class) (2)
76- 80 F5.3 --- z ? The spectroscopic redshift (redshift)
82- 85 A4 --- Flares Flag to indicates if significant flares in
the optical and/or γ-rays light
curves is display (Flares) (3)
87- 92 F6.2 d tlag ? The rest-frame time lag between optical
and {gama}-rays flares (Lags) (4)
94- 99 F6.2 d e_tlag ? Uncertainty of tlag (Lags) (4)
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Note (1): Source class type are as follows:
BCU = Blazar AGNs candidates of uncertain type,
240 occurences in our sample
BL Lac = BL Lacertae AGNs, 437 occurences in our sample
FSRQ = Flat-spectrum radio quasars, 503 occurences in our
sample
Note (2): SED types are as follows:
LSP = Low-synchrotron peaked blazars, 814 occurences in our sample
ISP = Intermediate synchrotron peaked blazars, 123 occurences in
our sample
HSP = High-synchrotron peaked blazars, 127 occurences in our sample
Padovani & Giommi (1995ApJ...444..567P 1995ApJ...444..567P) proposed an independent
classification based on peak of their spectral energy distribution
(SED; see also Abdo et al. 2010ApJ...716...30A 2010ApJ...716...30A, Cat. J/ApJ/716/30
and Ghisellini et al. 2011MNRAS.414.2674G 2011MNRAS.414.2674G): low-synchrotron peaked
blazars (LSP; νpeak ≤ 1014 Hz), intermediate synchrotron
peaked blazars (ISP; 1014 ≤ νpeak ≤ 1015 Hz), and
high-synchrotron peaked blazars (HSP; νpeak > 1015 Hz).
The HSP and ISP blazar groups are mostly BL Lacs, while the LSP
class is dominated by FSRQs (i.e see section Introduction).
Note (3): Significant flares are as follows:
none = Without prominent flares, 759 occurences in our sample
both = Having at least one flare in both bands, optical and
the γ-ray LCs, 175 occurences in our sample
opt = Prominent flare, only in optical bands ASAS-SN V and
g LCs, 166 occurences in our sample
gam = Prominent flare, only in γ-ray Fermi-LAT band LCs,
80 occurences in our sample
As explained in section 3, the flares detection procedure leads
to flux level selection on light curves in both bands (e.g.
equation 1 of this section). Finally, we visually inspect all
the flare candidates and remove the bad candidates as flares with
large photometric errors, optical flares due to seasonal gap edges,
or optical flares seen only in one optical band (V or g) during
the V/g band overlap period.
Note (4): As defined in section 3.2 Time lags, or all the blazars, we define
the rest-frame time lag (Tlag) as the difference in the epochs of
the Bayesian block peaks (the middle of the block in a Bayesian
Block Decomposition of LCs) and the associated uncertainty as half
the block widths. Example, for the object J0050.4-0452, the
{gamm}-ray and optical observed flare epochs are, respectively,
MJD 56557.25 ± 42.8 and MJD 56574.12 ± 38.2. So the rest-frame
is Tlag = 8.8 ± 21.1 d. Where a positive Tlag corresponds to
the {gamm}-ray emission leading to the optical emission.
From the 175 objects with flares in both bands, we found 133 blazars
with correlated flares and a redshift.
More, 42 objects have Tlag = 999.90 ± 999.90 days corresponding
to non physical values.
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 26-Feb-2026