J/ApJ/913/146 The blazar B2 1420+32 opt. & gamma LCs & opt. sp. (Mishra+, 2021)
The changing-look blazar B2 1420+32.
Mishra H.D., Dai X., Chen P., Cheng J., Jayasinghe T., Tucker M.A.,
Vallely P.J., Bersier D., Bose S., Do A., Dong S., Holoien T.W.-S.,
Huber M.E., Kochanek C.S., Liang E., Payne A.V., Prieto J., Shappee B.J.,
Stanek K.Z., Bhatiani S., Cox J., DeFrancesco C., Shen Z., Thompson T.A.,
Wang J.
<Astrophys. J., 913, 146 (2021)>
=2021ApJ...913..146M 2021ApJ...913..146M
ADC_Keywords: Active gal. nuclei; Photometry, UBV; Gamma rays; BL Lac objects;
QSOs; Spectra, optical
Keywords: Active galactic nuclei ; Blazars ; Radio loud quasars ;
Black hole physics ; Quasars ; Time domain astronomy
Abstract:
Blazars are active galactic nuclei with their relativistic jets
pointing toward the observer, comprising two major subclasses,
flat-spectrum radio quasars (FSRQs) and BL Lac objects. We present
multiwavelength photometric and spectroscopic monitoring observations
of the blazar B2 1420+32, focusing on its outbursts in 2018-2020.
Multiepoch spectra show that the blazar exhibited large-scale spectral
variability in both its continuum and line emission, accompanied by
dramatic gamma-ray and optical variability by factors of up to 40 and
15, respectively, on week to month timescales. Over the last decade,
the gamma-ray and optical fluxes increased by factors of 1500 and 100,
respectively. B2 1420+32 was an FSRQ with broad emission lines in
1995. Following a series of flares starting in 2018, it transitioned
between BL Lac and FSRQ states multiple times, with the emergence of a
strong Fe pseudocontinuum. Two spectra also contain components that
can be modeled as single-temperature blackbodies of 12000 and 5200K.
Such a collection of "changing-look" features has never been observed
previously in a blazar. We measure gamma-ray-optical and interband
optical lags implying emission-region separations of less than 800 and
130 gravitational radii, respectively. Since most emission-line flux
variations, except the Fe continuum, are within a factor of 2-3, the
transitions between FSRQ and BL Lac classifications are mainly caused
by the continuum variability. The large Fe continuum flux increase
suggests the occurrence of dust sublimation releasing more Fe ions in
the central engine and an energy transfer from the relativistic jet to
subrelativistic emission components.
Description:
Here we discuss multiple observations of the blazar B2 1420+32 over a
two year period.
For the γ-rays, we analyzed the full 12yr Fermi-LAT PASS8 data
in the 0.1-500GeV band from MJD 54689 to 59090. We used different
temporal bins depending on the brightness of the source.
See Section 2 for further details.
The optical data came from multiple sources. The earliest data is a
V-band light curve from CRTS (Drake+ 2009, J/ApJ/696/870). Next we
used the ASAS-SN V- and g-band data (Shappee+ 2014, J/ApJ/788/48 and
Kochanek+ 2017PASP..129j4502K 2017PASP..129j4502K), with the light curves obtained using
image subtraction as described in Jayasinghe+ (2018MNRAS.477.3145J 2018MNRAS.477.3145J)
and Jayasinghe+ (2019MNRAS.485..961J 2019MNRAS.485..961J). B2 1420+32 was observed by TESS
during Sector 23.
We monitored B2 1420+32 in the B, V, r and i bands with the Las
Cumbres Observatory Global Telescope Network (LCOGT) 1m telescope at
the McDonald Observatory. After basic reduction, the images were
downloaded from Las Cumbres Observatory Science Archive
(http://archive.lco.global/).
We have nine spectra to examine the spectra variability, the archival
SDSS spectrum from 2005 August, and eight spectroscopic follow-up
observations after the 2018 January outburst. See Section 3.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
14 22 30.38 +32 23 10.4 B2 1420+32 = QSO B1420+326
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 32 1708 B2 1420+32 optical lightcurves
table2.dat 30 464 B2 1420+32 Fermi LAT lightcurves
table3.dat 161 9 B2 1420+32 spectra continuum analysis
sp/* . 7 Spectra of B2 1420+32 from 7 observation dates
in ASCII format
fig4/* . 9 Spectra of B2 1420+32 from 8 observation dates
in MRT and FITS format
--------------------------------------------------------------------------------
See also:
II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)
J/A+A/375/739 : Hard X-ray properties of blazars (Donato+, 2001)
J/ApJ/613/682 : AGN masses and broad-line region sizes (Peterson+, 2004)
J/ApJ/696/870 : Catalina Real-time Transient Survey (CRTS) (Drake+, 2009)
J/ApJ/698/895 : Variations in QSOs optical flux (Kelly+, 2009)
J/A+A/495/691 : Multifreq. catalog of blazars, Roma-BZCAT (Massaro+, 2009)
J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/MNRAS/454/3864 : Orientation & QSO BH mass estimation (Brotherton+ 2015)
J/ApJ/804/7 : SaMOSA: opt. spectroscopy of 7 Fermi blazars (Isler+, 2015)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/ApJ/840/97 : Opt. reverberation mapping of 5 AGNs (Fausnaugh+, 2017)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.5 d MJD [53479.27/58967.95] Modified Julian Date
(JD-2400000.5)
13- 19 A7 --- Tel Telescope (1)
21- 21 A1 --- Filt Filter (g, B or V)
23- 27 F5.2 mag omag [14.16/19] Observed magnitude in Filt
29- 32 F4.2 mag e_omag [0/0.4] Uncertainty in omag
--------------------------------------------------------------------------------
Note (1): Telescope as follows:
TESS = the Transiting Exoplanet Survey Satellite during Sector 23
(1238 occurrences)
CRTS = the Catalina Real Time Survey (Drake+ 2009, J/ApJ/696/870);
289 occurrences
ASAS-SN = ASAS-SN V- and g-band data (Shappee+ 2014, J/ApJ/788/48 and
Kochanek+ 2017PASP..129j4502K 2017PASP..129j4502K); 159 occurrences
LCOGT = the Las Cumbres Observatory Global Telescope Network 1m telescope
at the McDonald Observatory (22 occurrences)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 d MJD [54772.66/59090.83] Modified Julian
Date (JD-2400000.5)
10- 17 A8 --- Bin Binning size
19- 24 F6.2 10-8ph/s/cm2 Flux [0.03/201] 0.1-500GeV Flux,
26- 30 F5.2 10-8ph/s/cm2 e_Flux [0.0/58.1] Uncertainty in Flux
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- Seq [1/9] Running sequence number of spectrum
3- 16 A14 --- Tel Telescope
18- 20 F3.1 0.1nm Res [2.5/7] Resolution in Å
22- 29 F8.2 d MJD [53472/58677.4] Modified Julian Date
31- 35 F5.1 10-18W/m2/nm Amp [2.3/160] Power-law amplitude normalized
to 3000Å with units of
10-16erg/s/cm2/Å
37- 42 F6.4 10-18W/m2/nm e_Amp [0.0042/1.4] Lower uncertainty on Amp
44- 49 F6.4 10-18W/m2/nm E_Amp [0.0042/1.3] Upper uncertainty on Amp
51- 55 F5.3 --- Index [0.45/1.9] Power-law index 1
57- 62 F6.4 --- e_Index [0.008/0.11] Lower uncertainty on Index
64- 69 F6.4 --- E_Index [0.008/0.1] Upper uncertainty on Index
71- 74 F4.2 --- Ind2 [2.78/2.78]? Power-law index 2
76- 79 F4.2 --- e_Ind2 [0.04/0.04]? Lower uncertainty on Ind2
81- 84 F4.2 --- E_Ind2 [0.04/0.04]? Upper uncertainty on Ind2
86- 90 I5 K bbT [5200/12000]? Blackbody temperature
92- 94 I3 K e_bbT [29/380]? Lower uncertainty on bbT
96- 98 I3 K E_bbT [29/320]? Upper uncertainty on bbT
100- 102 F3.1 10-14W/m2/nm bbF [4.8/6.2]? Blackbody flux in units of
10-12erg/s/cm2/Å
104- 107 F4.2 10-14W/m2/nm e_bbF [0.12/0.35]? Lower uncertainty on bbF
109- 112 F4.2 10-14W/m2/nm E_bbF [0.12/0.35]? Upper uncertainty on bbF
114- 161 A48 --- File Name of the spectrum file in
subdirectory "fig4"
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 F18.13 0.1nm lambda [3305/9697.1] Wavelength, Angstrom
20- 32 E13.8 cW/m2/nm Flux [7.5e-17/2.3e-14] Flux,
in erg/s/cm2/Angstrom units
34- 46 E13.8 cW/m2/nm e_Flux [3.5e-18/3.7e-15] Flux uncertainty
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Dec-2022