J/ApJS/275/23 Swift obs. of Mrk 421. IV. 5.5yrs obs. (Kapanadze+, 2024)
Swift observations of Mrk 421 in selected epochs.
IV. Physical implications of X-ray flaring activity and features of relativistic
magnetic reconnection in 2018 April-2023 December.
Kapanadze B., Gurchumelia A., Aller M.
<Astrophys. J. Suppl. Ser., 275, 23 (2024)>
=2024ApJS..275...23K 2024ApJS..275...23K
ADC_Keywords: BL Lac objects; X-ray sources; Photometry, ultraviolet; Optical;
Gamma rays; Radio sources
Keywords: Blazars
Abstract:
We present the spectral and timing results obtained during the intense
observations of Mrk 421 by the Swift-based ultraviolet to X-ray
instruments during 2018 April-2023 December. The source showed various
strengths of X-ray flaring activity, exceeding a level of
3.5x10-9erg/cm2/s during the strongest 0.3-10keV flares. Our study
identifies a number of intraday brightness variability, including
61 instances that occurred within 1ks exposures that are consistent
with the shock-in-jet scenario and accompanied by significant, fast
spectral changes. The source exhibited extreme spectral properties
with dominance of the log-parabolic distributions of photons with
energy and the frequent occurrence of hard photon indices in the
0.3-10keV and 0.3-300GeV bands, with the peak of synchrotron spectral
energy distribution Ep detected at the energies beyond 29keV for the
first time. The source showed very fast transitions of
log-parabolic-to-power-law spectra, most plausibly caused by
turbulence-driven relativistic magnetic reconnection. Our spectral
results also demonstrate the importance of the first-order Fermi
mechanism within the magnetic field of different confinement
efficiencies, stochastic acceleration, transitions in the turbulence
spectrum, and hadronic cascades. The X-ray, UV, and γ-ray fluxes
showed a lognormal variability, which hints at the imprint of
accretion disk instabilities on the blazar jet, as well as the
possible presence of hadronic cascades. The UV and γ-ray
variabilities demonstrated weak correlations with the X-ray flaring
activity, which is not consistent with simple synchrotron self-Compton
models and requires more complex particle acceleration and emission
scenarios.
Description:
In this paper, we present the results of our detailed study of the
timing/spectral behavior of Mrk 421 during the period 2018 April --
2023 December, which was covered by intensive Swift-XRT observations
when the source was "visible" to this space observatory.
Moreover, we examined correlations between the 0.3-10keV flux
variability and those observed with different instruments: the
Ultraviolet-Optical Telescope (UVOT) and the Burst Alert Telescope
(BAT) on board Swift, the Large Area Telescope (LAT) on board Fermi,
MAXI, and the First G-APD Cherenkov Telescope (FACT).
The XRT observational log of the target is presented in Table 1.
See Section 2.1.
Along with the particular XRT exposure, the source is observed with
the 30cm Cassegrain-type instrument UVOT, generally cycling through
the six optical-UV filters V, B, U, UVW1, UVM2, and UVW2, which are
centered at the wavelengths 5468, 4392, 3465, 2600, 2246, and
1928Å, respectively.
We retrieved the publicly available 43GHz (7mm wavelength) flux values
from the website of the Large Very Long Baseline Array (VLBA) Project
BEAM-medium-energy experiment(ME) program.
See Section 2.2.
Fermi-LAT monitored the target during the period of our study within
the scanning survey program, implementing the full γ-ray sky
observation every 3hr.
See Section 2.3.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
11 04 27.31 +38 12 31.7 Mrk 421 = QSO B1101+3828
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 94 478 Summary of XRT observations of Mrk 421 in 2018
table2.dat 116 479 Results from UVOT observations in the bands
UVW1-UVM2
table6.dat 234 266 The 0.3-10keV IDVs in Mrk 421 during 2018 April --
2023 December
table12.dat 83 267 Fastest variability of spectral parameters within
the 1-ks time interval
table13.dat 87 116 Results of the XRT spectral analysis with a simple
power-law model
table14.dat 1622 92 Fast transitions from logarithmic to powerlaw
spectra or/and conversely
--------------------------------------------------------------------------------
See also:
B/swift : Swift Master Catalog (HEASARC, 2004-)
J/ApJ/700/597 : FERMI LAT detected blazars (Abdo+, 2009)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJS/209/14 : The Swift/BAT hard X-ray transient monitor (Krimm+, 2013)
J/other/Nat/515.376 : Power of relativistic jets in blazars (Ghisellini+, 2014)
J/A+A/578/A22 : Mrk421 in March 2010 (Aleksic+, 2015)
J/A+A/593/A91 : Mrk 421 multi-wavelength var., 2007-2009 (Ahnen+, 2016)
J/ApJ/831/102 : Swift & NuSTAR obs. of Mrk421 (Kapanadze+, 2016)
J/ApJ/848/103 : ∼1.5yr Swift observations of Mrk 421 (Kapanadze+, 2017)
J/ApJ/854/66 : Swift obs. of Mrk 421. I. 2005-2008 (Kapanadze+, 2018)
J/ApJ/858/68 : Swift obs. of Mrk 421. II. (Kapanadze+, 2018)
J/ApJS/238/13 : Sp. and timing results of 1ES 1959+650 (Kapanadze+, 2018)
J/ApJS/247/33 : Fermi LAT fourth source catalog (4FGL) (Abdollahi+, 2020)
J/ApJS/247/27 : Swift obs. of Mrk 421. III. 2.5yrs (Kapanadze+, 2020)
J/A+A/655/A89 : Mrk421 multi-instrument obs. in 2017 (Acciari+, 2021)
J/A+A/668/A75 : Long-term MWL var. of 1ES 0033+595 (Kapanadze+, 2022)
J/ApJS/260/12 : Jet kinematics of blazars at 43GHz (Weaver+, 2022)
J/ApJS/268/20 : XRT/UVOT obs. of Mrk501 (Kapanadze+, 2023)
http://www.bu.edu/blazars/BEAM-ME.html : VLBA-BU Blazar Monitoring Program
(BEAM-ME) homepage
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- ObsID [10474007/97201004] Swift observation
identifier
10- 28 A19 "datime" Start Observation start data/time UTC
30- 48 A19 "datime" End Observation end data/time UTC
51- 59 F9.3 d MJD [58219/60319.1] Modified Julian Date
61- 64 I4 d Exp [139/3884] Exposure time
66- 71 F6.2 ct/s CRate [5.38/108] Mean 0.3-10keV count rate
73- 76 F4.2 ct/s e_CRate [0.07/0.5] Uncertainty in CRate
78- 84 F7.3 --- chi2 [0.08/199.5] Reduced χ2 value
86- 87 I2 --- DoF [1/46] Degrees of Freedom
89- 91 A3 s Bin Time bin used for light curve construction;
Or stands for Orbit
93- 94 A2 --- Var Existence of brightness variability code (1)
--------------------------------------------------------------------------------
Note (1): Variability code as follows:
V = variability detection (110 occurrences)
PV = possibly variable (14 occurrences)
NV = non-variable (354 occurrences)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- ObsID [10474007/97201004] Swift observation
identifier
10- 14 F5.2 mag UVW1mag [11.2/13.1]? Swift/UVOT UVW1 band
apparent magnitude
16- 19 F4.2 mag e_UVW1mag [0.03/0.04]? Uncertainty in UVW1mag
21- 25 F5.2 mJy UVW1Flux [5.6/30.2]? Swift/UVOT UVW1 band flux
density
27- 30 F4.2 mJy e_UVW1Flux [0.17/1.2]? Uncertainty in UVW1Flux
32- 38 F7.3 [mW/m2] logUVW1nfn [-10.21/-9.47]? Log Swift/UVOT UVW1 band
νFν; erg/s/cm2
40- 44 F5.3 [mW/m2] e_logUVW1nfn [0.01/0.021]? Uncertainty in logUVW1nfn
46- 50 F5.2 mag UVM2mag [11.19/13.04]? Swift/UVOT UVM2 band
apparent magnitude
52- 55 F4.2 mag e_UVM2mag [0.04]? Uncertainty in UVM2mag
57- 61 F5.2 mJy UVM2Flux [4.6/25.54]? Swift/UVOT UVM2 band flux
density
63- 66 F4.2 mJy e_UVM2Flux [0.09/0.4]? Uncertainty in UVM2Flux
68- 74 F7.3 [mW/m2] logUVM2nfn [-10.21/-9.46]? Log Swift/UVOT UVM2 band
νFν; erg/s/cm2
76- 80 F5.3 [mW/m2] e_logUVM2nfn [0.005/0.015]? Uncertainty in logUVM2nfn
82- 86 F5.2 mag UVW2mag [11.14/13.03]? Swift/UVOT UVW2 band
apparent magnitude
88- 91 F4.2 mag e_UVW2mag [0.03/0.04]? Uncertainty in UVW2mag
93- 97 F5.2 mJy UVW2Flux [4.4/25.8]? Swift/UVOT UVW2 band flux
density
99- 102 F4.2 mJy e_UVW2Flux [0.1/0.7]? Uncertainty in UVW2Flux
104- 110 F7.3 [mW/m2] logUVW2nfn [-10.2/-9.4]? Log Swift/UVOT UVW2 band
νFν; erg/s/cm2
112- 116 F5.3 [mW/m2] e_logUVW2nfn [0.007/0.016]? Uncertainty in logUVW2nfn
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- ObsID Swift observation identifier (1)
26- 55 A30 --- Dates Observation start dates
(YYYY-MM-DD)/Modified Julian Date
57- 62 F6.3 h Deltat [0.07/23.98] Total observation length;
includes interval between orbits
64- 70 F7.3 --- chi2 Model reduced χ2
72- 75 I4 --- dof Degrees of freedom
77- 79 I3 s Bin ? Time bin for variability search
81- 82 A2 --- f_Bin [Or] "Or"
84- 89 F6.2 % Fvar Fractional variability amplitude
90 A1 --- --- [(]
91- 94 F4.2 % e_Fvar Fvar uncertainty
95 A1 --- --- [)]
97-146 A50 --- alpGam Photon index value α Γ (2)
148-170 A23 --- b Curvature parameter (2)
172-196 A25 keV Ep Synchorotron SED peak energy (2)
198-223 A26 10-10mW/m2 Sp Synchrotron SED peak height (2)
225-234 A10 --- Notes Additional note code (s) (3)
--------------------------------------------------------------------------------
Note (1): "Or" stands for "Orbit". Note that the top source are detected at
the 99.997% confidence level. Starting with observation 31202231
obtained on 2018-04-18/58225, the confidence is 99.5%.
Note (2): Obtained via the log-parabolic or power-law (PL) fits with spectra
extracted from the separate orbits (or segments) of the
corresponding XRT observation. Associated errors are in parenthesis.
Note (3): A remark related to the variable spectral parameter make the basic
contribution in the observed IDV. Note as follows:
1 = photon index;
2 = curvature;
3 = Ep;
4 = Sp;
5 = transition from the log parabolic PED into the power law one and/or
vice versa.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table12.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- ObsID-1 ? Swift observation identifier for photon
index parameter
10- 13 F4.2 --- alpha [0.05/0.17]? Change in the photon index at 1
keV for ObsID-1
15- 18 F4.2 --- e_alpha [0.02/0.04]? Uncertainty in the photon index
change
20 A1 --- Type-1 ? Direction for ObsID-1 (1)
22- 25 F4.2 ks Deltat-1 [0.13/0.99]? Fraction of the 1-ks time
interval for ObsID-1
27- 28 A2 --- G Indicates the 0.3-10 keV photon index Gamma
30- 37 I8 --- ObsID-2 ? Swift observation identifier for curvature
parameter
39- 42 F4.2 --- b [0.1/0.31]? Curvature parameter for ObsID-2
44- 47 F4.2 --- e_b [0.03/0.08]? Uncertainty in b
49 A1 --- Type-2 Direction for ObsID-2 (1)
51- 54 F4.2 ks Deltat-2 [0.13/0.99]? Fraction of the 1-ks time
interval for ObsID-2
56- 63 I8 --- ObsID-3 [11325001/96557016] Swift observation
identifier for peak energy
65 A1 --- l_Ep Limit flag on Ep
66- 71 F6.3 keV Ep [0.1/20.53] Peak energy
73- 76 F4.2 keV e_Ep [0.09/0.9]? Uncertainty in Ep
78 A1 --- Type-3 Direction for ObsID-3 (1)
80- 83 F4.2 ks Deltat-3 [0.13/0.98] Fraction of the 1-ks time
interval for ObsID-3
--------------------------------------------------------------------------------
Note (1): The acronyms "i" and "d" denote "increase" and
"decrease", respectively.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table13.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- ObsID Swift observation identifier
19- 21 I3 s Exp [87/580]? Observation segment used for
analysis
23- 26 F4.2 --- alpha [0.3/6.2] Photon index at 0.3-10keV
28- 32 F5.2 --- e_alpha [0.01/0.1] Uncertainty in alpha
34- 37 F4.2 --- Norm [0.3/6.2] Normalization; 10xK
39- 42 F4.2 --- e_Norm [0.01/0.1] Uncertainty in Norm
44- 47 F4.2 --- chi2 [0.86/1.2] Reduced χ2 value
49- 51 I3 --- DoF [32/250] Degrees of Freedom
53- 58 F6.2 10-11mW/m2 F0.3-2 [11.38/167] Unabsorbed 0.3-2keV flux;
10-11erg/s/cm2
60- 63 F4.2 10-11mW/m2 e_F0.3-2 [0.24/2.71] Uncertainty in F0.3-2
65- 70 F6.2 10-11mW/m2 F2-10 [2.87/204] Unabsorbed 2-10keV flux;
10-11erg/s/cm2
72- 75 F4.2 10-11mW/m2 e_F2-10 [0.13/6] Uncertainty in F2-10
77- 82 F6.2 10-11mW/m2 F0.3-10 [14.26/371] Unabsorbed 0.3-10keV flux;
10-11erg/s/cm2
84- 87 F4.2 10-11mW/m2 e_F0.3-10 [0.2/6.02] Uncertainty in F0.3-10
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table14.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Time Observation time code (1)
3- 3 I1 --- Exp [1/8]? Observation segment used for analysis
5- 13 I9 --- ObsID [11445007/206476000] Swift observation identifier
15-1622 A1608 --- Trans Transition progress (2)
--------------------------------------------------------------------------------
Note (1): Observation code as follows:
A = 2018 April - 2023 December;
B = 2005 - 2008;
C = 2009 - 2012;
D = 2013 January - 2013 June;
E = 2013 November - 2015 June;
F = 2015 December - 2018 April.
Note (2): The acronyms "Or", "S", "LGP" and "PL" stand for "Orbit",
"Segment", "logparabolic" and "powerlaw", respectively. The values
that follow are the model value and the uncertainty inside
parentheses.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Kapanadze et al. Paper I. 2018ApJ...854...66K 2018ApJ...854...66K Cat. J/ApJ/854/66
Kapanadze et al. Paper II. 2018ApJ...858...68K 2018ApJ...858...68K Cat. J/ApJ/858/68
Kapanadze et al. Paper III. 2020ApJS..247...27K 2020ApJS..247...27K Cat. J/ApJS/247/27
Licences: cc-by
(End) Emmanuelle Perret [CDS] 09-Sep-2025