J/MNRAS/540/364 Multiwavelength study of OT 081 (Abe+, 2025)
Multiwavelength study of OT 081: broadband modelling of a transitional blazar.
Abe H., Abe S., Acciari V.A., Agudo I., Aniello T., Ansoldi S.,
Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D.,
Babic A., Baquero A., Barres De Almeida U., Batkovic I., Baxter J.,
Bernardini E., Bernardos M., Bernete J., Berti A., Bigongiari C.,
Biland A., Blanch O., Bonnoli G., Bosnjak Z., Burelli I., Busetto G.,
Campoy-Ordaz A., Carosi A., Carosi R., Carretero-castrillo M.,
Castro-Tirado A.J., Chai Y., Cifuentes A., Cikota S., Colombo E.,
Contreras J.L., Cortina J., Covino S., D'amico G., D'Elia V., Da Vela P.,
Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M.,
Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L.,
Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G.,
Escudero J., Farina L., Fattorini A., Foffano L., Font L., Fukami S.,
Fukazawa Y., Garcia Lopez R.J., Gasparyan S., Gaug M.,
Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Grau R.,
Green J.G., Hadasch D., Hahn A., Heckmann L., Herrera J., Hrupec D.,
Hutten M., Imazawa R., Inada T., Iotov R., Ishio K., Jimenez Martinez I.,
Jormanainen J., Kerszberg D., Kluge G.W., Kobayashi Y., Kubo H.,
Kushida J., Lainez Lezaun M., Lamastra A., Leone F., Lindfors E.,
Linhoff L., Lombardi S., Longo F., Lopez-moya M., Lopez-Oramas A.,
Loporchio S., Lorini A., Machado De Oliveira Fraga B., Majumdar P.,
Makariev M., Maneva G., Mang N., Manganaro M., Mangano S., Mannheim K.,
Mariotti M., Martinez M., Mas-aguilar A., Mazin D., Menchiari S.,
Mender S., Micanovic S., Miceli D., Miranda J.M., Mirzoyan R., Molina E.,
Mondal H.A., Morcuende D., Nanci C., Neustroev V., Nigro C., Nishijima K.,
Njoh Ekoume T., Noda K., Nozaki S., Ohtani Y., Otero-santos J., Paiano S.,
Palatiello M., Paneque D., Paoletti R., Paredes J.M., Pavletic L.,
Persic M., Pihet M., Pirola G., Podobnik F., Prada Moroni P.G.,
Prandini E., Principe G., Priyadarshi C., Rhode W., Ribo M., Rico J.,
Righi C., Sahakyan N., Saito T., Satalecka K., Saturni F.G., Schleicher B.,
Schmidt K., Schmuckermaier F., Schubert J.L., Schweizer T., Sitarek J.,
Spolon A., Stamerra A., Striskovic J., Strom D., Suda Y., Suric T.,
Suutarinen S., Tajima H., Takahashi M., Takeishi R., Tavecchio F.,
Temnikov P., Terzic T., Teshima M., Tosti L., Truzzi S., Ubach S.,
Van Scherpenberg J., Ventura S., Verguilov V., Viale I., Vigorito C.F.,
Vitale V., Walter R., Yamamoto T. (MAGIC Collaboration), Ait Benkhali F.,
Becherini Y., Bi B., Bottcher M., Bolmont J., Brown A., Bulik T.,
Casanova S., Chand T., Chandra S., Chibueze J., Chibueze O., Egberts K.,
Einecke S., Ernenwein J.-P., Fontaine G., Gabici S., Goswami P., Holler M.,
Jamrozy M., Joshi V., Kasai E., Katarzynski K., Khatoon R., Khelifi B.,
Kluzniak W., Kosack K., Lang R.G., Le Stum S., Lemiere A., Marx R.,
Moderski R., Moghadam M.O., De Naurois M., Niemiec J., O'Brien P.,
Ostrowski M., Peron G., Pita S., Puhlhofer G., Quirrenbach A., Rudak B.,
Sahakian V., Sanchez D.A., Santangelo A., Sasaki M., Schutte H.M.,
Seglar-arroyo M., Shapopi J.N.S., Steenkamp R., Steppa C., Suzuki H.,
Tanaka T., Tluczykont M., Venter C., Wagner S.J., Wierzcholska A.,
Zdziarski A.A., Zywucka N. (VHE Gamma-ray collaborators),
Becerra Gonzalez J., Ciprini S., Venters T.M. (from the Fermi-LAT
Collaboration) , D'Ammando F., Esteban-Gutierrez A., Fallah Ramazani V.,
Filippenko A.V., Hovatta T., Jermak H., Jorstad S., Kiehlmann S.,
Lahteenmaki A., Larionov V.M., Larionova E., Marscher A.P., Morozova D.,
Max-Moerbeck W., Readhead A.C.S., Reeves R., Steele I.A., Tornikoski M.,
Verrecchia F., Xiao H.B., Zheng W. (MWL collaborators)
<Mon. Not. R. Astron. Soc. 540, 364 (2025)>
=2025MNRAS.540..364A 2025MNRAS.540..364A (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Photometry ; Optical ; Gamma rays ;
Radio sources ; Energy distributions
Keywords: radiation mechanisms: non-thermal - galaxies: active -
galaxies: individual: OT 081 - galaxies: jets - quasars: general -
gamma-rays: galaxies
Abstract:
OT 081 is a well-known, luminous blazar that is remarkably variable in
many energy bands. We present the first broadband study of the source,
which includes very high energy (VHE, E>100GeV) γ-ray data
taken by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov
telescopes) and H.E.S.S. (High Energy Stereoscopic System) imaging
Cherenkov telescopes. The discovery of VHE γ-ray emission
happened during a high state of γ-ray activity in July 2016,
observed by many instruments from radio to VHE γ-rays. We
identify four states of activity of the source, one of which includes
VHE γ-ray emission. Variability in the VHE domain is found on
daily time-scales. The intrinsic VHE spectrum can be described by a
power law with index 3.27±0.44stat±0.15sys (MAGIC) and
3.39±0.58stat±0.64sys (H.E.S.S.) in the energy range of 55-300
and 120-500GeV, respectively. The broadband emission cannot be
successfully reproduced by a simple one-zone synchrotron self-Compton
model. Instead, an additional external Compton component is required.
We test a lepto-hadronic model that reproduces the data set well and a
proton-synchrotron-dominated model that requires an extreme proton
luminosity. Emission models that are able to successfully represent
the data place the emitting region well outside of the broad-line
region to a location at which the radiative environment is dominated
by the infrared thermal radiation field of the dusty torus. In the
scenario described by this flaring activity, the source appears to be
a flat spectrum radio quasar (FSRQ), in contrast with past
categorizations. This suggests that the source can be considered to be
a transitional blazar, intermediate between BL Lac and FSRQ objects.
Description:
In this work, we present the first detection of OT 081 (z = 0.32) at
VHE gamma-rays with the MAGIC and H.E.S.S. Cherenkov telescopes.
The VHE observations followed the flare in the HE band observed by
Fermi-LAT in July 2016. Due to moon and weather constraints, the VHE
observations could be performed only a few days after the HE flare
when the source was in a decay phase. An MWL study from radio to VHE
gamma-rays is carried out, and four different periods (named P1, P2,
P3, and P4) were chosen for their MWL coverage. P1 and P2 correspond
to the two peaks in the HE band, P3 represents the source state during
the VHE detection, and P4 corresponds to the lower flux state after
the flare, which is coincident with a high degree of polarization.
Objects:
--------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------
17 51 32.81 +09 39 00.7 OT 081 = 4FGL J1751.5+0938
--------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 108 4 *Parameters of the power-law fit to the VHE
gamma-ray spectra observed by MAGIC and
H.E.S.S. (this work)
fig2a.dat 110 180 MWL light curves of OT 081 during the period
from MJD 57575 to MJD 57602
(2016 July 6-August 2), fluxes
fig2b.dat 37 127 MWL light curves of OT 081 during the period
from MJD 57575 to MJD 57602
(2016 July 6-August 2), polarisation
fig2c.dat 36 127 MWL light curves of OT 081 during the period
from MJD 57575 to MJD 57602
(2016 July 6-August 2), electric vector
polarisation angle
fig4a.dat 88 29 OT081 Simultaneous data for the first point high
state in Fermi (MJD 57589.5) (P2)
fig4b.dat 88 40 OT081 broadband data for the flare in VHE.
23-24th of July (MJD 57592-57593) (P3)
fig4c.dat 88 32 OT081 Simultaneous data for the low state in VHE
(MJD 57594-57596) (P4)
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Note on table1.dat: The parameters are obtained from the observations during the
high-flux state in VHE gamma-rays, later defined as P3.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Inst Instrument (MAGIC or HESS)
7- 21 A15 d Tobs Observation time, or observation time
interval (MJD)
23- 25 F3.1 h teff ? Effective observing time
27- 31 A5 --- Type Type, observed (obs.) or intrinsic (intr.)
33- 35 I3 GeV Emin Minimum energy for the extraction of
spectral parameters
37- 39 I3 GeV Edec Decorrelation energy
41- 48 E8.2 1/cm2/s/TeV F0 Flux at decorrelation energy
50- 57 E8.2 1/cm2/s/TeV e_F0 Flux at decorrelation energy
statistical error
59- 66 E8.2 1/cm2/s/TeV s_F0 Flux at decorrelation energy
systematic error
68- 71 F4.2 --- Gamma Photon index
73- 76 F4.2 --- e_Gamma Photon index statistical error
78- 81 F4.2 --- E_Gamma Photon index systematic error
83- 90 E8.2 1/cm2/s/TeV F200GeV Flux at 200GeV
92- 99 E8.2 1/cm2/s/TeV e_F200GeV Flux at 200GeV statistical error
101-108 E8.2 1/cm2/s/TeV s_F200GeV Flux at 200GeV systematic error
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): fig2a.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Inst Instrument (1)
20- 33 F14.8 d MJD Observation date
34- 43 F10.8 d e_MJD ? Error on MJD (only for HESS and MAGIC data)
46- 58 E13.11 --- Flux Flux
62- 76 E15.13 ---- e_Flux Flux error
81- 93 A13 --- Band Band
95-110 A16 --- x_Flux Units of Flux
--------------------------------------------------------------------------------
Note (1): Instrument are HESS, MAGIC, Fermi-LAT, Swift-XRT, Swift-UVOT V,
Swift-UVOT B, Swift-UVOT U, Swift-UVOT W1, Swift-UVOT M2, Swift-UVOT W2,
ATOM B, KAIT, Steward, Tuorla, AZT-8+ST7, ATOM R, ALMA 250GHz, OVRO 15GHz
and ALMA 320GHz.
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): fig2b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Inst Instrument (1)
16- 24 F9.3 d MJD Observation date
26- 31 F6.3 % Pol Polarisation percentage
33- 37 F5.3 % e_Pol Polarisation percentage error
--------------------------------------------------------------------------------
Note (1): Instruments are Ringo Blue, Ringo Green, Ringo Red, Steward and
AZT-8+ST7
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): fig2c.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Inst Instrument (1)
14- 22 F9.3 d MJD Observation date
24- 30 F7.3 deg EVPA Electric vector polarisation angle
32- 36 F5.3 % e_EVPA Electric vector polarisation angle error
--------------------------------------------------------------------------------
Note (1): Instruments are Ringo Blue, Ringo Green, Ringo Red, Steward and
AZT-8+ST7
--------------------------------------------------------------------------------
Byte-by-byte Description of file (# headlines): fig4?.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Inst Instrument (1)
11- 27 E17.11 GeV E Energy
29 A1 --- l_SED Limit flag on SED
30- 48 E19.14 TeV/cm2/s SED Spectral energy distribution
51- 68 E18.13 TeV/cm2/s E_SED ?=0 Spectral energy distribution upper error
71- 88 E18.13 TeV/cm2/s e_SED ?=0 Spectral energy distribution lower error
--------------------------------------------------------------------------------
Note (1): Instruments are ALMA, Fermi-LAT, OVRO, Swift-XRT, UVOT B, UVOT M2,
UVOT U, UVOT W1 and UVOT W2 for fig4a.dat,
MAGIC, HESS, Fermi-LAT, Swift-XRT, UVOT B, UVOT U, UVOT M2, UVOT W1, UVOT W2,
AZT-8+ST7, Steward, ATOM B, ATOM R, Metsahovi and OVRO fir fig4b.dat,
HESS, Fermi-LAT, Swift-XRT, UVOT B, UVOT U, UVOT M2, UVOT W1, UVOT W2,
AZT-8+ST7, Steward, ALMA. Metsahovi and OVRO fir fig4c.dat
--------------------------------------------------------------------------------
Acknowledgements:
Marina Manganaro, marina.manganaro(at)uniri.hr
(End) Marina Manganaro [Uni Rijeka, Croatia], Patricia Vannier [CDS] 26-Jun-2025