Location of γ-ray emission and magnetic field strengths in OJ 287

J. A. Hodgson; T. P. Krichbaum; A. P. Marscher; S. G. Jorstad; B. Rani; I. Marti-Vidal; U. Bach; S. Sanchez; M. Bremer; Michael Lindqvist; M. Uunila; J. Kallunki; P. Vicente; L. Fuhrmann; E. Angelakis; V. Karamanavis; I. Myserlis; I. Nestoras; C. Chidiac; A. Sievers; M. Gurwell; J. A. Zensus

doi:10.1051/0004-6361/201526727

Location of γ-ray emission and magnetic field strengths in OJ 287

J. A. Hodgson, T. P. Krichbaum, A. P. Marscher, S. G. Jorstad, B. Rani, I. Marti-Vidal, U. Bach, S. Sanchez, M. Bremer, Michael Lindqvist, M. Uunila, J. Kallunki, P. Vicente, L. Fuhrmann, E. Angelakis, V. Karamanavis, I. Myserlis, I. Nestoras, C. Chidiac, A. SieversM. Gurwell, J. A. Zensus

Metsähovi Radio Observatory

Research output: Contribution to journal › Article › Scientific › peer-review

66 Citations (Scopus)

90 Downloads (Pure)

Abstract

Context. The γ-ray BL Lac object OJ 287 is known to exhibit inner-parsec "jet-wobbling", high degrees of variability at all wavelengths and quasi-stationary features, including an apparent (≈100°) position-angle change in projection on the sky plane. Aims: Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps, together with cm/mm total intensity and γ-ray observations from Fermi-LAT from 2008-2014, we aim to determine the location of γ-ray emission and to explain the inner-mas structural changes. Methods: Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and enable us to observe above the synchrotron self-absorption peak frequency. Fermi-LAT γ-ray data were reduced and analysed. The jet was spectrally decomposed at multiple locations along the jet. From this, we could derive estimates of the magnetic field using equipartition and synchrotron self-absorption arguments. How the field decreases down the jet provided an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics, we attempt to locate the site of γ-ray activity, radio flares, and spectral changes. Results: Strong γ-ray flares appeared to originate from either the so-called core region, a downstream stationary feature, or both, with γ-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be ≥1.6 G in the core and ≤0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the VLBI core as ≲6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss. The 3 mm GMVA data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A80

Original language	English
Article number	A80
Number of pages	29
Journal	Astronomy and Astrophysics
Volume	597
DOIs	https://doi.org/10.1051/0004-6361/201526727
Publication status	Published - 1 Jan 2017
MoE publication type	A1 Journal article-refereed

Keywords

BL Lacertae objects: individual: OJ 287
Galaxies: active
Galaxies: jets
Magnetic fields
Techniques: high angular resolution
Techniques: interferometric

Access to Document

10.1051/0004-6361/201526727

aa26727-15Final published version, 21.5 MB

http://adsabs.harvard.edu/abs/2017A%26A...597A..80H

Cite this

Hodgson, J. A., Krichbaum, T. P., Marscher, A. P., Jorstad, S. G., Rani, B., Marti-Vidal, I., Bach, U., Sanchez, S., Bremer, M., Lindqvist, M., Uunila, M., Kallunki, J., Vicente, P., Fuhrmann, L., Angelakis, E., Karamanavis, V., Myserlis, I., Nestoras, I., Chidiac, C., ... Zensus, J. A. (2017). Location of γ-ray emission and magnetic field strengths in OJ 287. Astronomy and Astrophysics, 597, Article A80. https://doi.org/10.1051/0004-6361/201526727

@article{d3d91d65c2a74e46bc76e87106115ba8,

title = "Location of γ-ray emission and magnetic field strengths in OJ 287",

abstract = "Context. The γ-ray BL Lac object OJ 287 is known to exhibit inner-parsec {"}jet-wobbling{"}, high degrees of variability at all wavelengths and quasi-stationary features, including an apparent (≈100°) position-angle change in projection on the sky plane. Aims: Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps, together with cm/mm total intensity and γ-ray observations from Fermi-LAT from 2008-2014, we aim to determine the location of γ-ray emission and to explain the inner-mas structural changes. Methods: Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and enable us to observe above the synchrotron self-absorption peak frequency. Fermi-LAT γ-ray data were reduced and analysed. The jet was spectrally decomposed at multiple locations along the jet. From this, we could derive estimates of the magnetic field using equipartition and synchrotron self-absorption arguments. How the field decreases down the jet provided an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics, we attempt to locate the site of γ-ray activity, radio flares, and spectral changes. Results: Strong γ-ray flares appeared to originate from either the so-called core region, a downstream stationary feature, or both, with γ-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be ≥1.6 G in the core and ≤0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the VLBI core as ≲6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss. The 3 mm GMVA data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A80",

keywords = "BL Lacertae objects: individual: OJ 287, Galaxies: active, Galaxies: jets, Magnetic fields, Techniques: high angular resolution, Techniques: interferometric",

author = "Hodgson, {J. A.} and Krichbaum, {T. P.} and Marscher, {A. P.} and Jorstad, {S. G.} and B. Rani and I. Marti-Vidal and U. Bach and S. Sanchez and M. Bremer and Michael Lindqvist and M. Uunila and J. Kallunki and P. Vicente and L. Fuhrmann and E. Angelakis and V. Karamanavis and I. Myserlis and I. Nestoras and C. Chidiac and A. Sievers and M. Gurwell and Zensus, {J. A.}",

year = "2017",

month = jan,

day = "1",

doi = "10.1051/0004-6361/201526727",

language = "English",

volume = "597",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

Hodgson, JA, Krichbaum, TP, Marscher, AP, Jorstad, SG, Rani, B, Marti-Vidal, I, Bach, U, Sanchez, S, Bremer, M, Lindqvist, M, Uunila, M, Kallunki, J, Vicente, P, Fuhrmann, L, Angelakis, E, Karamanavis, V, Myserlis, I, Nestoras, I, Chidiac, C, Sievers, A, Gurwell, M & Zensus, JA 2017, 'Location of γ-ray emission and magnetic field strengths in OJ 287', Astronomy and Astrophysics, vol. 597, A80. https://doi.org/10.1051/0004-6361/201526727

TY - JOUR

T1 - Location of γ-ray emission and magnetic field strengths in OJ 287

AU - Hodgson, J. A.

AU - Krichbaum, T. P.

AU - Marscher, A. P.

AU - Jorstad, S. G.

AU - Rani, B.

AU - Marti-Vidal, I.

AU - Bach, U.

AU - Sanchez, S.

AU - Bremer, M.

AU - Lindqvist, Michael

AU - Uunila, M.

AU - Kallunki, J.

AU - Vicente, P.

AU - Fuhrmann, L.

AU - Angelakis, E.

AU - Karamanavis, V.

AU - Myserlis, I.

AU - Nestoras, I.

AU - Chidiac, C.

AU - Sievers, A.

AU - Gurwell, M.

AU - Zensus, J. A.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - Context. The γ-ray BL Lac object OJ 287 is known to exhibit inner-parsec "jet-wobbling", high degrees of variability at all wavelengths and quasi-stationary features, including an apparent (≈100°) position-angle change in projection on the sky plane. Aims: Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps, together with cm/mm total intensity and γ-ray observations from Fermi-LAT from 2008-2014, we aim to determine the location of γ-ray emission and to explain the inner-mas structural changes. Methods: Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and enable us to observe above the synchrotron self-absorption peak frequency. Fermi-LAT γ-ray data were reduced and analysed. The jet was spectrally decomposed at multiple locations along the jet. From this, we could derive estimates of the magnetic field using equipartition and synchrotron self-absorption arguments. How the field decreases down the jet provided an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics, we attempt to locate the site of γ-ray activity, radio flares, and spectral changes. Results: Strong γ-ray flares appeared to originate from either the so-called core region, a downstream stationary feature, or both, with γ-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be ≥1.6 G in the core and ≤0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the VLBI core as ≲6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss. The 3 mm GMVA data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A80

AB - Context. The γ-ray BL Lac object OJ 287 is known to exhibit inner-parsec "jet-wobbling", high degrees of variability at all wavelengths and quasi-stationary features, including an apparent (≈100°) position-angle change in projection on the sky plane. Aims: Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps, together with cm/mm total intensity and γ-ray observations from Fermi-LAT from 2008-2014, we aim to determine the location of γ-ray emission and to explain the inner-mas structural changes. Methods: Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and enable us to observe above the synchrotron self-absorption peak frequency. Fermi-LAT γ-ray data were reduced and analysed. The jet was spectrally decomposed at multiple locations along the jet. From this, we could derive estimates of the magnetic field using equipartition and synchrotron self-absorption arguments. How the field decreases down the jet provided an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics, we attempt to locate the site of γ-ray activity, radio flares, and spectral changes. Results: Strong γ-ray flares appeared to originate from either the so-called core region, a downstream stationary feature, or both, with γ-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be ≥1.6 G in the core and ≤0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the VLBI core as ≲6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss. The 3 mm GMVA data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A80

KW - BL Lacertae objects: individual: OJ 287

KW - Galaxies: active

KW - Galaxies: jets

KW - Magnetic fields

KW - Techniques: high angular resolution

KW - Techniques: interferometric

UR - http://www.scopus.com/inward/record.url?scp=85009108042&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201526727

DO - 10.1051/0004-6361/201526727

M3 - Article

AN - SCOPUS:85009108042

SN - 0004-6361

VL - 597

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A80

ER -

Location of γ-ray emission and magnetic field strengths in OJ 287

Abstract

Keywords

Access to Document

Other files and links

Fingerprint

GMVA 86GHz images of OJ 287

Metsähovi Radio Observatory

Cite this

Location of γ-ray emission and magnetic field strengths in OJ 287

Abstract

Keywords

Access to Document

Other files and links

Fingerprint

Datasets

GMVA 86GHz images of OJ 287

Equipment

Metsähovi Radio Observatory

Cite this