A new period of activity in the core of NGC 660

Argo, M. K.; Bemmel, I. M. van; Connolly, S.; Beswick, R. J.

doi:10.1093/mnras/stv1348

Cited by 26 publications

(27 citation statements)

References 37 publications

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“…On the other hand, A-2 was discovered in a very different manner than that by which ordinary AGNs are selected and in an atypical environment, so the statistics on short-term variability based on blindly selected AGNs may not be representative. Also, while the sharp increase in radio flux of A-2 has no obvious precedent (although see Argo et al 2015 for one possible example), sudden changes in AGN fluxes and spectra at shorter wavelengths have been seen in some well-studied nearby AGNs, including NGC 2617 (Shappee et al 2014) and Mrk 590 (Koay et al 2016). …”

Section: Secondary Agnsmentioning

confidence: 99%

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

Perley

Dhawan

et al. 2017

ApJ

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We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of <0.5 mJy in 1989 to 4 mJy in 2016 (ν = 8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in Very Long Baseline Array observations down to a scale of 4 pc, and it is coincident with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, though an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 10 7 years.

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Section: Secondary Agnsmentioning

confidence: 99%

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

Perley

Dhawan

et al. 2017

ApJ

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“…NGC 660, located at a distance of 12.3 Mpc, is classified as a rare polar ring galaxy with a LINER-type (low-ionization nuclear emission-line region) nuclear spectrum in the optical. In 2013, a highresolution radio observation by e-MERLIN revealed a radio outburst at the centre of the galaxy from a compact and extremely bright continuum source (Argo et al 2015). The radio source, which was not detected in previous radio observations, is probably associated with a newly awoken AGN in the galaxy (Argo et al 2015).…”

Section: Ngc 660mentioning

confidence: 93%

“…In 2013, a highresolution radio observation by e-MERLIN revealed a radio outburst at the centre of the galaxy from a compact and extremely bright continuum source (Argo et al 2015). The radio source, which was not detected in previous radio observations, is probably associated with a newly awoken AGN in the galaxy (Argo et al 2015). The galaxy has been observed multiple times in the X-ray band at low energies by Chandra and XMM-Newton between 2001 and 2012 prior to the radio outburst.…”

Section: Ngc 660mentioning

confidence: 93%

NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?

Annuar

Alexander

Gandhi

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present NuSTAR observations of four active galactic nuclei (AGN) located within 15 Mpc. These AGN, namely ESO 121-G6, NGC 660, NGC 3486 and NGC 5195, have observed X-ray luminosities of L2-10 keV, obs ≲ 1039 erg s−1, classifying them as low luminosity AGN (LLAGN). We perform broadband X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM-Newton observations to directly measure their column densities (NH) and infer their intrinsic power. We complement our X-ray data with archival and new high angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (NH > 1023 cm−2; L2-10 keV, int ∼ 1041 erg s−1), and NGC 660 may be Compton-thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L2-10 keV, int < 1039 erg s−1; i.e., genuine LLAGN. Both of the heavily obscured AGN have Lbol > 1041 erg s−1 and λEdd ≳ 10−3, and are detected in high angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486 however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.

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“…In the X-ray regime, the data from Chandra telescope gives the X-ray flux 1.24 +0.37 −0.54 × 10 −13 erg cm −3 s −1 (Argo et al 2015) in the range 0.5 − 10 keV. In mid-2013, a radio outburst was observed using e-MERLIN Figure 5.…”

Section: Ngc 660mentioning

confidence: 99%

Secondary Radio and X-Ray Emissions from Galaxy Mergers

Yuan

Murase

Mészáros

2019

ApJ

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Shocks arising in galaxy mergers could accelerate cosmic-ray (CR) ions to TeV-PeV energies. While propagating in the intergalactic medium, these CRs can produce high-energy neutrinos, electronpositron pairs and gamma-rays. In the presence of intergalactic magnetic fields, the secondary pairs will radiate observable emissions through synchrotron radiation and inverse Compton scattering. In this paper, we demonstrate that these emissions can explain the radio and X-ray fluxes of merging galaxies such as NGC 660 and NGC 3256. Using our model in combination with the observations, we can constrain the gas mass, shock velocity, magnetic field and the CR spectral index s of these systems. For NGC 660 a single-zone model with a spectral index 2.1 ∼ < s ∼ < 2.2 is able to reproduce simultaneously the radio and X-ray observations, while a simple one-zone scenario with s ∼ 2 can describe the radio and a large fraction of X-ray observations of NGC 3256. Our work provides a useful approach for studying the dynamics and physical parameters of galaxy mergers, which can play an important part in future multi-messenger studies of similar and related extragalactic sources.

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A new period of activity in the core of NGC 660

Cited by 26 publications

References 37 publications

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?

Secondary Radio and X-Ray Emissions from Galaxy Mergers

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