The Outburst of HST‐1 in the M87 Jet

Harris, D. E.; Cheung, C. C.; Biretta, J. A.; Sparks, W. B.; Junor, W.; Perlman, E.; Wilson, A. S.

doi:10.1086/500081

Cited by 145 publications

(188 citation statements)

References 15 publications

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“…The first one, detected in 2005 (Aharonian et al 2006a), coincided with an extreme multi-frequency outburst of the jet feature HST-1 (Harris et al , 2006, 107 which has also been discussed as a possible VHE γ -ray emission site (e.g., Stawarz et al 2006;Cheung et al 2007;Harris et al 2009). During the second flaring episode, detected in 2008, HST-1 was in a low flux state, but radio measurements at 43 GHz with the Very Long Baseline Array (VLBA) showed a flux increase in the core region within a few hundred Schwarzschild radii of the SMBH, suggesting the direct vicinity of the SMBH as the origin of the VHE γ -ray emission (Acciari et al 2009).…”

Section: Introductionmentioning

confidence: 89%

“…Its prominent jet (Curtis 1918) is resolved from radio to X-rays, displaying complex structures (knots and diffuse emission; Perlman et al 1999Perlman et al , 2001a, strong variability (Harris et al , 2006, and apparent superluminal motion Cheung et al 2007). With its proximity (16.7 ± 0.2 Mpc; Mei et al 2007) and its very massive black hole of M BH (3-6)×10 9 M 105 Gebhardt & Thomas 2009) high-resolution very long baseline interferometry (VLBI) at radio wavelengths enables one to directly probe structures with sizes down to <200 Schwarzschild radii.…”

Section: Introductionmentioning

confidence: 99%

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The 2010 VERY HIGH ENERGY Γ-Ray FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

Abramowski¹,

Acero²,

Aharonian³

et al. 2012

ApJ

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168

145

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The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3−6)×10 9 M ) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ -ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ -ray emitter since 2006. The VHE γ -ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE γ -ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of τ rise (1-3) × 10 −11 photons cm −2 s −1 ), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ∼3 days after the peak of the VHE γ -ray emission reveal an enhanced flux from the core (flux increased by factor ∼2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE γ -ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: [2002][2003][2004][2005][2006][2007][2008][2009]). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE γ -ray emission from M 87 are reviewed in the light of the new data.

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Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

The 2010 VERY HIGH ENERGY Γ-Ray FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

Abramowski¹,

Acero²,

Aharonian³

et al. 2012

ApJ

Self Cite

168

145

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“…HST-1 has shown many flares exceeding the luminosity of the M87 core emission. Its X-ray brightness has increased by a factor 150 from 2000 to 2005 (Harris 2006). A correlation between radio, optical, and X-ray luminosity points to a common origin of the emission.…”

Section: Introductionmentioning

confidence: 94%

Very High Energy Gamma-Ray Observations of Strong Flaring Activity in M87 in 2008 February

Albert

Aliu

Anderhub

et al. 2008

ApJ

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M87 is the only known nonblazar radio galaxy to emit very high energy (VHE) gamma rays. During a monitoring program of M87, a rapid flare in VHE gamma-rays was detected by the MAGIC telescope in early 2008. The flux was found to be variable above 350 GeV on a timescale as short as 1 day at a significance level of 5.6 j. The highest measured flux reached 15% of the Crab Nebula flux. We observed several substantial changes of the flux level during the 13 day observing period. The flux at lower energies (150-350 GeV), instead, is compatible with being constant. The energy spectrum can be described by a power law with a photon index of 2.30 ‫ע‬ 0.11 stat ‫ע‬ 0.20 syst . The observed day-scale flux variability at VHE prefers the M87 core as source of the emission and implies that either the emission region is very compact (just a few Schwarzschild radii) or the Doppler factor of the emitting blob is rather large in the case of a nonexpanding emission region.

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“…ObsID 011119010 of NGC 4636 and 13814 of NGC 5195 met these criteria, but a visual inspection showed low number counts in the hard band and were rejected from the sample. Finally, NGC 4486 was rejected because it is well known that this source is dominated by the jet emission (Harris et al 2003(Harris et al , 2006(Harris et al , 2009(Harris et al , 2011.…”

Section: Sample and Datamentioning

confidence: 99%

X-ray spectral variability of LINERs selected from the Palomar sample

Hernández-García

González‐Martín

Masegosa

et al. 2014

A&A

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Context. Variability is a general property of active galactic nuclei (AGN). The way in which these changes occur at X-rays is not yet clearly understood. In the particular case of low-ionization nuclear emission line region (LINER) nuclei, variations on the timescales from months to years have been found for some objects, but the main driver of these changes is still debated. Aims. The main purpose of this work is to investigate the X-ray variability in LINERs, including the main driver of these variations, and to search for possible differences between type 1 and 2 objects. Methods. We examined the 18 LINERs in the Palomar sample with data retrieved from the Chandra and/or XMM-Newton archives that correspond to observations gathered at different epochs. All the spectra for the same object were fitted simultaneously to study long-term variations. The nature of the variability patterns were studied by allowing different parameters to vary during the spectral fit. Whenever possible, short-term variations from the analysis of the light curves and long-term UV variability were studied. Results. Short-term variations are not reported in X-rays. Three LINERs are classified as non-AGN candidates in X-rays, all of them are Compton-thick candidates; none of them show variations at these frequencies, and two of them vary in the UV. Long-term X-ray variations were analyzed in 12 out of 15 AGN candidates; about half of them showed variability (7 out of the 12). At UV frequencies, most of the AGN candidates with available data are variable (five out of six). Thus, 13 AGN candidates are analyzed at UV and/or X-rays, ten of which are variable at least in one energy band. None of the three objects that do not vary in X-rays have available UV data. This means that variability on long-timescales is very common in LINERs. These X-ray variations are mainly driven by changes in the nuclear power, while changes in absorptions are found only for NGC 1052. We do not find any difference between type 1 and 2 LINERs, neither in the number of variable cases (three out of five type 1 and four out of seven type 2 LINERs), nor in the nature of the variability pattern. We find indications of an anticorrelation between the slope of the power law, Γ, and the Eddington ratio. Conclusions. LINERs are definitely variable sources irrespective of whether they are classified as optical type 1 or 2. Their BH masses, accretion rates, and variability timescales place them in the same plane as more powerful AGN at X-rays. However, our results suggest that the accretion mechanism in LINERs may be different. UV variations of some type 2 LINERs were found, this could support the hypothesis of a torus that disappears at low luminosities.

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The Outburst of HST‐1 in the M87 Jet

Cited by 145 publications

References 15 publications

The 2010 VERY HIGH ENERGY Γ-Ray FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

The 2010 VERY HIGH ENERGY Γ-Ray FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 87

Very High Energy Gamma-Ray Observations of Strong Flaring Activity in M87 in 2008 February

X-ray spectral variability of LINERs selected from the Palomar sample

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