The X-ray variability of Mrk 421

Fidelis, V. V.; Iakubovskyi, Dmytro

doi:10.1134/s1063772908070020

Cited by 4 publications

(4 citation statements)

References 31 publications

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“…a moderate correlation between the flux and b. This finding is compatible with earlier findings (Fidelis & Iakubovskyi 2008). The (anti)correlation between a and the flux is significant: the non-directional chance probability of the derived correlation coefficient for the null-hypothesis is p < 10 −4 for the RXTE/ PCA data as well as for the Swift/XRT data.…”

Section: Veritas (2008)supporting

confidence: 91%

“…The Lorentz factors of the X-ray emitting electrons should thus be 1.5 order of magnitudes (factor ∼30) larger than the Lorentz factors of the optically emitting electrons. If the X-rays (and γ -rays, from IC scatterings of the electrons which emit X-rays as synchrotron emission) show flux variability on a timescale of 0.5 days (Fidelis & Iakubovskyi 2008;Gaidos et al 1996), then the optical fluxes should vary on a timescale of 15 days which is well compatible with the observed timescales in the optical and X-ray/TeV bands (Section 3.4). However, as discussed in Section 3.4, the optical light curve does not seem to be a delayed and stretched version of the X-ray light curve or the TeV γ -ray light curve, implying that the dominant fraction of the observed optical emission does not originate from the X-ray/TeV emission region.…”

Section: Summary and Discussionmentioning

confidence: 62%

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TeV AND MULTI-WAVELENGTH OBSERVATIONS OF Mrk 421 IN 2006-2008

Acciari¹,

Aliu²,

Arlen³

et al. 2011

ApJ

141

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We report on TeV γ -ray observations of the blazar Mrk 421 (redshift of 0.031) with the VERITAS observatory and the Whipple 10 m Cherenkov telescope. The excellent sensitivity of VERITAS allowed us to sample the TeV γ -ray fluxes and energy spectra with unprecedented accuracy where Mrk 421 was detected in each of the pointings. A total of 47.3 hr of VERITAS and 96 hr of Whipple 10 m data were acquired between 2006 January and 2008 June. We present the results of a study of the TeV γ -ray energy spectra as a function of time and for different flux levels. On 2008 May 2 and 3, bright TeV γ -ray flares were detected with fluxes reaching the level of 10 Crab. The TeV γ -ray data were complemented with radio, optical, and X-ray observations, with flux variability found in all bands except for the radio wave band. The combination of the Rossi X-ray Timing Explorer and Swift X-ray data reveal spectral hardening with increasing flux levels, often correlated with an increase of the source activity in TeV 1 The Astrophysical Journal, 738:25 (19pp), 2011 September 1 Acciari et al.γ -rays. Contemporaneous spectral energy distributions were generated for 18 nights, each of which are reasonably described by a one-zone synchrotron self-Compton model.

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Section: Veritas (2008)supporting

confidence: 91%

Section: Summary and Discussionmentioning

confidence: 62%

TeV AND MULTI-WAVELENGTH OBSERVATIONS OF Mrk 421 IN 2006-2008

Acciari¹,

Aliu²,

Arlen³

et al. 2011

ApJ

141

View full text Add to dashboard Cite

show abstract

“…Although the index a is not independent of the curvature parameter b, the conclusion can be reached that an increased flux is accompanied by a hardening of the spectrum (parameter a) since there is only a moderate correlation between the flux and b. This finding is compatible with earlier findings (Fidelis & Iakubovskyi 2008). The (anti)correlation between a and the flux is significant: the non-directional chance probability of the derived correlation coefficient for the nullhypothesis is p < 10 −4 for the RXTE/PCA data, as well as for the Swift/XRT data.…”

Section: Temporal and Spectralsupporting

confidence: 90%

Section: Summary and Discussionsupporting

confidence: 52%

TeV and Multi-wavelength Observations of Mrk 421 in 2006-2008

Acciari,

Aliu,

Arlen

et al. 2011

Preprint

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We report on TeV γ-ray observations of the blazar Mrk 421 (redshift of 0.031) with the VERITAS observatory and the Whipple 10 m Cherenkov telescope. The excellent sensitivity of VERITAS allowed us to sample the TeV γ-ray fluxes and energy spectra with unprecedented accuracy where Mrk 421 was detected in each of the pointings. A total of 47.3 hrs of VERITAS and 96 hrs of Whipple 10 m data were acquired between January 2006 and June 2008. We present the results of a study of the TeV γ-ray energy spectra as a function of time, and for different flux levels. On May 2nd and 3rd, 2008, bright TeV γ-ray flares were detected with fluxes reaching the level of 10 Crab. The TeV γ-ray data were complemented with radio, optical, and Xray observations, with flux variability found in all bands except for the radio waveband. The combination of the RXTE and Swift X-ray data reveal spectral hardening with increasing flux levels, often correlated with an increase of the source activity in TeV γ-rays. Contemporaneous spectral energy distributions were generated for 18 nights, each of which are reasonably described by a one-zone SSC model.

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Time-frequency learning machines for nonstationarity detection using surrogates

Amoud

Honeiné

Richard

et al. 2009

2009 IEEE/SP 15th Workshop on Statistical Signal Processing

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An operational framework has recently been developed for testing stationarity of any signal relatively to an observation scale. The originality is to extract time-frequency features from a set of stationarized surrogate signals, and to use them for defining the null hypothesis of stationarity. Our paper is a further contribution that explores a general framework embedding techniques from machine learning and timefrequency analysis, called time-frequency learning machines. Based on one-class support vector machines, our approach uses entire time-frequency representations and does not require arbitrary feature extraction. Its relevance is illustrated by simulation results, and spherical multidimensional scaling techniques to map data to a visible 3D space.

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The X-ray variability of Mrk 421

Cited by 4 publications

References 31 publications

TeV AND MULTI-WAVELENGTH OBSERVATIONS OF Mrk 421 IN 2006-2008

TeV AND MULTI-WAVELENGTH OBSERVATIONS OF Mrk 421 IN 2006-2008

TeV and Multi-wavelength Observations of Mrk 421 in 2006-2008

Time-frequency learning machines for nonstationarity detection using surrogates

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