X-ray spectra, light-curves and SEDs of blazars frequently observed by Swift

Giommi, P.; Perri, M.; Capalbi, M.; D'Elia, V.; de Almeida, U. Barres; Brandt, C. H.; Pollock, A. M. T.; Arneodo, F.; Di Giovanni, A.; Chang, Y. L.; Civitarese, O.; De Angelis, M.; Leto, C.; Verrecchia, F.; Ricard, N.; Di Pippo, S.; Middei, R.; Penacchioni, A. V.; Ruffini, R.; Sahakyan, N.; Israyelyan, D.; Turriziani, S.

doi:10.48550/arxiv.2108.07255

Cited by 3 publications

(5 citation statements)

References 43 publications

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“…On the other hand, during the second flare the linear-Pearson test resulted in 0.44 clearly showing a softer-when-brighter trend. Such a pattern was also observed in the X-ray emission of OJ 287 (e.g., Kapanadze et al 2018;Prince et al 2021;Giommi et al 2021). During this flare, the spectral index of 2.56 ± 0.03 was the softest ever observed, very different from the values normally observed in BL Lac (typically Γ X ≤ 2.0).…”

Section: Discussionsupporting

confidence: 57%

“…During the considered period, the Swift satellite (Gehrels et al 2004) observed BL Lac 610 times with single exposures ranging from 1.13 to 16.46 ks. All the data were downloaded and processed using Swift_xrtproc automatic tool for XRT data analysis developed within the Open Universe Initiative (Giommi et al 2021). This tool automatically downloads the raw data and processes it using the XRT-PIPELINE task adopting standard parameters and filtering criteria.…”

Section: Swift Xrtmentioning

confidence: 99%

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A thirteen-year-long broadband view of BL Lac

Sahakyan,

Giommi

2021

Preprint

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We report optical, ultraviolet, X-ray and 𝛾-ray observations of BL Lac objects prototype BL Lacertae carried out over a period of nearly 13 years, between 2008 and 2021. The source is characterized by strongly variable emission at all frequencies, often accompanied by spectral changes. In the 𝛾-ray band several prominent flares have been detected, the largest one reaching the flux of 𝐹 𝛾 (> 196.7 MeV) = (4.39 ± 1.01) × 10 −6 photon cm −2 s −1 , corresponding to the isotropic luminosity of 10 47 erg s −1 . At the time of the first major X-ray flare, on MJD 56268.65, a traditional harder-when-brighter trend was observed. During the brightest flare, which occurred on MJD 59128.18, the source instead exhibited a softer-when-brighter trend due to a shift of the synchrotron peak to 10 16 Hz, well into the HBL domain. The widely changing multi-wavelength emission of BL Lacertae was investigated by fitting one-zone and two-zone leptonic models to 520 high-quality and quasi-simultaneous broad-band spectral energy distributions. The HBL behaviour observed during the brightest X-ray flare is interpreted as due to the emergence of synchrotron emission from freshly accelerated particles in a second emission zone.

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Section: Discussionsupporting

confidence: 57%

Section: Swift Xrtmentioning

confidence: 99%

A thirteen-year-long broadband view of BL Lac

Sahakyan,

Giommi

2021

Preprint

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“…To search for X-ray variability we use the 1 keV X-ray light curves as obtained by Giommi et al (2021). The Swift/XRT data products are based on the pipeline, the procedure, and methodology developed for the Open Universe for Blazars project (Giommi et al 2018(Giommi et al , 2019.…”

Section: X-ray Light Curvesmentioning

confidence: 99%

“…The Swift/XRT data products are based on the pipeline, the procedure, and methodology developed for the Open Universe for Blazars project (Giommi et al 2018(Giommi et al , 2019. Here, we provide a brief outline of the analysis procedure, but for a comprehensive description we refer the reader to Giommi et al (2021). Xray source and background events were extracted from XRT data.…”

Section: X-ray Light Curvesmentioning

confidence: 99%

“…In this work, we present quantitative neutrino predictions of the hadronic X-ray flaring scenario of blazars. We compute the number of muon and antimuon neutrinos above 100 TeV expected for IceCube from X-ray flares of blazars that were observed more than 50 times with the X-ray Telescope (XRT, Burrows et al 2005) on board the Neil Gehrels Swift Observatory between November 2004 and November 2020 (Giommi et al 2021). To this end, we apply the Bayesian block algorithm to the 1 keV XRT light curves of these frequently observed blazars to characterize statistically significant variations and identify flares.…”

Section: Introductionmentioning

confidence: 99%

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High-energy neutrinos from X-rays flares of blazars frequently observed by the Swift X-Ray Telescope

Stathopoulos,

Petropoulou,

Giommi

et al. 2021

Preprint

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Blazar flares have been suggested as ideal candidates for enhanced neutrino production. While the neutrino signal of γ-ray flares has been widely discussed, the neutrino yield of X-ray flares has received less attention. Here, we compute the predicted neutrino signal from X-ray flares detected in 66 blazars observed more than 50 times with the X-ray Telescope (XRT) on board the Neil Gehrels Swift Observatory. We consider a scenario where X-ray flares are powered by synchrotron radiation of relativistic protons, and neutrinos are produced through photomeson interactions between protons with their own synchrotron X-ray photons. Using the 1 keV X-ray light curves for flare identification, the 0.5-10 keV fluence of each flare as a proxy for the all-flavour neutrino fluence, and the IceCube point-source effective area for different detector configurations, we calculate the number of muon and antimuon neutrinos above 100 TeV expected for IceCube from each flaring source. The bulk of the neutrino events from the sample originates from flares with durations ∼ 1−10 d. Accounting for the X-ray flare duty cycle of the sources in the sample, which ranges between ∼ 2 and 24 per cent, we compute an average yearly neutrino rate for each source. The median of the distribution (in logarithm) is ∼ 0.03 yr −1 , with Mkn 421 having the highest predicted rate 1.2 ± 0.3 yr −1 , followed by 3C 273 (0.33 ± 0.03 yr −1 ) and PG 1553+113 (0.25 ± 0.02 yr −1 ). Next-generation neutrino detectors together with regular X-ray monitoring of blazars could constrain the duty cycle of hadronic X-ray flares.

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Classification of the Fermi-LAT blazar candidates of uncertain type using extreme gradient boosting

Tolamatti

Singh

Yadav

2023

Monthly Notices of the Royal Astronomical Society

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Machine learning based approaches are emerging as very powerful tools for many applications including source classification in astrophysics research due to the availability of huge high quality data from different surveys in observational astronomy. The Large Area Telescope on board Fermi satellite (Fermi-LAT) has discovered more than 6500 high energy gamma-ray sources in the sky from its survey over a decade. A significant fraction of sources observed by the Fermi-LAT either remains unassociated or has been identified as Blazar Candidates of Uncertain type (BCUs). We explore the potential of eXtreme Gradient Boosting (XGBoost)- a supervised machine learning algorithm to identify the blazar subclasses among a sample of 112 BCUs of the 4FGL catalog whose X-ray counterparts are available within 95% uncertainty regions of the Fermi-LAT observations. We have used information from the multi-wavelength observations in IR, optical, UV, X-ray and γ-ray wavebands along with the redshift measurements reported in the literature for classification. Among the 112 uncertain type blazars, 62 are classified as BL Lacertae objects (BL Lacs) and 6 have been classified as Flat Spectrum Radio Quasars (FSRQs). This indicates a significant improvement with respect to the multi-perceptron neural network based classification reported in the literature. Our study suggests that the gamma-ray spectral index, and IR color indices are the most important features for identifying the blazar subclasses using the XGBoost classifier. We also explore the importance of redshift in the classification BCU candidates.

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X-ray spectra, light-curves and SEDs of blazars frequently observed by Swift

Cited by 3 publications

References 43 publications

A thirteen-year-long broadband view of BL Lac

A thirteen-year-long broadband view of BL Lac

High-energy neutrinos from X-rays flares of blazars frequently observed by the Swift X-Ray Telescope

Classification of the Fermi-LAT blazar candidates of uncertain type using extreme gradient boosting

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