Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Pal, Main; Kushwaha, Pankaj; Dewangan, G. C.; Pawar, Pramod

doi:10.3847/1538-4357/ab65ee

Cited by 28 publications

(24 citation statements)

References 55 publications

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“…The observed spectra cover all the possible spectral phases. In addition to its typical LBL spectra described by a power-law 28,30,60,73,74], it has shown a flat [Γ ∼ 1; 27,28, 63,75], extremely soft Γ > 2 [27,69,73, and references therein] as well as mixture of these [27,74,76]. Interestingly, most of the extremely soft spectral state seems to have been around (within a few years) the period of optical outbursts claimed to be thermal bremsstrahlung emission [44,77].…”

Section: Spectralmentioning

confidence: 98%

A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

Kushwaha

2020

Galaxies

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A diverse range of observational results and peculiar properties across the domains of observation have made OJ 287 one of the best-explored BL Lac objects on the issues of relativistic jets and accretion physics as well as the strong theory of gravity. We here present a brief compilation of observational results from the literature and inferences/insights from the extensive studies but focus on the interpretation of its ∼ 12-yr quasi-periodic optical outbursts (QPOOs) and high energy emission mechanisms. The QPOOs in one model are attributed to the disk-impact related to dynamics of the binary SMBHs while alternative models attribute it to the geometrical effect related to the precession of a single jet or double jets. We discuss implications of the new spectral features reported during the 2015-2017 multi-wavelength high activity of the source -a break in the NIR-optical spectrum and hardening of the MeV-GeV emission accompanied by a shift in the location of its peak, in the context of the two. The reported NIR-optical break nicely fits the description of a standard accretion disk emission from an SMBH of mass ∼ 10 10 M while the time of its first appearance in end-May 2013 (MJD 56439) is in close coincidence with the time of impact predicted by the disk-impact binary SMBH model. This spectral and temporal coincidence with the model parameters of the disk-impact binary SMBH model provides independent evidence in favor of the model over the geometrical models which argue a total central-engine mass in the range of 10 7−9 M . On the other hand, the MeV-GeV spectral change is naturally reproduced by the inverse Compton scattering of photons from the broad-line region and is consistent with the detection of broad emission lines during the previous cycles of quasi-periodic outbursts. Combining this with previous SED studies suggests that in OJ 287, MeV-GeV emission results from external Comptonization. 2 of 21 minutes and even less to decades 1 [∼ 6-7 orders of magnitude; e.g. 2]. Their radio and optical emission is highly polarized and have been observed to vary often with the source flux, all the way from 0 to > 50%. Imaging in radio, infra-red (IR), optical, and X-ray, on the other hand, show an extremely well collimated jet extending up to Mpc scales [∼ 9-13 orders of magnitude; e.g. 3,4] with frequent sighting of superluminal features in high-resolution imaging of the core. Taken together with the observational and theoretical understanding of other astrophysical objects combined with their high and rarely repeating observational behavior indicates that they are the site of complex, multi-level, multi-scale physics and thus, are normally called extreme sources among non-catastrophic events.Though studies in different energy bands finally culminated into a unified scheme for radio-loud AGNs [5], it also revealed that AGNs need well-coordinated multi-wavelength (MW) observations to go beyond the limits associated with individual bands. The launch of the gamma-ray survey observatory Fermi-LAT (Large Area Telescope...

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Section: Spectralmentioning

confidence: 98%

A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

Kushwaha

2020

Galaxies

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“…This phenomenon is called X-ray reprocessing. This type of phenomenon has been observed in several different types of AGNs (McHardy et al 2014;Pal et al 2017;Naik et al 2019;Hernández Santisteban et al 2020;Pal et al 2020).…”

Section: Introductionmentioning

confidence: 65%

Spectro-timing analysis of a highly variable narrow-line Seyfert 1 galaxy NGC 4748 with AstroSat and XMM-Newton

et al. 2021

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We present a detailed timing and spectral study of an extremely variable narrow-line Seyfert 1 galaxy NGC 4748 using observations in the year 2017 and 2014 performed with AstroSat and XMM-Newton, respectively. Both observations show extremely variable soft and hard X-ray emission that are correlated with each other. In the 2014 data set, the source retains its general behaviour of ''softer when brighter'' while the 2017 observation exhibits a ''harder when brighter'' nature. Such changing behaviour is rare in AGNs and is usually observed in the black hole binary systems. The ''harder when brighter'' is confirmed with the anticorrelation between the photon index and the 0.3-10 keV power-law flux. This suggests a possible change in the accretion mode from standard to the advection-dominated flow. Additionally, both the observations show soft X-ray excess below 2 keV over the power-law continuum. This excess was fitted with a single or multiple blackbody component(s). The origin of soft excess during the 2017 observation is likely due to the cool Comptonization as the photon index changes with time. On the other hand, the broad iron line and delayed UV emission during the 2014 observation strongly suggest that X-ray illumination onto the accretion disk and reflection and reprocessing play a significant role in this AGN.

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“…Spectra models from other observations do not show any correlation in peak alignment. Pal et al (2020) performed a spectral and temporal study of OJ 287 based on the 2015 and 2018 XMM-Newton observations (0761500201 and 0830190501). They state that the best-fit model in their research was the log-parabolic model.…”

Section: Oj 287mentioning

confidence: 99%

X-ray timing and spectral variability properties of blazars S5 0716+714, OJ 287, Mrk 501, and RBS 2070

Mohorian,

Bhatta,

Adhikari

et al. 2021

Preprint

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The X-ray emission from blazars has been widely investigated using several space telescopes. In this work, we explored statistical properties of the X-ray variability in the blazars S5 0716+714, OJ 287, Mkn 501 and RBS 2070 using the archival observations from the XMM-Newton telescope between the period 2002-2020. Several methods of timing and spectral analyses including fractional variability, minimum variability timescale, power spectral density analyses and countrate distribution were performed. In addition, we fitted various spectral models to the observations as well as estimated hardness ratio. The results show that the sources are moderately variable within the intra-day timescale. Three of the four sources exhibited a clear bi-modal pattern in their countrate distribution revealing possible indication of two distinct countrate states, that is, hard and soft countrate states. The slope indices of the power spectral density were found to be centered around 0.5. Furthermore, the spectra of the sources were fitted with single power-law, broken power-law, log-parabolic and black-body+log-parabolic models (the latter only for OJ 287). We conclude that for most of the observations log-parabolic model was the best fit. The power spectral density analysis revealed the variable nature of PSD slopes in the source light curves. The results of this analysis could indicate the non-stationary nature of the blazar processes on intra-day timescales. The observed features can be explained within the context of current blazar models, in which the non-thermal emission mostly arises from kilo-parsec scale relativistic jets.

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Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Cited by 28 publications

References 55 publications

A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

A Multi-Wavelength View of OJ 287 Activity in 2015–2017: Implications of Spectral Changes on Central-Engine Models and MeV-GeV Emission Mechanism

Spectro-timing analysis of a highly variable narrow-line Seyfert 1 galaxy NGC 4748 with AstroSat and XMM-Newton

X-ray timing and spectral variability properties of blazars S5 0716+714, OJ 287, Mrk 501, and RBS 2070

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