On the Spectral Changes of OJ 287: The Lowest X-ray state Spectrum -- extended at Optical-UV and Hard at X-rays

Optical-UV synchrotron spectrum has been argued to be the primary driver of the majority of X-ray spectral changes in the BL Lacertae object OJ 287 during its low and intermediate X-ray flux state. Here, we focus on the lowest recorded X-ray flux state of OJ 287 by the Swift facility and report the finding of a power-law optical-UV spectrum with a photon spectrum of $\rm 2.71\pm0.03$ continuing into X-rays. Considering this at X-rays, we found a power-law X-ray spectrum of photon spectral index $\rm 1.22\pm0.20$ that improves to $\rm 1.29\pm0.06$ when considering other observations with similar X-ray spectra. This is the hardest reported X-ray spectrum (0.3-10 keV) and is consistent with the reported Swift-BAT hard X-ray spectrum. We further show that this X-ray spectrum can reproduce most of the flat X-ray spectra when combined with the corresponding optical-UV continuum during the low and intermediate flux states strengthening synchrotron as the primary driver of most of the X-ray spectral changes in the LBL state of the source. Combined with sharp-steepening/cutoff of the optical-UV spectrum during bright phases, the extended-spectrum indicates a comparatively larger emission region and could be the large-scale jet emission. The optical-UV spectrum implies a high-energy power-law particle spectrum of $\rm \sim4.4$ while X-ray implies a hard low-energy particle spectrum of $\rm 1.3-1.6$ which could be the real or can result from a higher low-energy cut-off in the particle spectrum.Comment: 5 pages; 3 figures; submitte

High Energy Emission Processes in OJ 287 during 2009 Flare

The broadband spectrum of a BL Lac object, OJ 287, from radio to $\gamma$-rays obtained during a major $\gamma$-ray flare detected by \emph{Fermi} in 2009 are studied to understand the high energy emission mechanism during this episode. Using a simple one-zone leptonic model, incorporating synchrotron and inverse Compton emission processes, we show that the explanation of high energy emission from X-rays to $\gamma$-rays, by considering a single emission mechanism, namely, synchrotron self-Compton (SSC) or external Compton (EC) requires unlikely physical conditions. However, a combination of both SSC and EC mechanisms can reproduce the observed high energy spectrum satisfactorily. Using these emission mechanisms we extract the physical parameters governing the source and its environment. Our study suggests that the emission region of OJ 287 is surrounded by a warm infrared (IR) emitting region of $\sim 250 \, K$. Assuming this region as a spherical cloud illuminated by an accretion disk, we obtain the location of the emission region to be $\sim 9 pc$. This supports the claim that the $\gamma$-ray emission from OJ 287 during the 2009 flare arises from a location far away from the central engine as deduced from millimeter-gamma ray correlation study and very long baseline array images.Comment: 22 pages, 7 figures, 1 table, accepted for publication in MNRA

Transition from Modernity to Post-modernity

The era of enlightenment is known as “mother of modernityâ€. It has promoted human rationality, scientific development, and human supremacy and paves the way for the decline of religious understanding of the society. The rise of human rationality, materialization of industry, invention of printing press and rising trend of democratic principle, emerging market economy and technological development are characterised as modernity.  The idea of modernity is first stage of human era where human beings were treated as supreme authority of their spheres. With modernity, the concept of nation/state emerged which has the credit to organise the world, promote the rights of the individuals and pay its emphasis on the construction of the democratic society, participatory politics and free individuals. But modernity is criticised by scholars like Perry Anderson, who argue that modernity has actually created another layer and made society absolute. It has inserted empirical documentation and rejected the persons’ observation, including local reality. With these critiques, post-modernity emerged which has questioned the foundation of modernity. It advocated for ‘bottom to approach’ unlike modernity. The main objective of this paper to analysed the main tenets of modernity and discuss the actual principle of post-modernity. This analytical paper concludes with the major critics of post-modernity by taking the author’s understanding about modernity and post-modernity

Brightest Fermi-LAT Flares of PKS 1222+216: Implications on Emission and Acceleration Processes

We present a high time resolution study of the two brightest $\gamma$-ray outbursts from a blazar PKS 1222+216 observed by the \textit{Fermi} Large Area Telescope (LAT) in 2010. The $\gamma$-ray light-curves obtained in four different energy bands: 0.1--3, 0.1--0.3, 0.3--1 and 1--3 GeV, with time bin of 6 hr, show asymmetric profiles with a similar rise time in all the bands but a rapid decline during the April flare and a gradual one during the June. The light-curves during the April flare show $\sim 2$ days long plateau in 0.1--0.3 GeV emission, erratic variations in 0.3--1 GeV emission, and a daily recurring feature in 1--3 GeV emission until the rapid rise and decline within a day. The June flare shows a monotonic rise until the peak, followed by a gradual decline powered mainly by the multi-peak 0.1--0.3 GeV emission. The peak fluxes during both the flares are similar except in the 1--3 GeV band in April which is twice the corresponding flux during the June flare. Hardness ratios during the April flare indicate spectral hardening in the rising phase followed by softening during the decay. We attribute this behavior to the development of a shock associated with an increase in acceleration efficiency followed by its decay leading to spectral softening. The June flare suggests hardening during the rise followed by a complicated energy dependent behavior during the decay. Observed features during the June flare favor multiple emission regions while the overall flaring episode can be related to jet dynamics.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in Ap

Short-term X-ray Variability during Different Activity Phases of Blazars S5 0716+714 and PKS 2155-304

We explored the statistical properties of short-term X-ray variability using long-exposure {\it XMM-Newton} data during high X-ray variability phases of blazars S5 0716+714 and PKS 2155-304. In general, hardness ratio shows correlated variations with the source flux state (count rate), but in a few cases, mainly the bright phases, the trend is complex with correlation and anti-correlation both, indicating spectral evolution. Stationarity tests suggest the time series as non-stationarity or have trend stationarity. Except for one, none of the histograms fit resulted in a reduced-$\chi^2 \sim 1$ for a normal and log-normal profile but a normal profile is favored in general. On the contrary, the Anderson-Darling test favors lognormal with a test-statistic value lower for log-normal over normal for all the observations, even if out of significance limits. None of the IDs show linear RMS-flux relation. The contrary inferences from widely used different statistical methods indicate that a careful analysis is needed while the complex behavior of count rate with hardness ratio suggests spectral evolution over a few 10s of kilo-seconds during bright phases of the sources. In these cases, the spectrum extracted from whole observation may not be meaningful for spectral studies and certainly not a true representation of the spectral state of the source.Comment: 14 Pages, 4 figures, 2 Table

Multi-wavelength Temporal Variability of the Blazar 3C 454.3 during 2014 Activity Phase

We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during the high $\gamma$-ray active period from May-December, 2014. Except for X-rays, the period is well sampled at near-infrared (NIR)-optical by the \emph{SMARTS} facility and the source is detected continuously on daily timescale in the \emph{Fermi}-LAT $\gamma$-ray band. The source exhibits diverse levels of variability with many flaring/active states in the continuously sampled $\gamma$-ray light curve which are also reflected in the NIR-optical light curves and the sparsely sampled X-ray light curve by the \emph{Swift}-XRT. Multi-band correlation analysis of this continuous segment during different activity periods shows a change of state from no lags between IR and $\gamma$-ray, optical and $\gamma$-ray, and IR and optical to a state where $\gamma$-ray lags the IR/optical by $\sim$3 days. The results are consistent with the previous studies of the same during various $\gamma$-ray flaring and active episodes of the source. This consistency, in turn, suggests an extended localized emission region with almost similar conditions during various $\gamma$-ray activity states. On the other hand, the delay of $\gamma$-ray with respect to IR/optical and a trend similar to IR/optical in X-rays along with strong broadband correlations favor magnetic field related origin with X-ray and $\gamma$-ray being inverse Comptonized of IR/optical photons and external radiation field, respectively.Comment: 15 pages, 5 figures, 1 table, MNRAS accepte

Detection of a quasi-periodic oscillation in gamma-ray light curve of the high redshift blazar B2 1520+31

We detected a possible quasi-periodic oscillation (QPO) of ~ 71 days in the 0.1 -- 300 GeV gamma-ray Fermi-LAT light curve of the high redshift flat spectrum radio quasar B2 1520+31. We identify and confirm that quasi-period by Lomb Scargle periodogram (LSP), and weighted wavelet z-transform (WWZ) analyses. Using this QPO period, and assuming it originates from accretion-disc fluctuations at the innermost stable circular orbit, we estimate the central supermassive black hole mass to range between ~ 5.4 * 10$^{9}$ M$_{\odot}$ for a non-rotating black hole and ~ 6.0 * 10$^{10}$ M$_{\odot}$ for a maximally rotating black hole. We briefly discuss other possible radio-loud active galactic nuclei emission models capable of producing a gamma-ray QPO of such a period in a blazar.Comment: 6 pages, 4 figures, Submitted to MNRA