ABSTRACT
We present time series analyses of three-decade long radio observations of the BL Lacertae object AO 0235+164 made at the University of Michigan Radio Astronomical Observatory operating at ...three central frequencies of 4.8, 8.0, and 14.5 GHz. We detected a quasi-periodic oscillation of ∼965 d in all three frequency bands in the light curve of the effectively simultaneous observations, along with strong signals at ∼1950, ∼1350, and ∼660 d. The periodicity is analysed with three methods: data-compensated discrete Fourier transform, generalized Lomb–Scargle periodogram, and Weighted Wavelet Z-transform. These methods are chosen as they have different analysis approaches toward robust measurement of claimed periodicities. The quasi-periodic oscillation at 965 ± 50 d is found to be significant (at least 3.5σ) and is persistent throughout the observation for all three radio frequencies, and the others, which may be harmonics, are comparably significant in at least the 8.0 and 14.5 GHz bands. We briefly discuss plausible explanations for the origin of such long and persistent periodicity.
We present the results of our power spectral analysis for the BL Lac object PKS 0735+178, utilizing the Fermi-LAT survey at high-energy γ-rays, several ground-based optical telescopes, and ...single-dish radio telescopes operating at GHz frequencies. The novelty of our approach is that, by combining long-term and densely sampled intra-night light curves in the optical regime, we were able to construct for the first time the optical power spectrum of the blazar for a time domain extending from 23 years down to minutes. Our analysis reveals that: (1) the optical variability is consistent with a pure red noise, for which the power spectral density can be well approximated by a single power law throughout the entire time domain probed; (2) the slope of power spectral density at high-energy γ-rays (∼1) is significantly flatter than that found at radio and optical frequencies (∼2) within the corresponding time variability range; (3) for the derived power spectra, we did not detect any low-frequency flattening, nor do we see any evidence for cutoffs at the highest frequencies down to the noise floor levels due to measurement uncertainties. We interpret our findings in terms of a model where the blazar variability is generated by the underlying single stochastic process (at radio and optical frequencies), or a linear superposition of such processes (in the γ-ray regime). Along with the detailed PSD analysis, we also present the results of our extended (1998-2015) intra-night optical monitoring program and newly acquired optical photo-polarimetric data for the source.
We present X-ray flux and spectral analyses of the three pointed Suzaku observations of the TeV high synchrotron peak blazar Mrk 421 taken throughout its complete operational duration. The ...observation taken on 2008 May 5 is, at 364.6 ks (i.e., 101.3 hr), the longest and most evenly sampled continuous observation of this source, or any blazar, in the X-ray energy 0.8-60 keV until now. We found large amplitude intraday variability in all soft and hard bands in all the light curves. The discrete correction function analysis of the light curves in soft and hard bands peaks on zero lag, showing that the emission in hard and soft bands are cospatial and emitted from the same population of leptons. The hardness ratio plots imply that the source is more variable in the harder bands compared to the softer bands. The source is harder when brighter, following the general behavior of high synchrotron peak blazars. Power spectral densities of all three light curves are red noise dominated, with a range of power spectra slopes. If one assumes that the emission originates very close to the central super massive black hole, a crude estimate for its mass, of ∼4 × 108 M , can be made; but if the variability is due to perturbations arising there that are advected into the jet and are thus Doppler boosted, substantially higher masses are consistent with the quickest seen variations. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux and spectral variability.
Abstract
We have examined 13 pointed observations of the TeV-emitting high synchrotron peak blazar PKS 2155−304, taken by the Suzaku satellite throughout its operational period. We found that the ...blazar showed large-amplitude intraday variabilities in the soft (0.8–1.5 keV) and the hard (1.5–8.0 keV) bands in the light curves. Spectral variability on intraday timescales is estimated using the hardness ratio. The blazar usually becomes harder when brighter and vice versa, following the typical behavior of high synchrotron peak blazars. The power spectral density analyses of 11 out of 13 light curves in the total energy (0.8–8.0 keV) are found to be dominated by red noise, with power-law spectral indices that span a large range, from −2.81 to −0.88. Discrete correlation function analyses of all the 13 light curves between the soft and the hard bands show that they are well correlated and peak at, or very close to, zero lag. This indicates that the emissions in soft and hard bands are probably cospatial and emitted from the same population of leptons. Considering fluxes versus variability timescales, we found no correlation on intraday timescales, implying that X-ray emission from PKS 2155−304 is not dominated by simple changes in the Doppler factor. We briefly discuss the most likely emission mechanisms responsible for the observed flux and spectral variabilities and place constraints on magnetic field strength and Lorentz factors of the electrons emitting the X-rays in the most likely scenario.
We analysed the multiband optical behaviour of the BL Lacertae object, S5 0716+714, during its outburst state from 2014 November to 2015 March. We took data on 23 nights at three observatories, one ...in India and two in Bulgaria, making quasi-simultaneous observations in B, V, R, and I bands. We measured multiband optical fluxes, colour, and spectral variations for this blazar on intraday and short time-scales. The source was in a flaring state during the period analysed and displayed intense variability in all wavelengths. R-band magnitude of 11.6 was attained by the target on 2015 January 18, which is the brightest value ever recorded for S5 0716+714. The discrete correlation function method yielded good correlation between the bands with no measurable time lags, implying that radiation in these bands originate from the same region and by the same mechanism. We also used the structure function technique to look for characteristic time-scales in the light curves. During the times of rapid variability, no evidence for the source to display spectral changes with magnitude was found on either of the time-scales. The amplitude of variations tends to increase with increasing frequency with a maximum of ∼22 per cent seen during flaring states in B band. A mild trend of larger variability amplitude as the source brightens was also found. We found the duty cycle of our source during the analysed period to be ∼90 per cent. We also investigated the optical spectral energy distribution of S5 0716+714 using B, V, R, and I data points for 21 nights. We briefly discuss physical mechanisms most likely responsible for its flux and spectral variations.
The incidence of intranight optical variability (INOV) is known to differ significantly among different classes of powerful active galactic nuclei (AGN). A number of statistical methods have been ...employed in the literature for testing the presence of INOV in the light curves, sometimes leading to discordant results. In this paper, we compare the INOV characteristics of six prominent classes of AGN, as evaluated using three commonly used statistical tests, namely the χ2-test, the modified C-test and the F-test, which has recently begun to gain popularity. The AGN classes considered are: radio-quiet quasars, radio-intermediate quasars, lobe-dominated quasars, low optical polarization core-dominated quasars, high optical polarization core-dominated quasars and TeV blazars. Our analysis is based on a large body of AGN monitoring data, involving 262 sessions of intranight monitoring of a total 77 AGN, using 1-2 m class optical telescopes located in India. In order to compare the usefulness of the statistical tests, we have also subjected them to a 'sanity check' by comparing the number of false positives yielded by each test with the corresponding statistical prediction. The present analysis is intended to serve as a benchmark for future INOV studies of AGN of different classes.
We present a detailed spectral and temporal study of the intermediate-type blazar ON 231 during the TeV outburst phase in 2008 June with observations performed by Swift and XMM-Newton. The X-ray flux ...of the source, which was significantly dominated by the soft photons (below 3-4 keV), varies between 27% and 38% on day timescales, while mild variations were observed in the optical/UV emissions. We found a maximum soft lag of ∼1 hr between the UV and soft X-ray band, which can be understood if the magnetic field of the emitting region is ∼5.6 δ−1/3 G. The 0.6-10 keV spectra can be well represented by a broken power-law model, which indicates the presence of both synchrotron and inverse Compton components in the studied X-ray regime. The synchrotron part of the spectral energy distributions (SEDs) constructed with simultaneous optical/UV and X-ray data follows a log-parabolic shape. A time-resolved spectral analysis shows that the break energy varies significantly between 2.4 and 7.3 keV with the changing flux state of the source, and the similar variations of the spectral slopes of the two components support the synchrotron self-Compton scenario. The synchrotron tail, following a log-parabolic function, shows that the peak frequency ( p) varies by two orders of magnitude (∼1014-1016 Hz) during the event. A significantly positive Ep-β relation is observed from both SED and time-resolved spectral analyses. The most feasible scenario for the observed trend during the flaring event could be associated with a magnetic-field-driven stochastic process evolving toward an equilibrium energy level.
ABSTRACT
We explore the potential of the ongoing Zwicky Transient Facility (ZTF) survey for studying intranight optical variability (INOV) of active galactic nuclei (AGNs), in particular for picking ...rare events of large INOV amplitudes, whose detection may require extensive temporal coverage. For this, we have used the available high cadence subsets of the ZTF data base to build a well-defined large sample of 53 blazars and another sample of 132 radio-quiet quasars (RQQs), matched to the blazar sample in the redshift−magnitude plane. High-cadence ZTF monitoring of these two matched samples is available, respectively, for 156 and 418 intranight sessions. Median durations for both sets of sessions are 3.7 h. The two classes of powerful AGNs monitored in these sessions represent opposite extremes of jet activity. The present analysis of their ZTF light curves has revealed some strong INOV events that, although not exceptionally rare for blazars, are indeed so for RQQs, and their possible nature is briefly discussed.
Abstract
We present a long-term and intraday variability study of optical multiwaveband (
U
BV
RI
) data from the blazar AO 0235+164 collected by various telescopes for ∼44 yr (1975–2019). The blazar ...was found to be significantly variable over the years in all wave bands with a variation of about 6 mag between its low and active states. The variations in the different wave bands are highly correlated without any time lag. We did not observe any significant trend in color variation with time, but we observed a bluer-when-brighter trend between the
B
−
I
color index and the
R
magnitude. Optical
BV
R
-band spectral energy distributions always show a convex shape. Significant intraday variability was frequently seen in the quasi-simultaneous observations of AO 0235+164 made on 22 nights in the
R
and
V
bands by the CASLEO and CAHA telescopes during 1999–2019. We also estimated a central supermassive black hole mass of 7.9 × 10
7
M
⊙
by analyzing the broad Mg
ii
emission line in AO 0235+164's spectrum. We briefly explore the probable physical scenarios responsible for the observed variability.
Enhancing the efficacy of proteasome inhibitors (PI) is a central goal in myeloma therapy. We proposed that signaling-level responses after PI may reveal new mechanisms of action that can be ...therapeutically exploited. Unbiased phosphoproteomics after treatment with the PI carfilzomib surprisingly demonstrates the most prominent phosphorylation changes on splicing related proteins. Spliceosome modulation is invisible to RNA or protein abundance alone. Transcriptome analysis after PI demonstrates broad-scale intron retention, suggestive of spliceosome interference, as well as specific alternative splicing of protein homeostasis machinery components. These findings lead us to evaluate direct spliceosome inhibition in myeloma, which synergizes with carfilzomib and shows potent anti-tumor activity. Functional genomics and exome sequencing further support the spliceosome as a specific vulnerability in myeloma. Our results propose splicing interference as an unrecognized modality of PI mechanism, reveal additional modes of spliceosome modulation, and suggest spliceosome targeting as a promising therapeutic strategy in myeloma.
PDF
