We have undertaken a nearly simultaneous optical/UV and X-ray variability study of the flat spectrum radio quasar, 3C 273 using data available from the XMM−Newton satellite mission from June 2000 to July 2012. Here we focus on the multi-wavelength flux variability on both intra-day and long time scales of this very well known radio-loud source. We found high flux variability over long time scales in all bands for which observations were made. The optical/UV variability amplitude was more than twice than that in the X-ray bands. There is some frequency dependence of the variability in optical/UV bands in the sense that the variability amplitude increases with increasing frequency; however, the X-ray emissions disagree with this trend as the variability amplitude decreases from soft to hard X-ray bands. On intraday time scales 3C 273 showed small amplitude variability in X-ray bands. A hardness ratio analysis in the X-ray regime indicates that the particle acceleration mechanism dominates the cooling mechanism during most of the ∼12 year span of these observations.

Blazars can be divided into two sub-classes namely high energy and low energy peaked blazars. In spectral energy distribution, the first synchrotron hump of the former class peaks in UV/X-rays and in IR/optical bands for the latter class. The peak of the spectral energy distribution seems to be responsible for variability properties of these classes of blazars in X-ray and optical bands. Since, in low energy peaked blazars, the X-ray bands lies well below the synchrotron hump, one expects that the highest energy electrons available for the synchrotron emission would have slower effect of variability on X-ray intra-day timescale. In this paper, by taking the advantage of a sample of 12 low energy peaked blazars with total 50 observations from XMM−Newton since its launch, we confirm that this class is less variable in X-ray bands. We found that out of 50 observational light curves, genuine intra-day variability is present in only two of light curves i.e 4%. Similar results we obtained from our earlier optical intra-day variability studies of high energy peaked blazars where out of 144 light curves, only genuine intra-day variability was detected in 6 light curves i.e ∼ 4%. Since, X-ray bands lie below the peak of the spectral energy distribution of LSPs where inverse Compton mechanism is dominating rather than synchrotron radiation at the peak of the optical band, leads to slower variability in the X-ray bands. Hence, reducing their intra-day variability in X-ray bands as compared to the variability in optical bands.

. Several fragments weighing <2 kg and a single large fragment weighing ∼10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ∼340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. 26 Al and 22 Na activities as well as the 22 Na/ 26 Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low 60 Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ∼10 6 cm −2 in samples from the largest fragment to approximately (4-9) × 10 5 cm −2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ∼20 cm for the Dergaon meteorite.

We analyze the 2.5-10 keV X-ray spectra of the luminous quasar 3C 273 and simultaneous observations in UV wavelengths from XMM-Newton between 2000 and 2015. The lowest flux level ever was observed in 2015. The continuum emission from 3C 273 is generally best described by an absorbed power-law but during extremely low states the addition of fluorescence from the K-shell iron line improves the fit. We study the spectral evolution of the source during its extended quiescent state and also examine connections between the X-ray and ultraviolet emissions, which have been seen in some, but not all, previous work. We detect a possible anti-correlation between these two bands during the low state that characterized 3C 273 for most of this period; however, this was not present during a flaring state. A harderwhen-brighter trend for the X-ray spectrum was observed in these long-term observations of 3C 273 for the first time. We suggest that the X-ray emission in 3C 273 is the result of inverse Compton scattering of soft UV seed photons (emitted from the local environment of the AGN), most likely in a thermal corona. We can explain the significant temporal variation of the spectral continuum as an outcome of changing optical depth of the comptonizing medium, along the lines of the wind-shock model proposed by Courvoisier and Camenzind (1989).

We have used archival Rossi X‐ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data to investigate the timing and spectral characteristics of the transient XTE J1817–330. The data pertain to 160 PCA pointed observations made during the outburst period 2006 January 27 to August 2. A detailed analysis of quasi‐periodic oscillations (QPOs) in this black hole X‐ray binary is carried out. Power density spectra were obtained using the light curves of the source. QPOs have been detected in the 2–8 keV band in 10 of the observations. In eight of these observations, QPOs are present in the 8–14 keV and in five observations in the 15–25 keV band. XTE J1817–330 is the third black hole source from which low‐frequency QPOs are clearly detected in hard X‐rays. The QPO frequency lies in ≈4–9 Hz and the rms amplitude in the 1.7–13.3 per cent range, the amplitude being higher at higher energies. We have fitted the power density spectra of the observations with Lorentzian and power‐law models. Energy spectra are derived for those observations in which the QPOs are detected, in order to investigate any dependence of the QPO characteristic on the spectral parameters. These spectra are well fitted with a two‐component model, which includes the disc blackbody component and a power‐law component. The QPO characteristics and their variations are discussed and the implications on the origin of QPOs are examined.