Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe June 2016 Optical and Gamma-Ray Outburst and Optical Micro-Variability of the Blazar 3C454.3
62
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The quasar 3C454.3 underwent a uniquely-structured multi-frequency outburst in June 2016. The blazar was observed in the optical $R$ band by several ground-based telescopes in photometric and polarimetric modes, at $gamma$-ray frequencies by the emph{Fermi} Large Area Telescope, and at 43 GHz with the Very Long Baseline Array. The maximum flux density was observed on 2016 June 24 at both optical and $gamma$-ray frequencies, reaching $S^mathrm{max}_mathrm{opt}=18.91pm0.08$ mJy and $S_gamma^mathrm{max} =22.20pm0.18times10^{-6}$ ph cm$^{-2}$ s$^{-1}$, respectively. The June 2016 outburst possessed a precipitous decay at both $gamma$-ray and optical frequencies, with the source decreasing in flux density by a factor of 4 over a 24-hour period in $R$ band. Intraday variability was observed throughout the outburst, with flux density changes between 1 and 5 mJy over the course of a night. The precipitous decay featured statistically significant quasi-periodic micro-variability oscillations with an amplitude of $sim 2$-$3%$ about the mean trend and a characteristic period of 36 minutes. The optical degree of polarization jumped from $sim3%$ to nearly 20% during the outburst, while the position angle varied by $sim120degr$. A knot was ejected from the 43 GHz core on 2016 Feb 25, moving at an apparent speed $v_mathrm{app}=20.3cpm0.8c$. From the observed minimum timescale of variability $tau_mathrm{opt}^mathrm{min}approx2$ hr and derived Doppler factor $delta=22.6$, we find a size of the emission region $rlesssim2.6times10^{15}$ cm. If the quasi-periodic micro-variability oscillations are caused by periodic variations of the Doppler factor of emission from a turbulent vortex, we derive a rotational speed of the vortex $sim0.2c$.
rate research
Read More
In May - July 2014, the flat spectrum radio quasar 3C 454.3 exhibited strong flaring behaviour. Observations with the Large Area Telescope detector on-board the Fermi Gamma-ray Space Telescope captured the $gamma$-ray flux at energies 0.1 $leq E_{gamma}leq$ 300 GeV increasing fivefold during this period, with two distinct peaks in emission. The $gamma$-ray emission is analysed in detail, in order to study the emission characteristics and put constraints on the location of the emission region. We explore variability in the spectral shape of 3C 454.3, search for evidence of a spectral cutoff, quantify the significance of VHE emission and investigate whether or not an energy-dependence of the emitting electron cooling exists. $gamma$-ray intrinsic doubling timescales as small as $tau_{int} = 0.68$ $pm$ 0.01 h at a significance of > 5$sigma$ are found, providing evidence of a compact emission region. Significant $E_{gamma, emitted}geq$ 35 GeV and $E_{gamma, emitted}geq$ 50 GeV emission is also observed. The location of the emission region can be constrained to $rgeq1.3$ $times$ $R_{BLR}^{out}$, a location outside the broad-line region. The spectral variation of 3C 454.3 also suggests that these flares may be originating further downstream of the supermassive black hole than the emission before and after the flares.
We present recent optical photometric observations of the blazar OJ 287 taken during September 2015 -- May 2016. Our intense observations of the blazar started in November 2015 and continued until May 2016 and included detection of the large optical outburst in December 2016 that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of 9 ground based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~ 1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in March 2016. In addition, we investigated multi-band flux variations, colour variations, and spectral changes in the blazar on diverse timescales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour and spectral variability.
We present a multiwavelength analysis of the simultaneous optical and X-ray light curves of the microquasar V404 Cyg during the June 2015 outburst. We have performed a comprehensive analysis of all the INTEGRAL/IBIS, JEM-X, and OMC observations during the brightest epoch of the outburst, along with complementary NuSTAR, AAVSO, and VSNET data, to examine the timing relationship between the simultaneous optical and X-ray light curves, in order to understand the emission mechanisms and physical locations. We have identified all optical flares which have simultaneous X-ray observations, and performed cross-correlation analysis to estimate the time delays between the optical and soft and hard X-ray emission. We have also compared the evolution of the optical and X-ray emission with the hardness-ratios. We have identified several types of behaviour during the outburst. On many occasions, the optical flares occur simultaneously with X-ray flares, but at other times positive and negative time delays between the optical and X-ray emission are measured. We conclude that the observed optical variability is driven by different physical mechanisms, including reprocessing of X-rays in the accretion disc and/or the companion star, interaction of the jet ejections with surrounding material or with previously ejected blobs, and synchrotron emission from the jet.
We present optical photopolarimetric observations of the BL Lac object S4 0954+658 obtained with the 70-cm telescope in Crimea, 40-cm telescope in St.Petersburg, and 1.8-m Perkins telescope at Lowell Observatory (Flagstaff, Az). After a faint state with a brightness level R ~17.6 mag registered in the first half of January 2011, the optical brightness of the source started to rise and reached ~14.8 mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7 mag within ~7 hours. During the rise of the flux the position angle of optical polarization rotated smoothly over more than 200 degrees. S4 0954+658 is a gamma-ray blazar with gamma-ray flux of (5{pm}3)x10^{-10} phot/cm^2/s according to the Fermi 11-month Catalog Extragalactic Sources. Our analysis of contemporaneous Fermi LAT data does not show any sign of increased gamma-ray activity above the detection threshold except for an elevated flux on 2011 March 5, JD2455626, coincident with the local optical maximum.
Nearly one-third of the sources in the $Fermi$-LAT catalogs lack a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic $gamma$-ray sources. In $Fermi$-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofisico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
