N. V. Efimova

The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation

We present the results of polarimetric (R-band) and multicolor photometric (BH RI J H K) observations of the blazar AO 0235+16 during an outburst in 2006 December. The data reveal a short timescale of variability (several hours), which increases from optical to near-IR wavelengths; even shorter variations are detected in polarization. The flux density correlates with the degree of polarization, and at the maximum degree of polarization the electric vector tends to align with the parsec-scale jet direction. We find that a variable component with a steady power-law spectral energy distribution and very high optical polarization (30%-50%) is responsible for the variability. We interpret these properties of the blazar within a model of a transverse shock propagating down the jet. In this case a small change in the viewing angle of the jet, by 1°, and a decrease in the shocked plasma compression by a factor of ~1.5 are sufficient to account for the variability.

THE BRIGHTEST GAMMA-RAY FLARING BLAZAR IN THE SKY: AGILE AND MULTI-WAVELENGTH OBSERVATIONS OF 3C 454.3 DURING 2010 NOVEMBER

Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one ?-ray flare per year, becoming the most active ?-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, Swift, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary ?-ray flare of 3C 454.3 which occurred in 2010 November. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E >100?MeV) of Fp ? = (6.8 ? 1.0) ? 10?5?photons cm?2 s?1? on a timescale of about 12 hr, more than a factor of six higher than the flux of the brightest steady ?-ray source, the Vela pulsar, and more than a factor of three brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make possible a thorough study of the present event: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the ?-ray flare, we find that the radio, optical, and X-ray emission varies within a factor of 2-3, whereas the ?-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.

The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT

Since the launch of the Fermi satellite, BL Lacertae has been moderately active at ?-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST–AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily ?-ray observations by Fermi. Discrete correlation analysis between the optical and ?-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding ?-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and ?-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011–2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.

Near-Infrared Observations of the Type Ib Supernova SN 2006jc: Evidence of Interactions with Dust

In the framework of a program for the monitoring of supernovae in the near-infrared (NIR) carried out by the Teramo, Rome, and Pulkovo observatories with the AZT-24 telescope, we observed the supernova SN 2006jc in the J, H, and K photometric bands during a period of 7 months, starting ~36 days after its discovery. Our observations evidence a NIR rebrightening, peaking ~70 days after discovery, along with a reddening of (H − K) and (J − H) colors until 120 days after discovery. After that date, (J − H) seems to evolve toward bluer colors. Our data, complemented with IR and optical observations found in the literature, show that the rebrightening is produced by hot, newly formed dust surrounding the supernova.

Multi-frequency monitoring of γ-ray loud blazars I. Light curves and spectral energy distributions

Context. Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei. Aims. Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites. Methods. Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised. Results. Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.

Polarization angle swings in blazars: The case of 3C 279

International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Max Planck Institute for Radio Astronomy; Universities of Bonn and Cologne; Academy of Finland project [274477]; NASA Fermi GI grant [NNX11AQ03G]; Russian Foundation for Basic Research [13-02-12103, 14-02-31789]; RFBR [12-02-01237a]; UNAM DGAPA-PAPIIT [IN116211-3]; Ramon y Cajal grant of the Spanish Ministry of Economy and Competitiveness (MINECO); Spanish Ministry of Economy and Competitiveness (Spain); Regional Government of Andalucia (Spain) [AYA2010-14844, AYA2013-40825-P, P09-FQM-4784]; Fermi Guest Investigator [NNX08AW56G, NNX09AU10G, NNX12AO93G, NNX14AQ58G]; Russian RFBR [15-02-00949]; St. Petersburg University research [6.38.335.2015]; Shota Rustaveli National Science Foundation [FR/638/6-320/12, 31/77]

Comprehensive Monitoring of Gamma-Ray Bright Blazars. I. Statistical Study of Optical, X-Ray, and Gamma-Ray Spectral Slopes

We present -ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 -ray bright blazars over four years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma- ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their -ray behavior. We derive -ray, X-ray, and optical spectral indices, �γ, �X, ando, respectively (Fν ∝ � α ), and construct spectral energy distributions (SEDs) during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (i) significantly steeper -ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (ii) a small difference ofX within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (iii) a highly peaked distribution of X-ray spectral slopes of FSRQs at ∼ −0.60, but a very broad distribution ofX of BL Lacs during active states; (iv) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change ofo of BL Lacs between states; and (v) a positive correlation between optical and -ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.

The connection between the parsec-scale radio jet and γ-ray flares in the blazar 1156+295

The blazar 1156+295 was active atγ-ray energies, exhibiting three prominent flares during the year 2010. Here, we present results using the combination of broadband (X-ray through mm single dish) monitoring data and radio band imaging data at 43 GHz on the connection ofγ-ray events to the ejections of superluminal components and other changes in the jet of 1156+295. The kinematics of the jet over the interval 2007.0‐2012.5 using 43 GHz Very Long Baseline Array observations, reveal the presence of four moving and one stationary component in the inner region of the blazar jet. The propagation of the third a nd fourth components in the jet corresponds closely in time to the active phase of the source in γ rays. We briefly discuss the implications of the structural changes in the jet for the mec hanism of γ-ray production during bright flares. To localise the γ-ray emission site in the blazar, we performed the correlati on analysis between the 43 GHz radio core and the γ-ray light curve. The time lag obtained from the correlation constrains the γ-ray emitting region in the parsec-scale jet.

The slowly declining type Ia supernova 2008fv and the near-infrared second maximum

Aims. We present optical and near-infrared (NIR) photometry of supernova (SN) 2008fv and a brief investigation of SN type Ia to search for possible correlations between the properties of NIR light curves and the optical decline rate. Methods. We analyse our BVRI and JHK observations to derive light curves (LCs), colour curves, and the bolometric behaviour of SN2008fv. Data range from about five days before to two months after maximum. We also collect a database of the main characteristics of NIR LCs of SNeIa available in literature. Results. We find close similarities between the observed LCs of the SN event studied here and SN 2000E. SN 2008fv is a slow-declining SNeIa with a post-maximum decline of Δm15,B = 0.96 ± 0.08 mag and a B-band maximum luminosity of MB,0 = −19.40 ± 0.1 mag, close to the value of normal SNeIa. The optical and NIR data allow us to constrain the host galaxy reddening of NGC 3147, E(B−V) = 0.22 ± 0.05 mag and its distance μ = 33.2 ± 0.1 mag. Furthermore, we derive a synthesized 56 Ni mass of about 0.7 M� , by using the well-known relation between the maximum luminosity of the uvoir bolometric light curve and the initial content of 56 Ni. We investigate the correlation between the NIR characteristics of LCs and optical properties by collecting data of a sample of 40 SNe. We derive quantitative relationships involving the epoch of the secondary maximum in the JHK bands and the decline rate Δm15(B). Further, we find no correlations between Δm15 measured in the JHK bands and the optical Δm15(B). In contrast, quite evident correlations with the Δm15(B )a ndΔm40(J)/Δm15(H).

Analyzing polarization swings in 3C 279

Quasar 3C 279 is known to exhibit episodes of optical polarization angle rotation. We present new, well-sampled optical polarization data for 3C 279 and introduce a method to distinguish between random and deterministic electric vector position angle (EVPA) variations. We observe EVPA rotations in both directions with different amplitudes and find that the EVPA variation shows characteristics of both random and determin- istic cases. Our analysis indicates that the EVPA variation is likely dominated by a random process in the low brightness state of the jet and by a deterministic process in the flaring state.