The results of 8 yr R-band photopolarimetric data of blazar Mrk 421 collected from 2008 February to 2016 May are presented, along with extensive multiwavelength observations covering radio to TeV ...γ-rays around the flares observed in 2008 May, 2010 March, and 2013 April. The most important results are found in 2013, when the source displayed in the R band a very high brightness state of 11.29 0.03 mag (93.60 1.53 mJy) on April 10 and a polarization degree of 11.00% 0.44% on May 13. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over seven nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16, and 19. In addition, the flux shows a minimum variability timescale of Δt = 2.34 0.12 hr, and the polarization degree presents variations of ∼1%-2% on a timescale of Δ t ∼ minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of pc, which is the same order of magnitude as the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26 1.78 yr.
An exhaustive analysis of 9 yr optical R-band photopolarimetric data of the flat-spectrum radio quasar 3C 279 from 2008 February 27 to 2017 May 25 is presented, along with multiwavelength observing ...campaigns performed during the flaring activity exhibited in 2009 February/March, 2011 June, 2014 March/April, 2015 June, and 2017 February. In the R band, this source showed the maximum brightness state of 13.68 0.11 mag (1.36 0.20 mJy) on 2017 March 2 and the lowest brightness state ever recorded of 18.20 0.87 mag (0.16 0.03 mJy) on 2010 June 17. During the entire period of observations, the polarization degree varied between 0.48% 0.17% and 31.65% 0.77%, and the electric vector position angle (EVPA) exhibited large rotations between 82 98 0 92 and 446 32 1 95. Optical polarization data show that this source has a stable polarized component that varied from ∼6% (before the 2009 flare) to ∼13% after the flare. The overall behavior of our polarized variability data supports the scenario of jet precessions as responsible for the observed large rotations of the EVPA. Discrete correlation function analysis shows that the lags between gamma-rays and X-rays compared to the optical R-band fluxes are Δt ∼ 31 days and 1 day in 2009. Lags were also found among gamma-rays compared with X-rays and radio of Δt ∼ 30 and 43 days in 2011, and among radio and optical R band of Δt ∼ 10 days in 2014. A very intense flare in 2017 was observed in optical bands, with a dramatic variation in the polarization degree (from ∼6% to 20%) in 90 days without exhibiting flaring activity in other wavelengths.
A physical description of the formation and propagation of working surfaces inside the relativistic jet of the blazar PKS 1510−089 are used to model its γ-ray variability light curve using Fermi-LAT ...data from 2008 to 2012. The physical model is based on conservation laws of mass and momentum at the working surface as explained by Mendoza et al. (2009). The hydrodynamical description of a working surface is parametrized by the initial velocity and mass injection rate at the base of the jet. We show that periodic variations on the injected velocity profiles are able to account for the observed luminosity, fixing model parameters such as mass ejection rates of the central engine injected at the base of the jet, oscillation frequencies of the flow and maximum Lorentz factors of the bulk flow during a particular burst.
A physical description of the formation and propagation of working surfaces inside the relativistic jet of the blazar PKS 1510-089 are used to model its gamma -ray variability light curve using ...Fermi-LAT data from 2008 to 2012. The physical model is based on conservation laws of mass and momentum at the working surface as explained by Mendoza et al. (2009). The hydrodynamical description of a working surface is parametrized by the initial velocity and mass injection rate at the base of the jet. We show that periodic variations on the injected velocity profiles are able to account for the observed luminosity, fixing model parameters such as mass ejection rates of the central engine injected at the base of the jet, oscillation frequencies of the flow and maximum Lorentz factors of the bulk flow during a particular burst.
Context. Over the past few years, on several occasions, large, continuous rotations of the electric vector position angle (EVPA) of linearly polarized optical emission from blazars have been ...reported. These events are often coincident with high energy γ-ray flares and they have attracted considerable attention, since they could allow us to probe the magnetic field structure in the γ-ray emitting region of the jet. The flat-spectrum radio quasar 3C 279 is one of the most prominent examples showing this behaviour. Aims. Our goal is to study the observed EVPA rotations and to distinguish between a stochastic and a deterministic origin of the polarization variability. Methods. We have combined multiple data sets of R-band photometry and optical polarimetry measurements of 3C 279, yielding exceptionally well-sampled flux density and polarization curves that cover a period of 2008–2012. Several large EVPA rotations are identified in the data. We introduce a quantitative measure for the EVPA curve smoothness, which is then used to test a set of simple random walk polarization variability models against the data. Results. 3C 279 shows different polarization variation characteristics during an optical low-flux state and a flaring state. The polarization variation during the flaring state, especially the smooth ~360° rotation of the EVPA in mid-2011, is not consistent with the tested stochastic processes. Conclusions. We conclude that, during the two different optical flux states, two different processes govern polarization variation, which is possibly a stochastic process during the low-brightness state and a deterministic process during the flaring activity.
On the nature of the δ Scuti star HD 115520 Pena, J H; Fox, L; Cervantes-Sodi, B ...
Journal of physics. Conference series,
10/2008, Letnik:
118, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Observing Delta Scuti stars is most important as their multi-frequency spectrum of radial pulsations provide strong constraints on the physics of the stars interior; so any new detection and ...observation of these stars is a valuable contribution to asteroseismology. While performing uvby-beta photoelectric photometry of some RR Lyrae stars acquired in 2005 at the Observatorio Astronómico Nacional, México, we also observed several standard stars, HD115520 among them. After the reduction this star showed indications of variability. In view of this, a new observing run was carried out in 2006 during which we were able to demonstrate its variability and its nature as a Delta Scuti star. New observations in 2007 permitted us to determine its periodic content with more accuracy. This, along with the uvby-beta photoelectric photometry allowed us to deduce its physical characteristics and pulsational modes.
ABSTRACT
We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (
Crazy Diamond
) carried out in the period 2007 July–2009 January. In particular, we show the results of the
...AGILE
campaigns which took place on 2008 May–June, 2008 July–August, and 2008 October–2009 January. During the 2008 May–2009 January period, the source average flux was highly variable, with a clear fading trend toward the end of the period, from an average γ-ray flux
F
E>100 MeV
≳ 200 × 10
−8
photons cm
−2
s
−1
in 2008 May–June, to
F
E>100 MeV
∼ 80 × 10
−8
photons cm
−2
s
−1
in 2008 October–2009 January. The average γ-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from Γ
GRID
∼ 2.0 to Γ
GRID
∼ 2.2) toward the end of the observing campaign. Only 3σ upper limits can be derived in the 20–60 keV energy band with Super-
AGILE
, because the source was considerably off-axis during the whole time period. In 2007 July–August and 2008 May–June, 3C 454.3 was monitored by
Rossi X-ray Timing Explorer
(
RXTE
). The
RXTE
/Proportional Counter Array (PCA) light curve in the 3–20 keV energy band shows variability correlated with the γ-ray one. The
RXTE
/PCA average flux during the two time periods is
F
3-20 keV
= 8.4 × 10
−11
erg cm
−2
s
−1
, and
F
3-20 keV
= 4.5 × 10
−11
erg cm
−2
s
−1
, respectively, while the spectrum (a power law with photon index Γ
PCA
= 1.65 ± 0.02) does not show any significant variability. Consistent results are obtained with the analysis of the
RXTE
/High-Energy X-Ray Timing Experiment quasi-simultaneous data. We also carried out simultaneous
Swift
observations during all
AGILE
campaigns.
Swift
/XRT detected 3C 454.3 with an observed flux in the 2–10 keV energy band in the range (0.9–7.5) × 10
−11
erg cm
−2
s
−1
and a photon index in the range Γ
XRT
= 1.33–2.04. In the 15–150 keV energy band, when detected, the source has an average flux of about 5 mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007–2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the γ-ray fluxes shows that the γ-optical correlation occurs with a time lag of τ = −0.4
+0.6
−0.8
days, consistent with previous findings for this source. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July–2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher frequency data, allowing us to derive the value of the source magnetic field. Finally, the modeling of the broadband spectral energy distributions for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year.
Context. Since 2001, the radio quasar 3C 454.3 has undergone a period of high optical activity, culminating in the brightest optical state ever observed, during the 2004-2005 outburst. The Whole ...Earth Blazar Telescope (WEBT) consortium has carried out several multifrequency campaigns to follow the source behaviour. Aims. The GLAST-AGILE Support Program (GASP) was born from the WEBT to provide long-term continuous optical-to-radio monitoring of a sample of γ-loud blazars, during the operation of the AGILE and GLAST (now known as Fermi GST) γ-ray satellites. The main aim is to shed light on the mechanisms producing the high-energy radiation, through correlation analysis with the low-energy emission. Thus, since 2008 the monitoring task on 3C 454.3 passed from the WEBT to the GASP, while both AGILE and Fermi detected strong γ-ray emission from the source. Methods. We present the main results obtained by the GASP at optical, mm, and radio frequencies in the 2008-2009 season, and compare them with the WEBT results from previous years. Results. An optical outburst was observed to peak in mid July 2008, when Fermi detected the brightest γ-ray levels. A contemporaneous mm outburst maintained its brightness for a longer time, until the cm emission also reached the maximum levels. The behaviour compared in the three bands suggests that the variable relative brightness of the different-frequency outbursts may be due to the changing orientation of a curved inhomogeneous jet. The optical light curve is very well sampled during the entire season, which is also well covered by the various AGILE and Fermi observing periods. The relevant cross-correlation studies will be very important in constraining high-energy emission models.
Context. BL Lacertae is the prototype of the blazar subclass named after it. Yet, it has occasionally shown a peculiar behaviour that has questioned a simple interpretation of its broad-band emission ...in terms of synchrotron plus synchrotron self-Compton (SSC) radiation. Aims. In the 2007–2008 observing season we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite in July and December 2007, and January 2008, to study its emission properties, particularly in the optical-X-ray energy range. Methods. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. Flux changes had larger amplitude at the higher radio frequencies than at longer wavelengths. Results. The X-ray spectra acquired by the EPIC instrument onboard XMM-Newton are well fitted by a power law with photon index $\Gamma \sim 2$ and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the EPIC data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is very variable, since it can change from extremely steep to extremely hard, and can be more or less curved in intermediate states. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature $ \ga$$ 20\,000 \rm \, K$ and a luminosity $ \ga$$ 6 \times 10^{44} ~\rm erg \, s^{-1}$.
Prompted by a high optical state in 2007 September, the Whole Earth Blazar Telescope consortium organized an intensive optical, near-IR (JHK) and radio observing campaign on the intermediate BL Lac ...object 3C 66A throughout the fall and winter of 2007-2008. In this paper, we present data from 28 observatories in 12 countries, covering the observing season from late 2007 July through 2008 February. The source remained in a high optical state throughout the observing period and exhibited several bright flares on timescales of ~10 days. This included an exceptional outburst around 2007 September 15-20, reaching a peak brightness at R~ 13.4. Our campaign revealed microvariability with flux changes up to |dR/dt|~ 0.02 mag hr-1. Our observations do not reveal evidence for systematic spectral variability in the overall high state covered by our campaign, in agreement with previous results. In particular, we do not find evidence for spectral hysteresis in 3C 66A for which hints were found in an earlier campaign in a somewhat lower flux state. We also did not find any evidence for spectral lags in the discrete correlation functions between different optical bands. We infer a value of the magnetic field in the emission region of B~ 19 e 2/7 B t-6/7 h D 13/7 1 G, where eB is the magnetic field equipartition fraction, t h is the shortest observed variability timescale in units of hours, and D 1 is the Doppler factor in units of 10. From the lack of systematic spectral variability, we can derive an upper limit on the Doppler factor, D <= 28 t-1/8 h e 3/16 B . This is in perfect agreement with superluminal motion measurements with the VLBI/VLBA of bapp <= 27 and argues against models with very high Lorentz factors of 50, required for a one-zone synchrotron-self-Compton interpretation of some high-frequency-peaked BL Lac objects detected at TeV g-ray energies.
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