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Register a new userWide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state
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Authors
G. Tagliaferri
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The blazar 1ES 1959+650 was observed twice by BeppoSAX in September 2001 simultaneously with optical observations. We report here the X-ray data together with the optical, R_C magnitude, light curve since August 1995. The BeppoSAX observations were triggered by an active X-ray status of the source. The X-ray spectra are brighter than the previously published X-ray observations, although the source was in an even higher state a few months later, as monitored by the ASM onboard RossiXTE, when it was also detected to flare in the TeV band. Our X-ray spectra are well represented by a continuosly curved model up to 45 keV and are interpreted as synchrotron emission, with the peak moving to higher energies. This is also confirmed by the slope of the X-ray spectrum which is harder than in previous observations. Based on our optical and X-ray data, the synchrotron peak turns out to be in the range 0.1-0.7 keV. We compare our data with non simultaneous radio to TeV data and model the spectral energy distribution with a homogeneous, one-zone synchrotron inverse Compton model. We derive physical parameters that are typical of low power High Energy peaked Blazar, characterised by a relatively large beaming factor, low luminosity and absence of external seed photons.
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We present a comprehensive multi-frequency study of the HBL 1ES 1959+650 using data from various facilities during the period 2016-2017, including X-ray data from {it AstroSat} and {it Swift} during the historically high X-ray flux state of the source observed until February 2021. The unprecedented quality of X-ray data from high cadence monitoring with the {it AstroSat} during 2016-2017 enables us to establish a detailed description of X-ray flares in 1ES 1959+650. The synchrotron peak shifts significantly between different flux states, in a manner consistent with a geometric (changing Doppler factor) interpretation. A time-dependent leptonic diffusive-shock-acceleration and radiation transfer model is used to reproduce the spectral energy distributions (SEDs) and X-ray light curves, to provide insight into the particle acceleration during the major activity periods observed in 2016 and 2017. The extensive data of {it Swift}-XRT from December 2015 to February 2021 (Exp. = 411.3 ks) reveals a positive correlation between flux and peak position.
We report the results of quasi-simultaneous two filter optical monitoring of two high-energy peaked blazars, 1ES 1959+650 and 1ES 2344+514, to search for microvariability and short-term variability (STV). We carried out optical photometric monitoring of these sources in an alternating sequence of B and R pass-bands, and have 24 and 19 nights of new data for these two sources, respectively. No genuine microvariability (intra-night variability) was detected in either of these sources. This non-detection of intra-night variations is in agreement with the conclusions of previous studies that high-energy peaked BL Lacs are intrinsically less variable than low-energy peaked BL Lacs in the optical bands. We also report the results of STV studies for these two sources between July 2009 and August 2010. Genuine STV is found for the source 1ES 1959+650 but not for 1ES 2344+514. We briefly discuss possible reasons for the difference between the intra-night variability behaviour of high- and low-energy peaked blazars.
We report on the VERITAS observations of the high-frequency peaked BL Lac object 1ES 1959+650 in the period 2007-2011. This source is detected at TeV energies by VERITAS at 16.4 standard deviation (sigma) significance in 7.6 hours of observation in a low flux state. A multiwavelength spectral energy distribution (SED) is constructed from contemporaneous data from VERITAS, Fermi-LAT, RXTE PCA, and Swift UVOT. Swift XRT data is not included in the SED due to a lack of simultaneous observations with VERITAS. In contrast to the orphan gamma-ray flare exhibited by this source in 2002, the X-ray flux of the source is found to vary by an order of magnitude, while other energy regimes exhibit less variable emission. A quasi-equilibrium synchrotron self-Compton model with an additional external radiation field is used to describe three SEDs corresponding to the lowest, highest, and average X-ray states. The variation in the X-ray spectrum is modeled by changing the electron injection spectral index, with minor adjustments of the kinetic luminosity in electrons. This scenario produces small-scale flux variability of order >~2 in the HE (E>1 MeV) and VHE (E>100 GeV) gamma-ray regimes, which is corroborated by the Fermi-LAT, VERITAS, and Whipple 10m telescope light curves.
Following the detection of strong TeV gamma-ray flares from the BL Lac object 1ES 1959+650 with the Whipple 10 m Cherenkov telescope on May 16 and 17, 2002, we performed intensive Target of Opportunity (ToO) radio, optical, X-ray and TeV gamma-ray observations from May 18, 2002 to August 14, 2002. Observations with the X-ray telescope RXTE and the Whipple and HEGRA gamma-ray telescopes revealed several strong flares, enabling us to sensitively test the X-ray/gamma-ray flux correlation properties. Although the X-ray and gamma-ray fluxes seemed to be correlated in general, we found an ``orphan gamma-ray flare that was not accompanied by an X-ray flare. After describing in detail the radio (UMRAO, VLA), optical (Boltwood, Abastumani), X-ray (RXTE) and gamma-ray (Whipple, HEGRA) light curves and Spectral Energy Distributions (SEDs) we present initial modeling of the SED with a simple Synchrotron Self-Compton (SSC) model. With the addition of another TeV blazar with good broadband data, we consider the set of all TeV blazars to begin to look for a connection of the jet properties to the properties of the central accreting black hole thought to drive the jet. Remarkably, the temporal and spectral X-ray and gamma-ray emission characteristics of TeV blazars are very similar, even though the masses estimates of their central black holes differ by up to one order of magnitude.
Aim : The nearby TeV blazar 1ES 1959+650 (z=0.047) was reported to be in flaring state during June - July 2016 by Fermi-LAT, FACT, MAGIC and VERITAS collaborations. We studied the spectral energy distributions (SEDs) in different states of the flare during MJD 57530 - 57589 using simultaneous multiwaveband data to understand the possible broadband emission scenario during the flare. Methods : The UV/optical and X-ray data from UVOT and XRT respectively on board Swift and high energy $gamma$-ray data from Fermi-LAT are used to generate multiwaveband lightcurves as well as to obtain high flux states and quiescent state SEDs. The correlation and lag between different energy bands is quantified using discrete correlation function. The synchrotron self Compton (SSC) model was used to reproduce the observed SEDs during flaring and quiescent states of the source. Results : A decent correlation is seen between X-ray and high energy $gamma$-ray fluxes. The spectral hardening with increase in the flux is seen in X-ray band. The powerlaw index vs flux plot in $gamma$-ray band indicates the different emission regions for 0.1 - 3 GeV and 3-300 GeV energy photons. Two zone SSC model satisfactorily fits the observed broadband SEDs. The inner zone is mainly responsible for producing synchrotron peak and high energy $gamma$-ray part of the SED in all states. The second zone is mainly required to produce less variable optical/UV and low energy $gamma$-ray emission. Conclusions : Conventional single zone SSC model does not satisfactorily explain broadband emission during observation period considered. There is an indication of two emission zones in the jet which are responsible for producing broadband emission from optical to high energy $gamma$-rays.
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