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Register a new userCoordinated RXTE and multiwavelength observations of blazars
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Rita M. Sambruna
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Results from recent multiwavelength observations of blazars are reviewed, with particular emphasis on those involving the Rossi X-ray Timing Explorer (RXTE). I discuss blazars spectral energy distributions, their correlated variability at various energies, and the insights they offer on the physical processes in the jet. New results on Mrk 501, PKS 2155--304, and PKS 2005--489 are highlighted.
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The INTEGRAL mission has played a major role in blazar science, thanks to its sensitive coverage of a spectral region (3-100 keV) that is critical for this type of sources, to its flexibility of scheduling and to the large field of view of its cameras. A number of flat-spectrum radio quasars (up to z ~ 3) and BL Lac objects were observed by INTEGRAL together with facilities at all wavelengths. These results have advanced our knowledge of blazars from a physical and cosmological point of view. This paper reviews some of these outcomes, with particular reference to the INTEGRAL program for blazars in outburst as targets of opportunity, with a perspective into a future of multi-messenger astronomy
The TeV blazar PKS 2155--304 was the subject of an intensive 2 week optical and near-infrared observing campaign in 2004 August with the CTIO 0.9m telescope. During this time, simultaneous X-ray data from RXTE were also obtained. We compare the results of our observations to the results from two previous simultaneous multiwavelength campaigns on PKS 2155-304. We conclude that the correlation between the X-ray and UV/optical variability is strongest and the time lag is shortest (only a few hours) when the object is brightest. As the object becomes fainter, the correlations are weaker and the lags longer, increasing to a few days. Based on the results of four campaigns, we find evidence for a linear relationship between the mean optical brightness and lag time of X-ray and UV/optical events. Furthermore, we assert that this behavior, along with the different multiwavelength flare lag times across different flux states is consistent with a highly relativistic shock propagating down the jet producing the flares observed during a high state. In a quiescent state, the variability is likely to be due to a number of factors including both the jet and contributions outside of the jet, such as the accretion disk.
We present results from a long-term monitoring campaign on the TeV binary LSI +61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between September 2006 and February 2008. The binary was observed by VERITAS to be variable, with all integrated observations resulting in a detection at the 8.8 sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission above 500 GeV. The source was detected during active periods with flux values ranging from 5 to 20% of the Crab Nebula, varying over the course of a single orbital cycle. Additionally, the observations conducted in the 2007-2008 observing season show marginal evidence (at the 3.6 sigma significance level) for TeV emission outside of the apastron passage of the compact object around the Be star. Contemporaneous hard X-ray observations with RXTE and Swift show large variability with flux values typically varying between 0.5 and 3.0*10^-11 ergs cm^-2 s^-1 over a single orbital cycle. The contemporaneous X-ray and TeV data are examined and it is shown that the TeV sampling is not dense enough to detect a correlation between the two bands.
This review provides an overview of recent advances in multi-wavelength and multi-messenger observations of blazars, the current status of theoretical models for blazar emission, and prospects for future facilities. The discussion of observational results will focus on advances made possible through the Fermi Gamma-Ray Space Telescope and ground-based gamma-ray observatories (H.E.S.S., MAGIC, VERITAS) as well as the recent first evidence for a blazar being a source of IceCube neutrinos. The main focus of this review will be the discussion of our current theoretical understanding of blazar multi-wavelength and multi-messenger emission, in the spectral, time, and polarization domains. Future progress will be expected in particular through the development of the first X-ray polarimeter, IXPE, and the installation of the Cherenkov Telescope Array (CTA), both expected to become operational in the early to mid 2020s.
The X-ray spectrum of extreme HBL type blazars is located in the synchrotron branch of the broadband spectral energy distribution (SED), at energies below the peak. A joint fit of the extrapolated X-ray spectra together with a host galaxy template allows characterizing the synchrotron branch in the SED. The X-ray spectrum is usually characterized either with a pure or a curved power-law model. In the latter case, however, it is hard to distinguish an intrinsic curvature from excess absorption. In this paper, we focus on five well-observed blazars: 1ES 0229+200, PKS 0548-322, RX J1136+6737, 1ES 1741+196, 1ES 2344+514. We constrain the infrared-to-X-ray emission of these five blazars using a model that is characterized by the host galaxy, spectral curvature, absorption, and ultraviolet excess to separate these spectral features. In the case of four sources: 1ES 0229+200, PKS 0548-322, 1ES 1741+196, 1ES 2344+514 the spectral fit with the atomic neutral hydrogen from the Leiden Argentina Bonn Survey result in a significant UV excess present in the broadband spectral energy distribution. Such excess can be interpreted as an additional component, for example, a blue bump. However, in order to describe spectra of these blazars without such excess, additional absorption to the atomic neutral hydrogen from the Leiden Argentina Bonn Survey is needed.
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