The X-ray variability of Mrk 421

The results of monitoring the flaring activity of Mrk 421 with the XMM-Newton and RXTE orbiting observatories are presented. The ASM/RXTE data show that, during most of the observational period, 2002–2006, the source was in a very active state, with a mean 1.5–12 keV flux equals ∼17 mCrab. Analysis of daily and weekly averaged data shows strong X-ray variability of Mrk 421 on time scales from days to months. The long-term light curve demonstrates a rich variety of variability patterns and a complex hierarchical flare structure, in most cases superimposed on longer trends of rising and decreasing source activity. Quantitative estimates of the variability of Mrk 421 shows evidence of correlations between the source intensity in X-rays and the variability parameters, both for separate years and epochs and for most of the observational period. The soft and hard X-ray components (according to XMM-Newton data) are correlated with each other, and spectral changes (according to ASM/RXTE data) are characterized by increasing hardness with brightening of the object in X-rays. Moderate spectral variability at individual epochs and evidence for an energy dependence of the source variability are also observed. The 2–12 keV fluxes from Mrk 421 detected by XMM-Newton are consistent with the maximum 2–10 keV flux detected by ASCA ∼10 years ago. An analysis of simultaneous day-time-scale variability of Mrk 421 in X-rays (ASM/RXTE) and very-high-energy γ-rays (GT-48 Cherenkov telescope of the Crimean Astrophysical Observatory) in periods of increased activity of the source in December 2002 and April 2004 is also presented. Published in Russian in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 7, pp. 589–602. The article was translated by the authors.     

Tera-electron-volt radiation from the blazar 1ES 1959+650 in 2004

Observations of the blazar 1ES 1959+650, which has been identified as a point source of tera-electron-volt gamma-ray emission, were carried out on the GT-48 Cherenkov telescope of the Crimean Astrophysical Observatory from the middle of July to the middle of August 2004. Our analysis of data with an effective exposure time on-source of six hours under good weather conditions shows a clear excess of detected photons (with energies E ≥ 1 TeV) in the direction of this source, with a statistical significance of 5.2σ. Using observations of the Crab Nebula in 2002–2004 and the parameters of Cherenkov flashes similar to those observed for 1ES 1959+650 yields an estimated flux for this object of 2.0 ± 0.7 Crab (≥1 TeV). Comparison with the 2–12 keV emission of this source indicates a correlation between the mean fluxes in the two energy ranges in various observing periods.     

Evolution of the radio emission of the Crab nebula from long-term observations at 927 and 151.5 MHz

Radio flux measurements of the Crab nebula have been performed over many years relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. The inferred average secular rates of decrease in the radio flux of the Crab nebula are d _{927 MHz} = ?0.18 ± 0.10% yr^?1 over 1977–2000 and d _{151.5 MHz} = ?0.3 ± 0.1% yr^?1 over 1980–2003. The weighted mean flux-decrease rate averaged over several years of relative measurements at 86, 151.5, 927, and 8000 MHz is d _mw = ?0.17 ± 0.02% yr^?1. The secular flux decrease is frequency independent, with an upper limit of |dα/dt| < 3 × 10^?4 yr^?1 for the absolute value of the rate of change of the spectral index, and remains constant in time when averaged over long time intervals. The results of our measurements at 151.5 and 927 MHz combined with published absolute measurements at 81.5 and 8250 MHz are used to determine the radio spectrum of the Crab nebula for epoch 2010.0.     

Deviation of the arrival-time delay of pulses for the Crab pulsar from a quadratic frequency region

Our measurements of the arrival-time delays of radio pulses from the Crab pulsar, PSR B0531+21, at low frequencies 111, 63, and 44 MHz revealed additional delays compared to the usual quadratic frequency relation, Δt(v) ∝ v ^?2. These additional delays are 65 ms between 63 MHz and 111 MHz—i.e., a factor of two longer than the pulsar’s period, i.e., a factor of five longer than the pulsar period—and cannot be explained by the “twisting” of the magnetic-field lines by the rotation of the pulsar. We suggest the model in which a previously unknown high-density plasma layer with a high electron concentration is present along the line of sight in the Crab nebula, causing an additional frequency-dependent delay of the observed radio pulses at low frequencies due to the contribution of the n _e ² v ^?4 term in the dispersion-delay formula. The parameters of this inferred layer have been derived: emission measure EM ? 4 × 10⁶ pc/cm⁶, electron density n _e ? 10⁶ cm^?3, depth along the line of sight d ? 4 × 10^?6 pc, and electron temperature T _e ≥ 2 × 10⁶ K.     

Studies of cosmic plasma using radioastron VLBI observations of giant pulses of the pulsar B0531+21

The structure of the interstellar plasma in the direction of the pulsar in the Crab Nebula is studied using several sets of space-VLBI observations obtained with networks of ground telescopes and the RadioAstron space antenna at 18 and 92 cm. Six observing sessions spanning two years are analyzed. Giant pulses are used to probe the cosmic plasma, making it possible to measure the scattering parameters without averaging. More than 4000 giant pulses were detected. The interferometer responses (visibility functions) on ground and ground–space baselines are analyzed. On the ground baselines, the visibility function as a function of delay is dominated by a narrow feature at zero delay with a width of δ_τ ~ 1/B, where B is the receiver bandwidth. This is typical for compact continuum sources. On the ground–space baselines, the visibility function contains a set of features superposed on each other and distributed within a certain interval of delays, which we identify with the scattering time for the interfering rays τ. The amplitude of the visibility function on ground baselines falls with increasing baseline; the scattering disk is partially resolved at 18 cmand fully resolved at 92 cm. Estimates of the scattering angle ? give 0.5–1.3mas at 18 cm and 14.0 mas at 92 cm. The measured values of ? and τ are compared to estimate the distance from the source to the effective scattering screen, which is found at various epochs to be located at distances from 0.33 to 0.96 of the distance from the observer to the pulsar, about 2 kpc. The screen is close to the Crab Nebula at epochs of strong scattering, confirming that scattering on inhomogeneities in the plasma in the vicinity of the nebula itself dominates at these epochs.     

Parameters of giant pulses from the Crab pulsar measured with the Mark5A VLBI system

Radio observations of the Crab pulsar were performed on the 100-m radio telescope of the Green Bank Observatory at a frequency of 2100 MHz in a 64-MHz band in two channels with right-and left-circular polarization. The Mark5A recording system was used. During 15 min of observing time, 609 giant pulses were recorded; the brightest had a peak flux density of 670 kJy. The energy distribution has been constructed, polarization properties have been analyzed, and the characteristic temporal and frequency scales in the radio emission of the detected giant pulses have been found. Comparison of these parameters indicates that the properties of giant pulses detected at the main-pulse and interpulse longitudes do not differ, as is clearly observed at frequencies above 4 GHz. Probable origins of the frequency evolution of the properties of giant pulses are discussed.     

A sky survey at 102.5 MHz: Radio sources at declinations 27.5°–33.5° and 67.5°–70.5°

The results of observations on the Large Phased Array of the Lebedev Physical Institute made as part of a survey of the northern sky at 102.5 MHz are reported. Survey source lists for the declination ranges 27.5°–33.5° and 67.5°–70.5° are given, together with their coordinates, flux densities, and identifications with 4C objects. In total, there are 920 sources with flux densities S _102.5≥3.0 Jy in the two zones, which cover 0.73 star. The observing and data-reduction methods are described, and the reliability and completeness of the catalog are estimated.     

Bivalve contribution to benthic metabolism in a California Lagoon

Populations of suspension feeding bivalves constitute a metabolically important component of the benthos in Colorado Lagoon, Long Beach, California. Oxygen and nutrient flux were measuredin situ at monthly intervals over a two-year period. Estimates of bivalve metabolism were based on regressions of oxygen and ammonium flux on a measure of clam biomass adjusted allometrically. The introduced bivalve,Mercenaria mercenaria, occurs at maximum densities exceeding 400 per m². Based on mean densities (143 per m²), bivalves contributed more than 50% of the 77 mg O₂ per m² per hr mean annual oxygen uptake and the 191 μM per m² per hr mean ammonium release. Although bivalve biomass was not correlated with other inorganic nutrient flux, on an annual basis the sediments were a source of phosphate (26 μM per m² per hr annual average, range 5 to 50) and a small sink for nitrate and nitrite. Net primary production, ammonium flux, and phosphate flux showed great annual variability while respiration was relatively constant. Total community oxygen uptake was not correlated with temperature. Long term incubations revealed no obvious rhythms having a period between four hours and four days. The benthic flux of ammonium and phosphate was calculated to supply more than the annual requirement of Lagoon phytoplankton.     

The radio pulsar J0205+6449 in the supernova remnant 3C 58

The detection of pulsed radio emission from the recently discovered X-ray pulsar J0205+6449 in the young supernova remnant 3C 58 is reported together with the results of first studies of this emission. The observations were carried out at 111 and 88 MHz on radio telescopes of the Pushchino Observatory. The pulsar period, 65.68 ms, and period derivative, \(\dot P = 1.9 \times 10^{ - 13} \), have been confirmed. The integrated pulse profile at 111 MHz has been obtained and the flux density and spectral index α=2.8 measured. The pulsar dispersion measure DM=141 pc cm^?3 has been confirmed. This dispersion measure yields a distance to the pulsar of d=6.4 kpc, a factor of two or more greater than the previously favored distance to the supernova remnant 3C 58 (2.6 kpc). The problem of the age and distance of the pulsar-SNR system is discussed. If the age of the pulsar J0205+6449 is equal to that of the SNR (820 years), this pulsar is the youngest known radio pulsar. The synchrotron mechanism for the radio and X-ray emission is proposed to explain the lower radio and X-ray luminosity of this new pulsar compared to the Crab pulsar, which is similar to it in many ways. Optical emission with luminosity L_opt=10³¹ erg/s and gamma-ray emission with L_γ=7×10³⁵ erg/s are predicted, and the steep radio spectrum (α≈3) can be explained.     

Fast brightness variations of blazars in the radio and optical

We present coordinated synchronous observations of Active Galactic Nuclei in the radio and optical, aimed at searching for fast (intraday) flux variations and possible correlations in the flux variations in different wavebands. Our observations were performed with the 22-m radio telescope of the Crimean Astrophysical Observatory at 22.2 and 36.8 GHz and the Zeiss-1000 reflector of the Special Astrophysical Observatory in the R filter, using a CCD photometer. We performed five observing runs of 7–10 nights each in 2004–2006. We obtained radio and optical light curves for the variable extragalactic radio sources DA 55, 1633+382, 2134+004, 2145+067, and 2251+158. We detected short-duration flares of DA 55 and 2134+004 in the R band with variations of 0.2 ^m within about 15 minutes. The other sources did not show any considerable flux variations. The radio flux variations of DA 55 and 2134+004 reached 1.5 Jy in about 15 minutes, and those of 2145+067 reached 2 Jy in 2 hours. We observed chaotic flux variations in 2251+158, by 2–2.5 Jy in half an hour. We detected no correlation between the radiation in the optical and radio.     

Six-day modulation of the quiescent radio emission of SS 433

Two daily sets of monitoring data of the Galactic X-ray binary SS 433 (V1343 Aql) obtained on the RATAN-600 radio telescope (117 days in 1997 and 120 days in 1999) show variations in its quiescent radio emission with a period of 6.05±0.1 days at six frequencies from 0.96 to 22 GHz. This 10–15% modulation in the quiescent radio light curves differs significantly from the well-known 6.28-day periodicity in the emission of moving spectral features and in optical photometric data, which are related to nodding motions of the jets and accretion-disk wobble. This period coincides almost exactly with the theoretical value for the harmonic f=2(I _o+I _p), related to the orbital (T _o=13.08 days) and precessional (T _p=162.4 days) periods for slaved accretion-disk models. The 6.06-day period corresponds to the combined frequency. It is proved that the modulation of the radio flux of SS 433 may be associated with relativistic boosting of the jet emission due to periodic variation of the orientation of the jets, which are nodding with a period of six days. The synchrotron emission of the two jets contributes to the quiescent radio flux of SS 433, and the six-day harmonic has the same radio spectrum as the quiescent radio flux: S _v ～v ^?0.6.     

Probing cosmic plasma with giant pulses from the crab nebula pulsar

A review and comparative analysis of results from studies of the effects of scattering on the interstellar medium using giant pulses of the Crab Nebula pulsar (B0531+21) are presented. This analysis was based on eight epochs of Very Long Baseline Interferometry (VLBI) radio observations carried out as part of the scientific program of the Radio Astron mission during 2011–2015. The scintillation timescale t _scint and spectral index γ for the power-law energy distribution of the pulses were obtained for each observing epoch. The measured scintillation timescales are t _scint = 7.5?123 s at 1668 MHz and t _scint = 2.9 s at 327 MHz. The spectral indices are ?1.6...?2.5. The frequency and time characteristics of the scattering were measured using two independent methods: based on the decorrelation bandwidth Δν _d and the scattering timescale τ _SC. The angular size of the scattering disk θ _H of the pulsar was obtained, the phase structure functions constructed, and the distance to the effective scattering screen estimated. The derived diameter of the scattering disk θ _H at 1668 MHz ranges from 0.4 to 1.3 mas, while the scatteringdisk diameter at 327 MHz is 14.0 mas. The measured distance to the effective scattering screen ranges from 0.7 to 1.9 kpc, and varies from observation to observation in the same way as the scattering timescale and decorrelation bandwidth: τ _SC ≈ 0.9?5.8 μs and Δν _d ≈ 40.7?161 kHz at 1668 MHz. The scattering timescale and decorrelation bandwidth at 327 MHz are 2340 μs and 68 Hz.     

Activity of the Seyfert galaxy NGC 4151 in the near-IR in 1994–2011

We present the results of our infrared J H K L photometry of the Seyfert galaxy NGC 4151 during its active period in 1995–2011. The variable IR source was still in its active state in 2011, though its observed luminosity had almost halved compared to the maximum of 1995–1996. If the “cool” component of the galaxy’s variable source is a dust shell heated with the central “hot” source, its optical depth at 1.25 µm varied from 0.3 to almost 1.0, its temperature from 700 to 950 K, its size from 20 to 40 pc, and its mass from 2 to 40M _⊙ during our observations. A component with a period of 317 ± 5 days can be revealed in the flux variations observed in 1994–2011.     

A 27-Day Period in the Flux of Jovian Electrons at the Earth’s Orbit

Variations in the flux of Jovian electrons near the Earth in two synodic cycles of the Earth–Jupiter system, in 1974–1975 and 2007–2008, are considered. In the 1974–1975 cycle, Jovian electrons were observed by IMP-8 during 13 successive solar rotations; electrons were observed by SOHO during 14 solar rotations during the 2007–2008 cycle. The fluxes of these electrons in each solar revolution experienced variations with a characteristic time scale of ~27 ^d , with the maximum flux near the middle of the rotation. The mean period of the variations does not coincide with the synodic period for the Sun–Earth system, equal to 27.3 ^d . The mean variation periods for the electron fluxes were 26.8 ^d in 1974–1975 and 26.1 ^d in 2007–2008. The detected variations are interpreted as reflecting variations in the structure of the solar wind speed and associated magnetic traps, the confinement time of the electrons in thesemagnetic traps, and the influence of the relative positions of the Earth and Jupiter in space.     

Seasonal Prevalence of Hematodinium sp. Infections of Blue Crabs in Three South Carolina (USA) Rivers

Blue crab, Callinectes sapidus, commercial landings in the USA have been declining at an alarming rate. In South Carolina, these declines are significantly correlated with years of decreased rainfall and elevated salt marsh salinity. Previous studies suggest that higher salinity increases the risk of infection by Hematodinium sp., a dinoflagellate parasite of blue crabs, C. sapidus. A 4-year survey (June 2008 to March 2012) of blue crabs in the ACE Basin National Estuarine Research Reserve documented (1) the temporal and spatial patterns of Hematodinium sp. infection in relation to salinity, (2) some environmental correlates of disease prevalence, and (3) the characteristics of infected blue crabs. Sampling was conducted four times a year in March, June, September, and December in the South Edisto, Ashepoo, and Combahee rivers beginning in June 2008. Crab hemolymph samples were collected and preserved and DNA was successfully amplified for 2,303 individuals. Hematodinium sp. infection was evaluated by PCR amplification of its 18S rRNA gene and adjacent regions. Prevalence was highest in December 2008 in the Combahee River at sites closest to St. Helena Sound. The spatial and temporal pattern of Hematodinium sp. infection was correlated with several environmental parameters. Infected crabs exhibited differences in carapace shape and body condition compared to uninfected crabs. Overall, these results suggest that blue crabs in regions of higher salinity are at greater risk of infection by Hematodinium sp. and infected individuals exhibit sub-lethal effects of the disease.     

Observations of late-type variable stars in the water vapor radio line. The long-period variable R cassiopeia

Observations of circumstellar maser emission from the long-period variable R Cas in the 1.35-cm water-vapor line are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1980–2003 (JD=2444409–2452724). Over the 23 years of observations, strong flares in the H₂O line profile were recorded in 1982 (with a peak flux density up to 400 Jy) and 1986–1989 (up to 750 Jy). Subsequently, from 1990 to March 2003, the H₂O line flux was usually below the detection threshold of the radio telescope (<5–10 Jy). Episodic small increases of the emission with peak flux densities of 20–60 Jy were observed. The variations of the H₂O line flux F are correlated with variations in the visual brightness of the star. The phase delay Δ_γ of the F variations relative to the optical light curve of R Cas ranged from 0.2–0.3P during the observations (P=430.46^d is the star's period). A model for the variability of the H₂O maser in R Cas is discussed. If the variations are due to periodic impacts by shock waves driven by the stellar pulsations, the time for the shock to travel from the photosphere to the inner boundary of the H₂O-masing shell may reach 2–4P. The flares could be due to transient episodes of enhanced mass loss by the star or to the propagation of an exceptionally strong shock from the stellar surface.     

Changes in isotope ratio and content of dissolved helium through groundwater evolution

The dissolved He content and He isotope ratio are proxy indicators of groundwater evolution in the Shimokita peninsula. The record of ³H and excess bomb tritiogenic ³He reveals the intrusion depth of shallow and young groundwater into deep groundwater. The record of tritiogenic ³He suggests that prior to the period of nuclear testing, the natural production level of ³H irradiated by cosmic rays was probably 6 TU. Helium isotope ratios in the groundwater converge to that of the regional crustal He with increasing depth and dissolved He content. The regional degassed He has a ³He/⁴He (R) ratio of 7.24 × 10⁻⁷ which consists of 6% mantle He (with R=1. 1 × 10⁻⁵) and 94% radiogenic He (with R=1 ×10⁻⁸). The magnitude of degassing He flux is 5×10⁻⁹ m³/m² a. Based on the accumulation of He, and taking into consideration the degassing He flux, groundwater at depths greater than 300 m below sea level is estimated to be stagnant, exhibiting residence times in excess of 10² Ka.     

Can pelagic net heterotrophy account for carbon fluxes from eastern Canadian lakes?

Lakes worldwide are commonly oversaturated with CO₂, however the source of this CO₂ oversaturation is not well understood. To examine the magnitude of the C flux to the atmosphere and determine if an excess of respiration (R) over gross primary production (GPP) is sufficient to account for this C flux, metabolic parameters and stable isotopes of dissolved O₂ and C were measured in 23 Québec lakes. All of the lakes sampled were oversaturated with CO₂ over the sampling period, on average 221 ± 25%. However, little evidence was found to conclude that this CO₂ oversaturation was the result of an excess of pelagic R over GPP. In lakes Croche and à l’Ours, where CO₂ flux, R and GPP were measured weekly, the annual difference between pelagic GPP and R, or net primary production (NPP), was not sufficient to account for the size of the CO₂ flux to the atmosphere. In Lac Croche average annual NPP was 14.4 mg C m⁻² d⁻¹ while the average annual flux of CO₂ to the atmosphere was 34 mg C m⁻² d⁻¹. In Lac à l’Ours average annual NPP was −9.1 mg C m⁻² d⁻¹ while the average annual flux of CO₂ to the atmosphere was 55 mg C m⁻² d⁻¹. In all of the lakes sampled, O₂ saturation averaged 104.0 ± 1.7% during the ice-free season and the isotopic composition of dissolved O₂ (δ¹⁸O_DO) was 22.9 ± 0.3‰, lower than atmospheric values and indicative of net autotrophy. Carbon evasion was not a function of R, nor did the isotopic signature of dissolved CO₂ in the lakes present evidence of excess R over GPP. External inputs of C must therefore subsidize the lake to explain the continued CO₂ oversaturation. The isotopic composition of dissolved inorganic C (δ¹³C_DIC) indicates that the CO₂ oversaturation cannot be attributed to in situ aerobic respiration. δ¹³C_DIC reveals a source of excess C enriched in ¹³C, which may be accounted for by anaerobic sediment respiration or groundwater inputs followed by kinetic isotope fractionation during degassing under open system conditions.     

Monitoring of the radio emission of the Crab Nebula pulsar at low frequencies

Results of long-term (2002–2010) monitoring of giant radio pulses of the pulsar PSR B0531+21 in the Crab Nebula at ν = 44, 63, and 111 MHz are reported. The observations were conducted on the LPA and DKR-1000 radio telescopes of the Lebedev Physical Institute. The giant pulses were analyzed using specialized software for calculating the magnitude of the scattering τ _sc , signal-to-noise ratio, and other required parameters by modeling the propagation of a pulse in the scattering interstellar medium. Three pronounced sharp increases in the scattering were recorded in 2002–2010. Analysis of the dependence between the variations of the scattering and dispersion measure (data of Jodrell Bank Observatory) shows a strong correlation at all frequencies, ≈0.9. During periods of anomalous increase in scattering and the dispersion measure, the index γ in the frequency dependence of the scattering in the Crab Nebula, τ _sc (ν) ∝ ν ^−γ , was smaller than the generally accepted values γ = 4.0 for a Gaussian and γ = 4.4 for a Kolmogorov distribution. This difference in combination with the piece-wise power-law spectrum may be due to the presence of a dense plasma structure with developed Langmuir turbulence in the nebula, along the pulsar’s line of sight. The magnetic field in the Crab Nebula estimated from measurements of the rotation measure toward the pulsar is 100 μG.     

Time-window-based filtering method for near-surface detection of leakage from geologic carbon sequestration sites

We use process-based modeling techniques to characterize the temporal features of natural biologically controlled surface CO₂ fluxes and the relationships between the assimilation and respiration fluxes. Based on these analyses, we develop a signal-enhancing technique that combines a novel time-window splitting scheme, a simple median filtering, and an appropriate scaling method to detect potential signals of leakage of CO₂ from geologic carbon sequestration sites from within datasets of net near-surface CO₂ flux measurements. The technique can be directly applied to measured data and does not require subjective gap filling or data-smoothing preprocessing. Preliminary application of the new method to flux measurements from a CO₂ shallow-release experiment appears promising for detecting a leakage signal relative to background variability. The leakage index of ±2 was found to span the range of biological variability for various ecosystems as determined by observing CO₂ flux data at various control sites for a number of years.