D. Kazanas

Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279

The blazar 3C 279, one of the brightest identified extragalactic objects in the γ-ray sky, underwent a large (factor of ~10 in amplitude) flare in γ-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest γ-ray intensity ever recorded for this object. During the high state, extremely rapid γ-ray variability was seen, including an increase of a factor of 2.6 in ~8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray Timing Explorer (RXTE), Advanced Satellite for Cosmology and Astrophysics (ASCA; or, Astro-D), Roentgen Satellite (ROSAT), and International Ultraviolet Explorer (IUE) and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of 3) well correlated with the γ-ray flare without any lag larger than the temporal resolution of ~1 day. The optical-UV light curves, which are not well sampled during the high-energy flare, exhibit more modest variations (factor of ~2) and a lower degree of correlation. The flux at millimetric wavelengths was near a historical maximum during the γ-ray flare peak, and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The γ-rays vary by more than the square of the observed IR-optical flux change, which poses some problems for specific blazar emission models. The synchrotron self-Compton (SSC) model would require that the largest synchrotron variability occurred in the mostly unobserved submillimeter/far-infrared region. Alternatively, a large variation in the external photon field could occur over a timescale of a few days. This occurs naturally in the mirror model, wherein the flaring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to γ-ray energies.

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis of Multiwavelength Continuum Variability

For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)

Frequency-dependent Time Lags in the X-Ray Emission of the Seyfert Galaxy NGC 7469

We report the discovery of time lags in the cross spectra of the X-ray light curves of the Seyfert galaxy NGC 7469. This behavior is common in Galactic black hole and neutron star binaries and is in the sense that harder X-rays are delayed with respect to softer X-rays, with a time lag approximately proportional to the Fourier period. At the longest period probed by our observation (~6 days), we find a time lag of approximately 3.5 hr between the 2-4 and 4-10 keV X-rays. A similar lag and period dependence are found by comparing the 2-4 and 10-15 keV light curves, albeit with less significance. We find the coherence function of the light curves to be close to 1 in the frequency range between 10-5.5 and 10-3.5 Hz. The implications of these results for the X-ray production mechanism in active galactic nuclei are discussed.

The Extended Pulsar Magnetosphere

We present the structure of the 3D ideal MHD pulsar magnetosphere to a radius ten times that of the light cylinder, a distance about an order of magnitude larger than any previous such numerical treatment. Its overall structure exhibits a stable, smooth, well-defined undulating current sheet which approaches the kinematic split monopole solution of Bogovalov 1999 only after a careful introduction of diffusivity even in the highest resolution simulations. It also exhibits an intriguing spiral region at the crossing of two zero charge surfaces on the current sheet, which shows a destabilizing behavior more prominent in higher resolution simulations. We discuss the possibility that this region is physically (and not numerically) unstable. Finally, we present the spiral pulsar antenna radiation pattern.

Supernova Bounds on the Dark Photon Using Its Electromagnetic Decay

Abstract The hypothetical massive dark photon ( γ ′ ) which has kinetic mixing with the SM photon can decay electromagnetically to e + e − pairs if its mass m exceeds 2 m e , and otherwise into three SM photons. These decays yield cosmological and supernovae associated signatures. We briefly discuss these signatures, particularly in connection with the supernova SN1987A, and delineate the extra constraints that arise on the mass and mixing parameter of the dark photon. In particular, we find that for dark photon mass m γ ′ in the 5–20 MeV range arguments based on supernova 1987A observations lead to a bound on ϵ which is about 300 times stronger than the presently existing bounds based on energy loss arguments.

Broad Redshifted Line as a Signature of Outflow

We formulate and solve the diffusion problem of line photon propagation in a bulk outflow from a compact object (black hole or neutron star) using a generic assumption regarding the distribution of line photons within the outflow. Thomson scattering of the line photons within the expanding flow leads to a decrease of their energy which is of first order in v/c, where v is the outflow velocity and c is the speed of light. We demonstrate that the emergent line profile is closely related to the time distribution of photons diffusing through the flow (the light curve) and consists of a broad redshifted feature. We analyzed the line profiles for the general case of outflow density distribution. We emphasize that the redshifted lines are intrinsic properties of the powerful outflow that are supposed to be in many compact objects.

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. I. Ultraviolet Observations

Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines

THE MULTIFREQUENCY SPECTRAL EVOLUTION OF BLAZAR 3C 345 DURING THE 1991 OUTBURST

The blazar 3C 345 underwent a 2.5 mag optical outburst between 1990 November and 1991 May. We have obtained 10 nearly simultaneous multifrequency spectra during the course of the outburst in order to study the multifrequency spectral variations of 3C 345 as a function of time. Although our observations were not sampled frequently enough to completely resolve the variations in every frequency band, the general rise and decline of the outburst were seen in the UV through radio with differing rise times. Simulations of an electron distribution injected into a tangled magnetic field show a relationship between frequency and characteristic timescale that was also observed in the radio variations of 3C 345. The two X-ray observations made during the monitoring period showed no evidence of variability. The multifrequency spectrum was modeled with two major components: a relativistic jet and a relativistic thermal accretion disk. Models calculated for each spectrum indicate that the outburst can be explained in terms of these models by varying the high-energy cutoff of the injected electron distribution in the jet model, while also varying the mass accretion rate in the disk model. There is marginal evidence that the inferred accretion rate varies with the jet luminosity.

Fourier-resolved Spectroscopy of 4U 1543?47 during the 2002 Outburst

We have obtained Fourier-resolved spectra of the black hole binary 4U 1543-47 in the canonical states (high/soft, very high, intermediate, and low/hard) observed in this source during the decay of an outburst that took place in 2002. Our objective is to investigate the variability of the spectral components generally used to describe the energy spectra of black hole systems, namely a disk component, a power-law component attributed to Comptonization by a hot corona, and the contribution of the iron line due to reprocessing of the high-energy (E 7 keV) radiation. We find that (1) the disk component is not variable on timescales shorter than ~100 s, (2) the reprocessing emission as manifest by the variability of the Fe Kα line responds to the primary radiation variations down to timescales of ~70 ms in the high and very high states, but longer than 2 s in the low state, (3) the low-frequency QPOs are associated with variations of the X-ray power-law spectral component and not to the disk component, and (4) the spectra corresponding to the highest Fourier frequency are the hardest (show the flatter spectra) at a given spectral state. These results question models that explain the observed power spectra as due to modulations of the accretion rate alone, as such models do not provide any apparent reason for a Fourier frequency dependence of the power-law spectral indices.

Lyα Absorption-Line Systems in the Gravitational Lens Q0957+5611*

Far-ultraviolet spectra of the gravitational lens components Q0957+561A and B were obtained with the Hubble Space Telescope Faint Object Spectrograph (HST FOS). Two previously known absorption-line systems were detected at redshifts zdamped = 1.3911 and zLyα = 1.1249. Their prominent absorption features are superposed on intense QSO continuum emission between λλ900-1400 in the quasar rest frame. Strong O VI λ1033, Lyα λ1216, and N V λ1240 line emission found at the QSO redshift (zQSO = 1.41) accompany the absorption-line systems. Lyα through Ly associated with the damped absorption system were found in both lensed components, together with other ionic species of N I, N III, C II, C III, Si II, Si III, and O I. We tentatively identify O VI λλ1033, 1037 absorption at the damped Lyα redshift, which, if confirmed, would be the highest ionization species yet detected in such systems. The equivalent widths of the Lyman series in Q0957+561A are measurably greater compared with absorption in 0957+561B, consistent with the narrower and shallower depth of the Lyman series line profiles in image B. The differences of the damped Lyman series absorption in the lensed components are the only significant spectral characteristic that distinguishes the far-ultraviolet spectra of 0957+561A and B. These results indicate that the damped Lyα absorber is inhomogeneous over scale lengths of ~200 pc, which corresponds to the beam separation at the damped Lyα redshift. However, the equivalent widths of neutral and ionized metals in lens components A and B are correlated, which suggests these spectral features arise in an extended region. The metal line-absorption strength is consistent with lower column densities compared with the hydrogen line-forming region. Thus, the small coherence length scale indicated by the difference in hydrogen line absorption between the lensed components suggests the geometric ray paths intercept different regions of a galactic disk that is viewed pole-on, while the metal absorption occurs in the halo.