arXiv subjects
Publications and source records attributed to R. A. Remillard.
RXTE/ASM observations of PSR B1259-63 near the 1997 periastron passage find no emission brighter than appximately 10 times that detected by ASCA during the 1994 periastron encounter, demonstrating that the pulsar is unlikely to have undergone even brief episodes of accretion.
We report simultaneous X-ray and infrared (IR) observations of the Galactic microquasar GRS1915+105 using XTE and the Palomar 200-inch telescope on August 13-15, 1997 UTC. During the last two nights, the microquasar GRS 1915+105 exhibited quasi-regular X-ray/infrared (IR) flares with a spacing of $\sim 30$ minutes. While the physical mechanism triggering the flares is currently unknown, the one-to-one correspondence and consistent time offset between the X-ray and IR flares establish a close link between the two. At late times in the flares the X-ray and IR bands appear to ``decouple'', with the X-ray band showing large-amplitude fast oscillations while the IR shows a much smoother, more symmetrical decline. In at least three cases, the IR flare has returned to near its minimum while the X-rays continue in the elevated oscillatory state, ruling out thermal reprocessing of the X-ray flux as the source of IR flare. Furthermore, observations of similar IR and radio flares by Fender et al. (1997) imply that the source of the IR flux in such flares is synchrotron emission. The common rise and subsequent decoupling of the X-ray and IR flux and probable synchrotron origin of the IR emission is consistent with a scenario wherein the IR flux originates in a relativistic plasma which has been ejected from the inner accretion disk. In that case, these simultaneous X-ray/IR flares from a black-hole/relativistic-jet system are the first clear observational evidence linking of the time-dependent interaction of the jet and the inner disk in decades of quasar and microquasar studies.
We present multi-frequency spectra of the Seyfert 1 galaxy H2106-099, from radio to hard X-rays, spanning over a decade of observations. The hard X-ray (2-20 keV) spectrum measured with Ginga had a Log slope of -0.80 +/- 0.02 on 1988 May 18 and -1.02 +/- 0.10 on 1988 May 22 / 23 UT, with no observed flux changes. Other measurements showed variability and unusual spectral features: The V band flux changed by a factor of 1.8 (> 10 sigma) in six weeks. Only moderate optical Fe II emission is present, but strong [FeVII] and [Fe X] lines are present in some epochs. The Balmer lines show > 25% variations in flux relative to the mean, and He I changed by more than 100% relative to the mean in <~ six years. The most surprising finds came from the composite UV through near-IR spectrum: If the spectrum is de-reddened by the galactic extinction value (from 21 cm observations), a residual 2175 Angstrom absorption feature is present. Additional de-reddening to correct the feature yields E(B-V)=0.07 mag due to material outside our galaxy, most probably associated with the AGN or its host galaxy. No other clear indications of reddening are observed in this object, suggesting that blue bump strength measurements in low and intermediate red-shift AGN could be incorrect if derived without UV observations of the region near 2175 Angstrom in the AGN frame. After all reddening corrections are performed, the log slope of H2106-099 from the near IR (~12500 Angstrom) to the UV (~1400 Angstrom), -0.94 +/- 0.05, is steep compared to other AGN, suggesting that the blue bump in this object is intrinsically weak. Weak blue bumps are, therefore, not always an artifact caused by reddening.
The galactic superluminal motion source GRS 1915+105 was observed with RXTE at several occasions during its ongoing active state. The observed X-ray intensity changes drastically on a variety of time scales ranging from sub-seconds to days. In particular, the source exhibits quasi-periodic brightness sputters with varying duration and repetition time scale. These episodes occur occasionally, while the more common X-ray intensity variations are faster with much smaller amplitudes. The spectrum during the brightness sputters is remarkably different from the spectrum of the mean high state emission. We argue that such sputtering episodes are possibly caused by a major accretion disk instability. Based on the coincidence in time of two radio flares following the observed X-ray sputtering episodes we speculate that superluminal ejections (as observed from GRS 1915+105 during earlier activity periods) are related to episodes of large amplitude X-ray variations.
A comparison of ROSAT observations with simultaneous BATSE monitoring data shows a different intensity evolution in the soft and hard X-ray band of GRS 1915+105 since 1992. In addition, fits of simultaneous ROSAT/BATSE spectra require more than one spectral component. A short description of results of RXTE pointed observations of GRS 1915+105 since April 1996 is also presented.
We have detected transient X-ray activity from the X-ray burster 4U~0614+091 simultaneously with BATSE/CGRO (20-100 keV) and ASM/RXTE (1-12 keV). The peak fluxes reach approximately 40 mCrab in both instruments over a period of about 20 days. The variable emission shows a clear anticorrelation of the hard X-ray flux with the soft X-ray count rate. The observed anticorrelation is another clear counterexample to the notion that only black hole binaries exhibit such correlations. The individual spectra during this period can be fit by power laws with photon indices 2.2+-0.3 (ASM) and 2.7+-0.4 (BATSE), while the combined spectra can be described by a single power law with index 2.09+-0.08. BATSE and the ASM/RXTE are a good combination for monitoring X-ray sources over a wide energy band.