Craig Richard Robinson

Discovery of Correlated Behavior Between the Hard X-Ray and the Radio Bands in Cygnus X-3

Using Compton Gamma Ray Observatory BATSE hard X-ray (HXR) data and GHz radio monitoring data from the Green Bank Interferometer, we have performed a long-term study (~1800 days) of the unusual X-ray binary Cyg X-3, resulting in the discovery of a remarkable relationship between these two wavelength bands. We find that during quiescent radio states, the radio flux is strongly anticorrelated with the intensity of the HXR emission. The relationship switches to a correlation with the onset of major radio flaring activity. During major radio flaring activity, the HXR drops to a very low intensity during quenching in the radio and recovers during the radio flare. Injection of plasma into the radio jets of Cyg X-3 occurs during changes in the HXR emission and suggests that disk-related and jet-related components are responsible for the high energy emission.

Power-Law Decays in the Optical Counterparts of GRB 970228 and GRB 970508

We report on RC- and K-band observations of the optical counterpart to GRB 970508 with the Fred Lawrence Whipple Observatory (FLWO) 1.2 m telescope. Eleven RC-band observations were obtained on 1997 May 12, and three on May 14. The counterpart clearly faded between the two nights. On May 12 there was no evidence for variability (!9%) on 10‐70 minute timescales based on 11Rc-band observations. On May 19 a 1 hr observation set a limit on the K magnitude of . Comparison of these data points with those obtained by other authors K 1 18.6 shows that the decay of the optical counterpart can be well fitted by a power law of the form , where 2a f » t with occasional fluctuations superposed. We note that the decay of the optical counterpart to a 5 1.22 5 0.03 another burst, GRB 970228, can also be well fitted with a power law with exponent with occasional 10.2 a 5 1.020.5 fluctuations superposed. These two decay light curves are remarkably similar in form to that predicted by cosmicfireball models. Subject heading: gamma rays: bursts

RXTE observations of GRB afterglows

Abstract Variable X-ray sources that appear to be the afterglows of the strong gamma-ray bursts GRB 970616 and GRB 970828 have been discovered with the RXTE PCA. First seen less than 4 hours after the burst, the flux from the sources decreased with time. Although near the sensitivity limit of the PCA, the sources are the brightest afterglows yet seen in X-rays. Similar observations of two other bursts did not detect any afterglows. These results are part of a continuing collaboration between RXTE, BATSE, and IPN scientists to rapidly detect X-ray afterglows of bright gamma-ray bursts.

The CFA BATSE IMAGE SEARCH (CBIS) as used for a Galactic plane survey

The CFA BATSE IMAGE SEARCH (CBIS) system allows automated analysis of large sets of BATSE images. CBIS is being used to conduct a deep survey of the Galactic plane to search for faint transients (∼100 mCrab) in the archival data [2]. Furthermore, together with the earth occultation technique [3], CBIS is now applied to a real time imaging survey of the plane to discover new transients and monitor known sources. The CBIS processing is made of two sequential steps: First, the images are scanned to search for excesses. Second, the positions of all these excesses are cross-correlated to produce a list of candidate sources. In this paper, we will detail the algorithms of the scanner and the cross-correlator.

X-ray bursts from 4U 1608-52 and the associated low frequency noise

Three type I X-ray bursts and one burst candidate from 4U 1608-52 were observed with RXTE on March 22, 1996. Between the two strongest bursts, an enhanced noise component below 0.01 Hz was observed in the X-ray light curve with RXTE/PCA. It is probably caused by the subsequent time-dependent nuclear burning after the main X-ray burst. This supports the idea that there is a correlation between the Very-Low-Frequency-Noise (VLFN) in Low-Mass X-ray Binaries (LMXBs) and the nuclear burning. Assuming that the time scale of the variations is the time scale for one fire to ignite another, our result suggests the burning front was propagating at less than 3.0×104u2009cmu2009s−1 on the neutron star surface.