OSSE and RXTE Observations of GRS 1915+105: Evidence for Non-thermal Comptonization

GRS 1915+105 was observed by the CGRO/OSSE 9 times in 1995-2000, and 8 of those observations were simultaneous with those by RXTE. We present an analysis of all of the OSSE data and of two RXTE-OSSE spectra with the lowest and highest X-ray fluxes. The OSSE data show a power-law--like spectrum extending up to ~600 keV without any break. We interpret this emission as strong evidence for the presence of non-thermal electrons in the source. The broad-band spectra cannot be described by either thermal or bulk-motion Comptonization, whereas they are well described by Comptonization in hybrid thermal/ non-thermal plasmas.Comment: 4 pages in emulateapj5 style; Slightly modified version accepted to ApJ Letter

Quantum Electronics

Contains research objectives and summary of research for eight research projects split into three sections and a report on one research project.U. S. Air Force - Office of Scientific Research (Contract F44620-71-C-0051)Joint Services Electronics Program (Contract DAAB07-75-C-1346

Quantum Electronics

Contains research objectives and summary of research on eight research projects split into four sections.Joint Services Electronics Program (Contract DAAB07-76-C-1400)U. S. Air Force - Office of Scientific Research (Grant AFOSR-76-3042)U. S. Air Force - Office of Scientific Research (Contract F44620-76-C-0079

Quantum Electronics

Contains research objectives and summary of research on eight projects in three sections and reports on two research projects.U. S. Air Force - Office of Scientific Research (Contract F44620-71-C-0051)Joint Services Electronics Program (Contract DAAB07-74-C-0630)University of California, Livermore (Subcontract No. 7877409)U. S. Army Research Office - Durham (Contract DAHC04-72-C-0044

Interaction of Hawking radiation with static sources outside a Schwarzschild black hole

We show that the response rate of (i) a static source interacting with Hawking radiation of massless scalar field in Schwarzschild spacetime (with the Unruh vacuum) and that of (ii) a uniformly accelerated source with the same proper acceleration in Minkowski spacetime (with the Minkowski vacuum) are equal. We show that this equality will not hold if the Unruh vacuum is replaced by the Hartle-Hawking vacuum. It is verified that the source responds to the Hawking radiation near the horizon as if it were at rest in a thermal bath in Minkowski spacetime with the same temperature. It is also verified that the response rate in the Hartle-Hawking vacuum approaches that in Minkowski spacetime with the same temperature far away from the black hole. Finally, we compare our results with others in the literature.Comment: 18 pages (REVTEX

Quantum Electronics

Contains reports on three research projects.U. S. Air Force - Office of Scientific Research (Contract F44620-71-C-0051)Joint Services Electronics Program (Contract DAAB07-74-C-0630)University of California, Livermore (Subcontract 7877409

A Spectroscopic and Photometric Study of Short-Timescale Variability in NGC5548

Results of a ground-based optical monitoring campaign on NGC5548 in June 1998 are presented. The broad-band fluxes (U,B,V), and the spectrophotometric optical continuum flux F_lambda(5100 A) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha and Hbeta remained constant to within 5%. On June 22, a short continuum flare was detected in the broad band fluxes. It had an amplitude of about ~18% and it lasted only ~90 min. The broad band fluxes and the optical continuum F_lambda(5100 A) appear to vary simultaneously with the EUV variations. No reliable delay was detected for the broad optical emission lines in response to the EUVE variations. Narrow Hbeta emission features predicted as a signature of an accretion disk were not detected during this campaign. However, there is marginal evidence for a faint feature at lambda = 4962 A with FWHM=~6 A redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.Comment: 12 pages, 7 figures, accepted for publishing in A&

Quantum Electronics

Contains reports on three research projects.U. S. Air Force Office of Scientific Research (Contract F44620-71-C-0051)Joint Services Electronics Program (Contract DAAB07-71-C-0300)University of California, Livermore (Subcontract No. 7877409)U. S. Army Research Office - Durham (Contract DAHC04-72-C-0044

Study of the Largest Multiwavelength Campaign of the Microquasar GRS 1915+105

We present the results from a multiwavelength campaign of GRS 1915+105 performed from 2000 April 16 to 25. This is one of the largest coordinated set of observations ever performed for this source, covering the wide energy band in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1 keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the "plateau" (or low/hard) state but sometimes showed soft X-ray oscillations: before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were observed. The radio flares observed on April 17 shows frequency- dependent peak delay, consistent with an expansion of synchrotron-emitting region starting at the transition from the hard-dip to the soft-flare states in X-rays. On the other hand, infrared flares on April 20 appear to follow (or precede) the beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min. This implies that the infrared emitting region is located far from the black hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time variability. We find a good correlation between the quasi-steady flux level in the near-infrared band and in the X-ray band. From this we estimate that the reprocessing of X-rays, probably occurring in the outer parts of the accretion disk, accounts for about 20-30% of the observed K magnitude in the plateau state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The power-law slope above ~30 keV is found to be very similar between different states in spite of large flux variations in soft X-rays, implying that the electron energy distribution is not affected by the change of the state in the accretion disk.Comment: 31 pages, 11 figures. Accepted for publication in ApJ, vol. 571, 2002. Minor corrections. Figure 2 is revised (numbers on the top axis are corrected). References are update