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

We present the results from a multiwavelength campaign of GRS 1915+105performed from 2000 April 16 to 25. This is one of the largest coordinated setof observations ever performed for this source, covering the wide energy bandin radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1keV 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 wereobserved. The radio flares observed on April 17 shows frequency- dependent peakdelay, consistent with an expansion of synchrotron-emitting region starting atthe transition from the hard-dip to the soft-flare states in X-rays. On theother hand, infrared flares on April 20 appear to follow (or precede) thebeginning 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 blackhole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the timevariability. We find a good correlation between the quasi-steady flux level inthe near-infrared band and in the X-ray band. From this we estimate that thereprocessing of X-rays, probably occurring in the outer parts of the accretiondisk, accounts for about 20-30% of the observed K magnitude in the plateaustate. The OSSE spectrum in the 0.05-10 MeV band is represented by a singlepower law with a photon index of 3.1 extending to ~1 MeV with no cutoff. Thepower-law slope above ~30 keV is found to be very similar between differentstates in spite of large flux variations in soft X-rays, implying that theelectron energy distribution is not affected by the change of the state in theaccretion 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