MERLIN observations of relativistic ejections from GRS 1915+105

Abstract

We present high resolution MERLIN radio images of multiple relativistic ejections from GRS 1915+105 in 1997 October / November. The observations were made at a time of complex radio behaviour, corresponding to multiple optically-thin outbursts and several days of rapid radio flux oscillations. The radio imaging resolved four major ejection events from the system. As previously reported from earlier VLA observations of the source, we observe apparent superluminal motions resulting from intrinsically relativistic motions of the ejecta. However, our measured proper motions are significantly greater than those observed on larger angular scales with the VLA. Under the assumption of an intrinsically symmetric ejection, we can place an upper limit on the distance to GRS 1915+105 of 11.2 +/- 0.8 kpc. Solutions for the velocities unambiguously require a higher intrinsic speed by about 0.1c than that derived from the earlier VLA observations, whilst the angle to the line-of-sight is not found to be significantly different. At a distance of 11 kpc, we obtain solutions of v = 0.98 (-0.05,+0.02)c and theta = 66 +/- 2 degrees. The jet also appears to be curved on a scale which corresponds to a period of around 7 days. We observe significant evolution of the linear polarisation of the approaching component, with large rotations in position angle and a general decrease in fractional polarisation. The power input into the formation of the jet is very large, >10^38 erg/s at 11 kpc for a pair plasma. If the plasma contains a cold proton for each electron, then the mass outflow rate, >10^18 g/sec is comparable to inflow rates previously derived from X-ray spectral fits.Comment: 14 pages, 7 figures. Accepted for publication in MNRA

Evidence for local mass accretion rate variations in the disc of GRS 1915+105

“…Time-resolved evolution of the spectral parameters from the analysis of an RXTE orbit of the observation 20402-01-44-00. From top to bottom: 2-60 keV light curve (5 PCUs); power law spectral index Γ; inner disc temperature (kT in in keV); inner disc radius (R in in km); 3-25 keV luminosity of the power law component P 38 in units of 10 38 erg/s; bolometric luminosity of the disc component D 38 (in units of 10 38 erg/s) calculated using a distance of 11 kpc and a disc inclination of 66 • (Fender et al 1999). Typical 90% error bars are shown for a few points.…”

Multi-wavelength environment of the Galactic globular cluster Terzan 5

“…Another contribution to the high-energy emission may come from stellar binaries consisting of a normal star and a compact object, accelerating particles to the required energies possibly via non-thermal radio-emitting plasma ejections (described e.g. in Fender et al 1999). Due to its high core density favourable to dynamical interactions between stellar objects, Terzan 5 is expected to contain many binary systems (e.g.…”

A powerful bursting radio source towards the Galactic Centre

“…We next consider the possibility that the bursts from GCRT J1745−3009 could be relativistically beamed toward us as is the case for microquasars, which are accreting black holes in binary systems that occasionally power radio-bright relativistic jets (e.g., GRS 1915+105, whose apparent superluminal motion has a Lorentz factor of γ ∼ 5) 26,27 . While it is conceivable that relativistic beaming is responsible for the high calculated brightness temperature, the light curve of GCRT J1745−3009 does not resemble that for known microquasars or other sources of jet emission, most of which exhibit a fast rise and a slower decay and much longer time scales 3 .…”