VLBA and VLA Observations of the Relativistic Radio Jets of GRO J1655-40

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Session 109 -- Extragalactic Radio Sources, Jets
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[109.15] VLBA and VLA Observations of the Relativistic Radio Jets of GRO J1655-40

R.~M.~ Hjellming and M.~P.~ Rupen (NRAO)

The X-ray transient GROJ 1655-40, which was first detected by BATSE/GRO on July 27, 1994, produced a radio source that peaked at a flux level of 5.5 Jy at 1.49 GHz on about Aug. 19. We report on the results of more than 30 epochs of observation of this radio source with the VLA at frequencies of 1.49, 4.9, 8.4, 14.9, and 22.5 GHz, and seven epochs of high resolution VLBA observations at 1.6, 2.3, and 5 GHz from Aug. 18 through Sept. 21. The VLA observations show radio light curves of a largely optically thin, synchrotron radiation source, which was briefly optically thick only during the initial portions of rise of the first large flare, and just before a secondary flare that peaked at 0.5 Jy on about Sept. 18. VLA images at the highest frequencies show that the source was resolved with a size scale of 0.2$''$ on Aug. 17, and thereafter expanded to a double, triple and quadruple radio source lined up along a position angle of 47$^\circ$. The initial component ejected NE of the core showed an average proper motion of 0.04$''$ per day, and in the middle of September a second component appeared moving at the same rate, or faster, in the same NE direction away from the core. A much weaker component ejected SW of the core had a poorly determined proper motion of about 0.02$''$ per day. If the distance is 3.5 kpc, based upon HI absorption reported by McKay and Kesteven (IAUC 6062), this corresponds to apparent transverse motion at 0.8c and 0.4c.

The VLBA observations of the transient event in GRO J1655-40 show the detailed structure of the fast ejecta to the NE and SW together with a rapidly changing, twin-jet corkscrew of radio emission emanating from the core. Variations in proper motions in the first NE ejecta are seen, with the outermost edge appearing to be superluminal. The core radio source has behavior which is qualitatively similar to SS433, however the observed outward motion is more relativistic, and there are significant changes in the direction of ejection in a few days.

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