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[vsolj-alert 438] XTE J1859+226 radio observation



XTE J1859+226 radio observation

 電波では GM Sgr 転じて V4641 Sgr よりも速く減光しているようですが、メイン
 イベントがこれから来るのではないかとの期待が持たれています。

Date: Sat, 16 Oct 1999 07:28:55 -0600
From: "Robert M. (Bob) Hjellming" <rhjellmi@aoc.nrao.edu>
Subject: XTE J1859+226

Collegues,

    My earlier worries about the radio counterpart of XTE J1859+226
not showing significant radio variations over the first three days
of observation have proven to be VERY premature.  On Oct. 11-14 it was 
just staying near the evolutionary turnover from an optically thick 
to an optically thin synchtron-radiation radio source.

    After being 9 mJy at 15 GHz for the VLA on Oct. 14.11 UT, Guy
Pooley found it to be 6 mJy for the Ryle Telescope on Oct. 14.64 UT, and
on Oct. 16.14 UT, it was 1.3 mJy for the VLA.  In addition the radio 
spectrum from 1.4 to 15 GHz on Oct. 16.14 UT was well fit by a nearly
optically thin spectrum of ~4.7 nuGHz^(-0.48) mJy.

    So the initial radio event for XTE J1859+226 may be decaying
even faster than did XTE J1819-254.  Since the last reports from Don Smith
on the X-ray source on Oct. 15 were of a source at ~0.7 Crab for the
RXTE ASM, and still rising linearly with time since beginning Oct. 9, it 
may be that this is a fast radio "precursor" event such have been (poorly) 
sampled in previous X-ray transients (V404 Cyg, N Mus 1991, GRO J1655-40), 
and the main radio activity may still be to come.  

Bob (for the radio + ... collaboration on XTE J1859+226)

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