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[vsolj-alert 416] GM Sgr radio jet?



GM Sgr radio jet?

 GM Sgrに付随する電波源が分解されつつある兆候がみられているそうです。
 CI Camの時のようにジェットが生成されているのでしょうか。

From rhjellmi@zia.aoc.NRAO.EDU Wed Sep 22 01:55 JST 1999
Date: Tue, 21 Sep 1999 10:52:53 -0600
To: dasmith@space.mit.edu, michiel@astro.uva.nl, rpf@astro.uva.nl,
        rudy@space.mit.edu, gehrels@lheavx.gsfc.nasa.gov,
        giommi@napa.sdc.asi.it, jeanz@purple.sron.ruu.nl,
        jem@head-cfa.harvard.edu, lewin@space.mit.edu,
        rhjellmi@zia.aoc.NRAO.EDU, rr@space.mit.edu,
        shrader@grossc.gsfc.nasa.gov, stroh@pcasun1.gsfc.nasa.gov,
        swank@pcasun1.gsfc.nasa.gov, xteplan@xgo2.nascom.nasa.gov,
        bmg@space.mit.edu, tkato@kusastro.kyoto-u.ac.jp,
        HARMON@SSLMOR.msfc.nasa.gov, chaswell@star.cpes.susx.ac.uk,
        ehm@space.mit.edu, Jeno Sokoloski <jeno@astron.berkeley.edu>,
        gmarcy@etoile.berkeley.edu, Michael.McCollough@msfc.nasa.gov,
        Phil Charles <p.charles1@physics.oxford.ac.uk>,
        Paul Roche <paulr@nssc.co.uk>, eiken@astrosun.tn.cornell.edu,
        Shri Kulkarni <srk@astro.caltech.edu>,
        luisfr@astrosmo.unam.mx (Luis F. Rodriguez ),
        tavani@astro.columbia.edu, RHjellmi@zia.aoc.NRAO.EDU,
        ewaltman@rsd.nrl.navy.mil, fghigo@cv3.cv.nrao.edu, rmw@as.arizona.edu,
        mrupen@zia.aoc.NRAO.EDU, amiodusz@zia.aoc.NRAO.EDU
From: "Robert M. (Bob) Hjellming" <rhjellmi@aoc.nrao.edu>
Subject: The GM Sgr radio source

Collegues,

    This is an update on the VLA/VLBA/GBIradio work on GM Sgr.  We are
sending this to ensure appropriate attention to this "super" X-ray
transient.  

    VLA observations were made on Sept. 16.02, Sep. 16.94, and Sep. 17.93.
During that time the radio source decayed by roughly a factor of four
each day.  It was caught by the GBI Sep. 15.997 at 0.3 Jy and was much weaker
a couple of days later and thereafter.  The VLA and GBI data indicate
it was initially slightly optically thick, with the decay just mentioned
occuring as soon as the source became optically thick.

    The radio source is definitely resolved Sept. 16.02 and Sep. 17.93.  It
may also be resolved on the day in between but that has not yet been
determined one way
or another; the data were not taken under as ideal circumstances as  Sept.
16.02
17.93.  On Sept. 16.02 UT it was resolved at 6 and 2cm, with 
the former indicating weak components 0.3" N and 0.3" south of the
arcseconds part of
the declination 25.6" (IAUC 7254) for GM Sgr.  Extensions in the same
directions
are seen in the 14.9 GHZ data at the same time.  The position of
USNO0600.16547317 is
J2000 18 19 21.64, -25 24 25.7.  On Sept. 17.93 we did VLA observations
at 1.49, 4.9, 8.4, and 14.9 GHz, the latter done with fast switching
between GM Sgr and a calibrator 22' away.  The 14.9 GHz image with 0.14" HPBW
resolution shows a double radio source with a roughly N-S orientation: a 
centroid) 
and a ~9 mJy component at declination 25.85 (about where the southerly
extension
on Sept. 16.02 was located).

   VLBA observations were made Sept. ~18.0 and ~20.0, and there will be
another
be correlated.

   Since the total flux at 14.9 GHz is slightly higher than at 8.4 GHz on
Sept. 17.93 it seems as if the component at 25.85" may be somewhat optically
thick, and may be a "brightening" region such as seen in the superluminal
XTE J1748-288.  

   We are reducing the 21 cm line data on Sept. ~18.0 to get try to get
a distance estimate.  We have not yet found any distance estimates for
GM SGr; if you know of any please let us know.  If one assumes that
the radio extension of 0.3" started one day earlier, the ball park of
apparent velocity is 1.7c*dkpc, where dkpc is the distance in kiloparsecs.
This gives us the feeling that, just as some have said related to the
very high X-ray peak, the distance of this system may turn out to be
nearby, perhaps 0.3-0.5 kpc.

   Careful astrometry and optical spectroscopy of this system is
highly desirable because of the question of what is moving with respect
to what, and the possibility of a "brightening" region due to interaction
of moving plasma with external matter.


Bob Hjellming, Michael Rupen, Amy Mioduszewski

   

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