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[vsnet-campaign-xray 100] (fwd) MCQC J162847-4152 - a Possible Brightest Microquasar found
(fwd) MCQC J162847-4152 - a Possible Brightest Microquasar found
This message is from ATEL #80:
[Please use MCQC_J162847-4152 instead of the former designation J1628-41a
in future observation reports to vsnet-obs].
Title: MCQC J162847-4152 - a Possible Brightest Microquasar found
Author: G.S. Tsarevsky (ATNF, Sydney, & ASC, Moscow), N.S. Kardashev
(ASC), R.A. Stathakis (AAO, Sydney), O.B. Slee (ATNF), R. Ojha (ATNF)
Queries: Gregory.Tsarevsky@atnf.csiro.au
Posted: 11 Dec 2001; 10:19 UT
Subjects: Radio, Millimeter, Infra-Red, Optical, X-ray, Request for
Observations, Binaries, Black Holes, Neutron Stars, Transients, Variables,
Stars
MCQC J162847-4152 is one of 40 objects found in the course of our systematic
and complete survey for new microquasars in the whole Galactic plane (see
project description in <a href="http://arXiv.org/abs/astro-ph/0110511";>astro-ph/0110511</a>).
It is optically brightest and mostly definite microquasar candidate in
the list, which we describe as follows: 1) It is a bright ROSAT source,
1RXS J162848.1-415241, in the Galactic plane (b=4.7deg), with a hard X-ray
spectrum (HR1 = 1.00+/-0.04), which is characteristic of X-ray binaries
(Motch et al., AAS 132, 341, 1998). 2) It was detected at 4.8 and 8.6
GHz by the Australia Telescope Compact Array (ATCA) in October 2000 as
a ~7 mJy flat spectrum radio source with an unresolved core, but with
no conclusive evidence for the presence of a jet on an arcsec scale.
3) Using precision radio coordinates, MCQC J1628-4152 was identified
with a relatively bright star-like object as follows:
_________________________________________________________________
Source of data RA J2000 DEC J2000 r-o B V R
-----------------------------------------------------------------
USNO (PMM) 16h28m47s.267 -41o52'38".63 0".5 15.5 13.4 11.4
-----------------------------------------------------------------
V-magnitude is an averaged visual estimation by B. Monard (<a href="http://www.kusastro.kyoto-u.ac.jp/vsnet/etc/searchobs.html";>VSNET</a>).
Apparently large color-indices measured in different epochs may suggest
a possible strong source variability. 4) Low resolution spectroscopy
with 4-m (AAO) and 2.3-m (MSSSO) telescopes, showed MCQC J162847-4152
as a K5 spectrum star with a <a href="http://www.atnf.csiro.au/people/gtsarevs/J1628-41_Halpha.ps";>strong
and rapidly variable H-alpha emission</a>, i.e. consistent with a low
mass XRB (LMXB). 5) Our three observing sessions with the ATCA revealed
the following variability in flux density (RMS ~0.1 mJy, 4-sigma limit
of detection):
_____________________________________
Epoch of ATCA F_4.8 F_8.6 Spectral
observations [mJy] [mJy] Index
-------------------------------------
29.10.2000 7.2 6.6 -0.1
05.09.2001 8.8 12.3 +0.5
02.12.2001 <0.5 <0.4 -
-------------------------------------
It is evident from the table that the source shows a violent transient-
like radio activity. Significant variability on time scales of several
hours is also present. The above X-ray, optical and radio characteristics
are suggestive of microquasar behavior (which still is not well established
as there are only a few microquasars known, cf Mirabel and Rodriguez,
ARAA 37, 409, 1999). For all that, we cannot exclude the possibility that
the object is an active K-star. So we call for observations of MCQC
J162847-4152 in radio (flux monitoring and structure variability, preferably
by VLBI), optical spectroscopy (to find evidence for the object's binarity),
optical photometry (to monitor disc driven flare activity and evidence
for possible eclipse), and in X-rays (high spatial, spectral and time-resolved
observations by Chandra, XMM and RXTE may reveal the characteristic structure,
spectral features and flux variations found in the few established microquasars).
We have already sent out a call to <a href="http://www.kusastro.kyoto-u.ac.jp/vsnet/";>VSNET</a>
for photometric observations of this object.
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