Radio outburst of a probable microquaser MCQC J162847-4152

[vsnet-alert 7470]

In IAUC 7968, Rupen et al. (NRAO) reported that a strong (about 3-mJy) radio transient was detected by VLA on Sept. 9. The nominal position of this transient is R.A. = 16h28m47s.3, Decl. = -41o52'35" (2000.0, accuracy ~ a few arcsec), which agrees closely with the position of a probable microquaser 1RXS J162848.1-415241 = GSC 7861.1088. Urgent observations in any wavelength are highly urged.

Optical observations just before the radio outburst

Recent optical observation reports of this object ; 

MCQC_J162847-4152 recent (cont'd)

  YYYYMMDD(UT)   mag  observer
  20020606.741   136  (Berto Monard)
  20020608.794   135  (Berto Monard)
  20020614.710   135  (Berto Monard)
  20020628.766   135  (Berto Monard)
  20020629.746   135  (Berto Monard)
  20020711.733   135  (Berto Monard)
  20020713.737   135  (Berto Monard)
  20020727.722   135  (Berto Monard)
  20020805.801   135  (Berto Monard)
  20020901.757   134  (Berto Monard)

Past information

The discovery of this object by Tsarevsky et al. is described in [vsnet-campaign 1058] = [vsnet-campaign-xray 78] (2001 Aug. 3) and in [vsnet-campaign-xray 100, 101] (2001 Dec. 12) as follows:

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Date: Sat, 4 Aug 2001 08:47:44 +0900 (JST)
From: Taichi Kato
Subject: [vsnet-campaign 1058] (fwd) Microquasar candidate J1628-41: Call for observations

(fwd) Microquasar candidate J1628-41: Call for observations 

(Comment by T. Kato): The object has the following identifications:
GSC7861.1088 162847.30 -415239.0 (2000.0) 13.14 6
USNO0450.24415462 162847.294 -415238.76 (2000.0) 10.9 15.6
162848.0 -415240 (2000.0) 1RXS_J162848.1-415241 0.119 1.00 0.60

Date: Sat, 4 Aug 2001 01:24:54 +0400 (EEST)
From: "Gregory S. Tsarevsky"
Subject: [vsnet-alert 6183] Microquasar candidate J1628-41: Call for observations

Dear colleagues,

As you know microquasars are a very rare class of the X-ray binaries (XRB) showing relativistic radio jets closely resembling misterius jets from the extragalactic quasars/AGNs. Only a half of a dozen microquasars have been discovered up-to-date from the ~300 XRBs known (see comprehensive review by Mirabel and Rodriguez in Annual Review of Astronomy and Astrophysics, vol. 37, p. 409, 1999).

In the course of systematic search for new microquasars in the whole Galactic Plane, we have found a few tens of promising objects. One of them is a relatively bright microquasar candidate J1628-41a as follows:
-1) It is a bright ROSAT source in the Galactic Plane with a hard spectrum characteristic for the X-ray binaries (XRB).
-2) It was detected by the Australia Telescope Compact Array (ATCA) as a 7 mJy flat spectrum radio source with an unresolved core and some evidence of the jet.
-3) With precision radio coordinates, it was identified with a star-like object, which has the following USNO data:

     ===========================================================
      Name       RA_2000       DEC_2000    r-o"  Bmag  Rmag   
     -----------------------------------------------------------
      J1628-41a  16 28 47.267 -41 52 38.6  0.4   15.5  11.4
     ===========================================================
      (r-o" - the difference in the radio and optical positions)
Note:
Apparent color-index B-R=4.1 may suggest a possible strong source variability or/and large absorption in the source direction.

-4) Preliminary low resolution spectroscopy with the Anglo-Australian 4-m Telescope showed J1628-41a as a K5 spectrum object with a strong and variable H-alpha emission, i.e. possible low mass XRB (LMXRB).

We very much need help of the Southern VSNET community to start a multicolor photometry of our best microquasar candidate J1628-41a, to reveal its possible
- disc driven flare activity,
and
- eclipsing behavior with orbital period in a wide range say 0.1-20 d.

I would be happy to send a detailed description of the project to those VSNET colleagues who would like to participate in the observations requested.

Dr Elena Pavlenko from the Crimean Astroph. Observatory will report this in The Physics of Cataclismic Variables and Related Objects Conference to be held in Goetingen just next week, see
http://www.uni-sw.gwdg.de/CVConference/

A finding chart will be send by request.

On behalf of the international team of the project A Search for New Microquasars in X-ray, Radio and Optics,

Dr Gregory S. Tsarevsky 

 _____________________________________________________
 Australia Telescope National Facility, Sydney    ,    
 and Astro Space Centre, Moscow   	      ,--_|\   
                                             /      \   
 Tel: +612 9372 4260   Fax: +612 9372 4176   \_,--._#  
 http://www.atnf.csiro.au/people/gtsarevs/         v   
 -----------------------------------------------------

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Date: Wed, 12 Dec 2001 10:36:18 +0900 (JST)
From: Taichi Kato
Subject: [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 astro-ph/0110511). 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 (VSNET). 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 strong and rapidly variable H-alpha emission, 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 VSNET for photometric observations of this object.

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Date: Wed, 12 Dec 2001 11:08:13 +0900 (JST)
From: Taichi Kato
Subject: [vsnet-campaign-xray 101] (fwd) Re: MCQC J162847-4152 - a Possible Brightest Microquasar found

Date: Tue, 11 Dec 2001 19:06:37 -0700 (MST)
From: Brian Skiff

The best current position for this object is probably from UCAC1, which shows: 16 28 47.285 -41 52 39.00 (2000). Uncertainty is 8mas in RA and 11mas in Dec. The reported "orange" magnitude is 12.5. Note also that UCAC1 shows a proper motion of about 0".024/year, but the errors are of the same order, so the motion is not significant.

\Brian

---

Sincerely,
Hitoshi Yamaoka

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