Simultaneous VLBI/GMRT/RXTE observation of SS433
A&A
Astronomy & Astrophysics
S. K. Chakrabarti 0 1
S. Pal 0
A. Nandi 0
0 Centre for Space Physics , Chalantika 43, Garia Station Rd. Garia, Kolkata 700084 , India
1 S.N. Bose National Centre for Basic Sciences , JD Block, Salt Lake, Sector III, Kolkata 700098 , India
Aims. Our aim in this paper is to discover the spectral characteristics of the enigmatic compact object SS433 during a very rare occasion when the blue jet was pointing towards us (the precessional phase ψ = 0) and when the orbital phase φ of its companion was nearly zero (inferior conjunction) and compare this with the result obtained when φ ∼ 0.5 (superior conjunction). Methods. We employed the Giant Meter Radio Telescope (GMRT) for the photometric observation at 1280 MHz, European VLBI Network (EVN) for photometry and imaging at 4990 MHz, and the Rossi X-ray Timing Explorer (RXTE) for photometry and spectrum at 3−25 keV. Results. At this opportune moment, the companion totally blocked the disk and the base of the jet, the X-ray intensity was reduced by 20% with respect to the previous day, and the intensity went up by about 65% on the next day. The X-ray intensity is about onethird compared to RXTE results obtained during the superior conjunction on 13 March 2004. By taking the difference in the spectra, we obtained the spectrum of the system core including the contribution from any accretion shock that may have occurred during interaction between the accreting stream and the disk. The EVN observation clearly showed the separation of a radio blob, so using an adiabatic expansion model we estimate when the blob might have been separated. Conclusions. We see a clear dependence of X-ray intensity emitted from the base of the jet on the photon energy. We find that the core is much brighter in hard X-rays. The conjunction seems to have had no effect on the radio data.
accretion; accretion disks - stars; binaries; eclipsing - stars; winds; outflows - radio continuum; stars - X-rays; stars - methods; observational
1. Introduction
A large number of multiwavelength campaigns on SS433
(e.g.,
Neizvestnyj et al. 1980; Ciatti et al. 1981; Seaquist et al. 1982;
Vermeulen et al. 1993; Band & Gordon 1989; and Kotani et al.
1999; Revnivtsev et al. 2004; Chakrabarti et al. 2005)
have been
conducted so far and they have yielded very important results on
many detailed characteristics of this enigmatic object. However,
because of very large extinction, it has become impossible to
decipher the true nature of this compact object and its companion.
It is still not clear what causes the precession and nutation of the
disk and the blobby but continuous jet that comes out of it at a
nearly constant speed of 0.26 times the velocity of light. Because
of these difficulties, one has to plan observations of the object for
when it is in a special configuration at which some of the effects
can be ignored while others are enhanced.
In this work, we present the results of SS433 in a very
special time slot, when the blue-shifted jet is pointing directly
towards us (ψ = 0), while the companion is directly blocking the
disk and the base of the jet (φ = 0, inferior conjunction). This
opportune moment happened on 24 August 2004, at 7:12 UT
when the precessional phase ψ and the orbital phase φ of SS433
were nearly zero. Our observation is around this time frame
from August 23 till August 28, 2004. We present results from
the Giant Meter Radio Telescope (GMRT) for a 1.28 GHz
observation, the European VLBI Network (EVN) for a 4.99 GHz
observation, and the RXTE satellite for a 3−30 keV
observation. Some preliminary analysis of our results was presented in
Paragi et al. (2005)
. We also present the spectrum at the superior
conjunction (φ = 0.5) that occurred on March 13, 2004, while
the jet was pointing towards us (ψ = 0) and compare it with
the one taken at the inferior conjunction, thereby obtaining the
spectrum of the disk and the core of the jet.
In the next section, we briefly describe of the instruments
used in our campaign and in Sect. 3, we present the major results
and our interpretations of these results. Finally, in Sect. 4, we
make concluding remarks.
2. Instruments used in the multiwavelength campaign
The observations of SS433 by EVN are organised at 4.99 GHz
on 23, 25, and 27 August 2004, outside the EVN observing
sessions. Participating telescopes were Urumqi, Torun, Onsala,
Noto, Westerbork, Effelsberg, Shanghai, and Medicina (5 of
these telescopes at any single epoch). The recording rate was
256 Mbit/s, which resulted in 4 × 8 MHz channels in both left
and right circular polarization. SS433 was observed for 4 h per
epoch, and the data were correlated at JIVE. The NRAO AIPS
package was used for post-processing
(e.g. Diamond 1995)
.
Imaging was carried out in Difmap
(Shepherd 1997)
. The rms
noise levels achieved were 50−100 microJy/beam, about what
was expected with both our limited array and the short
observing time available.
The GMRT observations wer (...truncated)