Simultaneous VLBI/GMRT/RXTE observation of SS433

Astronomy & Astrophysics, Jul 2006

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 ) and when the orbital phase ϕ of its companion was nearly zero (inferior conjunction) and compare this with the result obtained when (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  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  with respect to the previous day, and the intensity went up by about on the next day. The X-ray intensity is about one-third 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.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://www.aanda.org/articles/aa/pdf/2006/27/aa4676-05.pdf

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)


This is a preview of a remote PDF: https://www.aanda.org/articles/aa/pdf/2006/27/aa4676-05.pdf

S. K. Chakrabarti, S. Pal, A. Nandi. Simultaneous VLBI/GMRT/RXTE observation of SS433, Astronomy & Astrophysics, 2006, pp. 965-968, Volume 453, Issue 3, DOI: 10.1051/0004-6361:20054676