X-ray to radio observations of SS 433 following the bright optical flare

ATel #6364; Sokolovsky K. V. (ASC Lebedev/SAI MSU), Goranskij V. P. (SAI MSU), Trushkin S. A., Fabrika S. N. (Special Astrophysical Observatory), Mescheryakov A. V. (IKI)
on 2 Aug 2014; 20:44 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

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Swift observations of the microquasar SS 433 were performed on 2014 July 28.65 UT following the extreme optical outburst on July 26 (ATel #6347, ATel #6355). Swift/XRT operating in the Windowed Timing mode for 2ks has detected SS 433 with the net count rate of 1.65 +/-0.03 counts/sec. The 0.3-10.0 keV spectrum can be described by two models equally well: 1) an absorbed power law with the photon index of 1.15 +/-0.11 and HI column density of (0.36 +/-0.08)x10^22 cm^-2; 2) a thermal bremsstrahlung spectrum with kT>80 keV absorbed by the HI column of (0.38 +/-0.05)x10^22 cm^-2. The best-fit HI column density in both models is consistent with the total Galactic value of 0.416x10^22 cm^-2 in the direction of SS 433 (Kalberla et al. 2005, A&A, 440, 775). We find no signs of additional absorption observed earlier by Brinkmann et al. (2005 A&A, 431, 575) and Medvedev & Fabrika (2010 MNRAS, 402, 479). The integrated 0.3-10.0 keV flux for both models is about 1.0x10^-10 ergs/cm^2/s which is 60% higher than the value observed by Swift/XRT in October 2012 (ATel #4490) after the prominent radio flare (ATel #4484), but a factor of two lower than the highest fluxes observed in 2005-2007 (see the monitoring page by A. Falcone and M. Stroh at http://www.swift.psu.edu/monitoring/source.php?source=SS433 ).

Swift/UVOT, observing simultaneously with the XRT, detected SS 433 in all bands except M2:

Band  mag  err  
W2   19.88 0.22  
M2  >19.43  
W1   18.78 0.14  
 U   17.69 0.09  
 B   16.43 0.04  
 V   14.51 0.03  
(Vega system). 

The optical fluxes are just above the typical values for this combination of orbital (0.107) and precession (0.330) phases (Goranskij 2011, PZ, 31, 5). Continuing optical monitoring (ATel #6347) indicates that the brightness of SS433 in the red band remained increased immediately after the flare but returned to quiescent level on August 1 ( http://vgoray.front.ru/SS433/ss433-1aug.gif ).

The optical flare occurred on the declining phase of a radio flare that peaked on July 23 at the 4.8 GHz flux density of 930 +/-30 mJy according to the long-term RATAN-600 multifrequency monitoring campaign observations (see the radio lightcurve at http://www.sao.ru/hq/lran/XB/SS433/ss433_lc_2014jul.png ). At frequencies below 22 GHz the flare is decaying exponentially as S ~ exp(-t/[10d]). The July 23 flare is preceded by another flare of similar shape peaking on July 18 at 840 +/-25 mJy (4.8 GHz). The cm-band fluxes were still above the quiescence level at the time of the Swift observations.

We thank the Swift PI Neil Gehrels and the mission operations team for performing these ToO observations.