SS 433 is a high-mass X-ray binary system (XRB) and one of the most persistent sources of relativistic jets in the Milky Way. The object has been intensively studied in radio at arcsecond scales, however the high-resolution observations (i.e. VLBI) are relatively scarce. In 2008 November the system was in outburst. Using the e-VLBI capabilities of the European VLBI Network (EVN) we observed SS 433 for three epochs during the active phase. The data offered a detailed view of the system’s behaviour in outburst at milliarcsecond scales. We used the “kinematic model" (which predicts the position along the jet of any knot ejected at some particular time in the past) to investigate the dynamic parameters of SS 433 and we examined the polarization properties of the ejected material. We report here the preliminary results

Fender, Rob

Garrett, Michael

Heald, George

Miller-Jones, James

Paragi, Zsolt

Rushton, A.

Soleri, Paolo

Spencer, R.

Trushkin, Sergei

Tudose, Valeriu

English

ZENODO

PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecondscaleValeriu Tudose∗1, Zsolt Paragi2,3, Rob Fender4, Mike Garrett1,5, James Miller-Jones6,Sergei Trushkin7, Anthony Rushton8, Ralph Spencer9, George Heald1, PaoloSoleri101Netherlands Institute for Radio Astronomy2Joint Institute for VLBI in Europe3MTA Research Group for Physical Geodesy and Geodynamics4University of Southampton5University of Leiden6Curtin Institute of Radio Astronomy7Special Astrophysical Observatory8European Southern Observatory9University of Manchester10University of GroningenE-mail: tudose@astron.nlSS 433 is a high-mass X-ray binary system (XRB) and one of the most persistent sources of rela-tivistic jets in the Milky Way. The object has been intensively studied in radio at arcsecond scales,however the high-resolution observations (i.e. VLBI) are relatively scarce. In 2008 November thesystem was in outburst. Using the e-VLBI capabilities of the European VLBI Network (EVN)we observed SS 433 for three epochs during the active phase. The data offered a detailed viewof the system’s behaviour in outburst at milliarcsecond scales. We used the “kinematic model”(which predicts the position along the jet of any knot ejected at some particular time in the past)to investigate the dynamic parameters of SS 433 and we examined the polarization properties ofthe ejected material. We report here the preliminary results.10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radioarraysSeptember 20-24, 2010Manchester UK∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecond scale Valeriu Tudose1. SS 433SS 433 is an X-ray binary system (XRB) comprising a compact object, likely a black hole[10, 20], accreting matter from a companion star of relatively high mass [4]. The XRB is locatedat a distance of 5.5 kpc [3] and has an orbital period of 13.1 days [5]. The object is embedded ina radio nebula, W50 [13, 6] and features a corkscrew-shaped double-sided radio jet on arcsecondscales (e.g. [22, 24, 16]). The radio jet is oriented close to the plane of the sky and is precessingwith a period of 162.5 days (e.g. [1, 11]). Extended X-ray emission (i.e. jets) has been alsoobserved [14, 15]. This emission is transient, oriented along the direction of the radio jets. Theexact connection between the radio and X-ray emissions is however still elusive [16].The radio jet has been extensively observed at arcsecond scales. Its derived geometrical pa-rameters are consistent with those obtained at other wavelengths: 78.8◦ inclination to the line ofsight, 19.8◦ opening angle of the precession cone, 0.26c jet speed [24]. The arcsecond scale ra-dio jet is linearly polarized. The fractional linear polarization ranges between 20–30%, with theexception of a region within about 0.5 arcsecond from the core, where the radiation is depolarized[18, 25, 16]. Circular polarization has also been detected at a level below 1% [9].Observations at milliarcsecond scales are relatively scarce (e.g. [21, 19, 8, 27, 17, 2]). At thesehigher resolutions, the apparently continuous structure of the jet seen at arcsecond scales is resolvedinto individual, compact radio emitting blobs. Also notable is the presence of an “equatorial wind”extending from the core in a plane perpendicular to the jets, as observed projected on the sky [17].2. ObservationsWe observed SS 433 at 5 GHz with the European VLBI Network (EVN) in real-time e-VLBImode on three occasions, 2008 November 6, 13, and 19, following an episode of major flaringactivity in the system [26]. Standard calibration was applied using AIPS and imaging was carriedout in Difmap. The resulting radio maps are presented in Fig. 1.3. The kinematic modelThe “kinematic model” of SS 433 is a geometric model for the precession (and nutation) of thejets in the system [1, 11]. Restricting the discussion to the radio wavelengths, basically it predictsthe positions along the jet of various blobs of matter that have been ejected at particular momentsin the past. The kinematic model has been tested extensively at arcsecond scales and on relativelyfewer occasions at milliarcsecond scales. The parameters of the model are remarkably stable overperiods of decades [7], although anomalies have been observed on a few occasions [19, 23, 12].We applied the model to the three e-VLBI epochs using the parameter values listed in Table1. We found that the precession of the jet alone can explain the general appearance of the system,however a significantly better match between the observations and the predictions of the modelis obtained when the nutation of the jet is also taken into account (Fig. 1). Considering that theparameters in Table 1 have been determined using lower spatial resolution data at radio frequenciesor data in the optical domain, the agreement between the model and the observations is notable.However, small discrepancies are present, as the kinematic model is an idealization. They could be2PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecond scale Valeriu TudoseTable 1: The precession and nodding parameters of the radio jet in SS 433 [24].Precession parameter Value Nodding parameter ValueInclination 78◦.83 5.8d Amplitude 0.00382Cone angle 19◦.85 5.8d Period 5.838 dPosition angle 98◦.2 5.8d Phase Reference MJD 43588.0Phase reference MJD 48615.5 6.3d Amplitude 0.00655Period 162.5 d 6.3d Period 6.290 dEjection velocity 0.2602c 6.3d Phase Reference MJD 43587.4explained for instance by variations in the ejection velocity of the blobs of matter (or decelerationdue to the interaction with the surrounding medium). Given the very limited time coverage of theobservations (representing a small fraction of the precession period) it is not possible to use thesedata to refine the parameters listed in Table 1, but an attempt at the study of the behaviour of theradio emitting regions will be undertaken. This is even more relevant as the blobs imaged duringthe three epochs are situated within and near the so called “brightening zone” [27], a still not fullyunderstood region where the flux densities of the individual blobs vary on timescales of days.4. Polarization at milliarcsecond scalesDespite a number of studies (e.g. [25, 16]), the polarization properties of SS 433 at arcsec-ond scales are not fully understood. The observations are contradictory and there is still a debatewhether the magnetic fields are preferentially oriented along the kinematic locus, or aligned withthe local velocity vectors. High spatial resolution observations cannot discriminate between thesetwo cases, but can offer information on the polarization properties close to the core of the system.These properties are virtually unknown at milliarcsecond scales. The only confident result seemsto be that the region within about 0.5 arcsec of the core is relatively depolarized (more severely atlower frequencies), perhaps due to the presence of a strong wind [18, 25, 16].We detected linear polarization of the order of a few percent (<5%) in the core of the system inat least one of the three epochs (work in progress). This would be the first time when polarization isdetected in SS 433 at such high spatial resolution (Fig. 2). What is to some extent puzzling is thatthe blobs separated from the core do not appear to be polarized (the 3σ upper limit to the linearlypolarized intensity is about 2 mJy/beam). Assuming these components expand adiabatically anddownstream in the jet interact with the surrounding medium, an ordered magnetic field shouldbe generated that produces linear polarization of the radio emission. Alternatively, if instead ofa fragmented, knotty structure, the jet of SS 433 is continuous, the bright knots are the result ofshocks propagating downstream, a process that also generates polarized radio emission. Takinginto account the low level of linear polarization present in the core and the fact that the individualknots are relatively less bright, one possible explanation for the lack of detection of polarizationis an insufficient signal to noise ratio (assuming implicitly that the degree of linear polarization isof the same order as in the core). This will be further investigated by analyzing the polarizationproperties of the other two epochs and comparing them with the partial results presented here.3PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecond scale Valeriu Tudose0 10 20DECLINATION (J2000)RIGHT ASCENSION (J2000)19 11 49.580 49.575 49.570 49.565 49.560 49.555 49.550 49.54504 58 57.9557.9057.8557.8057.7557.7057.650 10 20DECLINATION (J2000)RIGHT ASCENSION (J2000)19 11 49.580 49.575 49.570 49.565 49.560 49.555 49.550 49.54504 58 57.9557.9057.8557.8057.7557.7057.650 10 20DECLINATION (J2000)RIGHT ASCENSION (J2000)19 11 49.580 49.575 49.570 49.565 49.560 49.555 49.550 49.54504 58 57.9557.9057.8557.8057.7557.7057.652008 Nov 62008 Nov 132008 Nov 19Figure 1: 5 GHz e-EVN radio maps of SS 433. The contour levels are at -1, 1, 2, 4, 8, 16, 32, 64 timesthe average rms noise of 2.0 mJy/beam. The colour bars are expressed in mJy/beam. The images are atthe same scale. The slightly different spatial resolutions are due to different radiotelescopes present in thearrays. Overlaid are the predictions of the kinematic model when both the precession and nutation of the jetare taken into account. The red marks correspond to the locus of hypothetical blobs of matter ejected at oneday intervals.4PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecond scale Valeriu TudoseDECLINATION (J2000)RIGHT ASCENSION (J2000)19 11 49.580 49.575 49.570 49.565 49.560 49.555 49.550 49.54504 58 57.9557.9057.8557.8057.7557.7057.6557.600 5 10 15 20Figure 2: 5 GHZ e-EVN radio map of SS 433 from 2008 Nov 13 with the orientation of the electric vectorposition angles (EVPAs) superimposed. No galactic rotation measure correction and no PA calibration hasbeen applied. The colour code bar is expressed in mJy/beam and is associated to the total intensity map. Forthe polarization vectors 1 mas corresponds to 25 µJy/beam linearly polarized intensity.5. ConclusionsPreliminary analysis of 3 epochs of VLBI observations with the EVN of SS 433 during anoutburst revealed the behaviour of the system at infrequently probed high spatial resolutions. Wedetected linear polarization in the system for the first time at milliarcsecond scales, at levels of theorder of a few percent. The polarized emission is concentrated exclusively in the core, with nonebeing detected in the knots tens of milliarcsecond away. At the moment, one likely explanation isa lack of enough signal to noise ratio for a confident detection outside the core. A more in depthanalysis of the polarization properties is underway. We also tested the predictions of the kinematicmodel of the jet in SS 433 at milliarcsecond scales, where it has been relatively less well studied.We found that the model can explain the observations extremely well. However, discrepancies arepresent and the final analysis of the data might offer insights into the reasons behind them, possiblyruling out some of the explanations advanced based on lower spatial resolution data.Acknowledgmentse-VLBI developments in Europe are supported by NEXPReS, an Integrated Infrastructure Ini-tiative (I3), funded under the European Union Seventh Framework Programme (FP7/2007-2013)under grant agreement RI-261525. The European VLBI Network is a joint facility of European,Chinese, South African and other radio astronomy institutes funded by their national research coun-cils.References[1] Abell G.O., Margon B., 1979, Nature, 279, 701[2] Blundell K.M. et al., 2001, ApJ, 562, L79[3] Blundell K.M., Bowler M.G., 2004, ApJ, 616, L1595PoS(10th EVN Symposium)060An outburst of SS 433 observed on milliarcsecond scale Valeriu Tudose[4] Clark J.S., Barnes A.D., Charles P.A., 2007, MNRAS, 380, 263[5] Crampton D., Hutchings J.B., 1981, ApJ, 251, 604[6] Dubner G.M. et al., 1998, AJ, 116, 1842[7] Eikenberry S.S. et al., 2001, ApJ, 561, 1027[8] Fejes I., Schilizzi R.T., Vermeulen R.C., 1988, A&A, 189, 124[9] Fender R. et al., 2000, ApJ, 530, L29[10] Hillwig T.C., Gies D.R., 2008, ApJ, 676, L37[11] Hjellming R.M., Johnston K.J., 1981, ApJ, 246, L141[12] Jowett F.H., Spencer R.E., 1995, in Proc. 27th YERAC, D.A. Green & W. Steffen (eds.), p. 12[13] Margon B., 1984, ARA&A, 22, 507[14] Marshall H.L., Canizares C.R., Schulz N.S., 2002, ApJ, 564, 941[15] Migliari S., Fender R., Mendez M., 2002, Science, 297, 1673[16] Miller-Jones J.C.A. et al., 2008, ApJ, 682, 1141[17] Paragi Z. et al., 1999, A&A, 348, 910[18] Paragi Z. et al., 2004, in Proceedings of the 7th Symposium of the European VLBI Network, eds. R.Bachiller, F. Colomer, J.F. Desmurs and P. de Vicente, p. 221[19] Romney J.D. et al., 1987, ApJ, 321, 822[20] Seifina E., Titarchuk L., 2010, ApJ, 722, 586[21] Schilizzi R.T. et al., 1981, Nature, 290, 318[22] Spencer R.E. et al., 1984, MNRAS, 209, 869[23] Spencer R.E., Waggett P., 1984, IAUS, 110, 297[24] Stirling A.M. et al., 2002, MNRAS, 337, 657[25] Stirling A.M. et al., 2004, MNRAS, 354, 1239[26] Trushkin S.A., Nizhelskij N.N., 2008, ATel, 1819, 1[27] Vermeulen R.C. et al., 1993, A&A, 270, 1776

An outburst of SS 433 observed on milliarcsecond scale

https://zenodo.org/record/7031/files/10th%20EVN%20Symposium_060.pdf

An outburst of SS 433 observed on milliarcsecond scale

Abstract

Similar works

Full text

Available Versions

ZENODO