On the peak radio and X-ray emission from neutron star and black hole candidate X-ray transients

We have compiled and analysed reports from the literature of (quasi-)simultaneous observations of X-ray transients at radio and X-ray wavelengths and compared them with each other and with more unusual radio-bright sources such as Cygnus X-3, GRS 1915+105 and Circinus X-1. There exists a significant (>97 per cent likelihood) positive (rank) correlation between the peak X-ray flux PX and radio flux density PR for the black hole candidate (BHC) systems, and a marginally significant positive (rank) correlation for the neutron star (NS) systems. This is further evidence for a coupling between accretion and outflows in X-ray binary systems, in this case implying a relation between peak disc-accretion rate and the number of synchrotron-emitting electrons ejected. However, we also show that the distribution of ‘radio loudness’, PR/PX, is significantly different for the two samples, in the sense that the BHCs generally have a higher PR/PX ratio. The origin of this discrepancy is uncertain, but probably reflects differences in the energetics and/or radiative efficiency of flows around the neutron stars and black holes; we briefly discuss some of these possibilities. Furthermore, the data for the two recently discovered ‘fast transients’ (FTs), XTE J0421+560/CI Cam and SAX J1819.3−2525/V4641 Sgr are entirely compatible with the distribution of BHCs. As at least three of the BHCs and both FTs have been directly resolved into mildly relativistic jets, it seems likely that such outflows are the origin of the radio emission in all BHC and FT transients, and probably also for the NS transients. We further note that the range of X-ray and radio fluxes observed from the unusual superluminal source GRS 1915+105 is also entirely compatible with the distribution for transients, implying that there is nothing special about the physics of jet formation in that system. We conclude that these data point to the formation of a mildly relativistic jet whose luminosity is a function of the accretion rate in the majority, if not all, X-ray transient outbursts, but whose relation to the observed X-ray emission is dependent on the nature of the accreting compact object.

[1]  P. Serlemitsos,et al.  Evidence for a 16.6 day period from Circinus X-1 , 1976 .

[2]  Yasuo Tanaka,et al.  ASCA Observations of Transient X-Ray Sources in Quiescence , 1998 .

[3]  R. Hjellming,et al.  Radio properties of X-ray binaries. , 1995 .

[4]  V. M. Lyuty,et al.  Orbital, precessional and flaring variability of Cygnus X-1 , 1999, astro-ph/9906365.

[5]  P. Groot,et al.  The 1997 hard state outburst of the X-ray transient GS 1354-64/BW Cir , 2001 .

[6]  Yasuo Tanaka,et al.  X-ray novae , 1996 .

[7]  K. Johnston,et al.  Correlation between X-Ray Intensity and Radio Outbursts of Cygnus X-3 , 1994 .

[8]  R. Fender.  Powerful jets from black hole X-ray binaries in low/hard X-ray states , 2000, astro-ph/0008447.

[9]  G. Skinner,et al.  X-ray outburst from the direction of the galactic centre , 1975, Nature.

[10]  Simon T. Garrington,et al.  Light Curves and Radio Structure of the 1999 September Transient Event in V4641 Sagittarii (=XTE J1819–254=SAX J1819.3–2525) , 2000 .

[11]  S. Holt,et al.  The 1979 X-ray outburst of Centaurus X-4 , 1980 .

[12]  R. M. Hjellming,et al.  Radio observations of the 1989 transient event in V404 Cygni (=GS 2023+338) , 1992 .

[13]  L. Stella,et al.  On the Bolometric Quiescent Luminosity and Luminosity Swing of Black Hole Candidate and Neutron Star Low-Mass X-Ray Transients , 2000, astro-ph/0005118.

[14]  D. Walsh,et al.  Transient radio source near the galactic centre , 1976, Nature.

[15]  W. Goss,et al.  Simultaneous radio and optical observations of Circinus X-1 , 1978 .

[16]  B. A. Harmon,et al.  Radio and X-Ray Observations of the 1998 Outburst of the Recurrent X-Ray Transient 4U 1630–47 , 1999 .

[17]  R. Fender,et al.  ASOCAM Observations of CYG X-3: Search for a Hot Stellar Wind , 1997 .

[18]  W. Lewin,et al.  On the Nature of XTE J0421+560/CI Camelopardalis , 1999, astro-ph/9907124.

[19]  E. Kuulkers.  A `superoutburst' in XTE J1118+480 , 2001, astro-ph/0102066.

[20]  G. Clark,et al.  Discovery of X-ray bursts from several sources near the galactic centre. , 1976 .

[21]  R. Blandford,et al.  Electromagnetic extraction of energy from Kerr black holes , 1977 .

[22]  S. Corbel,et al.  Quenching of the Radio Jet during the X-Ray High State of GX 339–4 , 1999, astro-ph/9905121.

[23]  G. Pooley,et al.  The variable radio emission from GRS 1915 + 105 , 1997, astro-ph/9708171.

[24]  I. Mirabel,et al.  A superluminal source in the Galaxy , 1994, Nature.

[25]  D. J. McKay,et al.  Radio and X-Ray Flaring Events in X-Ray Nova Ophiuchi 1993 , 1996 .

[26]  B. Stappers,et al.  Transient radio emission from SAX J1808.4-3658 , 1999, astro-ph/9907111.

[27]  C. B. Moore,et al.  The evolution of Rapid Burster outbursts , 1998, astro-ph/9807110.

[28]  R. P. Fender,et al.  MERLIN observations of relativistic ejections from GRS 1915+105 , 1998, astro-ph/9812150.

[29]  G. Skinner,et al.  No Eclipses in A1742-289 Archival Data , 1996 .

[30]  B. A. Harmon,et al.  The Dual Nature of Hard X-Ray Outbursts from the Superluminal X-Ray Transient Source GRO J1655–40 , 1996, astro-ph/9610212.

[31]  A. Zijlstra,et al.  A connection between the X-ray spectral branches and the radio brightness in GX17 + 2 , 1988, Nature.

[32]  Kristen Menou,et al.  Black Hole and Neutron Star Transients in Quiescence , 1998, astro-ph/9810323.

[33]  I. Mirabel,et al.  Sources of Relativistic Jets in the Galaxy , 1999, astro-ph/9902062.

[34]  R. P. Fender,et al.  Multiple ejections during the 1975 outburst of A0620-00 , 1999 .

[35]  A. Brinkman,et al.  Observations of the Transient X-ray Source at the Galactic Centre (A 1742 – 28) , 1976 .

[36]  Discovery of Correlated Behavior Between the Hard X-Ray and the Radio Bands in Cygnus X-3 , 1998, astro-ph/9810212.

[37]  Mario Livio,et al.  The Properties of X-Ray and Optical Light Curves of X-Ray Novae , 1997 .

[38]  F. Ghigo,et al.  An image of a highly relativistic jet from a large flare in the X-ray binary Cyg X-3 , 1998 .

[40]  K. Koyama,et al.  A New Eclipsing X-Ray Burster near the Galactic Center: A Quiescent State of the Old Transient A1742—289 , 1996 .

[41]  Sumner Starrfield,et al.  The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32 , 1994 .

[42]  K. Johnston,et al.  The Evolution of Outbursts in Cygnus X-3 at 2.25 and 8.3 GHz , 1995 .

[43]  F. A. Cordova,et al.  Transient radio emission from the X-ray nova ASM 2000+25 , 1988 .

[44]  Yasuo Tanaka,et al.  Black-Hole Binaries , 2001 .

[46]  M. Rupen,et al.  A One-sided Highly Relativistic Jet from Cygnus X-3 , 2001, astro-ph/0102018.