X-ray binaries with ALMA in Q-band

1. X-ray binaries with ALMA in Q-band • Tom Maccarone (University of Southampton)‏

2. Classes of sources • Black hole X-ray binaries • Neutron star X-ray binaries • Focus on low B neutron stars • High B disrupts accretion disk and no jets are seen • White dwarf binaries • Focus here will be on black hole X-ray binaries Computer generated image of GRO J1655-40, made using Rob Hynes' visualization tool

3. ING archive/Nick Szymanek Russell et al. 2007 Stirling et al. 2001

4. The fundamental advantages of X-ray binaries over AGN for understanding black hole jets • Viscous timescale from inner disk in typical AGN is ~decades • Less than this from the outer edge of the disk in most XRBs • Many XRBs vary by 7 orders of magnitude in luminosity on years timescales • Allows flux-flux correlations to be useful • Sources are brighter than AGN in most wavebands, allowing high S/N detections • Comparing AGN with XRBs gives a much bigger lever arm on mass effects than AGN alone • Masses are also better measured • BHXRBs are close in mass to neutron stars, allowing for testing whether the BH itself is important or just the deep potential well

5. from Fender et al. 1999

6. Jet-disk coupling in the low/hard state • LR LX0.7 • In agreement with relatively simple models for jet production provided LX mdot2 • This L-mdot relation comes from ADAF models • Faint sources are flat spectrum, so frequency of observations doesn't matter • But also means higher frequency is closest to the black hole • Not clear why the high luminosity intermediate states lie on the extrapolation of this relation. • X-ray spectra and hence geometry is quite different • Radio emission for many data points in that region are for optically thin emission from Gallo, Fender & Pooley (2003)‏

7. Neutron star jets • Fainter than black holes when hard X-rays are strong • consistent with square of black hole relation, implying advection in black holes, but surface effects in neutron stars (Koerding et al. 2006)‏ • But still based on small number of points with relatively large uncertainties • Better sensitivity is essential for such faint objects • Brighter than black holes in soft states • not yet well understood, but maybe a boundary layer effect (e.g. Livio 1999; Maccarone 2009)? from Migliari & Fender 2006

8. Rapid variability From Hynes et al. 2009 From Gallo et al. 2006

9. Some open questions • What happens at very low radio luminosity? • Is there soft state emission from black hole X-ray binaries? • There is scatter in the L_X vs L_R relation. How much is due to: • Real physical scatter that requires complex explanations? • BH spin? • Variable relationships of magnetic field to equipartition (e.g. Pe'er & Casella 2009)‏ • Non-simultaneity of data (i.e. rapid variability)?‏ • Highest frequencies best for studying rapid variability • Would like to monitor over hours to days timescales in radio and X-rays

10. Quiescent black hole X-ray binaries • Important for understanding physics of accretion • Also useful for understanding black hole populations • Most black hole X-ray binaries spend most of their time in quiescence (i.e. LX ~ 1031-32 ergs/sec)‏ • Surveys of the Galactic Plane/GC region in radio combined with other wavelengths should allow a real population study of quiescent black hole X-ray binaries • Should be ~1000-10000 BH XRBs in the Galaxy (e.g. Romani 1992; Portegies Zwart et al. 1997)‏ • A survey for quiescent black hole X-ray binaries should produce a large enough sample to say something real about the mass distribution of black holes in binaries

11. Globular cluster black holes in the Galaxy 47 Tuc – X-ray from Heinke et al., FUV from Knigge et al. • Recent extragalactic globular cluster work shows good evidence for stellar mass black holes • None known in Milky Way clusters • BUT quiescent cataclysmic variables and qBHXBs look almost identical in optical/UV/X-rays • Radio emission at 5-10 Jy should be detectable from qBHXBs, but not from qDNe

12. Neutron star X-ray binaries • Is LR really prop. to Lx1.4? • Any correlation with rotation rate? • Do all neutron stars show soft state radio emission? • What causes this emission? • What are the spectral shapes for emission from low L neutron star accretors? • Does the BH analogy hold up for spectra? • Also, maybe worth another look at the high B neutron stars Migliari & Fender 2006

13. ALMA vs EVLA • Southern hemisphere a key advantage • Most X-ray binaries are in/near the Galactic Plane • Also opens up the LMC sources, which have known distances, a key problem for most current X-ray binary studies • Plus, the opportunity to go up to higher frequencies

14. ALMA vs ATCA • Big advantage for rapidly variable sources if multi-wavelength spectral energy distributions wanted • ALMA at the same longitude as the VLT, VLA • In some cases will allow nearly uninterrupted frequency coverage from 1 GHz to 10^21 Hz, with data taken nearly simultaneously • Not possible from Australia, especially for optically faint sources

15. Why Q-band? • Transient phenomena • Black hole X-ray binary outbursts typically happen 1-2 times per year • Don't want to be limited by weather during these outbursts • Larger field of view for cases of new X-ray transients, star clusters • Want some frequency overlap with the Compact Array • Will allow 24-hour coverage during outbursts

16. Conclusions • X-ray binaries probe interesting ranges of parameter space for jet physics • They are highly, rapidly variable phenomena. Flexible scheduling needed, and continuous coverage for days could produce interesting results • High frequency variability likely to be the fastest variability – high sensitivity, high frequency observations most likely to see the most interesting things • ALMA is in the best hemisphere for observing these sources, both in terms of latitude and longitude