4 Accreting Millisecond X-ray Pulsars
197
XMM-Newton, Chandra and Swift. Long-term monitoring of future AMXP outbursts will allow measurement of long-term spin and orbital behaviour, something
that has at present only been done for four systems. Increased collecting area will
increase sensitivity to pulsations by orders of magnitude, leading (we hope) to the
discovery of sub-millisecond pulsars or strengthening the 730 Hz spin distribution
cutoff. In the former case this would place very tight constraints on the EoS of ultradense matter. Modeling of high signal to noise pulse profiles will reveal the subtle
features imparted by strong gravity, enabling us to measure the NS compactness.
We will be able to test models for kHz QPOs and burst oscillations with sufficient
precision that we can finally determine the underpinning mechanism.
Of the many open problems, there are several that stand out. One big mystery is
why do so very few LMXBs show pulsations? If magnetic field evolution and decay
is involved, we may finally be able to understand the origin and the evolution of
nature’s strongest magnetic fields. What happens when accretion takes place during
an outburst? Why we do not detect the effect of accretion torques in some AMXPs,
contrary to expectations ? Are gravitational waves involved as a braking mechanism
that counteracts the effect of accretion or are we again missing some fundamental
ingredient? When do accreting pulsar switch on as radio pulsars ? Are all AMXPs
turning on as radio millisecond pulsars during quiescence ? What is the relation
between AMXPs and the radio pulsar “black-widows” and “red-backs” ? We look
forward to discovering the answers to these questions in the years ahead.
Acknowledgments We would like to thank C. Heinke, J. Poutanen, R. Lovelace, M. Linares, T.
Tauris, D. Altamirano, B. Haskell, P. D’Avanzo, D. Bhattacharya, J. Hessels, C. D’Angelo and N.
Masetti for providing useful comments and suggestions. We acknowledge support from two NWO
Vidi fellowships.
References
1. M.A. Alpar, A.F. Cheng, M.A. Ruderman, J. Shaham, Nature, 300, 728 (1982)
2. D. Altamirano, P. Casella, A. Patruno, R. Wijnands, M. van der Klis, Astrophys. J. Lett. 674,
L45 (2008)
3. D. Altamirano, A. Patruno, C.O. Heinke, C. Markwardt, T.E. Strohmayer, M. Linares,
R. Wijnands, M. van der Klis, J.H. Swank, Astrophys. J. Lett. 712, L58 (2010)
4. D. Altamirano, A. Watts, M. Linares, C.B. Markwardt, T. Strohmayer, A. Patruno, Mon. Not.
R. Astron. Soc. 409, 1136 (2010)
5. D. Altamirano, R. Wijnands, M. van der Klis, A. Patruno, A. Watts, M. Armas Padilla,
Y. Cavecchi, N. Degenaar, M. Kalamkar, R. Kaur, Y.J. Yang, P. Casella, M. Linares, P. Soleri,
N. Rea, Astron. Tel. 2565, 1 (2010)
6. D. Altamirano, Y. Cavecchi, A. Patruno, A. Watts, M. Linares, N. Degenaar, M. Kalamkar,
M. van der Klis, N. Rea, P. Casella, M. Armas Padilla, R. Kaur, Y.J. Yang, P. Soleri,
R. Wijnands, Astrophys. J. Lett. 727, L18 (2011)
7. N. Andersson, K. Glampedakis, B. Haskell, A.L. Watts, Mon. Not. R. Astron. Soc. 361, 1153
(2005)
8. M. Annala, J. Poutanen, Astron. Astrophys. 520, A76 (2010)
197
XMM-Newton, Chandra and Swift. Long-term monitoring of future AMXP outbursts will allow measurement of long-term spin and orbital behaviour, something
that has at present only been done for four systems. Increased collecting area will
increase sensitivity to pulsations by orders of magnitude, leading (we hope) to the
discovery of sub-millisecond pulsars or strengthening the 730 Hz spin distribution
cutoff. In the former case this would place very tight constraints on the EoS of ultradense matter. Modeling of high signal to noise pulse profiles will reveal the subtle
features imparted by strong gravity, enabling us to measure the NS compactness.
We will be able to test models for kHz QPOs and burst oscillations with sufficient
precision that we can finally determine the underpinning mechanism.
Of the many open problems, there are several that stand out. One big mystery is
why do so very few LMXBs show pulsations? If magnetic field evolution and decay
is involved, we may finally be able to understand the origin and the evolution of
nature’s strongest magnetic fields. What happens when accretion takes place during
an outburst? Why we do not detect the effect of accretion torques in some AMXPs,
contrary to expectations ? Are gravitational waves involved as a braking mechanism
that counteracts the effect of accretion or are we again missing some fundamental
ingredient? When do accreting pulsar switch on as radio pulsars ? Are all AMXPs
turning on as radio millisecond pulsars during quiescence ? What is the relation
between AMXPs and the radio pulsar “black-widows” and “red-backs” ? We look
forward to discovering the answers to these questions in the years ahead.
Acknowledgments We would like to thank C. Heinke, J. Poutanen, R. Lovelace, M. Linares, T.
Tauris, D. Altamirano, B. Haskell, P. D’Avanzo, D. Bhattacharya, J. Hessels, C. D’Angelo and N.
Masetti for providing useful comments and suggestions. We acknowledge support from two NWO
Vidi fellowships.
References
1. M.A. Alpar, A.F. Cheng, M.A. Ruderman, J. Shaham, Nature, 300, 728 (1982)
2. D. Altamirano, P. Casella, A. Patruno, R. Wijnands, M. van der Klis, Astrophys. J. Lett. 674,
L45 (2008)
3. D. Altamirano, A. Patruno, C.O. Heinke, C. Markwardt, T.E. Strohmayer, M. Linares,
R. Wijnands, M. van der Klis, J.H. Swank, Astrophys. J. Lett. 712, L58 (2010)
4. D. Altamirano, A. Watts, M. Linares, C.B. Markwardt, T. Strohmayer, A. Patruno, Mon. Not.
R. Astron. Soc. 409, 1136 (2010)
5. D. Altamirano, R. Wijnands, M. van der Klis, A. Patruno, A. Watts, M. Armas Padilla,
Y. Cavecchi, N. Degenaar, M. Kalamkar, R. Kaur, Y.J. Yang, P. Casella, M. Linares, P. Soleri,
N. Rea, Astron. Tel. 2565, 1 (2010)
6. D. Altamirano, Y. Cavecchi, A. Patruno, A. Watts, M. Linares, N. Degenaar, M. Kalamkar,
M. van der Klis, N. Rea, P. Casella, M. Armas Padilla, R. Kaur, Y.J. Yang, P. Soleri,
R. Wijnands, Astrophys. J. Lett. 727, L18 (2011)
7. N. Andersson, K. Glampedakis, B. Haskell, A.L. Watts, Mon. Not. R. Astron. Soc. 361, 1153
(2005)
8. M. Annala, J. Poutanen, Astron. Astrophys. 520, A76 (2010)