Bachetti, Matteo3; Miyasaka, Hiromasa12; Harrison, Fiona12; Fürst, Felix12; Barret, Didier3; Bellm, Eric C.12; Boggs, Steven E.5; Chakrabarty, Deepto13; Chenevez, Jérôme1; Christensen, Finn Erland1; Craig, William W.5; Grefenstette, Brian W.12; Hailey, Charles J.14; Madsen, Kristin K.12; Natalucci, Lorenzo8; Pottschmidt, Katja9; Stern, Daniel12; Tomsick, John A.5; Walton, Dominic J.12; Wilms, Jörn10; Zhang, William15
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 Université de Toulouse4 California Institute of Technology5 University of California at Berkeley6 Massachusetts Institute of Technology7 Columbia University8 National Institute for Astrophysics9 University of Maryland10 Dr. Karl-Remeis-Sternwarte and Erlangen Center for Astroparticle Physics11 NASA Goddard Space Flight Center12 California Institute of Technology13 Massachusetts Institute of Technology14 Columbia University15 NASA Goddard Space Flight Center
The NuSTAR hard X-ray telescope observed the transient Be/X-ray binary GS 0834􀀀430 during its 2012 outburst. The source is detected between 3 – 79 keV with high statistical significance, and we were able to perform very accurate spectral and timing analysis. The phase-averaged spectrum is consistent with that observed in many other magnetized accreting pulsars. We fail to detect cyclotron resonance scattering features in either phase-averaged nor phase-resolved spectra that would allow us to constrain the pulsar’s magnetic field. We detect a pulse period of ∼ 12.29 s in all energy bands. The pulse profile can be modeled with a double Gaussian and shows a strong and smooth hard lag of up to 0.3 cycles in phase, or about 4s between the pulse at ∼ 3 and >∼ 30 keV. This is the first report of such a strong lag in high-mass X-ray binary (HMXB) pulsars. Previously reported lags have been significantly smaller in phase and restricted to low-energies (E<10 keV). We investigate the possible mechanisms that might produce such lags. We find the most likely explanation for this eect to be a complex beam geometry.
E P J Web of Conferences, 2014, Vol 64
Main Research Area:
International Conference on Physics at the Magnetospheric Boundary, 2014