We test different X-ray spectrum models to find the one that best represents the observed Rossi X-ray Timing Explore/Proportional Counter Array (RXTE/ PCA) spectra of Her X-1 during Main High state (MH). We then apply this model to MH observations taken over the lifetime of RXTE. From the results, we obtain patterns in the spectral parameters vs. 35-day phase during MH. The precessing-disc occultation model explains the 35-day cycle by changes in observer view of the emission regions by the accretion disc 35-day precession. Qualitatively, we find that this model can describe the main spectral changes. However, several spectral parameters show detailed changes that the models have not addressed yet. These changes will likely require modifications to the basic precessing-disc model for the 35-day cycle.
References
[1]
Wang, Y. and Leahy, D. (2022) The Evolution of the Orbital Lightcurve of Hercules X-1 with 35 Day Phase. The Astrophysical Journal, 927, Article No. 143. https://doi.org/10.3847/1538-4357/ac496f
[2]
Leahy, D. and Wang, Y. (2021) The 35-Day Cycle of Hercules X-1 in Multiple Energy Bands from MAXI and Swift/BAT Monitoring. Universe, 7, 60. https://doi.org/10.3390/universe7060160
[3]
Scott, D., et al. (2000) The 35 Day Evolution of the Hercules X-1 Pulse Profile: Evidence for a Resolved Inner Disk Occultation of the Neutron Star. The Astrophysical Journal, 539, 392-412. https://doi.org/10.1086/309203
[4]
Scott, D.M. and Leahy, D.A. (1999) Rossi X-Ray Timing Explorer All-Sky Monitor Observations of the 35 Day Cycle of Hercules X-1. The Astrophysical Journal, 510, 974-985. https://doi.org/10.1086/306631
[5]
Parmar, A.N., Pietsch, W., McKechnie, S., et al. (1995) An Extended X-Ray Low State from Hercules X-1. Nature, 313, 119-121. https://doi.org/10.1038/313119a0
[6]
Leahy, D.A. (2004) Mass-Radius from a Pulse Shape Model for Hercules X-1. The Astrophysical Journal, 613, 517-521. https://doi.org/10.1086/422905
[7]
McCray, R.A., Shull, J.M., Boynton, P.E., et al. (1982) Einstein Observatory Pulse-Phase Spectroscopy of HER X-1. Astrophysical Journal, 262, 301-307. https://doi.org/10.1086/160421
[8]
Leahy, D.A. (2002) Modelling RXTE/ASM Observations of the 35-d Cycle in Her X-1. Monthly Notices of the Royal Astronomical Society, 334, 847-854. https://doi.org/10.1046/j.1365-8711.2002.05547.x
[9]
Leahy, D.A. and Marshall, H. (1999) Extreme-Ultraviolet Explorer Observations of Hercules X-1 at the End of the Short High State. The Astrophysical Journal, 521, 328-331. https://doi.org/10.1086/307540
[10]
Leahy, D.A. (2015) Hercules X-1: Using Eclipse to Measure the X-Ray Corona. The Astrophysical Journal, 800, Article No. 32. https://doi.org/10.1088/0004-637X/800/1/32
[11]
Bradt, H.V.D. and McClintock, J.E. (1983) The Optical Counterparts of Compact Discrete Galactic X-Ray Sources. Annual Review of Astronomy and Astrophysics, 21, 13-66. https://doi.org/10.1146/annurev.aa.21.090183.000305
[12]
Jahoda, K., Swank, J.H. and Giles, A.B. (1996) In-Orbit Performance and Calibration of the Rossi X-Ray Timing Explorer (RXTE) Proportional Counter Array (PCA). Proceedings of SPIE, 2808, 59-70. https://doi.org/10.1117/12.256034
[13]
Jahoda, K., Markwardt, C.B., Radeva, Y., et al. (2006) Calibration of the Rossi X-Ray Timing Explorer Proportional Counter Array. The Astrophysical Journal Supplement Series, 163, 401-423. https://doi.org/10.1086/500659
[14]
Staubert, R., Klochkov, D. and Wilms, J. (2009) Updating the Orbital Ephemeris of Hercules X-1; Rate of Decay and Eccentricity of the Orbit. Astronomy and Astrophysics, 500, 883-889. https://doi.org/10.1051/0004-6361/200911690
[15]
Leahy, D.A. and Igna, C.D. (2010) RXTE-Based 35 Day Cycle Turn-On Times for Hercules X-1. The Astrophysical Journal, 713, 318-324. https://doi.org/10.1088/0004-637X/713/1/318
[16]
Igna, C.D. and Leahy, D.A. (2011) Hercules X-1’s Light-Curve Dips as Seen by the RXTE/PCA: A Study of the Entire 1996 February-2005 August Light Curve. Monthly Notices of the Royal Astronomical Society, 418, 2283-2291. https://doi.org/10.1111/j.1365-2966.2011.19550.x
[17]
Leahy, D.A. and Yoshida, A. (1995) Analysis of an Eclipse INGRESS during a High State of Hercules X-1. Monthly Notices of the Royal Astronomical Society, 276, 607-613. https://doi.org/10.1093/mnras/276.2.607
[18]
Leahy, D.A. and Igna, C.D. (2011) The Light Curve of Hercules X-1 as Observed by the Rossi X-Ray Timing Explorer. The Astrophysical Journal, 736, Article No. 74. https://doi.org/10.1088/0004-637X/736/1/74
Tanaka, Y. (1986) Observations of Compact X-Ray Sources. Proceedings of IAU Colloq 89, Copenhagen, 11-20 June 1985, 198. https://doi.org/10.1007/3-540-16764-1_12
[21]
Mihara, T. (1995) Observational Study of X-Ray Spectra of Binary Pulsars with Ginga. Ph.D. Thesis, Dept. of Physics, Univ. of Tokyo, Tokyo.
[22]
Coburn, W., Heindl, W.A., Rothschild, R.E., et al. (2002) Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer. The Astrophysical Journal, 580, 394-412. https://doi.org/10.1086/343033
[23]
Leahy, D.A., Yoshida, A. and Matsuoka, M. (1994) Spectral Evolution during Pre-Eclipse Dips in Hercules X-1. Astrophysical Journal, 434, 341. https://doi.org/10.1086/174732
[24]
Mihara, T., Ohashi, T. and Makishima, K. (1991) X-Ray Spectrum of Hercules X-1 in the Low State of the 35-Day Cycle. Publications of the Astronomical Society of Japan, 43, 501-501.
[25]
Leahy, D.A. (2001) Ginga Observations of Hercules X-1: Spectrum Dependence on 35 Day Phase. The Astrophysical Journal, 547, 449-456. https://doi.org/10.1086/318368
[26]
Vasco, D., Staubert, R. and Klochkov, D. (2013) Pulse Phase and Precession Phase Resolved Spectroscopy of Hercules X-1: Studying a Representative Main-On with RXTE. Astronomy & Astrophysics, 550, A111. https://doi.org/10.1051/0004-6361/201220181
[27]
Nagase, F., Hayakawa, S., Sato, N., Masai, K. and Inoue, H. (1986) Circumstellar Matter in the VELA X-1/HD 77581 System. Publications of the Astronomical Society of Japan, 38, 547-569.
[28]
Leahy, D.A. and Dupuis, J. (2010) Extreme Ultraviolet Explorer Observations of Hercules X-1 over a 35 Day Cycle. The Astrophysical Journal, 715, 897-901. https://doi.org/10.1088/0004-637X/715/2/897
[29]
Reynolds, C.S. (1999) Compton Reflection and Iron Fluorescence in Active Galactic Nuclei and Galactic Black Hole Candidates. Proceedings of High Energy Processes in Accreting Black Holes, Graftavallen, 29 June-4 July 1998, 178.
[30]
Makishima, K., Mihara, T., Nagase, F. and Tanaka, Y. (1999) Cyclotron Resonance Effects in Two Binary X-Ray Pulsars and the Evolution of Neutron Star Magnetic Fields. The Astrophysical Journal, 525, 978-994. https://doi.org/10.1086/307912
[31]
Kallman, T.R. (1991) Iron Lines from X-Ray Binaries. Proceedings of a Workshop, Varenna, 9-12 October 1990, 85-97. https://doi.org/10.1007/BFb0031278
[32]
Leahy, D.A. (1999) Monte Carlo Calculations of X-Ray Reflection Spectra from a Cloud. Journal of the Royal Astronomical Society of Canada, 93, 33.
[33]
Leahy, D.A., Postma, J. and Chen, Y. (2020) AstroSat UVIT Observations of Her X-1. The Astrophysical Journal, 889, Article No. 131. https://doi.org/10.3847/1538-4357/ab65f9
