X-ray spectral evolution of Her X-1 in a low state and the following short high state

Inam, SC
Baykal, Altan
We analysed spectral variations of similar to 8.5-d long Rossi X-ray Timing Explorer (RXTE) monitoring observations of Her X-1 in 2001 December. This set of observations enables, for the first time, frequent continuous monitoring (111 pointings in similar to 8.5 d) of the source with RXTE including a similar to 1.7-d-long low state part and the following similar to 6.8-d-long short high state part. We used an absorbed power-law model with an iron line energy complex modelled as a Gaussian to fit both the 3-60 keV Proportional Counter Array-High Energy X-ray Timing Experiment (PCA-HEXTE) overall short high state spectrum and 3-20 keV individual PCA spectra. An additional partial cold absorber model was used for both cases. Using 3-20 keV individual PCA spectra, absorption in anomalous dips (ADs) and pre-eclipse dips (PDs) in the short high state was compared. Decreasing the ratio of unabsorbed to absorbed flux with increasing unabsorbed flux in ADs and PDs was interpreted as evidence of the fact that the regions causing opaque obscuration and soft absorption are not geometrically far away from each other. Higher iron line peak energies in the low state and the short high state (similar to 6.6-6.9 keV) were interpreted as a clue of the presence of iron line components other than the K alpha emission line.


X-ray flux related timing and spectral features of 2S 1417-62
Inam, SC; Baykal, Altan; Scott, DM; Finger, M; Swank, J (Oxford University Press (OUP), 2004-03-21)
Rossi X-ray Timing Explorer (RXTE) observations of the X-ray transient pulsar 2S 1417-62 between 1999 November and 2000 August with a total exposure of similar to394 ks have been analysed. Observations include a main outburst followed by a series of mini outbursts. Changes in pulse morphology and pulse fraction were found to be related to the changes in X-ray flux. Particularly low X-ray flux regions were found to have significantly lower pulse fractions with different pulse morphologies. The 3-60 keV Propo...
Avdan, H.; Avdan, S.; AKYÜZ, AYSUN; Balman, Şölen; AKSAKER, NAZIM; AKKAYA ORALHAN, Inci (American Astronomical Society, 2016-09-10)
We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L-X similar to 2 x 10(39) erg s(-1) in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and the spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In...
Analysis of RXTE-PCA Observations of SMC X-1
İNAM, SITKI ÇAĞDAŞ; Baykal, Altan; Beklen, E. (Oxford University Press (OUP), 2010-03-21)
We present timing and spectral analysis of Rossi X-ray Timing Explorer-Proportional Counter Array observations of SMCX-1 between 1996 January and 2003 December. From observations around 1996 August 30 with a time-span of similar to 6 d, we obtain a precise timing solution for the source and resolve the eccentricity as 0.00089(6). We find an orbital decay rate of (P) over dot(orb)/P(orb) = -3.402(7) x 10(-6) yr(-1) which is close to the previous results. Using our timing analysis and the previous studies, we...
RXTE-PCA observations of XMMU J054134.7-682550
İNAM, SITKI ÇAĞDAŞ; Townsend, L. J.; McBride, V. A.; Baykal, Altan; Coe, M. J.; Corbet, R. H. D. (Oxford University Press (OUP), 2009-05-21)
We analysed Rossi X-ray Timing Explorer Proportional Counter Array observations of a recent outburst of the X-ray pulsar XMMU J054134.7-682550. We calculated the pulse frequency history of the source. We found no sign of a binary companion. The source spins up when the X-ray flux is higher, with a correlation between the spin-up rate and X-ray flux, which may be interpreted as a sign of an accretion disc. On the other hand, the source was found to have an almost constant spin frequency when the X-ray flux i...
Discovery of a transient magnetar: XTE J1810-197
Ibrahim, AI; Markwardt, CB; Swank, JH; Ransom, S; Roberts, M; Kaspi, V; Woods, PM; Safi-Harb, S; Balman, Şölen; Parke, WC; Kouveliotou, C; Hurley, K; Cline, T (IOP Publishing, 2004-07-01)
We report the discovery of a new X-ray pulsar, XTE J1810 - 197, that was serendipitously discovered on 2003 July 15 by the Rossi X-Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806 - 20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum ( with a photon index of approximate to 4), and is detectable in earlier RXTE observations back to 2003 January but not before. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the source's pe...
Citation Formats
S. Inam and A. Baykal, “X-ray spectral evolution of Her X-1 in a low state and the following short high state,” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, pp. 1393–1398, 2005, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/34493.