We present results based on XMM-Newton observation of the nearby spiral galaxy M 51 (NGC 5194 and NGC 5195). We confirm the presence of the seven known ULXs with luminosities exceeding the Eddington luminosity for a 10M ⊙ black hole, a low luminosity active galactic nucleus with 2 − 10 keV luminosity of 1.6 × 10 39 erg s −1 , and soft thermal extended emission from NGC 5194 detected with Chandra. In addition, we also detected a new ULX with luminosity ∼ 10 39 erg s −1 . We have studied the spectral and temporal properties of the LLAGN and 8 ULXs in NGC 5194, and an ULX in NGC 5195. Two ULXs in NGC 5194 show evidence for short-term variability, and all but two ULXs vary on long time scales (over a baseline of ∼ 2.5 years), providing strong evidence that these are accreting sources. One ULX in NGC 5194, source 69, shows possible periodic behavior in its X-ray flux. We derive a period of 5925 ± 200 s at a confidence level of 95%, based on three cycles. This period is lower than the period of 7620 ± 500 s derived from a Chandra observation in 2000. The higher effective area of XMM-Newton enables us to identify multiple components in the spectra of ULXs. Most ULXs require at least two components -a power law and a soft X-ray excess component which is modeled by an optically thin plasma or multicolor disk blackbody (MCD). However, the soft excess emission, inferred from all ULXs except source 69, are unlikely to be physically associated with the ULXs as their strengths are comparable to that of the surrounding diffuse emission. The soft excess emission of source 69 is well described either by a two temperature mekal plasma or a single temperature mekal plasma (kT ∼ 690 eV) and an MCD (kT ∼ 170 eV). The MCD component suggests a cooler accretion disks compared to that in Galactic X-ray binaries and consistent with that expected for intermediate mass black holes (IMBHs). An iron Kα line (EW ∼ 700 eV) or K absorption edge at ∼ 7.1 keV is present in the EPIC PN spectrum of source 26. The spectrum of the ULX in NGC 5195, source 12, is consistent with a simple power law. The LLAGN in NGC 5194 shows an extremely flat hard X-ray power-law (Γ ∼ 0.7), a narrow iron Kα line at 6.4 keV (EW ∼ 3 keV), and strong soft X-ray excess emission. The full band spectrum is well described by a two component mekal plasma and reflection from cold material such as putative torus.
Multi-wavelength observations of Galactic black hole candidate sources indicate a close connection between the accretion disk emission and the jet emission. The recent discovery of an anti-correlated time lag between the soft and hard X-rays in Cygnus X-3 (Choudhury & Rao 2004) constrains the geometric picture of the diskjet connection into a truncated accretion disk, the truncation radius being quite close to the black hole. Here we report the detection of similar anti-correlated time lag in the superluminal jet source GRS 1915+105. We show the existence of the pivoting in the X-ray spectrum during the delayed anti-correlation and we also find that the QPO parameters change along with the spectral pivoting. We explore theoretical models to understand this phenomenon.
The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the 'low' (as well as 'hard') state, correlated to the radio emission. The time scale of the soft and hard X-rays' anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE-ASM and CGRO-BATSE. In this Letter we report the detection of a lag of 1000s in the anti-correlation of the hard X-ray emission (20-50 keV) to that of the soft X-ray emission (2-7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointed observation when an episode of the rearranging of the accretion system is serendipitously observed. This is the first such observation of hard X-ray delay seen in the persistent Galactic microquasars, within the precincts of the hard state.
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