A Wavelet‐Based Algorithm for the Spatial Analysis of Poisson Data

Accretion shocks have been recognized as an important X-ray emission mechanism for pre-main sequence stars, and yet the X-ray properties of FUor outbursts, events that are caused by violent accretion, have been given little attention. We observed the FUor object Z CMa during optical outburst and quiescence with Chandra. No significant changes in X-ray brightness and spectral shape were found, suggesting that the X-ray emission is coronal. The binary nature of Z CMa makes the origin of the X-ray source ambiguous. However, the moderate hydrogen column density derived from our data makes it unlikely that the embedded primary star is the Xray source. The secondary star, which is the FUor object, is thus responsible for both the X-ray emission and the ongoing accretion outburst, which seem, however, to be unrelated phenomena. The secondary is also known to drive a large outflow and jet, which we detect here for the first time in X-rays. The distance of the X-ray emitting outflow source to the central star is greater than in jets of low-mass stars.

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“…Source detection was carried out with the wavdetect algorithm (Freeman et al 2002). We used wavelet scales between 1 and 8 in steps of √ 2.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

Stelzer¹,

Hubrig

Orlando³

et al. 2009

A&A

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“…The PSF map information was used as input at the next stage where we carried out point source detection by correlating the data with wavelet functions (WAVDETECT in CIAO, Freeman et al 2002) in the 0.5-8.0 keV energy band. Below 0.5 keV the response is not well calibrated, while above 8.0 keV both the mirror effective area drops and the particle background rises.…”

Section: Point Source Detection and Photometrymentioning

confidence: 99%

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

Tzanavaris

Hornschemeier²,

Gallagher

et al. 2016

ApJ

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We obtain total galaxy X-ray luminosities, L X , originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the ±1σ scatter of the Mineo et al. L X -star formation rate (SFR) correlation or have higher L X than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L X -stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low-or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L X values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L X values can be observed due to strong XRB variability.

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“…In order to get the X-ray position for the sources in the ACIS-S field of view, we used a wavelet transform detection algorithm, the wavdetect program within the CIAO data analysis system (Freeman et al 2002). The output file of the previous procedure is input to the AE software.…”

Section: X-ray Observations and Data Reductionmentioning

confidence: 99%

X-ray and multiwavelength view of NGC 4278

Younes

Porquet

Sabra

et al. 2010

A&A

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Context. The emission mechanism responsible for the bulk of energy from radio to X-rays in low ionization emission line regions (LINERs) and low luminosity active galactic nuclei (LLAGN) has been long debated. Based on UV to X-ray and radio to UV flux ratios, some argue that LINERs/LLAGN are a scaled-down version of their more luminous predecessors Seyfert galaxies. Others, based on the lack of X-ray short (hours) time-scale variability, the non detection of an iron line at 6.4 keV, and the faint UV emission compared to typical AGNs, suggest the truncation of the classical thin accretion disk in the inner regions of the AGN where a radiatively inefficient accretion flow (RIAF) structure forms. Aims. We investigate the LINER-Seyfert connection by studying the unabsorbed LINER galaxy NGC 4278 that accretes at a low rate (L bol/Edd ∼ 7 × 10 −6 ) but exhibits a broad Hα line, and a point-like nucleus in radio, optical, UV and X-rays. Methods. We analyzed one XMM-Newton and seven Chandra X-ray observations of NGC 4278 spread over a three year period, allowing the study of the X-ray variability at different time-scales (hours, months, years). We also examined the radio to X-ray spectral energy distribution to constrain the accretion mode in the nucleus of NGC 4278. Results. Long time-scale (months) variability is observed where the flux increased by a factor of ∼3 on a time-scale of a few months and by a factor of 5 between the faintest and the brightest observation separated by ∼3 years. During the XMM-Newton observation, where the highest flux level is detected, we found a 10% flux increase on a short time-scale of a few hours, while the light curves for the different Chandra observations do not show short time-scale (minutes to hours) variability. A combination of an absorbed power law (N H ≈ 10 20 cm −2 , Γ = 2.2 +0.1 −0.2 ) plus a thermal component (kT ≈ 0.6 keV) were able to fit the Chandra spectra. The XMM-Newton spectra, where the highest X-ray flux is detected, are well fitted with an absorbed power-law with no need for a thermal component as the emission from the power-law component is dominant. The power-law photon index is ∼2.1 and the hydrogen column density is of the order of 10 20 cm −2 . Neither a narrow nor a broad Fe Kα emission line at 6.4 keV are detected with a 22 eV and 118 eV upper limits derived on their equivalent widths. We derive optical fluxes from archival HST ACS observations and detected optical variability on time-scales of years. For the first time for this source, thanks to the optical/UV monitor on board XMM-Newton, we obtained simultaneous UV and X-ray flux measurements. We constructed SEDs based on simultaneous or quasi simultaneous observations and compared them to LINER, radio-loud, and radio-quiet quasar SEDs. We find that at a low X-ray flux the NGC 4278 SED resembles that of typical LINER sources where the radio to X-ray emission can be considered as originating from a jet and/or RIAF, whereas at a high X-ray flux, NGC 4278 SED is more like a low luminosity Seyfert SED...

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A Wavelet‐Based Algorithm for the Spatial Analysis of Poisson Data

Cited by 563 publications

References 28 publications

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

The X-ray emission from Z Canis Majoris during an FUor-like outburst and the detection of its X-ray jet

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

X-ray and multiwavelength view of NGC 4278

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