Unsupervised spectral decomposition of X-ray binaries with application to GX 339-4

In this paper we explore unsupervised spectral decomposition methods for distinguishing the effect of different spectral components for a set of consecutive spectra from an X-ray binary. We use well-established linear methods for the decomposition, namely principal component analysis, independent component analysis and non-negative matrix factorisation (NMF). Applying these methods to a simulated dataset consisting of a variable multicolour disc black body and a cutoff power law, we find that NMF outperforms the other two methods in distinguishing the spectral components. In addition, due the non-negative nature of NMF, the resulting components may be fitted separately, revealing the evolution of individual parameters. To test the NMF method on a real source, we analyse data from the low-mass X-ray binary GX 339-4 and found the results to match those of previous studies. In addition, we found the inner radius of the accretion disc to be located at the innermost stable circular orbit in the intermediate state right after the outburst peak. This study shows that using unsupervised spectral decomposition methods results in detecting the separate component fluxes down to low flux levels. Also, these methods provide an alternative way of detecting the spectral components without performing actual spectral fitting, which may prove to be practical when dealing with large datasets.Comment: 12 pages, 13 figure

A Gaia view of the optical and X-ray luminosities of compact binary millisecond pulsars

In this paper, we study compact binary millisecond pulsars with low- and very low-mass companion stars (spiders) in the Galactic field, using data from the latest Gaia data release (DR3). We infer the parallax distances of the optical counterparts to spiders, which we use to estimate optical and X-ray luminosities. We compare the parallax distances to those derived from radio pulse dispersion measures and find that they have systematically larger values, by 40 per cent on average. We also test the correlation between X-ray and spin-down luminosities, finding that most redbacks have a spin-down to X-ray luminosity conversion efficiency of ~0.1 per cent, indicating a contribution from the intrabinary shock. On the other hand, most black widows have an efficiency of ~0.01 per cent, similar to the majority of the pulsar population. Finally, we find that the bolometric optical luminosity significantly correlates with the orbital period, with a large scatter due to different irradiated stellar temperatures and binary properties. We interpret this correlation as the effect of the increasing size of the Roche Lobe radius with the orbital period. With this newly found correlation, an estimate of the optical magnitude can be obtained from the orbital period and a distance estimate.Peer ReviewedPostprint (published version

A Gaia view of the optical and X-ray luminosities of compact binary millisecond pulsars

In this paper, we study compact binary millisecond pulsars with low- and very low-mass companion stars (spiders) in the Galactic field, using data from the latest Gaia data release (DR3). We infer the parallax distances of the optical counterparts to spiders, which we use to estimate optical and X-ray luminosities. We compare the parallax distances to those derived from radio pulse dispersion measures and find that they have systematically larger values, by 40% on average. We also test the correlation between X-ray and spin-down luminosities, finding that most redbacks have a spin-down to X-ray luminosity conversion efficiency of $\sim$0.1%, indicating a contribution from the intrabinary shock. On the other hand, most black widows have an efficiency of $\sim$0.01%, similar to the majority of the pulsar population. Finally, we find that the bolometric optical luminosity significantly correlates with the orbital period, with a large scatter due to different irradiated stellar temperatures and binary properties. We interpret this correlation as the effect of the increasing size of the Roche Lobe radius with the orbital period. With this newly found correlation, an estimate of the optical magnitude can be obtained from the orbital period and a distance estimate.Comment: 24 pages, 17 figures, 9 tables. This article has been accepted for publication in MNRAS published by Oxford University Press on behalf of the Royal Astronomical Societ

The obscured X-ray binaries V404 Cyg, Cyg X-3, V4641 Sgr, and GRS 1915+105

V404 Cyg, Cyg X-3, V4641 Sgr, and GRS 1915+105 are among the brightest X-ray binaries and display complex behavior in their multiwavelength emission. Apart from Cyg X-3, the other three sources have large accretion disks, and there is evidence of a high orbital inclination. Therefore, any large scale geometrical change in the accretion disk can cause local obscuration events. On the other hand, Cyg X-3 orbits its Wolf-Rayet companion star inside the heavy stellar wind obscuring the X-ray source. We study here whether the peculiar X-ray spectra observed from all four sources can be explained by local obscuration events. We fit the source spectra with two physically motivated models describing either a scenario where all the intrinsic emission is reprocessed in the surrounding matter or where the emitter is surrounded by a thick torus with variable opening angle. We show that the X-ray spectra during specific times are similar in all four sources likely arising from the high-density environments where they are embedded. The fitted models suggest that a low-luminosity phase preceding an intense flaring episode in the 2015 outburst of V404 Cyg is heavily obscured, but intrinsically very bright (super-Eddington) accretion state. Similar spectral evolution to that of V404 Cyg is observed from the recent, unusually low-luminosity state of GRS 1915+105. The modeling results point to a geometry change in the (outflowing) obscuring matter in V404 Cyg and GRS 1915+105, which is also linked to the radio (jet) evolution. All sources display obscured X-ray emission but with different intrinsic luminosities which points towards different factors causing the obscuration. This work highlights the importance of taking into account the reprocessing of the X-ray emission in the surrounding medium in the modeling of the X-ray spectra that may well take place in other sources as well.Comment: 24 pages, 14 figures, 8 tables. Accepted for publication in A&A. Abstract slightly abridged to meet ArXiv size limi

ALMA/NICER observations of GRS 1915+105 indicate a return to a hard state

Context. GRS 1915 +105 is a transient black hole X-ray binary consistently emitting 10-100% of the Eddington luminosity in the X-ray band over the last three decades until mid-2018 when the source luminosity suddenly decreased by an order of magnitude. This phase was followed by a change to a state with even lower average X-ray fluxes never seen before during the outburst but presenting renewed flaring activity at di fferent wavelengths, albeit with mean fluxes still in decline.Aims. GRS 1915 +105 has the longest orbital period known among low-mass X-ray binaries, the largest accretion disk size, and therefore the largest mass supply for accretion. The high inclination of the disk allows the study of geometrical e ffects of the accretion flow such as changes in the height-to-radius ratio or the e ffect of accretion disk winds on the intrinsic emission that is expected during the outburst decay. In addition, the transient jet is expected to change to a compact, self-absorbed, steady jet.Methods. We conducted two full polarization Atacama Large Millimeter Array observations to study the jet properties during the outburst decay by analyzing the spectral, polarization, and intra-epoch variability for both observation epochs. In addition, we analyzed almost daily Neutron Star Interior Composition Explorer pointing observations, modeling X-ray power spectral densities, spectral energy distributions, and light curves with a physically motivated model to follow the changing accretion disk properties throughout the outburst decay and relating them to the jet emission.Results. We show that the X-ray and millimeter (mm) spectral, timing, and polarization properties are consistent with those of a typical decaying X-ray binary outburst and that GRS 1915 +105 has descended into the low-luminosity hard X-ray state. The jet emission in the mm is consistent with a compact, steady jet with similar to 1% linear polarization, and the magnetic field is likely aligned with the jet position angle. Relating the mm emission to the X-ray emission reveals that the source has changed from a higher radio /X-ray correlation index to a lower one; L-radio proportional to L-X(0.6)

TURVALLISUUSTOIMIJUUTTA ETSIMÄSSÄ

This article is a shortened version of CPT Lahtinen´s master´s thesis that he did on cadets´ and police students´ understanding of themselves as representatives of their own profession. The aim of study was to produce content to facilitate professional growth and to support the personal identity projects of the individuals themselves by comparing the professional identities of the two groups of security actors and by describing the nature of being a security actor. The main research question in the study was: Are there such similarities in cadets´and police students´ descriptions of understanding their professional identity that could be summarized as being shared by all security actors? The question is answered by categorizing the descriptions of understanding given by the respondents concerning their professional identity and by describing the ways the two groups describe the meaning of their chosen profession in terms of their own personal identity projects and how the decision to become a security actor has affected their own identity. The study also considers the impact the respondents' notions of professional identity have on overall security. The study is qualitative in nature and uses a phenomenographic research approach. The research material was collected with an open questionnaire and analyzed by phenomenographic analysis. The results are shown as professional identity categories of the two respondent groups and summarized as common features of security actors. It was found out in the study that he most descriptive feature of being a security actor was the respondents´ own belief of their profession´s necessity in a functional society. Conserning overall security it is relevant that the individuals that work as security actors see their profession not only to be an instrument of security but also as an object worth securing. With this professional identity category that rose hierarchically above the other categories the security actors were also able to add different features of professional identity to their identity projects such as the identities of being the enablers of safe and secure living, the backbones of order in the society and the adaptable multitools of security

Quantifying irradiation in spider pulsars: the extreme case of PSR J1622-0315

We present the first multi-band optical light curves of PSR J1622-0315, among the most compact known redback binary millisecond pulsars, with an orbital period Porb=3.9 h. We find a flux modulation with two maxima per orbital cycle and a peak-to-peak amplitude of about 0.3 mag, which we attribute to the ellipsoidal shape of the tidally distorted companion star. The optical colours imply a late-F to early-G spectral type companion and do not show any detectable temperature changes along the orbit. This suggests that the irradiation of the star's inner face by the pulsar wind is unexpectedly missing despite its short orbital period. To interpret these results, we introduce a new parameter fsd, defined as the ratio between the pulsar wind flux intercepted by the companion star and the companion intrinsic flux. This flux ratio fsd, which depends on the spin-down luminosity of the pulsar, the base temperature of the companion and the orbital period, can be used to quantify the effect of the pulsar wind on the companion star and turns out to be the most important factor in determining whether the companion is irradiated or not. We find that the transition between these two regimes occurs at fsd=2-4 and that the value for PSR J1622-0315 is fsd=0.7, placing it firmly in the non-irradiated regime

Joint XMM-Newton and NuSTAR observations of the reflection spectrum of III Zw 2

Detecting and modeling the reprocessed hard X-ray emission component in the accretion flow, the so-called reflection spectrum, is a main tool used to estimate black hole spins in a wide range of astrophysical black holes, regardless of their mass or distance. In this work, we study the X-ray spectra of the Seyfert I galaxy III Zw 2 by using multiepoch XMM-Newton, NuSTAR, and Suzaku observations. The X-ray spectra exhibit a soft-excess below 1 keV and a prominent excess at the location of the broad Fe K alpha line at 6.4 keV. To account for these spectral features, we fit the spectra with multiple models including an ionized partially covering absorber and an accretion disk reflection model. To fully resolve the reflection component, we analyzed jointly the XMM-Newton and NuSTAR observations taken in 2017 and archival XMM-Newton data from 2000. Assuming the reflection scenario, the resulting model fits support for a rapidly spinning black hole (a >= 0.98) in this radio-intermediate source. The X-ray spectra in 2000 and 2017 are remarkably similar; the only difference pertains to the reflection fraction, which is possibly due to a change in the geometry of the accretion flow. However, the Suzaku observation is markedly different, and we suggest this could be an effect of a jet contribution in the X-ray band, which is supported by the elevated radio flux during this observation

Microquasar Cyg X-3 -- a unique jet-wind neutrino factory?

The origin of astrophysical neutrinos is one of the most debated topics today. Perhaps the most robust evidence of neutrino counterpart comes from supermassive black holes in active galactic nuclei associated with strongly collimated outflows, or jets, that can accelerate particles to relativistic energies and produce neutrinos through hadronic interactions. Similar outflows can also be found from X-ray binaries, or `microquasars', that consist of a neutron star or a stellar-mass black hole accreting matter from a non-degenerate companion star. In some cases, these systems can accelerate particles up to GeV energies implying an efficient acceleration mechanism in their jets. Neutrino production in microquasar jets can be expected with suitable conditions and a hadronic particle population. Microquasar Cyg X-3 is a unique, short orbital period X-ray binary hosting a Wolf-Rayet companion star with a strong stellar wind. The interaction of the dense stellar wind with a relativistic jet leads to particle collisions followed by high-energy gamma-ray and potentially neutrino emission. Here, using the 10-year neutrino candidate sample of the IceCube neutrino observatory, we find that the events with the highest spatial association with Cyg X-3 occur during short-lived high-energy gamma-ray flaring periods indicating the possible astrophysical nature of these events.Comment: 5 pages, 2 figures, 1 table. This article has been accepted for publication in MNRAS published by Oxford University Press on behalf of the Royal Astronomical Societ

The Radio/X-Ray Correlation in X-Ray Binaries-Insights from a Hard X-Ray Perspective

The radio/X-ray correlation is one of the most important pieces of observational evidence of the disk-jet connection in accreting compact objects. However, a growing number of X-ray binaries (XRB) seem to present deviations from the universal radio/X-ray correlation, and the origin of these outliers are still very much debated. In previous studies, the X-ray bolometric luminosity used in the radio/X-ray correlation has been estimated using a narrow, soft X-ray band. We study how estimating the X-ray bolometric luminosity using broadband observations of XRB affects the radio/X-ray correlation. We found that the ratio between the broadband (3-200 keV) and narrowband (3-9 keV) luminosities varies between 5 and 10 in the hard X-ray state. Overall, the resulting radio/X-ray correlation slopes and normalizations did not present a very significant change, suggesting that they are not affected greatly by observational biases but are caused by real physical effects. We found that all sources that reach high enough luminosity change their correlation slopes from the universal slope to a much steeper one. In addition, sources in the steeper radio/X-ray track show a distinct cutoff in the high-energy X-ray spectrum at tens of keV. These results suggest that the accretion flow presents a morphological change at a certain critical luminosity during the outburst rise from radiatively inefficient to radiatively efficient flow that is in turn more efficient in cooling the hot accretion flow producing the hard X-ray emission. This change could also affect to the jet launching properties in these systems