Low/hard state of microquasars at low luminosities

Galactic black hole transients (GBHTs) spend most of their time in the low/hard spectral state during the outburst decay. This state exhibits a hard X-ray spectrum with X-ray flux correlating with both the radio and the infrared flux. As the luminosity declines, the spectra of the GBHTs got harder. However, for a few sources at very low luminosity levels a softening of the spectrum has been observed. In this work we discuss the evolution of GBHTs at the very lowest luminosity levels using RXTE data and discuss the behavior of the X-ray spectrum, as well as the reported correlations

Complete Multiwavelength Evolution of Galactic Black Hole Transients During Outburst Decay II: Compact Jets and X-ray Variability Properties

We investigated the relation between compact jet emission and X-ray variability properties of all black hole transients with multiwavelength coverage during their outburst decays. We studied the evolution of all power spectral components (including low frequency quasi-periodic oscillations), and related this evolution to changes in jet properties tracked by radio and infrared observations. We grouped sources according to their tracks in radio/X-ray luminosity relation, and show that the standards show stronger broadband X-ray variability than outliers at a given X-ray luminosity when the compact jet turned on. This trend is consistent with the internal shock model and can be important for the understanding of the presence of tracks in the radio/X-ray luminosity relation. We also observed that the total and the QPO rms amplitudes increase together during the earlier part of the outburst decay, but after the compact jet turns either the QPO disappears or its rms amplitude decreases significantly while the total rms amplitudes remain high. We discuss these results with a scenario including a variable corona and a non-variable disk with a mechanism for the QPO separate from the mechanism that create broad components. Finally, we evaluated the timing predictions of the magnetically dominated accretion flow model which can explain the presence of tracks in the radio/X-ray luminosity relation.Comment: Accepted for publication by Ap

Hard state manifestations of galactic black holes

This thesis is aimed at understanding the accretion-ejection processes and the physical environment in the vicinity of the Galactic black hole transients (GBHT) in the hard state. In this context, X-ray spectral and temporal, optical/infrared (OIR) photometric and radio properties of GBHTs during the outburst decay are examined. As part of developing analysis techniques for this aim, we first investigate a jet associated brightening in the OIR light curves of GX 339-4 during its 2011 outburst decay. The spectral energy distributions taken at the rising part of the OIR rebrightening yield flat spectra, indicating components other than optically thin emission from the compact jet. Again during the rising part of the brightening we detected fluctuations with the binary period of the system. Then, for a large sample of sources, we investigate the relation between the jet formation and the changes or differences in the short term X-ray variability, especially low frequency quasi periodic oscillations. We find that the X-ray variability patterns differ with respect to the source’s track in the radio X-ray correlation. We also discuss the nature of X-ray spectral softening within a few days prior to or following the start of the indications of the jet activity. Finally, we compare the relation between the spectral hardness and the reflection amplitude of black hole and neutron star systems to discuss the nature of their differences

Multiwavelength observations of the black hole transient XTE J1752-223 during its 2010 outburst decay

Galactic black hole transients show many interesting phenomena during outburst decays. We present simultaneous X-ray (RXTE, Swift, and INTEGRAL), and optical/near-infrared (O/NIR) observations (SMARTS), of the X-ray transient, XTE J1752-223 during its outburst decay in 2010. The multi- wavelength observations of 150 days in 2010 cover the transition from soft to hard spectral state. The evolution of ATCA/VLBI radio observations are shown to confirm the compact jet appearance. The source shows flares in O/NIR during changes in X-ray and radio properties. One of those flares is bright and long, and starts about 20 days after the transition in timing. Other, smaller flares occur along with the transition in timing and increase in power-law flux, and also right after the detection of the core with VLBI. Furthermore, using the simultaneous broadband X-ray spectra including IN- TEGRAL, we found that a high energy cut-off is necessary with a folding energy at around 250 keV around the time that the compact jet is forming. The broad band spectrum can also be fitted equally well with a Comptonization model. In addition, using photoelectric absorption edges in the XMM– Newton RGS X-ray spectra and the extinction of red clump giants in the direction of the source, we found a lower limit on the distance of > 5 kpc

Connections between jet formation and multiwavelength spectral evolution in black hole transients

Multiwavelength observations are the key to understand conditions of jet formation in Galactic black hole transient (GBHT) systems. By studying radio and optical-infrared evolution of such systems during outburst decays, the compact jet formation can be traced. Comparing this with X-ray spectral and timing evolution we can obtain physical and geometrical conditions for jet formation, and study the contribution of jets to X-ray emission. In this work, first X-ray evolution - jet relation for XTE J1752-223 will be discussed. This source had very good coverage in X-rays, optical, infrared and radio. A long exposure with INTEGRAL also allowed us to study gamma-ray behavior after the jet turns on. We will also show results from the analysis of data from GX 339-4 in the hard state with SUZAKU at low flux levels. The fits to iron line fluorescence emission show that the inner disk radius increases by a factor of >27 with respect to radii in bright states. This result, along with other disk radius measurements in the hard state will be discussed within the context of conditions for launching and sustaining jets

Çok Kriterli Karar Verme Problemleri İçin Promethee Yöntemi ve Gaıa Düzlemiyle Görsel Analizler: Türkiye’de Bölgesel Sosyo-Ekonomik Gelişmişlik Düzeylerinin Belirlenmesi Üzerine Bir Uygulama

DergiPark: 326176trakyasobedIn this study, it is aimed to show the consistency of the results of PROMETHEE and GAIA Plane, one of the Multi Criteria Decision Making Methods and the applicability of these methods in the field of socio-economic development. For these purposes, it is realized to determine the level of socioeconomic development and to outrank the regions according to selected socioeconomic criteria. In this study 7 geographic regions are includedBu çalışmada, Çok Kriterli Karar Verme (ÇKKV) yöntemlerinden olan ve çeşitli alanlara uygulanan PROMETHEE yöntemi ve GAIA düzleminin tanıtılması, uygulanabilirliği ile bu yöntemle elde edilen sonuçların tutarlılığının gösterilmesi hedeflenmektedir. Bu hedef doğrultusunda sosyal ve ekonomik alanlardan seçilen değişkenler baz alınarak, bölgelerin sosyo-ekonomik gelişmişlik düzeylerinin belirlenmesi ve bu belirleme doğrultusunda sıralama işlemleri gerçekleştirilmiştir. Bu amaçlar doğrultusunda gerçekleştirilen çalışma mevcut idari yapı çerçevesinde 7 coğrafi bölgeyi kapsamaktadı

Multiwavelength observations of the black hole transient Swift J1745-26 during the outburst decay

We characterized the broad-band X-ray spectra of Swift J1745-26 during the decay of the 2013 outburst using INTEGRAL ISGRI, JEM-X and Swift XRT. The X-ray evolution is compared to the evolution in optical and radio. We fit the X- ray spectra with phenomenological and Comptonization models. We discuss possible scenarios for the physical origin of a ~50 day flare observed both in optical and X- rays ~170 days after the peak of the outburst. We conclude that it is a result of enhanced mass accretion in response to an earlier heating event. We characterized the evolution in the hard X-ray band and showed that for the joint ISGRI-XRT fits, the e-folding energy decreased from 350 keV to 130 keV, while the energy where the exponential cut-off starts increased from 75 keV to 112 keV as the decay progressed.We investigated the claim that high energy cut-offs disappear with the compact jet turning on during outburst decays, and showed that spectra taken with HEXTE on RXTE provide insufficient quality to characterize cut-offs during the decay for typical hard X-ray fluxes. Long INTEGRAL monitoring observations are required to understand the relation between the compact jet formation and hard X-ray behavior. We found that for the entire decay (including the flare), the X-ray spectra are consistent with thermal Comptonization, but a jet synchrotron origin cannot be ruled out.Comment: Accepted for publication by MNRA

X-ray, Optical and Infrared Observations of GX 339-4 During Its 2011 Decay

We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift and SMARTS. Based on the X-ray spectral, temporal, and the optical/infrared (OIR) properties, the source evolved from the soft-intermediate to the hard state. Twelve days after the start of the transition towards the hard state, a rebrightening was observed simultaneously in the optical and the infrared bands. Spectral energy distributions (SED) were created from observations at the start, and close to the peak of the rebrightening. The excess OIR emission above the smooth exponential decay yields flat spectral slopes for these SEDs. Assuming that the excess is from a compact jet, we discuss the possible locations of the spectral break that mark the transition from optically thick to optically thin synchrotron components. Only during the rising part of the rebrightening, we detected fluctuations with the binary period of the system. We discuss a scenario that includes irradiation of the disk in the intermediate state, irradiation of the secondary star during OIR rise and jet emission dominating during the peak to explain the entire evolution of the OIR light curve.Comment: 10 pages with 11 figures, accepted for publication in Ap

Complete multiwavelength evolution of galactic black hole transients during outburst decay I: conditions for "compact" jet formation

Compact, steady jets are observed in the near infrared and radio bands in the hard state of Galactic black hole transients as their luminosity decreases and the source moves towards a quiescent state. Recent radio observations indicate that the jets turn o completely in the soft state, therefore multiwavelength monitoring of black hole transients are essential to probe the formation of jets. In this work we conducted a systematic study of all black hole transients with near infrared and radio coverage during their outburst decays. We characterized the timescales of changes in X-ray spectral and temporal properties and also in near infrared and/or in radio emission. We confirmed that state transitions occur in black hole transients at a very similar fraction of their respective Eddington luminosities. We also found that the near infrared flux increase that could be due to the formation of a compact jet is delayed by a time period of days with respect to the formation of a corona. Finally, we found a threshold disk Eddington luminosity fraction for the compact jets to form. We explain these results with a model such that the increase in the near infrared flux corresponds to a transition from a patchy, small scale height corona along with an optically thin out flow to a large scale height corona that allows for collimation of a steady compact jet. We discuss the timescale of jet formation in terms of transport of magnetic fields from the outer parts of the disk, and also consider two alternative explanations for the multiwavelength emission: hot inner accretion flows and irradiation

Eskişehir’de Yaşam Boyu Öğrenme Başlığı Altında Yetişkin Eğitiminin Analizi

Günümüzde en hızlı eskiyen argümanların başında bilgi gelmektedir. Bilim ve teknoloji öylesine hızlı gelişim gösterir ki, sadece kırk yıl önceki bilgiler değil beş yıl öncesindeki bilgiler dahi yeterliliğini yitirmektedir. Bilginin güncelliğini bu derece hızlı kaybettiği bir dünyada yaşam boyu öğrenme, önemi gittikçe artan kavramlardan biri olarak karşımız çıkar. Yaşam boyu öğrenme; kişisel, toplumsal, sosyal ve istihdam ile ilişkili bir yaklaşımla bireyin; bilgi, beceri, ilgi ve yeterliliklerini geliştirmek amacıyla hayatı boyunca katıldığı her türlü öğrenme etkinlikleri olarak tanımlanmaktadır. Bu kavram gelişmiş ülkelerde çok uzun yıllardır gündemde olan, daha da önemlisi yaşama geçmiş bir niteliğe sahiptir. Hatta öyle ki; Amerika Birleşik Devletlerinde eğitim bütçesinin yarıdan fazlasının, yetişkinlerin eğitimi için harcandığı bilinmektedir. Türkiye için ise kavram yeni olmamakla birlikte yaygın görülmemekte ve günümüz koşullarının çok uzağında yürütülmektedir. Yaşam boyu öğrenmede sadece meslek sahibi olmayanlara ya da meslek değiştirmek isteyenlere yeni meslek kazandırmak değil, aynı zamanda bilgileri sürekli tazelemekte amaçtır. Ancak Türkiye’deki duruma bakıldığında amacın bilgi tazelemek yerine daha çok istihdama yönelik olduğu görülmektedir. Bu araştırmada Türkiye’deki uygulamaların Eskişehir platformu üzerinde masaya yatırılması ve başarılı bir yetişkin eğitiminin kent düzeyinde profilinin çıkarılması amaçlanmaktadır. Meslek edindirme kursları başlığı altında faaliyet gösteren kurumlar üzerinde yürütülecek çalışmada, “Eskişehir’de halk yetişkin eğitiminde neyi öğrenmek istiyor?”, “Bunu nasıl ve hangi yöntemlerle öğrenmek istiyor?” gibi sorulara yanıtlar aranmaktadır. Araştırmada ayrıca şehrin demografik haritasının çıkarılması ve kent halkının şimdiye kadarki memnuniyetlerinin tespit edilip ölçümlenmesi de hedeflenmektedir. Bu çerçevede öncelikle demografik veriler taranıp, sonra genel olarak kent halkına uygulanacak anketlerle beklenti, imkan ve istekler ortaya çıkarılmıştır. Bir dönem kurs almış ve halen kurs alan kursiyerlere uygulanacak ikinci düzey anketlerle kişilerin memnuniyeti ölçümlenirken, kurs müdürleri ve öğretmenleriyle yapılan görüşmelerde uygulayıcıların görüşleri alınarak, başarılı örnek olaylar irdelenmiştir. Nicel ve nitel yöntemlerin birlikte kullanılacağı bu projede Eskişehir halkının yaşam boyu öğrenme perspektifinde şu ana kadar aldıkları ve bundan sonraki beklentileri üzerine genel bir değerlendirmeye ulaşılmıştır. Bu araştırma aynı zamanda sertifikasyonun işletme ve kuruluşlar açısından öneminin irdeleneceği ikinci bir çalışma açısından da öncül bir niteliğe sahiptir