arXiv subjects

E. N. Ercan

Publications and source records attributed to E. N. Ercan.

15 recordsLinked to original sources

arXiv2023

A Possible Discovery of the Optical Counterpart of the X-ray source NuSTAR J053449+2126.0

We report the observation of a possible optical counterpart to the recently discovered X-ray source NuSTAR J053449+2126.0 (J0534 in short). We observed the source location using the 1.5-m Telescope (RTT150) to search for an optical counterpart, and detected a possible optical counterpart and analysed its spectrum using the $B$, $V$, $R$, and $I$ images of J0534, and found that the possible optical counterpart of J0534 is likely to be a long-known optical source, namely PSO J083.7063+21.4333. However, this source has been misclassified as a star rather than being an extragalactic source. We determined the source distance accurately for the first time based on our spectral analysis. J0534 could be a high-redshift ($z\simeq2.2$) member of an Active Galactic Nucleus (AGN) sub-group identified as quasars. Our analysis favours an accreting black hole of mass $\sim 7\times 10^8 M_{\odot}$ as a power supply for the quasar. Further observations in optical and other wavelengths are needed to confirm its precise nature.

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arXiv2022

Water megamaser and central black hole masses in a large sample of galaxies

Extragalactic water maser emissions at 22 GHz have been playing vital roles in astrophysics. The limited detection rate of these masers has been motivating researchers to find clues that can help characterise them. The physical environments 22 GHz masers formed in are still ambiguous. Accordingly, statistical studies have been thoroughly used to resolve these favourable environments. This work goes through the essential parameter of Active Galactic Nuclei (AGN), namely, the mass of the central supermassive black hole (MBH) of the maser host galaxy. We study the correlation between maser luminosity (LH2O) and MBH in sub-samples of megamasers (MMs), kilomasers (KMs), and disc masers. The regression line of the relation is also calculated for these sub-samples. Unlike the results of previous works, dividing the maser sample into MMs and KMs gives no privilege to MM galaxies. Contrary to expectation, KMs have weak and low significant LH2O - MBH correlation, while MMs show no correlation. The positive correlation in KMs can be explained by the role of AGN therein, while the diversity of MMs types, with some of which are not strongly related to AGN, may explain the correlation missing. Surprisingly, the 28 disc maser sample, where tight correlation is expected, shows a very weak and low significant LH2O-MBH correlation. Future VLBI studies will eventually lead to a specific classification of a good number of maser galaxies, which is essential to establishing the LH2O-MBH relation.

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arXiv2020

Tracing circumnuclear dense gas in H2O maser galaxies

A sample of 30 H2O extra-galactic maser galaxies with their published HCN(J=1-0) and HCO+(J=1-0) observations has been compiled to investigate the dense gas correlation with H2O maser emission. Our sample number exceeds the size of the previous HCN samples studied so far by a factor of three, and it is the first study on the possible relation with the dense gas tracer HCO+. We find a strong correlation between normalized H2O maser emission luminosity (LH2O\LCO) and normalized HCO+ line luminosity (LHCO+\LCO). Moreover, a weak correlation has been found between LH2O\LCO and normalized HCN line luminosity (LHCN\LCO). The sample is also studied after excluding Luminous and Ultraluminous infrared galaxy (U)LIRG sources, and the mentioned correlations are noticeably stronger. We show that 'Dense gas' fractions as obtained from HCN and HCO+ molecules tightly correlate with maser emission, especially for galaxies with normal IR luminosity(LIR< 10^11Lsun) and we show that HCO+ is a better 'dense gas' tracer than HCN. Further systematic studies of these dense gas tracers with higher transition level lines are vital to probe megamaser physical conditions and to accurately determining how maser emission interrelates with the dense gas.

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arXiv2020

NGC 2366 : An optical search for possible supernova remnants

The results of an optical search for supernova remnants (SNRs) in the nearby irregular galaxy NGC 2366 are presented. We took interference filter images and collected spectral data in three epochs with the f/7.7 1.5 m Russian Turkish Telescope (RTT150) at TÜBİTAK National Observatory (TUG) located in Antalya, Turkey. The continuum-subtracted H$α$ and continuum-subtracted [SII]$λλ$6716, 6731 images and their ratios were used for the identification of SNRs. With [SII]/H$α$ $\geq$ 0.4 criteria, four possible SNR candidates were identified in NGC 2366 with [SII]/H$α$ ratios of $\sim$(0.68, 0.57, 0.55 and 0.75), H$α$ intensities of $\sim$(2.10, 0.36, 0.14, 0.11)$\times 10^{-15}$ erg cm$^{-2}$ s$^{-1}$ [SII]$λ$6716/$λ$6731 average flux ratios of $\sim$(1.01 and 1.04), electron densities of $N_{\rm e}$ $\sim$(582 and 513) cm$^{-3}$ and [OIII] $λ$5007/H$β$ $λ$4861 $\sim$(3.6 and 2.6) line ratio values are obtained for two of the SNR candidates. A shock velocity $V_{\rm s}$ of 80 $\leq$ $V_{\rm s}$ $\leq$ 100 km s$^{-1}$ is reported. The spectral parameters are obtained for the first time for these possible SNR candidates. The locations of the four SNRs obtained here are found to be consistent with optical and radio results reported so far. One of the sources categorised earlier by XMM-Newton observations as an extended X-ray source position is found to be consistent with one of four possible SNR candidates reported here.

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arXiv2019

Exploring the multiphase medium in MKW 08: from the central active galaxy up to cluster scales

The study of the brightest cluster galaxy (BCG) coronae embedded in noncool core (NCC) galaxy clusters is crucial to understand the BCG's role in galaxy cluster evolution as well as the activation of the self-regulated cooling and heating mechanism in the central regions of galaxy clusters. We explore the X-ray properties of the intracluster medium (ICM) of the NCC galaxy cluster MKW 08 and the BCG corona, along with their interface region. With recent and deep archival Chandra observations, we study the BCG corona in detail, and with archival XMM-Newton observations, we investigate the implications of the central active galactic nuclei (AGN) on the BCG. We carry out imaging and spectral analyses of MKW 08 with archival XMM-Newton and Chandra X-ray observations. Our spectral analysis suggests the presence of a central AGN by a power-law with a photon index of $Γ$ ~ 1.8 at the core of its BCG. Although the ICM does not exhibit a cluster scale cool core, the BCG manifests itself as a mini cool core characterized by a cooling time as short as 64 Myr at r = 3 kpc centered at the galaxy. The isothermality of the BCG corona seems to favor mechanical feedback from the central AGN as the major source of gas heating. The gas pressure profile of this mini cool core suggests that the BCG coronal gas reaches pressure equilibrium with the hotter and less dense ICM inside an interface of nearly constant pressure, delimited by radii 4 < r < 10 kpc at the galactic center. As revealed by the presence of a metal enriched tail (Z ~ 0.5 - 0.9 Solar) extending up to 40 kpc, the BCG corona seems to be experiencing ram-pressure stripping by the surrounding ICM and/or interacting with a nearby galaxy, IC 1042.}

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arXiv2019

Iron abundance distribution in the hot gas of merging galaxy clusters

We present XMM-Newton/EPIC observations of six merging galaxy clusters and study the distributions of their temperature, iron (Fe) abundance and pseudo-entropy along the merging axis. For the first time, we focus simultaneously, and in a comprehensive way, on the chemical and thermodynamic properties of the freshly collided intracluster medium (ICM). The Fe distribution of these clusters along the merging axis is found to be in good agreement with the azimuthally-averaged Fe abundance profile in typical non-cool-core clusters out to $r_{500}$. In addition to showing a moderate central abundance peak, though less pronounced than in relaxed systems, the Fe abundance flattens at large radii towards $\sim$0.2-0.3 $Z_\odot$. Although this shallow metal distribution is in line with the idea that disturbed, non-cool-core clusters originate from the merging of relaxed, cool-core clusters, we find that in some cases, remnants of metal-rich and low entropy cool cores can persist after major mergers. While we obtain a mild anti-correlation between the Fe abundance and the pseudo-entropy in the (lower entropy, $K$ = 200-500 keV cm$^2$) inner regions, no clear correlation is found at (higher entropy, $K$ = 500-2300 keV cm$^2$) outer radii. The apparent spatial abundance uniformity that we find at large radii is difficult to explain through an efficient mixing of freshly injected metals, particularly in systems for which the time since the merger is short. Instead, our results provide important additional evidence in favour of the early enrichment scenario - in which the bulk of the metals are released outside galaxies at $z$ > 2-3 - and extend it from cool-core and (moderate) non-cool-core clusters to a few of the most disturbed merging clusters as well. These results constitute a first step towards a deeper understanding of the chemical history of merging clusters.

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arXiv2015

Optical observations of the nearby galaxy IC342 with narrow band [SII] and H$α$ filters. II - Detection of 16 Optically-Identified Supernova Remnant Candidates

We present the detection of 16 optical supernova remnant (SNR) candidates in the nearby spiral galaxy IC342. The candidates were detected by applying [SII]/H$α$ ratio criterion on observations made with the 2 m RCC telescope at Rozhen National Astronomical Observatory in Bulgaria. In this paper, we report the coordinates, diameters, H$α$ and [SII] fluxes for 16 SNRs detected in two fields of view in the IC342 galaxy. Also, we estimate that the contamination of total H$α$ flux from SNRs in the observed portion of IC342 is 1.4%. This would represent the fractional error when the star formation rate (SFR) for this galaxy is derived from the total galaxy's H$α$ emission.

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arXiv2014

Origin of gamma-ray emission in the shell of Cassiopeia A

Non-thermal X-ray emission from the shell of Cassiopeia A (Cas A) has been an interesting subject of study, as it provides information about relativistic electrons and their acceleration mechanisms in the shocks. Chandra X-ray observatory revealed the detailed spectral and spatial structure of this SNR in X-rays. The spectral analysis of Chandra X-ray data of Cas A shows unequal flux levels for different regions of the shell, which can be attributed to different magnetic fields in those regions. Additionally, the GeV gamma-ray emission observed by Large Area Telescope on board Fermi Gamma Ray Space Telescope showed that the hadronic processes are dominating in Cas A, a clear signature of acceleration of protons. In this paper we aim to explain the GeV-TeV gamma-ray data in the context of both leptonic and hadronic scenario. We modeled the multi-wavelength spectrum of Cas A. We use synchrotron emission process to explain the observed non-thermal X-ray fluxes from different regions of the shell. These result in estimation of the model parameters, which are then used to explain TeV gamma-ray emission spectrum. We also use hadronic scenario to explain both GeV and TeV fluxes simultaneously. We show that a leptonic model alone cannot explain the GeV-TeV data. Therefore, we need to invoke a hadronic model to explain the observed GeV-TeV fluxes. We found that although pure hadronic model is able to explain the GeV-TeV data, a lepto-hadronic model provides the best fit to the data.

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arXiv2013

Modeling the Shell of Cassiopeia A to find the TeV Gamma-ray Emission Region

We will present the multi-wavelength modeling of the supernova remnant Cassiopeia A's shell based on radio, X-rays, and GeV-TeV gamma rays. Our aim is to estimate the location of TeV gamma rays with the help of spectral analysis of X-rays from different regions of the shell, because Chandra X-ray observations have a far better angular resolution than the gamma-ray measurements. Our analysis shows X-ray flux levels from various regions of the remnant to be different. We find that leptonic model is unable to explain the GeV and TeV data, simultaneously. So, we invoke a hadronic model as an additional component to explain the GeV and TeV data.

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arXiv2013

Studying the Supernova Remnant G31.9+0.0 in Gamma and X-Rays

G31.9+0.0 (3C 391) is a Galactic mixed-morphology supernova remnant observed in GeV gamma rays by Fermi Gamma Ray Space Telescope's LAT (Fermi-LAT), as well as in the 0.3-10 keV X-ray band by Suzaku. In this paper, we will present the analysis results of X- and gamma-ray data of 3C 391 taken with Suzaku and Fermi-LAT. The X-ray spectrum of 3C 391 was fitted to a single-temperature variable abundance non-equilibrium ionization model with an electron temperature of kTe ~ 0.57 keV, an absorbing column density of NH ~ 3.1 x 10^{22} cm^{-2} and a very high ionization age (τ> 10^{12} cm^{-3} s), which suggest that the plasma has reached ionization equilibrium. The spectrum shows clearly detected emission lines of Mg, Si, and S. 3C 391 was detected in GeV gamma rays with a significance of ~ 13 sigma. The spectrum was fitted with a log-parabola function, where the spectral index and beta parameters were found to be α= 2.35 +- 0.07 and β= 0.366 +- 0.339. The integrated flux above 200 MeV was found as F = (2.34 +- 0.37) x 10^{-8} ph cm^{-2} s^{-1}. These results are in agreement with the Fermi-LAT results given in the 2nd Fermi-LAT catalog.

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arXiv2011

{\it Suzaku} observation of Galactic supernova remnant CTB 37A (G348.5+0.1)

We present here the results of the observation of CTB 37A obtained with the X-ray Imaging Spectrometer onboard the {\it Suzaku} satellite. The X-ray spectrum of CTB 37A is well fitted by two components, a single-temperature ionization equilibrium component (VMEKAL) with solar abundances, an electron temperature of $kT_{\rm e}\sim0.6$ keV, absorbing column density of $N_{\rm H}\sim3\times10^{22}$ ${\rm cm^{-2}}$ and a power-law component with photon index of $Γ$ $\sim 1.6$. The X-ray spectrum of CTB 37A is characterized by clearly detected K-shell emission lines of Mg, Si, S, and Ar. The plasma with solar abundances supports the idea that the X-ray emission originates from the shocked interstellar material. The ambient gas density, and age of the remnant are estimated to be $\sim1f^{-1/2}$${\rm cm^{-3}}$ and $\sim3\times10^{4}f^{1/2}$ yr, respectively. The center-filling X-ray emission surrounded by a shell-like radio structure and other X-ray properties indicate that this remnant would be a new member of mixed-morphology supernova remnant class.

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arXiv2011

Suzaku Observations of Ejecta-Dominated Galactic Supernova Remnant G346.6-0.2

We present here the results of the X-ray analysis of Galactic supernova remnant G346.6-0.2 observed with {\it Suzaku}. K-shell emission lines of Mg, Si, S, Ca and Fe are detected clearly for the first time. Strong emission lines of Si and S imply that X-ray emission nature of G346.6-0.2 is ejecta-dominated. The ejecta-dominated emission is well fitted with a combined model consisting of thermal plasma in non-equilibrium ionization and a non-thermal component, which can be regarded as synchrotron emission with a photon index of $Γ$ $\sim 0.6$. Absorbing column density of $N_{\rm H}\sim2.1\times10^{22}$ ${\rm cm^{-2}}$ is obtained from the best-fitting implying a high-density medium, high electron temperature of $kT_{\rm e}\sim1.2$ keV, and ionization timescale of $n_{\rm e}t\sim2.9\times10^{11}$ ${\rm cm^{-3}s}$ indicating that this remnant may be far from full ionization equilibrium. The relative abundances from the ejecta show that the remnant originates from a Type Ia supernova explosion.

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arXiv2008

Multi-Band Analysis of Abell 2255

We analyzed the data for the nearby cluster of galaxies Abell 2255 from archival XMM-Newton observations in order to search for the properties of X-ray point like structures in the outskirts. 11 point-like X-ray emission is detected. Detected X-ray sources are then observed with the 1.5 meter RTT-150 at Turkish National Observatory for possible optical counterparts. The cluster field is covered through 5 ANDOR photometer pointings. 3 sources have no optical follow-ups. 2 QSOs and 1 star are observed from the field. For 4 sources we have obtained the corresponding redhifts. The cumulative log(N)-log(S) is studied and the cluster source number is calculated to be 4 times higher than the field at Fx~10E-13 ergs cm-2 s-1. This phenomenon is interpreted as increased galaxy activity as they first encounter high density ICM environment at the cluster outskirt. We suggest that X-ray emission is triggered by either increased accretion onto LMXBs, fueling of AGNs and/or awakening of BHs.

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arXiv2002

The Effects of Shear and Rotation Anisotropy Upon the Process of Gravitational Instability

In this paper, we study the role of shear fields on the evolution of density perturbations embedded in a Friedmann flat background universe, by studying the evolution of a homogeneous ellipsoid model. In this context, we show that while the effect of the shear is that of increasing the growth rate of the density contrast of a mass element, the angular momentum acquired by the ellipsoid has the right magnitude to counterbalance the shear. Finally, our result show that initial asphericities and tidal interaction induce a slowing down of the collapse after the system has broken away from the general expansion, in perfect agreement with the previrialization conjecture (Peebles & Groth 1976; Davis & Peebles 1977).

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arXiv2002

Dynamical evolution of clusters of galaxies: the effect of high- velocity substructure clumps

In the Cold Dark Matter (hereafter CDM) scenario even isolated density peaks contain a high fraction of small scale clumps having velocities larger than the average escape velocity from the structure. These clumps populate protoclusters, especially in the peripheral regions, r > R_f (where R_f is the filtering scale). During the cluster collapse and the subsequent secondary infall, collapsing or infalling clumps (having v v_esc. We study the interaction between these two kind of clumps by means of the impulse approximation and we find that the collapse of bound clumps is accelerated with respect to the homogeneous case (Gunn & Gott's model). The acceleration of the collapse increases with decreasing height of the peak, ν. We finally compare the acceleration produced by this effect to the slowing down effect produced by the gravitational interaction of the quadrupole moment of the system with the tidal field of the matter of the neighboring proto-clusters studied in Del Popolo & Gambera. We find that the magnitude of the slowing down effect is larger than the acceleration produced by the effect studied in this paper, only in the outskirts of the cluster. We want to stress that the one which we study in this paper is also present in an isolated protocluster, being produced by the interaction of the collapsing clumps with the unbound substructure internal to the collapsing clumps itself while that studied in Del Popolo & Gambera (1998) is produced by substructure external to the density peak.

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