arXiv subjects

Ebru Aktekin

Publications and source records attributed to Ebru Aktekin.

7 recordsLinked to original sources

arXiv2026

Optical observations and atomic environment of supernova remnant G25.1-2.3

The supernova remnant (SNR) G25.1-2.3 was identified in the radio band during the Sino-German $\lambda$6 cm survey of the Galactic plane. We present a detailed investigation of the optical, HI, and CO emission towards the G25.1-2.3 to better understand its characteristics and environment. In this study, optical spectroscopic data of the remnant and its environment have been analysed for the first time, providing new insights into their emission properties. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and 1.5-m Russian-Turkish Telescope (RTT150) data show variations across the observed regions, with [SII]/H$\alpha$ ranging from 0.16 to 0.83. We identified shock-heated gas in the northern and southern regions and several photoionized regions around the SNR based on their [SII]/H$\alpha$ ratios derived from spectra. The [SII]$\lambda$6716/$\lambda$6731 ratio observed in the northern region suggests electron densities ($n_{\rm e}$) ranging from 120 to 1030 cm$^{-3}$, whereas the southern regions show higher values, between 490 and 4500 cm$^{-3}$. The variations in the observed H$\alpha$/H$\beta$ ratios indicate significant differences in extinction across the regions. H$\alpha$ images obtained using the 1-m Turkish Telescope (T100) reveal optical emission in the northern and southern, characterized by filamentary and diffuse structures. We newly found a hole-like distribution of HI, whose spatial extent is roughly consistent with the diameter of the SNR. Based on radio data, we examine the evolutionary stage of G25.1-2.3 using the surface brightness-diameter ($\Sigma-D$) relation and the equipartition method.

astro-ph.HE↗

arXiv2026

First detailed optical spectroscopic observations of the supernova remnants G107.7-5.1 and G150.3+4.5

We present optical spectroscopic observations of the supernova remnants (SNRs) G107.7$-$5.1 and G150.3+4.5, each spanning nearly 3 degree. Both remnants were recently examined in the optical band through a deep H$\alpha$ and [OIII] emission-line imaging survey, which led to the discovery of G107.7$-$5.1. Using long-slit spectra obtained with the 1.5-m Russian-Turkish Telescope (RTT150), we investigate the physical conditions of the pre-shock and post-shock gas in the optical filamentary regions of the SNRs. The SNR nature of G107.7$-$5.1 is confirmed by the measured [SII]/H$\alpha$ and [NII]/H$\alpha$ ratios, which range from 0.56 to 0.86 and from 0.7 to 1.4, respectively. A similar conclusion is reached for G150.3+4.5, where the observed [SII]/H$\alpha$ (0.43-0.92) and [NII]/H$\alpha$ (0.49-1.29) ratios likewise support a shock-excitation origin. Further confirmation of the shock-excited nature of both SNRs comes from their consistency with recent diagnostic diagrams based on multiple emission-line ratios. The [OIII]/H$\beta$ line ratios measured in both remnants indicate shocks with complete recombination zones and are consistent with shock velocities of $\gtrsim$100 km s$^{-1}$. The electron densities ($n_{\rm e}$), derived from the [SII] $\lambda$6716/$\lambda$6731 line ratios, exhibit substantial variation in the spectra of both SNRs. Additionally, extinction variations observed across the remnants suggest the presence of significant dust structures along the line of sight. We conclude that these two remnants display remarkable similarities across multiple diagnostic spectral properties, consistent with previous reports indicating comparable GeV gamma-ray characteristics.

astro-ph.HE↗

arXiv2025

Investigation of X-ray emission from the unidentified TeV gamma-ray source HESS J1832-085 with Suzaku

Observations conducted with H.E.S.S. at high energies have led to the discovery of numerous gamma-ray sources in the Galactic plane at TeV energies. One of these sources, HESS J1832-085, has been suggested to be a pulsar wind nebula (PWN); however, its nature is not yet fully understood. In this work, we analyze Suzaku data to investigate the X-ray spectral properties of HESS J1832-085. We found that the X-ray spectra are highly absorbed and well-represented by a power-law model with a photon index of $\Gamma \sim 1.5$, and an unabsorbed X-ray flux of $F_{\rm X} \sim 0.3 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ in the 2-10 keV energy band. The gamma-ray flux is approximately 66 times higher than the X-ray flux. Based on our X-ray analysis, we discuss the origin of the source HESS J1832-085. We propose that the PWN scenario is possible, although several issues still need to be resolved.

astro-ph.HE↗

arXiv2025

Optical investigation of supernova remnant G206.7+5.9

The shell-type supernova remnant (SNR) G206.7+5.9 was recently discovered in the radio band with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The remnant spans about 3.5 in diameter and exhibits bilateral shells. In this work, we present optical spectra of G206.7+5.9 with the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST), and narrow-band (H$\alpha$ and [SII]) images with the 1-m T100 telescope. The filamentary structure seen in H$\alpha$ image shows a clear correlation with the radio emission. We use optical line ratios to determine the physical parameters of G206.7+5.9. The LAMOST spectra reveal large ratios of [SII]/H$\alpha$ $\sim$ (0.61-1.78) and [NII]/H$\alpha$ $\sim$ (0.63-1.92) consistent with that expected for a shock-heated SNR. The emission lines [OI] $\lambda$6300, $\lambda$6363 detected in the spectra also support the presence of shocks. Electron density ($n_{\rm e}$) measurements based on the [SII] $\lambda$6716/$\lambda$6731 ratio suggest densities between 117 and 597 cm$^{-3}$. We estimate the pre-shock cloud density ($n_{\rm c}$) to be approximately 2.6$-$13.3 cm$^{-3}$. We also investigate the archival HI data and have newly identified an expanding gas motion of the HI, whose velocity span is approximately 10 km s$^{-1}$. We conclude that G206.7+5.9 is an SNR exhibiting properties remarkably similar to those seen in Galactic SNRs.

astro-ph.HE↗

arXiv2024

Optical and HI observations of IC 443 and G189.6+3.3 in a complex environment

The supernova remnant (SNR) IC 443 is one of the best-studied Galactic SNRs at many wavelengths. It is interacting with a very complex environment, including the SNR G189.6+3.3 and HII regions. In this paper, we observed IC 443 and G189.6+3.3 using 1.5- and 1-m telescopes to better understand the nature of these SNRs in the optical band. We perform H_alpha images showing both filamentary and diffuse structures, and long-slit spectra from many locations with Balmer and forbidden lines detected for IC 443 and G189.6+3.3. The [SII]/ H_alpha ratios confirm the SNR nature of G189.6+3.3. The ranges of our estimated electron density and pre-shock cloud density clearly indicate the complex structure surrounding IC 443 and G189.6+3.3. We also investigated the archival HI data and newly found some shell-like distributions of HI that are possibly associated with G189.6+3.3.

astro-ph.HE↗

arXiv2023

Discovery of optical emission from the supernova remnant G108.2-0.6 and its atomic environment

We report the first detection of optical emission from the shell-type Galactic supernova remnant (SNR) G108.2$-$0.6. We obtained H$α$ images and long-slit spectra using the 1.5-m RTT150 telescope to examine the morphological and spectral characteristics of the SNR. We detected several filaments along its north and south regions, which is consistent with its SNR nature. The spectra exhibit [SII]/H$α$ ratios in the range of 0.4$-$1.1, indicating emission from shock-heated gas. The oxygen doublet emission lines [OI]$λ$6300, $λ$6363 detected in the south region also support the indicator of the presence of shocks. We estimate the electron density using the [SII] 6716/6731 ratio ranging from 15 to 1800 cm$^{-3}$. The spectra show a relatively low shock velocity of $V_{\rm s}$ $\sim$ 80 km s$^{-1}$ with the pre-shock cloud density of $n_{\rm c}$ $\sim$18$-$57 cm$^{-3}$. The H$α$/H$β$ ratios show significant variation across the observed regions with extinction $E(B-V)$ ranging from 0.22 to 1.65. We also analyzed the archival HI data and estimated the kinematic distance to the SNR of $\sim$0.8 kpc and dynamical age as $\sim$70$\pm$10 kyr of G108.2$-$0.6.

hep-ph↗

arXiv2018

Optical and X-ray Observational Search for the Possible Supernova Remnant Candidates in the Nearby Galaxy NGC 1569

We report the results of our investigation on the possible existence of supernova remnants (SNRs) in the nearby galaxy, NGC 1569, using the CCD imaging and spectroscopic observations from the RTT150 telescope of TUG-TUBITAK in Antalya, Turkey for two different observing periods. Using [S\,{\sc ii}]/H$α$ $\geq$ 0.4 standard criteria, the identification of 13 new SNR candidates for this galaxy is proposed for two different epochs. We found the [S\,{\sc ii}]/H$α$ ratios ranging from 0.46--0.84 and H$α$ intensities ranging from (2.2--32) $\times$ 10$^{-15}$ erg cm$^{-2}$ s$^{-1}$. [S\,{\sc ii}]$λλ$6716/6731 average flux ratio is calculated from the optical spectra for only one possible SNR candidate. By using this ratio the electron density, $N_{\rm e}$, is estimated to be 121 $\pm$ 17 cm$^{-3}$ and by using the [O\,{\sc iii}]$λ$5007/H$β$ ratio of the same spectrum, the shock wave velocity, $V_{\rm s}$, is estimated to be between 100 < Vs < 150 km s$^{-1}$. Using {\it Chandra} data, we find that out of 13 SNR candidates only 10 of them have yielded a spectrum with good statistics, confirming the existence of 10 SNR candidates with matched positions in X-ray region as well. We measure the 0.5--2 keV band flux down to 0.58 $\times$ 10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ for 10 X-ray sources. Our spectral analysis revealed that spectra of the SNR candidates are best modelled with the Collisional Ionisation Equilibrium plasma with a temperature range of 0.84 keV < \textit{kT$_{e}$} < 1.36 keV.

astro-ph.HE↗