arXiv subjects

Aytap Sezer

Publications and source records attributed to Aytap Sezer.

At least 19 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

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$-$0.6. We obtained H$\alpha$ 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$\alpha$ ratios in the range of 0.4$-$1.1, indicating emission from shock-heated gas. The oxygen doublet emission lines [OI]$\lambda$6300, $\lambda$6363 detected in the south region also support the indicator of the presence of shocks. We estimate the electron density using the [SII] 6716/6731 ratio ranging from 15 to 1800 cm$^{-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}$. The H$\alpha$/H$\beta$ 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↗

arXiv2023

Discovery of optical emission associated with the supernova remnant G107.5-1.5

We present the first results from an imaging and a spectroscopic survey of the optical emission associated with supernova remnant (SNR) G107.5$-$1.5. We discovered optical diffuse and filamentary emission from G107.5$-$1.5 using the 1.5-m and 1-m telescopes. The optical emission from the North East (NE) and North West (NW) regions show the diffuse structure, while the South East (SE) and East (E) regions show filamentary structure. From long-slit spectra, we found [SII]/H$α$ $>$ 0.5 for the SE and E regions, which supports the origin of the emission being from shock-heated gas. The average [SII]/H$α$ ratio is found to be $\sim$0.4 and $\sim$0.3 for the NW and NE regions, respectively, indicating that the optical emission is coming from ionized gas in an HII region. From the ratios of [SII]$λλ$ 6716/6731, we estimate an average electron density of $\sim$2400 cm$^{-3}$ for the NW region, which can be attributed to the dense ionized gas. The average [SII]$λλ$ 6716/6731 ratios are $\sim$1.25 and $\sim$1.15 for the SE and E regions, respectively, which are indicative of low electron density.

astro-ph.HE↗

arXiv2021

Origin of the gamma-ray emission from supernova remnant HB9

HB9 (G160.9+2.6) is a mixed-morphology Galactic supernova remnant (SNR) at a distance of $\sim$0.6 kpc. Previous analyses revealed recombining plasma emission in X-rays and an expanding shell structure in HI and CO emission, which were correlating with the spatial extent of HB9. In GeV energies, HB9 was found to show extended gamma-ray emission with a morphology that is consistent with the radio continuum emission showing a log-parabola-type spectrum. The overlap reported between the gas data and the excess gamma-ray emission at the southern region of the SNR's shell could indicate a possible interaction between them. We searched for hadronic gamma-ray emission signature in the spectrum to uncover possible interaction between the molecular environment and the SNR. Here we report the results of the gamma-ray spectral modelling studies of HB9.

astro-ph.HE↗

arXiv2019

Suzaku and Fermi view of the supernova remnant 3C 396

3C 396 is a composite supernova remnant (SNR), consisting of a central pulsar wind nebula (PWN) and a bright shell in the west, which is known to be interacting with molecular clouds (MCs). We present a study of X-ray emission from the shell and the PWN of the SNR 3C 396 using archival Suzaku data. The spectrum of the SNR shell is clearly thermal, without a signature of a non-thermal component. The abundances of Al and Ca from the shell are slightly enhanced, which indicates the presence of metal-enriched supernova ejecta. The PWN spectra are well described by a power-law model with a photon index of $\sim$1.97 and a thermal component with an electron temperature of $\sim$0.93 keV. The analysis of about 11-years of Fermi data revealed an 18 sigma-detection of gamma-ray emission from the location overlapping with the position of 3C 396 / 4FGL J1903.8+0531. The spectrum of 3C 396 / 4FGL J1903.8+0531 is best-fitted with a log-parabola function with parameters of $α$ = 2.66 and $β$ = 0.16 in the energy range of 0.2$-$300 GeV. The luminosity of 3C 396 / 4FGL J1903.8+0531 was found to be $>$10$^{35}$ erg s$^{-1}$ at 6.2 kpc, which rules out the inverse Compton emission model. Possible scenarios of gamma-ray emission are hadronic emission and bremsstrahlung processes, due to the fact that the SNR is expanding into dense MCs in the western and northern regions of the SNR.

astro-ph.HE↗

arXiv2019

Discovery of recombining plasma inside the extended gamma-ray supernova remnant HB9

We present the results from the Suzaku X-ray Imaging Spectrometer observation of the mixed-morphology supernova remnant (SNR) HB9 (G160.9+2.6). We discovered recombining plasma (RP) in the western Suzaku observation region and the spectra here are well described by a model having collisional ionization equilibrium (CIE) and RP components. On the other hand, the X-ray spectra from the eastern Suzaku observation region are best reproduced by the CIE and non-equilibrium ionization model. We discuss possible scenarios to explain the origin of the RP emission based on the observational properties and concluded that the rarefaction scenario is a possible explanation for the existence of RP. In addition, the gamma-ray emission morphology and spectrum within the energy range of 0.2$-$300 GeV are investigated using $\sim$10 years of data from the Fermi Large Area Telescope (LAT). The gamma-ray morphology of HB9 is best described by the spatial template of radio continuum emission. The spectrum is well-fit to a log-parabola function and its detection significance was found to be $\sim$25$σ$. Moreover, a new gamma-ray point source located just outside the south-east region of the SNR's shell was detected with a significance of $\sim$6$σ$. We also investigated the archival HI and CO data and detected an expanding shell structure in the velocity range of $-10.5$ and $+1.8$ km s$^{-1}$ that is coinciding with a region of gamma-ray enhancement at the southern rim of the HB9 shell.

astro-ph.HE↗

arXiv2019

A study of the composite supernova remnant MSH 15-56 with Suzaku

The Galactic supernova remnant (SNR) MSH 15-56 is a member of the class of composite SNRs that consists of the remnant shell and a displaced pulsar wind nebula (PWN). The earlier X-ray observations reported the comet-like morphology of the PWN and the ejecta distribution of the SNR. In this work, we present a study of MSH 15-56 using archival Suzaku data. We investigate the nature of the emission and spectral parameters of the remnant. The X-ray spectra are well fitted with a combination of a thermal and non-thermal model with temperature ~0.6 keV and photon index ~2.0. The slightly enhanced abundances of Ne, Mg, S and enhanced abundance of Si confirm the presence of ejected material.

astro-ph.HE↗

arXiv2018

A Suzaku X-ray study of the mixed-morphology supernova remnant Kes 69 and searching for its gamma-ray counterpart

Kes 69 is a mixed-morphology (MM) supernova remnant (SNR) that is known to be interacting with molecular clouds based on 1720 MHz hydroxyl (OH) maser emission observations in the northeastern and southeastern regions. We present an investigation of Kes 69 using $\sim$67 ks Suzaku observation. The X-ray spectrum of the whole SNR is well fitted by a non-equilibrium ionization model with an electron temperature of $kT_{\rm e}$ $\sim$ 2.5 keV, ionization time-scale of $τ$ $\sim$ 4.1$\times10^{10}$ cm$^{-3}$ s and absorbing column density of $N_{\rm H}$ $\sim$ 3.1$\times10^{22}$ cm$^{-2}$. We clearly detected the Fe-K$α$ line at $\sim$6.5 keV in the spectra. The plasma shows slightly enhanced abundances of Mg, Si, S and Fe indicating that the plasma is likely to be of ejecta origin. We find no significant feature of a recombining plasma in this SNR. In order to characterize radial variations in the X-ray spectral parameters, we also analyze annular regions in the remnant. We investigate the explosive origin of Kes 69 and favor the core-collapse origin. Additionally, we report a lack of significant gamma-ray emission from Kes 69, after analyzing the GeV gamma-ray data taken for about 9 years by the Large Area Telescope on board Fermi. Finally, we discuss the properties of Kes 69 in the context of other interacting MM SNRs.

astro-ph.HE↗

arXiv2017

A New Gamma-Ray Source in the Vicinity of the Galactic Supernova Remnant G306.3$-$0.9

A new extended gamma-ray source, which was named as Source A, in the southwest of Galactic supernova remnant (SNR) G306.3$-$0.9 was detected with a significance of $\sim$13$σ$ at the location of R.A. (J2000) = 13$^{\rm{h}}$ 17$^{\rm{m}}$ 52$^{\rm{s}\!\!}$.80, Decl. (J2000) = $-$63$^{\circ}$ 55$'$ 48$"\!\!$.00 using about 9 years of Fermi-LAT data. In order to investigate this unidentified gamma-ray source in multi-wavelengths, we performed Swift observations of Source A. In this presentation we summarize the published gamma-ray results, report about the recent ToO Swift observations of Source A, and show our preliminary results of the gamma-ray analysis that we conducted using the new X-ray data.

astro-ph.HE↗

arXiv2017

Detection of an Unidentified Extended Gamma-ray Source Close to the Galactic Supernova Remnant 3C 400.2

A new extended gamma-ray source (PS J1934.5+1845) was detected with a significance of $\sim$13$σ$ at a location of 1$^{\circ}\!\!$.83 away from the radio location of the Galactic supernova remnant 3C 400.2 using about 9 years of Fermi-LAT data. The 68% containment radius of PS J1934.5+1845's extension was found to be 0$^{\circ}\!\!$.61 and PS J1934.5+1845 is showing a power-law type spectrum with a spectral index of $\sim$2.38. In this presentation we will summarize the gamma-ray analysis methods and report on the analysis results related to the extension and spectrum of PS J1934.5+1845.

astro-ph.HE↗

arXiv2016

Suzaku Analysis of the Supernova Remnant G306.3-0.9 and the Gamma-ray View of Its Neighborhood

We present an investigation of the supernova remnant (SNR) G306.3$-$0.9 using archival multi-wavelength data. The Suzaku spectra are well described by two-component thermal plasma models: The soft component is in ionization equilibrium and has a temperature $\sim$0.59 keV, while the hard component has temperature $\sim$3.2 keV and ionization time-scale $\sim$$2.6\times10^{10}$ cm$^{-3}$ s. We clearly detected Fe K-shell line at energy of $\sim$6.5 keV from this remnant. The overabundances of Si, S, Ar, Ca, and Fe confirm that the X-ray emission has an ejecta origin. The centroid energy of the Fe-K line supports that G306.3$-$0.9 is a remnant of a Type Ia supernova (SN) rather than a core-collapse SN. The GeV gamma-ray emission from G306.3$-$0.9 and its surrounding were analyzed using about 6 years of Fermi data. We report about the non-detection of G306.3$-$0.9 and the detection of a new extended gamma-ray source in the south-west of G306.3$-$0.9 with a significance of $\sim$13$σ$. We discuss several scenarios for these results with the help of data from other wavebands to understand the SNR and its neighborhood.

astro-ph.HE↗

arXiv2016

Searching for the Time Variation in Supernova Remnant RX J1713.7-3946

Supernova Remnant RX J1713.7-3946 emits synchrotron X-rays and very high energy $γ$-rays. Recently, thermal X-ray line emission is detected from ejecta plasma. CO and HI observations indicate that a highly inhomogeneous medium surrounding the SNR. It is interacting with dense molecular clouds in the northwest and the southwest of the remnant. The origin of the $γ$-ray emission from RX J1713.7-3946 is still uncertain. Detection of rapid variability in X-ray emission from RX J1713.7-3946 indicates the magnetic field $B$ $\sim$ mG. In this work, we investigate the time variation in X-ray flux, luminosity and photon index of RX J1713.7-3946. For this investigation, we study the northwest part of the remnant using Suzaku data in 2006 and 2010. We present preliminary results based on our analysis and interpretations about these X-ray time variability.

astro-ph.HE↗

arXiv2016

Investigating the X-ray and Gamma-ray Properties of the Galactic Supernova Remnants Kes 69, 3C 396, 3C 400.2

Kes 69, 3C 396, and 3C 400.2 are mixed-morphology (MM) Galactic supernova remnants (SNRs), where Kes 69 and 3C 396 are interacting with molecular clouds (MCs). Previous X-ray studies showed that the emission from these SNRs is thermal. It has been suggested that MM SNRs interacting with MCs are potential candidates for recombining plasma (RP) in X-rays and hadronic gamma-ray emission. Recently, Chandra observations revealed signs of RP in 3C 400.2. Our preliminary analyses show that the X-ray emission of NW and SE region of 3C 400.2 arises from recombining plasma. We detected GeV gamma-ray emission from Kes 69 and 3C 396 above 5$σ$.

astro-ph.HE↗

arXiv2015

Searching for Overionized Plasma in the Gamma-ray Emitting Supernova Remnant G349.7$+$0.2

G349.7$+$0.2 is a supernova remnant (SNR) expanding in a dense medium of molecular clouds and interacting with clumps of molecular material emitting gamma rays. We analyzed the gamma-ray data of Large Area Telescope on board Fermi Gamma Ray Space Telescope and detected G349.7$+$0.2 in the energy range of 0.2$-$300 GeV with a significance of $\sim$13$σ$ showing no extended morphology. Modeling of the gamma-ray spectrum revealed that the GeV gamma-ray emission dominantly originates from the decay of neutral pions, where the protons follow a broken power-law distribution with a spectral break at $\sim$12 GeV. To search for features of radiative recombination continua in the eastern and western regions of the remnant, we analyzed the Suzaku data of G349.7$+$0.2 and found no evidence for overionized plasma. In this paper we discuss possible scenarios to explain the hadronic gamma-ray emission in G349.7$+$0.2 and the mixed morphology nature of this SNR.

astro-ph.HE↗

arXiv2014

Fe-rich ejecta in the supernova remnant G352.7-0.1 with Suzaku

In this work, we present results from a $\sim$201.6 ks observation of G352.7$-$0.1 by using the X-ray Imaging Spectrometer onboard {\it Suzaku} X-ray Observatory. The X-ray emission from the remnant is well described by two-temperature thermal models of non-equilibrium ionization with variable abundances with a column density of $N_{\rm H}$ $\sim$ 3.3$\times$10$^{22}$ cm$^{-2}$. The soft component is characterized by an electron temperature of $kT_{\rm e}$ $\sim$ 0.6 keV, an ionization time-scale of $τ$ $\sim$ 3.4$\times$10$^{11}$ cm$^{-3}$ s, and enhanced Si, S, Ar, and Ca abundances. The hard component has $kT_{\rm e}$ $\sim$ 4.3 keV, $τ$ $\sim$ 8.8$\times$10$^{9}$ cm$^{-3}$ s, and enhanced Fe abundance. The elemental abundances of Si, S, Ar, Ca, and Fe are found to be significantly higher than the solar values that confirm the presence of ejecta. We detected strong Fe K-shell emission and determined its origin to be the ejecta for the first time. The detection of Fe ejecta with a lower ionization time-scale favor Type Ia origin for this remnant.

astro-ph.HE↗