Yazar "Akyuz, A." seçeneğine göre listele

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  • [ X ]
    Öğe
    A search for supernova remnants in the nearby spiral galaxy M74 (NGC 628)
    (Edp Sciences S A, 2010) Sonbas, E.; Akyuz, A.; Balman, S.; Ozel, M. E.
    An optical search was carried out for supernova remnants (SNRs) in the Sc type nearby spiral galaxy M 74, using ground-based observations at the TUBITAK National Observatory (TUG, Antalya/Turkey) and the Special Astrophysics Observatory (SAO, Russia). Observations were supplemented by the spectral analysis of archived X-ray data from XMM-Newton and Chandra. The survey of M74 covered similar to 9 arcmin(2) with [S II], H alpha, and their continuum filters. Interference filter images of M 74 were obtained the with the 1.5 m Russian Turkish Telescope (RTT150) at TUG and spectral data taken with the 6 m Bolsoi Azimuthal Telescope (BTA) at SAO. The emission nebulae with continuum-subtracted line ratio values of [S II]lambda lambda 6716,6731 /H alpha >= 0.4 are identified as SNRs. Followup spectroscopy confirmed optical SNR identifications. We have identified nine new SNR candidates in M 74 with [S II]/H alpha >= 0.4 as the basic criterion. The [S II]/H alpha ratio ranges from 0.40 to 0.91 and H alpha intensities from 2.8 x 10(-15) erg cm(-2) s(-1) to 1.7 x 10(-14) erg cm(-2) s(-1). We also present spectral follow-up observations of these SNR candidates, however, we are able to spectrally confirm only three of them (SNR2, SNR3, and SNR5). The lack of confirmation for the rest might come from contamination by the nearby H II emission regions, as well as from the inaccurate positioning of the long slit on these objects. In addition, we searched the XMM-Newton and Chandra Observatory archival data for the X-ray counterparts to the optically identified candidates. We find positional coincidence with only three SNR candidates, SNR1, SNR2, and SNR8. The spectrum of SNR2 yields a shock temperature of 10.8 keV with an ionization timescale of 1.6 x 10(10) s cm(-3), indicating a relatively young remnant in an early Sedov phase, which is not supported by our optical wavelength analysis. Given the high luminosity of 10(39) erg s(-1) and the characteristics of the X-ray spectrum, we favor an ultra luminous X-ray source interpretation for this source associated with an SNR. We calculated an X-ray flux upper limit of 9.0 x 10(-15) erg cm(-2) s(-1) for the rest of the SNRs, including spectroscopically identified SNR3 and SNR5.
  • Küçük Resim
    Öğe
    Xmm-newton observatıons of lumınous sources ın nearby galaxıes ngc 4395, ngc 4736, and ngc 4258
    (IOP PUBLISHING LTD, 2013) Akyuz, A.; Kayaci, S.; Avdan, H.; Özel, Mehmet Özel; Sonbas, E.; Balman, S.
    We present the results of a study of non-nuclear discrete sources in a sample of three nearby spiral galaxies (NGC 4395, NGC 4736, and NGC 4258) based on XMM-Newton archival data supplemented with Chandra data for spectral and timing analyses. A total of 75 X-ray sources have been detected within the D-25 regions of the target galaxies. The large collecting area of XMM-Newton makes the statistics sufficient to obtain spectral fitting for 16 (about 20%) of these sources. Compiling the extensive archival exposures available, we were able to obtain the detailed spectral shapes of diverse classes of point sources. We have also studied temporal properties of these luminous sources. Eleven of them are found to show short-term (less than 80 ks) variation while eight of them show long-term variation within factors of similar to 2-5 during a time interval of similar to 2-12 years. Timing analysis provides strong evidence that most of these sources are accreting X-ray binary systems. One source that has properties different from others was suspected to be a supernova remnant, and our follow-up optical observation confirmed this. Our results indicate that sources within the three nearby galaxies are showing a variety of source populations, including several ultraluminous X-ray sources, X-ray binaries, transients together with a super soft source, and a background active galactic nucleus candidate.