Avdan, H.
Avdan, S.
Balman, Şölen
We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L-X similar to 2 x 10(39) erg s(-1) in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and the spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST/Advanced Camera for Surveys, three optical sources have been identified as counterpart candidates within the 1 sigma error radius of 0 ''.3. The brightest one has an absolute magnitude of M-V approximate to -7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M-V approximate to -5.8 and -5.3. The possible spectral types of the candidates from brightest to dimmest were determined as B6-A5, B0-A7, and B2-A3. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10-15M(circle dot), indicating that the compact source is most likely a stellar-mass black hole.


Upper limits to the SN1006 multi-TeV gamma-ray flux from HESS observations
Aharonian, F; et. al. (EDP Sciences, 2005-07-01)
Observations of the shell-type supernova remnant SN1006 have been carried out with the HESS system of Cherenkov telescopes during 2003 (18.2 h with two operating telescopes) and 2004 (6.3 h with all four telescopes). No evidence for TeV gamma-ray emission from any compact or extended region associated with the remnant is seen and resulting upper limits at the 99.9% confidence level are up to a factor 10 lower than previously-published fluxes from CANGAROO. For SN1006 at its current epoch of evolution we def...
Chandra observation of the shell of Nova Persei 1901 (GK Persei): Detection of localized nonthermal X-ray emission from a miniature supernova remnant
Balman, Şölen (IOP Publishing, 2005-07-10)
I present data on the shell of classical Nova Persei (1901) obtained by the Advanced CCD Imaging Spectrometer S3 detector on board the Chandra X-Ray Observatory. The X-ray nebula is affected mostly by the complex interstellar medium around the nova and has not developed a regular shell. The X-ray nebula is lumpy and asymmetric, with the bulk of the emission coming from the southwestern quadrant. The brightest X-ray emission is detected as an arc that covers the region from the west to the south of the centr...
AKYÜZ, AYSUN; Kayaci, S.; Avdan, H.; Ozel, M. E.; SONBAŞ, EDA; Balman, Şölen (IOP Publishing, 2013-03-01)
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 expo...
X-ray spectral evolution of Her X-1 in a low state and the following short high state
Inam, SC; Baykal, Altan (Oxford University Press (OUP), 2005-08-21)
We analysed spectral variations of similar to 8.5-d long Rossi X-ray Timing Explorer (RXTE) monitoring observations of Her X-1 in 2001 December. This set of observations enables, for the first time, frequent continuous monitoring (111 pointings in similar to 8.5 d) of the source with RXTE including a similar to 1.7-d-long low state part and the following similar to 6.8-d-long short high state part. We used an absorbed power-law model with an iron line energy complex modelled as a Gaussian to fit both the 3-...
RXTE and Swift Observations of SWIFT J0513.4-6547
Sahiner, S.; Serim, Muhammed Miraç; Baykal, Altan; İNAM, SITKI ÇAĞDAŞ (Oxford University Press (OUP), 2016-02-11)
We present timing and spectral analysis of Swift-XRT (X-ray Telescope) and RXTE-PCA (Rossi X-ray Timing Explorer-proportional Counter Array) observations of the transient Be/X-ray pulsar SWIFT J0513.4-6547 during its outburst in 2009 and its rebrightening in 2014. From 2009 observations, short-term spin-up rate of the source after the peak of the outburst is found to have about half of the value measured at the peak of the outburst by Coe et al. When the source is quiescent between 2009 and 2014, average sp...
Citation Formats
H. Avdan, S. Avdan, A. AKYÜZ, Ş. Balman, N. AKSAKER, and I. AKKAYA ORALHAN, “X-RAY SPECTRAL AND OPTICAL PROPERTIES OF A ULX IN NGC 4258 (M106),” ASTROPHYSICAL JOURNAL, pp. 0–0, 2016, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/49812.