We present six Chandra X-ray spectra and light curves obtained for the nova V1494 Aql (1999 #2) in outburst. The first three observations were taken with ACIS-I on days 134, 187, and 248 after outburst. The count rates were 1.00, 0.69 and 0.53 cps, respectively. We found no significant periodicity in the ACIS light curves. The X-ray spectra show continuum emission and lines originating from N and O. We found acceptable spectral fits using isothermal APEC models with significantly increased elemental abundances of O and N for all observations. On day 248 after outburst a bright soft component appeared in addition to the fading emission lines. The Chandra observations on days 300, 304, and 727 were carried out with the HRC/LETGS. The spectra consist of continuum emission plus strong emission lines of O and N, implying a high abundance of these elements. On day 300, a flare occurred and periodic oscillations were detected in the light curves taken on days 300 and 304. This flare must have originated deep in the outflowing material since it was variable on short time scales. The spectra extracted immediately before and after the flare are remarkably similar, implying that the flare was an extremely isolated event. Our attempts to fit blackbody, Cloudy, or APEC models to the LETG spectra failed, owing to the difficulty in disentangling continuum and emission line components. The spectrum extracted during the flare shows a significant increase in the strengths of many of the lines and the appearance of several previously undetected lines. In addition, some of the lines seen before and after the flare are not present during the flare. On day 727 only the count rate from the zeroth order could be derived, and the source was too faint for the extraction of a light curve or spectrum.
Deep Dive into Evolution of X-ray spectra and light curves of V1494 Aquilae.
We present six Chandra X-ray spectra and light curves obtained for the nova V1494 Aql (1999 #2) in outburst. The first three observations were taken with ACIS-I on days 134, 187, and 248 after outburst. The count rates were 1.00, 0.69 and 0.53 cps, respectively. We found no significant periodicity in the ACIS light curves. The X-ray spectra show continuum emission and lines originating from N and O. We found acceptable spectral fits using isothermal APEC models with significantly increased elemental abundances of O and N for all observations. On day 248 after outburst a bright soft component appeared in addition to the fading emission lines. The Chandra observations on days 300, 304, and 727 were carried out with the HRC/LETGS. The spectra consist of continuum emission plus strong emission lines of O and N, implying a high abundance of these elements. On day 300, a flare occurred and periodic oscillations were detected in the light curves taken on days 300 and 304. This flare must have
When hydrogen-rich material is lost by a low-mass main sequence star and accrets onto a white dwarf (WD) primary in a Cataclysmic Variable (CV), it settles onto the WD and eventually the bottom of the accreted layer becomes degenerate. When enough material has accumulated and the temperatures become high enough, a thermonuclear runaway is initiated and a Classical Nova (CN) outburst results. There is an initial short phase of X-ray emission which quickly fades as the ejecta expand and become optically thick. When the ejected shell expands and cools enough to become again transparent to X-rays, a soft, luminous X-ray source is typically observed, although, each CN evolves differently in Xrays. This phase of evolution in X-rays is called the SSS phase because X-ray spectra at this time resemble those of the class of super-soft X-ray sources (SSS; Kahabka & van den Heuvel 1997).
V1494 Aql was discovered in the optical by Pereira (1999b) on 1.785 December, 1999 at m v ∼ = 6 (Pereira 1999a) and reached maximum light in the optical two days later, on 3.4 December, 1999 at m v ∼ = 4.0. It subsequently declined by two magnitudes in 6.6 ± 0.5 days thus classifying V1494 Aql as a fast nova (Kiss & Thomson 2000). The distance to the nova was determined to be 1.6 ± 0.2 kpc by Iijima & Esenoglu (2003) and an 1 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA: [Jonathan.Rohrbach, Jan-Uwe.Ness, Sumner.Starrfield]@asu.edu 2 European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain: juness@sciops.esa.int orbital period of 0.13467 days has been suggested by Retter et al. (2000). The hydrogen column density was estimated to N H ≈ 4 × 10 21 cm -2 by Iijima & Esenoglu (2003) from sodium lines in the optical.
X-ray spectra were taken with Chandra, and Krautter et al. (2001) reported that the early evolution showed only emission lines, but that by Aug. 6, 2000 the spectrum had evolved into an SSS spectrum. They also reported an X-ray burst occurred (flare) and the presence of oscillations in one of the grating observations taken during the SSS phase. A detailed timing analysis was presented by Drake et al. (2003).
We re-extracted all Chandra observations, and here we present the light curves and X-ray spectra. We carried out timing analyses, searching for periodic behavior in all observations. We present spectral modeling of the early observations that contain emission lines (Krautter et al. 2001) and provide a qualitative description of the SSS spectra. We also investigated spectral changes from spectra extracted before and after the flare event.
In the next section we present the observations and explain the extraction techniques. We then focus on the timing analysis in §3 and the spectral analysis in § §4 and 5. We discuss spectral models in §6 and summarize our results in §7.
We present six observations of V1494 Aql taken with Chandra in 2000 and 2001. sId), exposure time, net count rate and count rate for ‘soft’ photons with an energy less than 0.6 keV. The first three observations were taken with the S-array of the Advanced CCD Imaging Spectrometer (ACIS-S), which is an array of CCD chips providing moderate spectral resolution in the energy range 0.2-10 keV 3 . After the SSS was detected with the ACIS observation taken on day 248 (Krautter et al. 2001), the next observation used the High Resolution Camera (HRC-S) in combination with Low Energy Transmission Grating Spectrometer (LETGS), yielding higher spectral resolution. While the HRC detector has no energy resolution, the LETGS disperses the incoming light and projects a dispersed spectrum onto the HRC. LETG spectra are extracted in wavelength units (range 1-170 Å), but for consistency with the ACIS spectra we converted the LETG spectra to energy units.
We carried out the reduction with the Chandraspecific CIAO software suite, version 3.3. Since the CIAO standard data processing procedures (a.k.a. the ‘pipeline’) have changed since the time of the observations, we began our treatment of the images with the level 1 event files which were taken from the Chandra archives along with the accompanying calibration files. With the newest or most applicable calibration routines the exposures were reprocessed mimicking the pipeline reduction using standard routines from CIAO version 3.3.0.1 (Fruscione et al. 2006). These newly constructed event 2 files were used to create our light curves and spectra.
The light curves were extracted using tools developed by Ness et al. (2007a) which determine point spread function (PSF) corrected source count rates. The PSF for each observation was constructed by following the CIAO threads and are specific to observation, detector location, and energy (Fruscione et al. 2006). The light curves extracted from the ACIS and the non-dispersed photons in the LETG observations (zeroth order) were extracted in 20 second time bins from a source extraction region of 20 pixels. T
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