X-ray Spectral Component Research Articles

The first outburst of the new magnetar candidate SGR 0501+4516

We report here on the outburst onset and evolution of the new Soft Gamma Repeater SGR 0501+4516. We monitored the new SGR with XMM-Newton starting on 2008 August 23, one day after the source became burst-active, and continuing with 4 more observations, with the last one on 2008 September 30. Combining the data with the Swift-XRT and Suzaku data, we modelled the outburst decay over 160 days, and we found that the source flux decreased exponentially with a timescale of t_c=23.8 days. In the first XMM-Newton observation a large number of short X-ray bursts were observed, the rate of which decayed drastically in the following observations. We found large changes in the spectral and timing behavior of the source during the outburst, with softening emission as the flux decayed, and the non-thermal soft X-ray spectral component fading faster than the thermal one. Almost simultaneously to our XMM-Newton observations (on 2008 August 29 and September 2), we observed the source in the hard X-ray range with INTEGRAL, which clearly detected the source up to ~100keV in the first pointing, while giving only upper limits during the second pointing, discovering a variable hard X-ray component fading in less than 10 days after the bursting activation. We performed a phase-coherent X-ray timing analysis over about 160 days starting with the burst activation and found evidence of a strong second derivative period component (\ddot{P} = -1.6(4)x10^{-19} s/s^{-2}). Thanks to the phase-connection, we were able to study the the phase-resolved spectral evolution of SGR 0501+4516 in great detail. We also report on the ROSAT quiescent source data, taken back in 1992 when the source exhibits a flux ~80 times lower than that measured during the outburst, and a rather soft, thermal spectrum.

SWIFTX-RAY AND ULTRAVIOLET MONITORING OF THE CLASSICAL NOVA V458 VUL (NOVA VUL 2007)

We describe the highly variable X-ray and UV emission of V458 Vul (Nova Vul 2007), observed by Swift between 1 and 422 days after outburst. Initially bright only in the UV, V458 Vul became a variable hard X-ray source due to optically thin thermal emission at kT = 0.64 keV with an X-ray band unabsorbed luminosity of 2.3 × 1034 erg s–1 during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2+0.3 –0.1 solar), consistent with a Suzaku measurement around the same time. On day 315 we find a new X-ray spectral component which can be described by a blackbody with temperature of kT = 23+9 –5 eV, while the previous hard X-ray component has declined by a factor of 3.8. The spectrum of this soft X-ray component resembles those typically seen in the class of supersoft sources (SSS) which suggests that the nova ejecta were starting to clear and/or that the white dwarf photosphere is shrinking to the point at which its thermal emission reaches into the X-ray band. We find a high degree of variability in the soft component with a flare rising by an order of magnitude in count rate in 0.2 days. In the following observations on days 342.4-383.6, the soft component was not seen, only to emerge again on day 397. The hard component continued to evolve, and we found an anticorrelation between the hard X-ray emission and the UV emission, yielding a Spearman rank probability of 97%. After day 397, the hard component was still present, was variable, and continued to fade at an extremely slow rate but could not be analyzed owing to pile-up contamination from the bright SSS component.

Discovery of Rapid Hard X‐Ray Variability and New Jet Activity in the Symbiotic Binary R Aquarii

Two Chandra observations of the R Aqr symbiotic binary system taken 3.3 years apart show dramatic changes in the X-ray morphology and spectral characteristics in the inner 500 AU of this system. The morphology of the soft X-ray emission has evolved from a nearly circular region centered on the binary system to an hourglass shape that indicates the formation of a new southwest jet. Synchrotron radiation from the new jet in contemporaneous VLA radio spectra implies the physical conditions in the early stages of jet development are different from those in the more extended outer thermal jets known to exist for decades in this system. The central binary source has two X-ray spectral components in each of the two epochs, a soft component and a highly absorbed hard component characterized by T ~ 10^8 K if fit with a thermal plasma model. The spectrum hardened considerably between 2000.7 and 2004.0, primarily due to increased flux above 5 keV, suggesting a change in the accretion activity of the white dwarf on a timescale of a few years or less. Point-source Fe K emission is detected at the position of the central binary system in both observations. While the earlier observation shows evidence of only a single emission peak near Fe K alpha at 6.4 keV, the later observation shows a more complex emission structure between 6 and 7 keV. Finally, we have discovered a modulation in the hard X-ray flux with a period of 1734 s at a 95% confidence level in the 2004 observation only. The modulation potentially arises from standing shocks in an accretion column and we have explored the possibility that the white dwarf in R Aqr is analogous to the magnetic white dwarfs in Intermediate Polar.

Magnetars: Time Evolution, Superfluid Properties, and the Mechanism of Magnetic Field Decay

We calculate the coupled thermal evolution and magnetic field decay in relativistic model neutron stars threaded by superstrong magnetic fields (B > 1015 G). Our main goal is to evaluate how such "magnetars" evolve with time and how field decay modifies the transitions to core superfluidity and cooling dominated by surface X-ray emission. Observations of a thermal X-ray spectral component and fast timing noise place strong constraints on the presence of a superfluid core. We find that the transition to core superfluidity can be significantly delayed by magnetic field decay in the age range ~103-105 yr. The mechanism of Hall drift is related to the stability of the core magnetic field and to currents flowing outward through the crust. The heating effect is enhanced if it is continuous rather than spasmodic. Condensation of a heavy element layer at the surface is shown to cause only modest changes in the outward conduction of heat.

ChandraX‐Ray Observations of the X‐Ray Faint Elliptical Galaxy NGC 4697

(abridged) A Chandra ACIS S3 observation of the X-ray faint elliptical galaxy NGC 4697 resolves much of the X-ray emission (61% of the counts from within one effective radius) into 90 point sources, of which ~80 are low mass X-ray binaries (LMXBs) associated with this galaxy. The dominance of LMXBs indicates that X-ray faint early-type galaxies have lost much of their interstellar gas. On the other hand, a modest portion of the X-ray emission from NGC 4697 is due to hot gas. The X-ray emitting gas in NGC 4697 has a rather low temperature (kT = 0.29 keV). The emission from the gas is very extended, with a much flatter surface brightness profile than the optical light, and has an irregular, L-shaped morphology. X-ray spectra of the resolved sources and diffuse emission show that the soft X-ray spectral component, found in this and other X-ray faint ellipticals with {\it ROSAT}, is due to interstellar gas. The cumulative LMXB spectrum is well-fit by thermal bremsstrahlung at kT = 8.1 keV, without a significant soft component. Three of the resolved sources in NGC 4697 are supersoft sources. In the outer regions of NGC 4697, seven of the LMXBs (about 20%) are coincident with candidate globular clusters, which indicates that globulars have a high probability of containing X-ray binaries compared to the normal stellar population. The luminosity function of the LMXBs has a ``knee'' at 3.2 x 10^38 ergs/s, which is approximately the Eddington luminosity of a 1.4 Msun neutron star (NS). This knee appears to be a characteristic feature of the LMXB population of early-type galaxies, and we argue that it separates black hole and NS binaries. This characteristic luminosity could be used as a distance estimator.

On the Integrated Spectrum of the X-Ray Binaries and the Origin of Soft X-Ray Emission from the Bulge of M31

Using ROSAT PSPC data, we have performed several tests aimed at understanding the origin of the soft X-ray spectral component detected from the bulge of M31. We find that a significant soft component in the spectrum of the bulge is spatially correlated with the unresolved X-ray emission near the core of M31, which is probably a hot interstellar medium or perhaps a population of multiple faint sources. For the first time, we extracted the spectrum of this unresolved emission, by removing point sources dominating the integral spectrum of the bulge, and found it to be responsible for most of the soft excess. A soft spectral component is not at all needed to fit the point-source spectrum that remains after subtracting the unresolved emission. The integral spectra of bright point sources, both inside and outside of the M31 bulge, can be fitted with a single power law in the ROSAT band. Our analysis rules out the previous suggestion that all bulge emission in M31 may be generated by low-mass X-ray binaries (Irwin & Bregman).

ASCAObservations of the Starburst‐driven Superwind Galaxy NGC 2146: Broadband (0.6–9 keV) Spectral Properties

We report ASCA GIS and SIS observations of the nearby (D=11.6 Mpc), nearly edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT PSPC and HRI imaging already discussed in the literature. The broadband (0.6-9 keV) X-ray spectrum of NGC 2146 is best described by a two-component model, the soft X-ray emission being modeled by a Raymond-Smith thermal plasma model with a temperature of kT~0.8 keV, while the hard X-ray emission is modeled by a thermal plasma model with kT~8 keV, or by a power-law model with a photon index of ~1.7. We do not find compelling evidence of substantial excess absorption above the Galactic value. The total luminosities of NGC 2146 in the soft (0.5-2.0 keV), hard (2-10 keV), and broad (0.5-10.0 keV) energy bands are ~1.3×1040, ~1.8×1040, and ~3.1×1040 ergs s-1 , respectively. The soft and hard thermal components provide about 30% and 70%, respectively, of the total luminosity in the 0.5-2.0 keV energy band, while in the 2-10 keV energy range only the hard component plays a major role. The spectral results allow us to set tighter constraints on the starburst-driven superwind model, which we show can satisfactorily account for the luminosity, mass, and energy content represented by the soft X-ray spectral component. We estimate that the mass outflow rate (~9 M☉ yr-1) is about an order of magnitude greater than the predicted rate at which supernova and stellar winds return mass into the interstellar medium, and therefore we argue that the flow is strongly "mass loaded" with material in and around the starburst. The estimated outflow velocity of the hot gas is close to the escape velocity from the galaxy, so the fate of the gas is not clear. We suggest that the hard X-ray spectral component is due to the combined emission of X-ray binaries and/or young supernova remnants associated with the starburst.

The Kilohertz QPO Frequency and Flux Decrease in Aquila X-1 and the Effect of Soft X-Ray Spectral Components

We report on a Rossi X-Ray Timing Explorer observation of Aquila X-l during its outburst in 1997 March in which, immediately following a type I burst, the broadband 2-10 keV flux decreased by about 10% and the kilohertz quasi-periodic oscillation (kHz QPO) frequency decreased from 813 +/- 3 to 776 +/- 4 Hz. This change in kHz QPO frequency is much larger than expected from a simple extrapolation of a frequency-flux correlation that was established in data before the burst. Meanwhile, a very low frequency noise component in the broadband fast Fourier transform power spectra, with a fractional rms amplitude of 1.2% before the burst, ceased to exist after the burst. All these changes were accompanied by a change in the energy spectral shape. If we characterize the energy spectra with a model composed of two blackbody (BB) components and a power-law component, almost all the decrease in flux was in the two BE components. We attribute the two BE components to the contributions from a region very near the neutron star, or even from the neutron star itself, and from the accretion disk, respectively.

Two X-Ray Sources in 30 Doradus: Wolf-Rayet + Black Hole Binaries?

view Abstract Citations (35) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two X-Ray Sources in 30 Doradus: Wolf-Rayet + Black Hole Binaries? Wang, Q. Daniel Abstract I report the detection of two X-ray sources of luminosities ∼1036 ergs s-1 in the central region of 30 Doradus. These two sources appear pointlike in images taken with the ROSAT HRI. One of the sources is most likely associated with a close spectroscopic binary R140a2 (WN6) with an orbital period of 2.76 days. The mass of the unknown binary partner is likely in the range of 2.4-15 Msun. This suggests that the X-ray source could represent a long-sought class of binaries containing a Wolf-Rayet star and a black hole. The other source, which coincides spatially with Mrk 34 (WN4.5), may have a similar nature. Available X-ray spectral data support this Wolf-Rayet + black hole binary explanation of the two sources. I have used a ROSAT PSPC observation to show the presence of an ultrasoft component and possible intrinsic absorption in the spectra of the sources. Modeled with multicolor blackbody disks, the spectra provide estimates of the disks' characteristic inner radii, which are in agreement with those obtained for the known black hole candidates. An ASCA observation has further revealed a hard X-ray spectral component from the central 30 Doradus region. This component, represented by a power law with a photon index of ∼2.4, may belong to the two sources. The characteristics of both the power-law and ultrasoft components strongly indicates that the two sources are black hole candidates in high-mass X-ray binaries. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176441 arXiv: arXiv:astro-ph/9503123 Bibcode: 1995ApJ...453..783W Keywords: STARS: WOLF-RAYET; GALAXIES: MAGELLANIC CLOUDS; X-RAYS: STARS; STARS: BINARIES: CLOSE; BLACK HOLE PHYSICS; Astrophysics E-Print: To appear in the Astrophysical Journal, 16 pages of AAS Latex text, plus 6 Postscript figures (tar compressed and uuencoded using uufiles csh script) full text sources arXiv | ADS | data products SIMBAD (19) NED (1) HEASARC (1)

Simultaneous Observations of Seyfert 1 Galaxies by IUE, ROSAT and GINGA

Simultaneous observations of 8 Seyfert 1 type AGN (Fairall-9, Mrk 590, NGC 4051, 3C 273, NGC 5548, Mrk 841, Q 1821+643 and 3C 390.3) obtained with ROSAT and IUE (RIASS program), and for 5 sources (Fairall-9, NGC 4051, 3C 273, Mrk 841 and Q 1821+643) with Ginga, have been analysed with the aim of describing the UV to soft X-ray spectral component in these sources.

Signatures of Cooling Flows

AbstractThe evidence for cooling flows in clusters of galaxies is discussed. Peaked X-ray surface brightness profiles and the presence of soft X-ray spectral components are characteristic signatures of cooling flows. The best available data are consistent with gas cooling at a rate of ~ 100M⊙yr-1 and depositing cooled matter over a radius of 100 – 200 kpc. The same rate is obtained from observations of gas cooling over a range of temperatures and thus a range of cooling times covering less than 3 × 107 yr to more than 3 × 109 yr. It appears that cooling flows are both steady and long-lived. Some indirect optical evidence for distant cooling flows (0.5 < z < 1) is presented.

High-resolution X-ray spectra of solar flares. IX - Mass upflow in the long-duration flare of 1979 June 5

Blueshifted X-ray spectral line components in Fe and Ca spectra of a large long-duration flare observed on June 5, 1979. It is found that blueshifted emission exists for a time interval of at least 28 minutes indicating upflowing plasma at about 250 km/s. Emission measures for both the blueshifted and stationary plasma are derived and the results are interpreted in terms of chromospheric evaporation. The total amount of hot upflowing plasma during the flare rise time exceeds the amount of stationary plasma contained in the loop close to the time of the peak of the flare. This result contradicts the simplest version of the evaporation model. Evaporation can account for the observations only if some of the upflowing plasma cools on time scales much shorter than the rise time of the event, which was about 40 minutes.

Uncorrelated soft and hard X-ray short-term variations from AM Herculis

An investigation of the short-term X-ray variability of AM Her in its high state, based on data obtained with the high resolution imager and the monitor proportional counter on board the Einstein Observatory, is reported. Analysis performed using correlation techniques reveals that the time variations in the soft and the hard X-ray spectral components of the source were uncorrelated at short time delays, although the light curves of the two components showed a very similar behavior, mostly consisting of about 400 s quasi-periodic fluctuations. These findings are difficult to reconcile with the simplest current models of one pole accretion onto magnetized white dwarfs, since these predict the soft X-ray component will mimic the variations of the hard X-ray component. 23 references.

The soft X-ray spectrum of NGC 4151

EXOSAT observations of the Seyfert galaxy NGC 4151 over the period July 1983 to April 1984 have revealed a decreasing flux in the 2 –10 keV band. In accord with previous measurements a power law spectrum attenuated with a simple column of cold gas does not provide a satisfactory spectral fit below ∼3 keV, where a lower relative opacity is required. Inclusion of additional low energy data from the EXOSAT telescopes allows the modelling of the absorbing column to be improved and reveals a second, separate, soft X-ray spectral component.