ASCA Results Research Articles

CHANDRASTUDIES OF THE X-RAY GAS PROPERTIES OF GALAXY GROUPS

We present a systematic analysis of 43 nearby galaxy groups (kT 500 = 0.7-2.7 keV or M 500 = 1013-1014 h –1 M ☉, 0.012 0.15 r 500 and are consistent with a universal temperature profile. We present the K-T relations at six characteristic radii (30 kpc, 0.15 r 500, r 2500, r 1500, r 1000, and r 500), for 43 groups from this work and 14 clusters from the Vikhlinin et al. (2008) sample. Despite large scatter in the entropy values at 30 kpc and 0.15 r 500, the intrinsic scatter at r 2500 is much smaller and remains the same (~ 10%) to r 500. The entropy excess at r 500 is confirmed, in both groups and clusters, but the magnitude is smaller than previous ROSAT and ASCA results. We also present scaling relations for the gas fraction. It appears that the average gas fraction between r 2500 and r 500 has no temperature dependence, ~ 0.12 for 1-10 keV systems. The group gas fractions within r 2500 are generally low and have large scatter. This work shows that the difference of groups from hotter clusters stems from the difficulty of compressing group gas inside of r 2500. The large scatter of the group gas fraction within r 2500 causes large scatter in the group entropy around the center and may be responsible for the large scatter of the group luminosities. Nevertheless, the groups appear more regular and more like clusters beyond r 2500 from the results on gas fraction and entropy. Therefore, mass proxies can be extended into low-mass systems. The M 500-T 500 and M 500-Y X,500 relations derived in this work are indeed well behaved down to at least 2 ×1013 h–1 M ☉.

An XMM-Newton survey of broad iron lines in Seyfert galaxies

We present an analysis of the X-ray spectra of a sample of 37 observations of 26 Seyfert galaxies observed by XMM–Newton in order to characterize their iron Kα emission. All objects show evidence for iron line emission in the 6–7 keV band. A narrow ‘core’ at 6.4 keV is seen almost universally in the spectra, and we model this using a neutral Compton reflection component, assumed to be associated with distant, optically thick material such as the molecular torus. Once this, and absorption by a zone of ionized gas in the line of sight is accounted for, less than half of the sample observations show an acceptable fit. Approximately two-thirds of the sample shows evidence for further, broadened emission in the iron K band. When modelled with a Gaussian, the inferred energy is close to that expected for neutral iron, with a slight redshift, and an average velocity width of ∼0.1c. The mean parameters are consistent with previous ASCA results and support the idea that the broad components can be associated with the accretion disc. Before proceeding to that conclusion, we test an alternative model comprising a blend of three to four narrow, unshifted emission lines (including the 6.4-keV core), together with one to two zones of highly ionized gas in the line of sight. Around one-third of the objects are not adequately fitted by this model, and in general better fits are obtained with a relativistic disc line model, which has fewer free parameters. None the less we find that absorption by ionized gas affects the spectrum above 2.5 keV in approximately half the sample. There is evidence for multiple ionized zones in at least three objects, but in all those cases a blurred reflector is required in addition to the complex absorption. We also identify a number of narrow emission and absorption features around the Fe complex, and the significance and interpretation of these lines is discussed. After accounting for these additional complexities, we determine the typical parameters for the broad reflection. The emission is found to come, on average, from a characteristic radius ∼15 rg and the average disc inclination is ∼ 40°. The broad reflection is on average significantly weaker, by a factor of ∼2, than that expected from a flat disc illuminated by a point source. Notwithstanding these average properties, the objects exhibit a significant and wide range of reflection parameters. We find that 30 per cent of the sample observations can be explained solely with narrow-line components, with no evidence for broadened emission at all. A further 25 per cent show evidence for significant broad emission, but at a characteristic radius relatively far from the black hole. The remaining ∼45 per cent are best fitted with a relativistically blurred reflection model. In 12/37 observations the characteristic emission radius is constrained to be <50 rg, where the gravitational redshift is measurable. For at least this subsample, our observations verify the potential for X-ray spectroscopy to diagnose the strong-gravity regime of supermassive black holes.

The broad iron line physics: summary and outlook

AbstractA brief overview of the ESAC/XMM‐Newton Science Operations Centre Workshop on “Variable and Broad Iron Lines around Black Holes” is presented. Following the relativistic disk‐line theory of accreting black holes, ASCA discovered such broad iron lines from several AGN. XMM‐Newton and Chandra confirmed the ASCA results, but also found more complexities. It was pointed out that poor modelling of the continuum may mimic broad iron line, if ionized absorbers are present. This degeneracy between the broad line and the continuum shape was shown to be resolved by separately determining the continuum and the reflection component with use of an accurate hard X‐ray spectrum obtained with Suzaku. As a result, the relativistic broad iron lines are now robust. Time variations of the primary continuum and the reflection component are often decoupled, the latter varying little. This is explained by the light bending model that applies in the region near to an extreme Kerr hole. The red‐ and/or blueshifted transient iron line features were found with XMM‐Newton, some of which revealed a possible quasi‐periodicity. Such transient features are important dynamical probes of the black hole vicinity. The remaining issues are briefly mentioned. Finally, there is no doubt that the broad line physics continues to be extremely important. Prospects for the future development are discussed, which justify large next‐generation missions. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Fecal ASCA Measurements in the Assessment of Pediatric Patients with Known or Suspected Crohnʼs Disease

Purpose: To examine the utility of measuring fecal ASCA levels as a non-invasive screening measure for CD in children with known or suspected IBD. Methods: 105 patients aged ≤ 18 years, including 86 patients with CD, 17 with UC, 2 with acute colitis, and 16 healthy controls submitted stool and serum specimens for ASCA analysis. Diagnosis of IBD was based on endoscopic, radiologic, and histologic findings. Fecal samples were diluted 1:10 and analyzed using a qualitative ASCA ELISA immunoassay. Fecal ASCA samples were measured blinded of a subject's diagnosis. Results: 52% (45/86) of patients with CD and 30% (5/17) patients with UC tested positive for fecal ASCA. None of the healthy controls tested positive for fecal ASCA. The sensitivity and specificity for fecal ASCA testing was 52% and 62%, respectively. Serum ASCA results were available from 71 subjects. The sensitivity and specificity of serum ASCA measurements in these subjects was 86% and 55%, respectively. Conclusions: The prevalence of antibodies to ASCA appears to be comparable in stool or serum. The specificity of serum ASCA testing is superior to that measured in the feces. However, fecal ASCA testing offers the advantage of being inexpensive and noninvasive. When combined with other fecal diagnostic assays, such as lactoferrin, fecal ASCA testing may prove useful for the assessment of children suspected of having IBD.

X‐Ray Study of Herbig Ae/Be Stars

We present the ASCA results of intermediate-mass pre-main-sequence stars (PMSs), or Herbig Ae/Be stars (HAeBes). Among the 35 ASCA pointed-sources, we detect 11 plausible X-ray counterparts. X-ray luminosities of the detected sources in the 0.5-10 keV band are in the range of log LX ~30-32 ergs s-1, which is systematically higher than those of low-mass PMSs. This fact suggests that the contribution of a possible low-mass companion is not large. Most of the bright sources show significant time variation, particularly, two HAeBes - MWC 297 and TY CrA - exhibit flare-like events with long decay timescales (e-folding time ~ 10-60 ksec). These flare shapes are similar to those of low-mass PMSs. The X-ray spectra are successfully reproduced by an absorbed one or two-temperature thin-thermal plasma model. The temperatures are in the range of kT ~1-5 keV, which are significantly higher than those of main-sequence OB stars (kT < 1 keV). These X-ray properties are not explained by wind driven shocks, but are more likely due to magnetic activity. On the other hand, the plasma temperature rises as absorption column density increases, or as HAeBes ascend to earlier phases. The X-ray luminosity reduces after stellar age of a few x10^6 years. X-ray activity may be related to stellar evolution. The age of the activity decay is apparently near the termination of jet or outflow activity. We thus hypothesize that magnetic activity originates from the interaction of the large scale magnetic fields coupled to the circumstellar disk. We also discuss differences in X-ray properties between HAeBes and main-sequence OB stars.

XMM-Newton EPIC observations of 21 low-redshift PG quasars

We present an X-ray spectral analysis of 21 low redshift quasars observed with XMM-Newton EPIC. All the sources are Palomar Green quasars with redshifts between 0.05 and 0.4 and have low Galactic absorption along the line-of-sight. A large majority of quasars in the sample (19/21) exhibit a significant soft excess below ~1–1.5 keV, whilst two objects (PG 1114+445 and I Zw1) show a deficit of soft X-ray flux due to the presence of a strong warm absorber. Indeed, contrary to previous studies with ASCA and ROSAT, we find that the presence of absorption features near 0.6–1.0 keV is common in our sample. At least half of the objects appear to harbor a warm absorber, as found previously in Seyfert 1 galaxies. We find significant detections of Fe Kα emission lines in at least twelve objects, whilst there is evidence for some broadening of the line profile, compared to the EPIC-pn resolution, in five of these quasars. The determination of the nature of this broadening (e.g., Keplerian motion, a blend of lines, relativistic effects) is not possible with the present data and requires either higher S/N or higher resolution spectra. In seven objects the line is located between 6.7–7 keV, corresponding to highly ionized iron, whereas in the other five objects the line energy is consistent with 6.4 keV, i.e. corresponding to near neutral iron. The ionized lines tend to be found in the quasars with the steepest X-ray spectra. We also find a correlation between the continuum power law index Γ and the optical Hβ width, in both the soft and hard X-ray bands, whereby the steepest X-ray spectra are found in objects with narrow Hβ widths, which confirms previous ROSAT and ASCA results. The soft and hard band X-ray photon indices are also strongly correlated, i.e. the steepest soft X-ray spectra correspond the steepest hard X-ray spectra. We propose that a high accretion rate and a smaller black hole mass is likely to be the physical driver responsible for these trends, with the steep spectrum objects likely to have smaller black hole masses accreting near the Eddington rate.

XMM-NewtonObservations of Two High-Redshift Quasars: RX J1028-0844 and BR 0351-1034

We report the results of XMM-Newton observations of two high-redshift quasars, one radio-loud, RX J1028.6-0844 (z = 4.276) and one radio-quiet, BR 0351-1034 (z = 4.351). We find that the evidence for strong excess absorption toward RX J1028-0844 is marginal at best, contrary to previous claims. The superior sensitivity and broader, softer energy range of XMM-Newton (0.2–10 keV) allows better determination of spectral parameters than much deeper ASCA observations (0.8–7 keV). Our XMM-Newton observations call into question several other ASCA results of strong absorption toward high-redshift radio-loud quasars. RX J1028.6-0844 occupies the same parameter space in broadband spectral properties as the low-redshift BL Lac objects, showing no obvious evolution with redshift. The radio-quiet quasar BR 0351-1024 became fainter between ROSAT and XMM observations by a factor of at least 5, but with the present data we cannot determine whether there is an associated spectral change. These observations do not support previous claims of weaker X-ray emission from high-redshift, radio-quiet quasars. The soft X-ray spectral slope required to reconstruct the ROSAT PSPC hardness ratio of BR 0351-1034 is about αX = 3.5, the steepest X-ray slope ever observed in a high-redshift quasar and similar to that of low-redshift narrow-line Seyfert 1 galaxies.

Review of Discrete X-Ray Sources in the Small Magellanic Cloud: Summary of the ASCA Results and Implication on the Recent Star-Forming Activity

Abstract We made 22 observations on the Small Magellanic Cloud (SMC) and covered full regions of the main body and the eastern wing by the end of the ASCA mission. We detected 106 discrete sources with a criterion of $\mathrm{S/N} \gt 5$$\mathrm{S/N} \gt 5$ and performed systematic analyses on all of the sources. We determined the source positions with an $\sim {40{}^{\mathrm {\prime \prime }}}$ error radius (90% confidence) for sources detected in the central ${20{}^{\mathrm {\prime }}}$ radius of the GIS. We detected coherent pulsations from 17 sources. Among them, eight were newly discovered during this study. We classified most of these pulsars as X-ray binary pulsars (XBPs) based on their properties, such as the flux variability and the existence of an optical counterpart. We detected X-ray emission from eight supernova remnants (SNRs). Among them, five SNRs showed emission lines in their spectra, hence we regarded the five as thermal SNRs. We found that XBPs and thermal SNRs in the SMC can be clearly separated by their spectral hardness ratio. Applying this empirical law to faint (thus unclassified) sources, we found 19 XBP candidates and four thermal SNR candidates. We also found several tens of candidates for active galactic nuclei, both from the hardness ratio and the $\log N \hbox{--}\log S$ relation of extragalactic sources. Based on these ASCA results and further information from ROSAT, SAX, RXTE, CGRO, Chandra, and XMM-Newton, we compiled comprehensive catalogues of discrete X-ray sources in the Small Magellanic Cloud. Using the catalogues, we derived the spatial distributions of XBPs and SNRs. XBPs and SNRs were found to be concentrated in the main body and eastern wing, which resembles the distribution of young stars with ages of $\sim 2 \times 10^7 \,\mathrm{yr}$. By comparing the source populations in the SMC and our Galaxy, we suggest that the star-forming rate (per unit mass) in the SMC was much higher than the Galaxy $\sim 10^7 \,\mathrm{yr}$ ago. We also discuss the recent change of the star-forming rate in the SMC.

XMM‐Newtonand Very Large Array Observations of the Variable Wolf‐Rayet Star EZ Canis Majoris: Evidence for a Close Companion?

We present new X-ray and radio observations of the Wolf-Rayet star EZ CMa (HD 50896) obtained with XMM-Newton and the Very Large Array (VLA). This WN4 star exhibits optical and UV variability at a period of 3.765 days whose cause is unknown. Binarity may be responsible, but the existence of a companion has not been proven. The radio spectral energy distribution of EZ CMa determined from VLA observations at five frequencies is in excellent agreement with predictions for free-free wind emission, and the ionized mass-loss rate allowing for distance uncertainties is = 3.8 (±2.6) × 10-5 M☉ yr-1. The CCD X-ray spectra show prominent Si XIII and S XV emission lines and can be acceptably modeled as an absorbed multitemperature optically thin plasma, confirming earlier ASCA results. Nonsolar abundances are inferred with Fe notably deficient. The X-ray emission is dominated by cooler plasma at a temperature kTcool ≈ 0.6 keV, but a harder component is also detected, and the derived temperature is kThot ≈ 3.0-4.2 keV if the emission is thermal. This is too high to be explained by radiative wind shock models, and the X-ray luminosity of the hard component is 3 orders of magnitude lower than expected for accretion onto a neutron star companion. We show that the hard emission could be produced by the Wolf-Rayet wind shocking onto a normal (nondegenerate) stellar companion at close separation. Finally, using comparable data sets we demonstrate that the X-ray and radio properties of EZ CMa are strikingly similar to those of the WN5-6 star WR 110. This similarity points to common X-ray and radio emission processes in WN stars and discredits the idea that EZ CMa is anomalous within its class.

Merger Shocks in Galaxy Clusters A665 and A2163 and Their Relation to Radio Halos

We present Chandra gas temperature maps for two hot, intermediate-redshift clusters A665 and A2163. Both show strong temperature variations in their central r=1 Mpc regions, naturally interpreted as product of the subcluster mergers. The A665 map reveals a shock in front of the cool core, while the temperature structure of A2163 is more complicated. On a larger linear scale, our data on A2163 indicate a radial temperature decline in agreement with earlier ASCA results, although the uncertainties are large. Both these clusters exhibit previously known synchrotron radio halos. Comparison of the radio images and the gas temperature maps indicates that radio emission predominantly comes from the hot gas regions, providing a strong argument in favor of the hypothesis that relativistic electrons are accelerated in merger shocks.

ASCA Temperature Maps of Three Clusters of Galaxies: Abell 1060, AWM 7, and the Centaurus Cluster

Abstract We present two-dimensional temperature maps of three bright clusters of galaxies (Abell 1060, AWM 7, and the Centaurus cluster), based on multi-pointing observations with the ASCA GIS. The temperatures were derived from hardness ratios by taking into account the XRT response. For the Centaurus cluster, we subtracted the central cool component using the previous ASCA and ROSAT results, and the metallicity gradients observed in AWM 7 and the Centaurus cluster were included in deriving the temperatures. The intracluster medium in Abell 1060 and AWM 7 is almost isothermal from the center to the outer regions with temperatures of 3.3 and $3.9$ keV, respectively. The Centaurus cluster exhibits remarkable hot regions within about ${30{}^{\mathrm {\prime }}}$ from the cluster center, showing a temperature increase of $+0.8$ keV from the surrounding level of 3.5 keV, and the outer cool regions with lower temperatures by $-1.3$ keV. These results imply that a strong merger has occurred in the Centaurus in the recent 2–3 Gyr, and that the central cool component has survived it. In contrast, the gas in Abell 1060 was well-mixed in an early period, which probably has prevented the development of a central cool component. In AWM 7, mixing of the gas should have occurred in a period earlier than the epoch of metal enrichment.

A Moving Cold Front in the Intergalactic Medium of A3667

We present results from a Chandra observation of the central region of the galaxy cluster A3667 with emphasis on the prominent sharp X-ray brightness edge spanning 0.5 Mpc near the cluster core. Our temperature map shows large-scale nonuniformities characteristic of the ongoing merger, in agreement with earlier ASCA results. The brightness edge turns out to be a boundary of a large cool gas cloud moving through the hot ambient gas, very similar to the fronts discovered by Chandra in A2142. The higher quality of the A3667 data allows the direct determination of the cloud velocity. At the leading edge of the cloud, the gas density abruptly increases by a factor of 3.9 ± 0.8, while the temperature decreases by a factor of 1.9 ± 0.2 (from 7.7 to 4.1 keV). The ratio of the gas pressures inside and outside the front shows that the cloud moves through the ambient gas at near-sonic velocity, M = 1 ± 0.2 or v = 1400 ± 300 km s-1. In front of the cloud, we observe the compression of the ambient gas with an amplitude expected for such a velocity. A smaller surface brightness discontinuity is observed further ahead, ~350 kpc in front of the cloud. We suggest that it corresponds to a weak bow shock, implying that the cloud velocity may be slightly supersonic. Given all the evidence, the cold front appears to delineate the remnant of a cool subcluster that recently has merged with A3667. The cold front is remarkably sharp. The upper limit on its width, 35 or 5 kpc, is several times smaller than the Coulomb mean free path. This is a direct observation of suppression of the transport processes in the intergalactic medium, most likely by magnetic fields.

The X-ray nebula of the filled center supernova remnant 3C 58 and its interaction with the environment

An XMM-Newton observation of the plerionic supernova remnant 3C 58 has allowed us to study the X-ray nebula with unprecedented detail. A spatially resolved spectral analysis with a resolution of 8 00 has yielded a precise determination of the relation between the spectral index and the distance from the center. We do not see any evidence for bright thermal emission from the central core. In contrast with previous ASCA and Einstein results, we derive an upper limit to the black-body 0.5{10 keV luminosity and emitting area of 1: 81 0 32 erg s 1 and 1: 31 0 10 cm 2 , respectively, ruling out emission from the hot surface of the putative neutron star and also excluding the \outer-gap model for hot polar caps. We have performed for the rst time a spectral analysis of the outer regions of the X-ray nebula, where most of the emission is still non-thermal, but where the addition of a soft (kT =0 :2 0:3 keV) optically thin plasma component is required to t the spectrum at E< 1k eV. This component provides 6% of the whole remnant observed flux in the 0.5{10.0 keV band. We show that a Sedov interpretation is incompatible with the SN 1181{3C 58 association, unless there is a strong deviation from electron-ion energy equipartition, and that an origin of this thermal emission in terms of the expansion of the nebula into the ejecta core nicely ts all the radio and X-ray observations.

BeppoSAX spectroscopy of the luminous X-ray sources in M 33

The nearby galaxy M 33 was observed by the imaging X-ray instruments on-board BeppoSAX. Two observations at different phases of the 105.9 day intensity cycle of the luminous central source X-8 failed to reveal the expected modulation, suggesting that it is probably transitory. Similar behavior has been observed from several X-ray binary sources. This strengthens somewhat the idea that M 33 X-8 is a black hole accreting from a binary companion. The 0.2-10 keV spectrum of M 33 X-8 can best be modeled by an absorbed power-law with a photon index, α, of and a disk-blackbody with a temperature, kT, of keV and a projected inner-disk radius of km. This spectral shape is in good agreement with earlier ASCA results. The 2-10 keV spectra of M 33 X-4, X-5, X-7, X-9 and X-10 are all consistent with power-law or bremsstrahlung models, whilst that of X-6 appears to be significantly more complex and may be reasonably well modeled with a disk-blackbody with keV and a projected inner-disk radius of km. The spectrum of M 33 X-9 is rather hard with . Compared to earlier Einstein and ROSAT observations, M 33 X-7 and X-9 varied in intensity, M 33 X-4, X-6, and X-10 may have varied and M 33 X-5 remained constant.

The XMM-Newton view of stellar coronae: High-resolution X-ray spectroscopy of Capella

We present the high-resolution RGS X-ray spectrum of the stellar binary Capella observed by the XMM-Newton satellite. A multi-thermal approach has first been applied to fit the data and derive elemental abundances. Using the latter, the emission measure distribution has been reconstructed using a Chebychev polynomial fit. Its shape is found to display a sharp peak around 7 MK, consistent with previous EUVE and ASCA results. A smaller but significant amount of emission measure is required around 1.8 MK in order to explain the Ovii He-like triplet and the Cvi Lyα line. We have applied the temperature diagnostics of dielectronic recombination satellite lines to the He-like Ovii triplet to constrain the cool plasma temperature, and have obtained a lower limit consistent with the global reconstruction of the emission measure distribution. We have used line ratios from the forbidden, intercombination, and resonance lines of the Ovii triplet to derive an average density for the cool coronal plasma ( cm-3). Implications for the coronal structure of Capella are discussed.

Highlights of X-Ray Astronomy Mainly Based on ASCA Results

Highlights of X-Ray Astronomy Mainly Based on ASCA Results

ASCAObservations of the Sagittarius B2 Cloud: An X‐Ray Reflection Nebula

We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low-energy cutoff below about 4 keV, and a pronounced edge structure at 7.1 keV. The X-ray image is extended, and its peak position is shifted from the core of the molecular cloud toward the Galactic center by about 1'-2'. The X-ray spectrum and the morphology are well reproduced by a scenario that X-rays from an external source located in the Galactic center direction are scattered by the molecular cloud Sgr B2 and come into our line of sight. Thus, Sgr B2 may be called an X-ray reflection nebula. Possible implications of the Galactic center activity related to this unique source are presented.

ASCA Observations of RX J1838.4–0301

The results of ASCA observations of RX J1838.4–0301 are presented. The source was found to be faint and there was no obvious X-ray flare during the ASCA observation. No evidence for pulsations was found near to the 5.45 s period previously reported from ROSAT observations. The source energy spectrum cannot be fitted well with either a single-component power law, thermal bremsstrahlung, or blackbody emission model, while a variety of two component models do give acceptable fits. The flux which we derive is consistent with that measured in the quiescent state with ROSAT. On the basis of the ROSAT and ASCA results, we suggest that RX J1838.4–0301 may be a transient source in which the quiescent state has a fairly constant flux level. However, our results do not yet enable a clear determination of whether this source is an anomalous X-ray pulsar or some other type of object.

Observation of FE-line emission from sagittarius B2 — Evidence for past activities of our galaxy

We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low energy cutoff below 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted in the direction of the Galactic center by about 1–2 arcminute from the core of the molecular cloud. The X-ray spectrum and morphology are well reproduced by a scenario that X-rays from a source located at the Galactic center side are scattered by the molecular cloud Sgr B2, and come into our line of sight. Thus Sgr B2 may be called an X-ray reflection nebula.

The ASCA observation of GRO J1744-28

The ASCA results of the bursting X-ray pulsar GRO J1744-28 are reported. The observations were made twice, in February 1996 and March 1997. We detected 12 and 17 Type II bursts during the two observations, with mean bursting intervals of about 27 min and 37 min. Each burst is followed by an intensity dip with the depleted flux depending on the burst fluence. The energy spectra are approximated by an absorbed power law with additional structure around 6–7 keV, which is most probably due to iron and maybe reproduced by the disk line model with additional broadening mechanism. The absorption column is constant ((5 − 6) × 10 22 cm −2), independent of the observation dates and emission phase (persistent, burst and dip). This means the source may be actually located near the galactic center (8.5kpc).