Medium Energy Concentrator Spectrometer Research Articles

ABeppoSAXObservation of the IC 1262 Galaxy Cluster

We present an analysis of BeppoSAX observations of the IC 1262 galaxy cluster and report the first temperature and abundance measurements, along with preliminary indications of diffuse, nonthermal emission. By fitting a 6' (~360 h kpc) region with a single Mewe-Kaastra-Liedahl model with photoelectric absorption, we find a temperature of 2.1-2.3 keV and an abundance of 0.45-0.77 (both 90% confidence). We find that the addition of a power-law component provides a statistically significant improvement (F-test = 90%) to the fit. The addition of a second thermal component also improves the fit, but we argue that it is physically implausible. The power-law component has a photon index (ΓX) of 0.4-2.8 and a nonthermal flux of (4.1-56.7) × 10-5 photons cm-2 s-1 over the 1.5-10.5 keV range in the Medium Energy Concentrator Spectrometer detector. An unidentified X-ray source found in the ROSAT High Resolution Imager observation (~09 from the center of the cluster) is a possible explanation for the nonthermal flux; however, additional evidence of diffuse, nonthermal emission comes from the NRAO VLA Sky Survey and the Westerbork Northern Sky Survey radio measurements, in which excess diffuse radio flux is observed after point-source subtraction. The radio excess can be fitted to a simple power law with a spectral index of ~1.8, which is consistent with the nonthermal X-ray emission spectral index. The steep spectrum is typical of diffuse emission, and the size of the radio source implies that it is larger than the cD galaxy and not due to a discreet source.

BeppoSAXObservations of Synchrotron X‐Ray Emission from Radio Quasars

We present new BeppoSAX Low Energy Concentrator Spectrometer (LECS), Medium Energy Concentrator Spectrometer (MECS), and Phoswich Detector System (PDS) observations of four flat-spectrum radio quasars (FSRQs) having effective spectral indices αro and αox typical of high-energy peaked BL Lac objects. Our sources have X-ray-to-radio flux ratios on average ~70 times larger than "classical" FSRQs and lie at the extreme end of the FSRQ X-ray-to-radio flux ratio distribution. The collected data cover the energy range 0.1-10 keV (observer's frame), reaching ~100 keV for one object. The BeppoSAX band in one of our sources, RGB J1629+4008, is dominated by synchrotron emission peaking at ~2 × 1016 Hz, as also shown by its steep (energy index αX ~ 1.5) spectrum. This makes this object the first known FSRQ whose X-ray emission is not due to inverse Compton radiation. Two other sources display a flat BeppoSAX spectrum (αX ~ 0.7), with weak indications of steepening at low X-ray energies. The combination of BeppoSAX and ROSAT observations, (nonsimultaneous) multifrequency data, and a synchrotron inverse Compton model suggests synchrotron peak frequencies ≈1015 Hz, although a better coverage of their spectral energy distributions is needed to provide firmer values. If confirmed, these values would be typical of "intermediate" BL Lac objects for which the synchrotron and inverse Compton components overlap in the BeppoSAX band. Our sources, although firmly in the radio-loud regime, have powers more typical of high-energy peaked BL Lac objects than of FSRQs, and indeed their radio powers put them near the low-luminosity end of the FSRQ luminosity function. We discuss this in terms of an anticorrelation between synchrotron peak frequency and total power, based on physical arguments, and also as possibly due to a selection effect.

Gravitating mass profiles of nearby galaxy clusters and relations with X-ray gas temperature, luminosity and mass

We consider a sample of 22 nearby clusters of galaxies observed with the Medium Energy Concentrator Spectrometer (MECS) on board of BeppoSAX. They cover the range in gas temperature between 3 and 10 keV, with bolometric X-ray luminosity between 2e44 erg/s and 6e45 erg/s. Using the de-projected gas temperature and density profiles resolved in a number of bins between 5 and 7 and obtained from this dataset only, we recover the total gravitating mass profiles for 20 objects just applying the (i) spherical symmetry and (ii) hydrostatic equilibrium assumptions. We investigate the correlations between total mass, gas temperature, luminosity at several overdensities values and find that the slopes of these relations are independent from the considered overdensity and consistent with what is predicted from the cluster scaling laws. The best-fit results on the normalization of the M-T relation are slightly lower, but still consistent considering the large errors that we measure, with hydrodynamical simulations. A segregation between relaxed and non-relaxed systems is present in each plane of these relations pointing out to a significant component in their intrinsic scatter. This segregation becomes more evident at higher overdensities and when physical quantities, like M_gas and L, that are direct function of the amount of gas observed, are considered.

CLC][ITAL]BeppoSAX[/ITAL][/CLC] Observation of NGC 3079

Using the BeppoSAX observatory, we have observed a nearby LINER/Seyfert 2 galaxy, NGC 3079, which is known as an outflow galaxy and a bright H2O maser source. Using the Phoswich Detection System, we have revealed that the NGC 3079 nucleus suffers from a Compton-thick absorption, with a hydrogen column density ~1025 cm-2. After corrected the absorption, the 2-10 keV luminosity becomes 1042-1043 ergs s-1 at a distance of 16 Mpc. It is 2-3 orders of magnitude higher than that observed in the Medium Energy Concentrator Spectrometer band (below 10 keV). We also detected a strong Fe K line at 6.4 keV with an equivalent width of 2.4 keV, which is consistent with the heavy absorption.

The Discovery of Quiescent X-Ray Emission from SAX J1808.4−3658, the Transient 2.5 Millisecond Pulsar

We report on a 20 ks BeppoSAX observation of the transient 2.5 ms X-ray pulsar SAX J1808.4-3658 in its quiescent state. A source at a level of ~3 × 10-3 counts s-1 was detected with the BeppoSAX Medium Energy Concentrator Spectrometer at a position consistent with that of SAX J1808.4-3658. The inferred 0.5-10 keV luminosity was ~(2-3) × 1032 ergs s-1 (for a distance of 4 kpc), a value similar to that measured from other quiescent low-mass X-ray transients hosting an old neutron star. This result is discussed in the light of the propeller and radio pulsar shock emission models for the quiescent emission of these systems.

How Abundant Is Iron in the Core of the Perseus Cluster?

The analysis of Perseus data collected with the Medium-Energy Concentrator Spectrometer (MECS) on board BeppoSAX shows that the ratio of the flux of the 8 keV line complex (dominated by Fe Kβ emission) to the 6.8 keV line complex (dominated by Fe Kα emission) is significantly larger than predicted by standard thermal emission codes. Moreover, the analysis of spatially resolved spectra shows that the above ratio decreases with increasing cluster radius. We find that, among the various explanations that we consider, the most likely requires the plasma to be optically thick for resonant scattering at the energy of the Fe Kα line. We argue that if this is the case, then measures of the iron abundance made using standard thermal emission codes that assume optically thin emission may significantly underestimate the true iron abundance. In the case of the core of Perseus, we estimate the true abundance to be ~0.9 solar in a circular region with a radius of ~60 kpc and centered on NGC 1275. Finally, we speculate that similar results may hold for the core of other rich clusters.

Early Results from the Low-Energy Concentrator Spectrometer on-board BeppoSAX

SAX, an acronym for “Satellite Italiano per Astronomia a raggi X”, now renamed “BeppoSAX” in honor of Giuseppe Occhialini, is the first X-ray mission sensitive in the very broad energy range between 0.1 and 300 keV (Boella et al. 1997a). The Narrow Field Instruments (NFI) have approximately 1° fields of view and consist of the imaging low- and medium-energy concentrator spectrometers (LECS, 0.1-10 keV, Parmar et al. 1997; and MECS, 1-10 keV, Boella et al. 1997b), and the non-imaging high pressure gas scintillation proportional counter (HPGSPC, 3-120 keV, Manzo et al. 1997) and Phoswich detector system (PDS, 15-300 keV, Frontera et al. 1997). All the NFI are coaligned and are normally operated simultaneously. In addition, the payload includes two wide field cameras (WFC, 2-30 keV; Jager et al. 1997) which observe in directions perpendicular to the NFI. These allow the detection of X-ray transient phenomena, as well as long-term variability studies.

The medium-energy concentrator spectrometer on board the BeppoSAX X-ray astronomy satellite

The scientic instrumentation on board the X-ray Astronomy Satellite BeppoSAX includes a Medium Energy Concentrator Spectrometer (MECS), operating in the energy range 1:3 10 keV, which consists of three units, each composed of a grazing incidence Mirror Unit and of a position sensitive Gas Scintillation Proportional Counter. The design and performance of the MECS in- strument are here described, together with its on-ground calibration.