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M. Matsuoka

Publications and source records attributed to M. Matsuoka.

At least 37 records · Page 2Linked to original sources
arXiv2003

HETE-2 Observations of the Extremely Soft X-Ray Flash XRF 020903

We report HETE-2 WXM/FREGATE observations of the X-ray flash, XRF 020903. This event was extremely soft: the ratio log(S_X/S_gamma) = 0.7, where S_X and S_gamma are the fluences in the 2-30 and 30-400 keV energy bands, is the most extreme value observed so far by HETE-2. In addition, the spectrum has an observed peak energy E^{obs}_{peak} < 5.0 keV (99.7 % probability upper limit) and no photons were detected above ~10 keV. The burst is shorter at higher energies, which is similar to the behavior of long GRBs. We consider the possibility that the burst lies at very high redshift and that the low value of E^{obs}_{peak} is due to the cosmological redshift, and show that this is very unlikely. We find that the properties of XRF 020903 are consistent with the relation between the fluences S(7-30 keV) and S(30-400 keV) found by Barraud et al. for GRBs and X-ray-rich GRBs, and are consistent with the extension by a decade of the hardness-intensity correlation (Mallozzi et al. 1995) found by the same authors. Assuming that XRF 020903 lies at a redshift z = 0.25 as implied by the host galaxy of the candidate optical and radio afterglows of this burst, we find that the properties of XRF 020903 are consistent with an extension by a factor ~300 of the relation between the isotropic-equivalent energy E_iso and the peak E_peak of the nu F_nu spectrum (in the source frame of the burst) found by Amati et al. for GRBs. The results presented in this paper therefore provide evidence that XRFs, X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon. The results also impose strong constraints on models of XRFs and X-ray-rich GRBs.

astro-ph↗
arXiv2003

Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2

The Wide-field X-ray Monitor (WXM) is one of the scientific instruments carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on 2000 October 9. HETE-2 is an international mission consisting of a small satellite dedicated to provide broad-band observations and accurate localizations of gamma-ray bursts (GRBs). A unique feature of this mission is its capability to determine and transmit GRB coordinates in almost real-time through the burst alert network. The WXM consists of three elements: four identical Xe-filled one-dimensional position-sensitive proportional counters, two sets of one-dimensional coded apertures, and the main electronics. The WXM counters are sensitive to X-rays between 2 keV and 25 keV within a field-of-view of about 1.5 sr, with a total detector area of about 350 cm$^2$. The in-flight triggering and localization capability can produce a real-time GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of $10^{-7}$ erg cm$^{-2}$. In this report, the details of the mechanical structure, electronics, on-board software, ground and in-flight calibration, and in-flight performance of the WXM are discussed.

astro-ph↗
arXiv2003

HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211

A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1 and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211 is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt localization allowed the detection of an optical afterglow for what would otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that some fraction of burst afterglows are ``optically dark'' because their optical afterglows at times > 1 hr after the burst are very faint, and thus have often escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have very bright afterglows at times < 20 min after the burst.

astro-ph↗
arXiv2003

Spectral analysis of 35 GRBs/XRFs observed with HETE-2/FREGATE

We present a spectral analysis of 35 GRBs detected with the HETE-2 gamma-ray detectors (the FREGATE instrument) in the energy range 7-400 keV. The GRB sample analyzed is made of GRBs localized with the Wide Field X-ray Monitor onboard HETE-2 or with the GRB Interplanetary Network. We derive the spectral parameters of the time-integrated spectra, and present the distribution of the low-energy photon index, alpha, and of the peak energy, e_peak . We then discuss the existence and nature of the recently discovered X-Ray Flashes and their relationship with classical GRBs.

astro-ph↗
arXiv2002

HETE-2 Localization and Observations of the Short, Hard Gamma-Ray Burst GRB020531

The {\it HETE-2} (hereafter \HETE) French Gamma Telescope (FREGATE) and the Wide-field X-ray Monitor (WXM) instruments detected a short ($t_{50} = 360$ msec in the FREGATE 85-300 keV energy band), hard gamma-ray burst (GRB) that occurred at 1578.72 SOD (00:26:18.72 UT) on 31 May 2002. The WXM flight localization software produced a valid location in spacecraft (relative) coordinates. However, since no on-board real-time star camera aspect was available, an absolute localization could not be disseminated. A preliminary localization was reported as a GCN Position Notice at 01:54:22 UT, 88 min after the burst. Further ground analysis produced a refined localization, which can be expressed as a 90% confidence rectangle that is 67 arcminutes in RA and 43 arcminutes in Dec (90% confidence region), centered at RA = +15$^{\rm h}$ 14$^{\rm m}$ 45$^{\rm s}$, Dec = -19$^\circ$ 21\arcmin 35\arcsec (J2000). An IPN localization of the burst was disseminated 18 hours after the GRB (Hurley et al. 2002b). A refined IPN localization was disseminated $\approx$ 5 days after the burst. This hexagonal-shaped localization error region is centered on RA = 15$^{\rm h}$ 15$^{\rm m}$ 03.57$^{\rm s}$, -19$^\circ$ 24\arcmin 51.00\arcsec (J2000), and has an area of $\approx$ 22 square arcminutes (99.7% confidence region). The prompt localization of this short, hard GRB by \HETE and the anti-Sun pointing of the \HETE instruments, coupled with the refinement of the localization by the IPN, has made possible rapid follow-up observations of the burst at radio, optical, and X-ray wavelengths.

astro-ph↗
arXiv2002

GRB010921: Localization and Observations by the HETE Satellite

On September 21 at 18950.56 SOD (05:15:50.56) UT the FREGATE gamma-ray instrument on the High Energy Transient Explorer (HETE) detected a bright gamma-ray burst (GRB). The burst was also seen by the X-detector on the WXM X-ray instrument and was therefore well-localized in the X direction; however, the burst was outside the fully-coded field-of-view of the WXM Y-detector, and therefore information on the Y direction of the burst was limited. Cross-correlation of the HETE and Ulysses time histories yielded an Interplanetary Network (IPN) annulus that crosses the HETE error strip at a ~45 degree angle. The intersection of the HETE error strip and the IPN annulus produces a diamond-shaped error region for the location of the burst having an area of 310 square arcminutes. Based on the FREGATE and WXM light curves, the duration of the burst is characterized by a t90 = 18.4 s in the WXM 4 - 25 keV energy range, and 23.8 s and 21.8 s in the FREGATE 6 - 40 and 32 - 400 keV energy ranges, respectively. The fluence of the burst in these same energy ranges is 4.8 10^{-6}, 5.5 10^{-6}, and 11.4 10^{-6} erg cm^{-2}, respectively. Subsequent optical and radio observations by ground-based observers have identified the afterglow of GRB010921 and determined an apparent redshift of z = 0.450.

astro-ph↗
arXiv2001

SSC of MAXI experiment

Monitor of All-sky X-ray Image (MAXI) on the International Space Station (ISS) has two kinds of X-ray detectors: the Gas Slit Camera (GSC) and the Solid-state Slit Camera (SSC). SSC is an X-ray CCD array, consisting of 16 chips, which has the best energy resolution as an X-ray all-sky monitor in the energy band of 0.5 to 10 keV. Each chip consists of 1024x1024 pixels with a pixel size of 24$μ$m, thus the total area is ~200 cm^2. We have developed an engineering model of SSC, i.e., CCD chips, electronics, the software and so on, and have constructed the calibration system. We here report the current status of the development and the calibration of SSC.

astro-ph↗
arXiv2001

A Rapid X-ray Flare in the Radio-loud Narrow Line Quasar PKS 0558-504

We report the detection of a very short time scale flare in the radio-loud narrow line quasars PKS 0558-504 by using ASCA. The X-ray count rates increased and decreased by a factor of two in 33 minutes, and possibly by 40% in as short as two minutes during this flare, confirming that such flare event does occur in this object with imaging detectors. The implied largest rate of change in luminosity in 0.8-10 keV alone, dL/dt=(1.8+/-0.4) 10^{42} ergs s^-2, is several times higher than the limit sets for the isotropic emitting plasma around a Kerr black hole. Either emission from a relativistic boosting jet or a magnetic heated corona may explain such high radiative efficiency. Magnetic field with a strength of at least a few 10^4 Gauss is required in the latter case. The spectrum during this flare is significant harder than the average one. Three radio loud narrow line active galactic nuclei (AGN) possess considerably smaller black holes than in radio loud AGN in bright quasar survey, indicating they are still in a phase of the rapid growth of the black hole by accretion.

astro-ph↗
arXiv2000

Development of Superconducting Linac for the Kek/Jaeri Joint Project

The JAERI/KEK Joint Project for the high-intensity proton accelerator facility has been proposed with a superconducting (SC) linac option from 400 MeV to 600MeV. System design of the SC linac has been carried out based on the equipartitioning concept. The SC linac is planned to use as an injector to a 3GeV rapid cycling synchrotron (RCS) for spallation neutron source after it meets requirement to momentum spread less than +-0.1%. In the R&D work for SC cavities, vertical tests of single-cell and 5 cell cavities were performed. Experiments on multi-cell (5 cell) cavities of b=0.50 and b=0.89 at 2K were carried out with values of maximum electric surface peak fields of 23MV/m and 31MV/m, respectively. A model describing dynamic Lorentz detuning for SC cavities has been developed for pulse mode operation. Validity of the model was confirmed experimentally to simulate the performance.

physics.acc-ph↗
arXiv2000

Evidence of thick obscuring matter revealed in the X-ray spectrum of the Z=4.28 quasar RXJ1028.6-0844

We report the discovery of an unambiguous, substantial low-energy cutoff in the broad band X-ray spectrum of the radio quasar RXJ1028.6-0844 at a redshift of 4.276 obtained with the ASCA satellite, which we preferably explained as indication of excess X-ray absorption. The equivalent hydrogen column density of the absorbing matter, depending on the redshift and metallicity, ranges from 2.5x10**21 cm**(-2) for local absorption up to 2.1x10**23 cm**(-2) (solar metallicity) or 1.6x10**24 cm**(-2) (10% solar metallicity) for absorption at the quasar redshift. Such a value is among the largest found for high-redshift radio quasars. The absorption, if interpreted as being produced close to the quasar, may indicate the presence of a remarkably large amount of obscuring matter in the quasar environment in the early universe. Implications of the result for the possible origins of the absorbing matter are discussed, concerning especially galactic intervening matter, cool intracluster gas, and ambient medium around the quasar jet. The quasar itself has an enormous apparent luminosity of at least about 2.6x10**47 erg/s (H0=50, q0=0.5) and a power law photon index of 1.67(+0.07,-0.04) in the 2-50keV band in the source rest frame.

astro-ph↗
arXiv2000

Multiple BeppoSAX Observations of IC 4329A to Probe the Origin of the Compton Reflection Component in Seyfert 1 Galaxies

IC 4329A is the brightest known Seyfert galaxy in hard (~2-30 keV) X-rays and is likely to be representative of Seyfert 1 galaxies as a class. A recent 100 ks BeppoSAX observation (Perola et al. 1999) clearly confirmed the presence of a warm absorber, a reflection component (R~0.6), and a high-energy cut-off in the power law at Ec~270 keV. Its richness in spectral features, combined with its large flux (~1.6 x 10**-10 erg/cm2s between 2-10 keV), make this target ideal for multiple observations (in particular with BeppoSAX) to search for spectral variations. Results obtained from 3 follow-up observations (40 ks each) are presented here. The first and most important goal of this study was to probe the origin of the Compton reflection component observed in Seyfert galaxies by monitoring the variability of the reflection continuum and FeK line in response to primary continuum variations. The second goal was to search for variability in the high energy cutoff. We obtain however no conclusive results on any of these issues. In fact, all four observations unfortunately caught the source at almost the same flux, showing only little, and marginal, spectral changes between different observations.

astro-ph↗
arXiv2000

X-ray observation of the super-luminal quasar 4C+73.18 (1928+738) by ASCA

The results of an X-ray observation of the nearby core-dominated, super- luminal quasar 4C+73.18 (1928+738) with ASCA are reported. Variations of the 1-10keV flux on time-scales of the order of 10 hours were found while the 0.5-1keV flux remained almost unchanged. The quasar shows a curved spectrum in the 0.8-10keV band, which can be modeled as a power law plus a soft component. Both, the spectrum and the uncorrelated flux variations indicate the presence of a soft X-ray excess, which might be the high-energy extension of the intense UV bump emission found in this quasar. The hard X-ray emission is dominated by the flat power law (photon index 1.1-1.5). The results are consistent with models in which the hard X-rays are emitted from the relativistic jet. An iron line emission as reported in a previous Ginga observation (Lawson & Turner 1997) was not detected. We suggest that the line detected by Ginga might be not associated with the quasar. There are indications for a tentative weak emission line-like feature around 1.25keV (1.63keV in the quasar frame) in both, the SIS and GIS spectra. The energy is surprisingly close to that of an unexplained line found in the flat-spectrum quasar PKS0637-752 by Yaqoob et al. (1998).

astro-ph↗
arXiv1999

Recent ASCA and SAX observations of intermediate BL Lac objects

We present 6 ASCA and SAX observations of 4 intermediate BL Lac objects (1034+5727, 1055+5644, 1424+2401, 1741+1936). Their X-ray spectral properties and spectral energy distributions are compared to typical X-ray and radio selected BL Lacs. 1055+5644 varied by a factor of ten in flux without significant spectral changes.

astro-ph↗
arXiv1999

How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?

Recently, convincing evidence was found for extremely large X-ray absorption by column densities $> 10^{23} cm^{-2}$ in broad absorption line quasars. One consequence of this is that any soft X-ray emission from these QSOs would be the scattered light or leaked light from partially covering absorbing material. A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent will allow to determine the total column density as well as the effective covering factor of the absorbing material, which can be hardly obtained from the UV absorption lines. Brinkmann et al. (1999) showed that both the unabsorbed and absorbed components are detected in the nearby very bright broad absorption line quasar PG 1411+442. In this letter, we make a further analysis of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate that broad absorption lines are completely saturated at the bottom of absorption troughs.

astro-ph↗
arXiv1999

The X-ray CCD camera of the MAXI Experiment on the ISS/JEM

MAXI, Monitor of All-sky X-ray Image, is the X-ray observatory on the Japanese experimental module (JEM) Exposed Facility (EF) on the International Space Station (ISS). MAXI is a slit scanning camera which consists of two kinds of X-ray detectors: one is a one-dimensional position-sensitive proportional counter with a total area of $\sim 5000 cm^2$, the Gas Slit Camera (GSC), and the other is an X-ray CCD array with a total area $\sim 200 cm^2$, the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1$^\circ\times 180^\circ$ while the SSC subtends a field of view with an angular dimension of 1$^\circ$ times a little less than 180$^\circ$. In the course of one station orbit, MAXI can scan almost the entire sky with a precision of 1$^\circ$ and with an X-ray energy range of 0.5-30 keV. We have developed the engineering model of CCD chips and the analogue electronics for the SSC. The energy resolution of EM CCD for Mn K$α$ has a full-width at half maximum of $\simeq$ 182 eV. Readout noise is $\simeq$ 11 e^- rms.

physics.ins-det↗
arXiv1999

An ASCA observation of the radio-loud narrow-line Seyfert 1 galaxy RGB J0044+193

We present the results of an ASCA observation of the radio-loud NLS1 galaxy RGB J0044+193. The X-ray data are complemented by radio observations and a new optical spectrum for this source. We find evidence for variable radio emission and an inverted radio spectrum. The optical continuum turned out to be extremely blue. This may either indicate additional line emission, for example from Fe I, or scattering of a blue intrinsic continuum. The X-ray spectrum shows a clear break around 1.8 keV. Above this energy the spectrum is characterized by a power law with a photon index of 2.1. For energies below 2 keV the spectrum can either be modeled with a steeper power law (2.7) or a blackbody component with a temperature around 0.2 keV. The X-ray count rate of the source decreased by a factor of two within one day and there is evidence for low amplitude variability on much shorter time scales. Given its average 2-10 keV X-ray luminosity of 1.35e+44 erg/s, RGB J0044+193 is significantly more variable than a typical broad line Seyfert 1 galaxy of comparable X-ray luminosity, but consistent with the bulk of NLS1 galaxies. The spectral as well as the variability properties of RGB J0044+193 are indistinguishable from those of radio-quiet NLS1s. In particular, we find no evidence for a flat X-ray component due to inverse Compton emission related to the putative non-thermal radio emission from RGB J0044+193. We argue, however, that this does not rule out a pole-on orientation for RGB J0044+193.

astro-ph↗
arXiv1999

Broad Band X-Ray Observations of the Narrow Line X-Ray Galaxy NGC 5506

We present a detailed analysis of broad band X-ray data of the Seyfert 2 galaxy NGC5506. 2-10 keV band are detected during a 1-day ASCA observation, while no significant change in the 2-10 keV continuum shape is found. The ASCA spectrum consists of an absorbed power-law, a 'soft excess' below 2 keV, and an Fe K$α$ emission line at 6.4 keV. The 'soft excess' can be well described by either thermal emission from very low abundance material at a temperature kT$\simeq$0.8 keV, or scattered/leaking flux from the primary power-law plus a small amount of thermal emission. Analysis of ROSAT HRI data reveals that the soft X-ray emission is extended on kpc scales in this object, and the extended component may account for most of the soft X-ray excess observed by the ASCA. The result suggests that in this type 2 AGN, the 'soft excess' at least partly comes from an extended region, imposing serious problem for the model in which the source is partially covered. Fe K$α$ profile is complex and can not be satisfactorily modeled by a single gaussian. Models of either double gaussians, or a narrow gaussian plus a line from a relativistic accretion disk viewed at an inclination of about 40$\pm10^\circ$ provide good fits to the data. However, the inclination of the disk can be substantially larger if there is a small amount of excessive Fe K edge absorption. The intermediate inclinations for NLXGs are consistent with the ideas that the inner accretion disk is aligned with the outer obscuring torus.

astro-ph↗