-
Tadayuki Takahashi,
Kazuhisa Mitsuda,
Richard Kelley,
Henri AartsFelix Aharonian,
Hiroki Akamatsu,
Fumie Akimoto,
Steve Allen,
Naohisa Anabuki,
Lorella Angelini,
Keith Arnaud, [......],
Takahiro Yamada,
Shinya Yamada,
Hiroya Yamaguchi,
Noriko Yamasaki,
Shigeo Yamauchi,
Makoto Yamauchi,
Yoichi Yatsu,
Daisuke Yonetoku,
Atsumasa Yoshida,
Takayuki Yuasa
[show abstract]
[hide abstract]
ABSTRACT: The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.
10/2012;
-
Tatehiro Mihara,
Motoki Nakajima,
Mutsumi Sugizaki,
Motoko Serino,
Masaru Matsuoka,
Mitsuhiro Kohama,
Kazuyoshi Kawasaki,
Hiroshi Tomida,
Shiro Ueno,
Nobuyuki Kawai, Jun Kataoka,
Mikio Morii,
Atsumasa Yoshida,
Kazutaka Yamaoka,
Satoshi Nakahira,
Hitoshi Negoro,
Naoki Isobe,
Makoto Yamauchi,
Ikuya Sakurai
[show abstract]
[hide abstract]
ABSTRACT: The Gas Slit Camera (GSC) is an X-ray instrument on the MAXI (Monitor of
All-sky X-ray Image) mission on the International Space Station. It is designed
to scan the entire sky every 92-minute orbital period in the 2--30 keV band and
to achieve the highest sensitivity among the X-ray all-sky monitors ever flown
so far. The GSC employs large-area position-sensitive proportional counters
with the total detector area of 5350 cm$^2$. The on-board data processor has
functions to format telemetry data as well as to control the high voltage of
the proportional counters to protect them from the particle irradiation. The
paper describes the instruments, on-board data processing, telemetry data
formats, and performance specifications expected from the ground calibration
tests.
03/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We report results from the observations of the well-studied TeV blazar Mrk 421 with the Swift and the Suzaku satellites in 2008 December. During the observation, Mrk 421 was found in a relatively low activity state, with the corresponding 2-10 keV flux of 3 × 10–10 erg s–1 cm–2. For the purpose of robustly constraining the UV-to-X-ray emission continuum we selected only the data corresponding to truly simultaneous time intervals between Swift and Suzaku, allowing us to obtain a good-quality, broadband spectrum despite a modest length (0.6 ks) exposure. We analyzed the spectrum with the parametric forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different representations of the underlying electron energy distribution, both well motivated by the current particle acceleration models: a power-law distribution above the minimum energy γmin with an exponential cutoff at the maximum energy γmax, and a modified ultra-relativistic Maxwellian with an equilibrium energy γeq. We found that the latter implies unlikely physical conditions within the blazar zone of Mrk 421. On the other hand, the exponentially moderated power-law electron distribution gives two possible sets of the model parameters: (1) flat spectrum dN' e /dγ γ–1.91 with low minimum electron energy γmin < 103, and (2) steep spectrum γ–2.77 with high minimum electron energy γmin 2 × 104. We discuss different interpretations of both possibilities in the context of a diffusive acceleration of electrons at relativistic, sub- or superluminal shocks. We also comment on exactly how the γ-ray data can be used to discriminate between the different proposed scenarios.
The Astrophysical Journal 11/2010; 724(2):1509. · 6.02 Impact Factor
-
Tadayuki Takahashi,
Kazuhisa Mitsuda,
Richard Kelley,
Felix Aharonian,
Fumie Akimoto,
Steve Allen,
Naohisa Anabuki,
Lorella Angelini,
Keith Arnaud,
Hisamitsu Awaki, [......],
Nicholas White,
Takahiro Yamada,
Hiroya Yamaguchi,
Kazutaka Yamaoka,
Noriko Yamasaki,
Makoto Yamauchi,
Shigeo Yamauchi,
Yoichi Yatsu,
Daisuke Yonetoku,
Atsumasa Yoshida
[show abstract]
[hide abstract]
ABSTRACT: The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of Delta E ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued. Comment: 18 pages, 12 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray"
10/2010;
-
Hiroyasu Tajima,
Roger Blandford,
Teruaki Enoto,
Yasushi Fukazawa,
Kirk Gilmore,
Tuneyoshi Kamae, Jun Kataoka,
Madoka Kawaharada,
Motohide Kokubun,
Philippe Laurent, [......],
Rie Sato,
Hiromitsu Takahashi,
Tadayuki Takahashi,
Takaaki Tanaka,
Makoto Tashiro,
Yukikatsu Terada,
Yasunobu Uchiyama,
Shin Watanabe,
Kazutaka Yamaoka,
Daisuke Yonetoku
[show abstract]
[hide abstract]
ABSTRACT: ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (40-600 keV) at a background level 10 times better than the current instruments on orbit. SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance. Comment: 17 pages, 15 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray"
10/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We investigate the prospects for discovering blazars at very high-redshifts (z>3-6) with the Fermi Gamma-Ray Space Telescope (Fermi), employing a model for the evolving gamma-ray luminosity function (GLF) of the blazar population. Our previous GLF model is used as a basis, which features luminosity-dependent density evolution implied from X-ray data on active galactic nuclei, as well as the blazar sequence paradigm for their spectral energy distribution, and which is consistent with EGRET and current Fermi observations of blazars.Here we augment the high-redshift evolution of this model by utilizing the luminosity function of quasars from the Sloan Digital Sky Survey (SDSS), which is well-constrained up to z~5. We find that Fermi may discover a few blazars up to z~6 in the entire sky during its 5-year survey. We further discuss how such high-redshift blazar candidates may be efficiently selected in future Fermi data. Comment: 6 pages, 2 figures, accepted for publication in MNRAS
07/2010;
-
Motohide Kokubun,
Kazuhiro Nakazawa,
Teruaki Enoto,
Yasushi Fukazawa,
Kirk Gilmore, Jun Kataoka,
Madoka Kawaharada,
Philippe Laurent,
Francois Lebrun,
Olivier Limousin, [......],
Hiroyasu Tajima,
Hiromitsu Takahashi,
Tadayuki Takahashi,
Takaaki Tanaka,
Yukikatsu Terada,
Hideki Uchiyama,
Yasunobu Uchiyama,
Shin Watanabe,
Yoichi Yatsu,
Kazutaka Yamaoka
[show abstract]
[hide abstract]
ABSTRACT: The Hard X-ray Imager (HXI) is one of four detectors on board the ASTRO-H mission (6th Japanese X-ray satellite), which is scheduled to be launched in 2014. Using the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride double-sided strip detector, the instrument fully covers the energy range of photons collected with the hard X-ray telescope up to 80 keV with a high quantum efficiency. High spatial resolution of 250 μm and an energy resolution of 1-2 keV (FWHM) are both achieved with low noise front-end ASICs. In addition, the thick BGO active shields surrounding the main detector package is a heritage of the successful performance of the Hard X-ray Detector on board the Suzaku satellite. This feature enables the instrument to achieve an extremely high background reduction caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we present the detector concept, design, latest results of the detector development, and the current status of the hardware.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
07/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The latest determination of the extragalactic gamma-ray background (EGRB) radiation by Fermi is compared with the theoretical prediction of the blazar component by Inoue & Totani (2009; hereafter IT09). The Fermi EGRB spectrum is in excellent agreement with IT09, indicating that blazars are the dominant component of the EGRB, and contributions from any other sources (e.g., dark matter annihilations) are minor. It also indicates that the blazar SED (spectral energy distribution) sequence taken into account in IT09 is a valid description of mean blazar SEDs. The possible contribution of MeV blazars to the EGRB in the MeV band is also discussed. In five total years of observations, we predict that Fermi will detect ~1200 blazars all sky down to the corresponding sensitivity limit. We also address the detectability of the highest-redshift blazars. Updating our model with regard to high-redshift evolution based on SDSS quasar data, we show that Fermi may find some blazars up to z~6 during the five-year survey. Such blazars could provide a new probe of early star and galaxy formation through GeV spectral attenuation signatures induced by high-redshift UV background radiation. Comment: 2009 Fermi Symposium, Washington, D.C., Nov. 2-5, eConf Proceedings C091122
12/2009;
-
Masayoshi Ushio,
Takaaki Tanaka,
Grzegorz Madejski,
Tadayuki Takahashi,
Masaaki Hayashida, Jun Kataoka,
Daniel Mazin,
Stefan Rügamer,
Rie Sato,
Masahiro Teshima,
Stefan Wagner,
and Yuichi Yaji
[show abstract]
[hide abstract]
ABSTRACT: We present the results of X-ray observations of the well studied TeV blazar Mrk 421 with the Suzaku satellite in 2006 April 28. During the observation, Mrk 421 was undergoing a large flare and the X-ray flux was variable, decreasing by ~50%, from 7.8 × 10–10 to 3.7 × 10–10 erg s–1 cm–2 in about 6 hr, followed by an increase by ~35%. Thanks to the broad bandpass coupled with high sensitivity of Suzaku, we measured the evolution of the spectrum over the 0.4-60 keV band in data segments as short as ~1 ks. The data show deviations from a simple power-law model, but also a clear spectral variability. The time-resolved spectra are fitted by a synchrotron model, where the observed spectrum is due to a exponentially cutoff power-law distribution of electrons radiating in uniform magnetic field; this model is preferred over a broken power law. As another scenario, we separate the spectrum into "steady" and "variable" components by subtracting the spectrum in the lowest-flux period from those of other data segments. In this context, the difference ("variable") spectra are all well described by a broken power-law model with photon index Γ ~ 1.6, breaking at energy brk 3 keV to another photon index Γ ~ 2.1 above the break energy, differing from each other only by normalization, while the spectrum of the "steady" component is best described by the synchrotron model. We suggest that the rapidly variable component is due to relatively localized shock (Fermi I) acceleration, while the slowly variable ("steady") component is due to the superposition of shocks located at larger distance along the jet, or due to other acceleration process, such as the stochastic acceleration on magnetic turbulence (Fermi II) in the more extended region.
The Astrophysical Journal 06/2009; 699(2):1964. · 6.02 Impact Factor
-
Masaru Matsuoka,
Kazuyoshi Kawasaki,
Shiro Ueno,
Hiroshi Tomida,
Mitsuhiro Kohama,
Motoko Suzuki,
Yasuki Adachi,
Masaki Ishikawa,
Tatehiro Mihara,
Mutsumi Sugizaki, [......],
Kazutaka Yamaoka,
Osamu Yamazaki,
Satoshi Nakahira,
Tetsuya You,
Ryoji Ishiwata,
Sho Miyoshi,
Satoshi Eguchi,
Kazuo Hiroi,
Haruyoshi Katayama,
Ken Ebisawa
[show abstract]
[hide abstract]
ABSTRACT: The MAXI (Monitor of All-sky X-ray Image) mission is the first astronomical payload to be installed on the Japanese Experiment Module-Exposed Facility (JEM-EF) on the ISS. It is scheduled for launch in the middle of 2009 to monitor all-sky X-ray objects on every ISS orbit. MAXI will be more powerful than any previous X-ray All Sky Monitor (ASM) payloads, being able to monitor hundreds of AGN. MAXI will provide all sky images of X-ray sources of about 20 mCrab in the energy band of 2-30 keV from observation on one ISS orbit (90 min), about 4.5 mCrab for one day, and about 1 mCrab for one month. A final detectability of MAXI could be 0.2 mCrab for 2 year observations. Comment: 12 pages, 11 figures, accepted for publication in Publications of the Astronomical Society of Japan
06/2009;
-
Shin Watanabe,
Rie Sato,
Tadayuki Takahashi, Jun Kataoka,
Greg Madejski,
Marek Sikora,
Fabrizio Tavecchio,
Rita Sambruna,
Roger Romani,
Philip G. Edwards,
and Tapio Pursimo
[show abstract]
[hide abstract]
ABSTRACT: We report the Suzaku observations of the high luminosity blazar SWIFT J0746.3+2548 (J0746) conducted in 2005 November. This object, which, with z = 2.979, is the highest redshift source observed in the Suzaku Guaranteed Time Observer period, is likely to show high gamma-ray flux peaking in the MeV range. As a result of the good photon statistics and high signal-to-noise ratio spectrum, the Suzaku observation clearly confirms that J0746 has an extremely hard spectrum in the energy range of 0.3-24 keV, which is well represented by a single power-law with a photon index of Γph 1.17 and Galactic absorption. The multiwavelength spectral energy distribution of J0746 shows two continuum components, and is well modeled assuming that the high-energy spectral component results from Comptonization of the broad-line region photons. In this paper, we search for the bulk Compton spectral features predicted to be produced in the soft X-ray band by scattering external optical/UV photons by cold electrons in a relativistic jet. We discuss and provide constraints on the pair content resulting from the apparent absence of such features.
The Astrophysical Journal 03/2009; 694(1):294. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report detailed studies of the X-ray emission from the kiloparsec-scale jet in the nearest active galaxy, Centaurus A. By analyzing the highest quality X-ray data obtained with the Chandra ACIS-S, 41 compact sources (mostly bright jet knots) were found within the jet on angular scales less than 4'', 13 of which were newly identified. We construct the luminosity function for the detected jet knots and argue that the remaining emission is most likely to be truly diffuse, rather than resulting from the sum of many unresolved fainter knots. We subtracted the contributions of the bright knots from the total X-ray jet flux, and show that the remaining extended emission has a relatively flat-topped intensity profile in the transverse jet direction, with the intensity peaking at the jet boundaries between 50'' and 170''. We note that limb-brightened morphologies have been observed previously at radio frequencies in a few FR I and FR II jet sources, but never so clearly at higher photon energies. Our result therefore supports a stratified jet model, consisting of a relativistic outflow including a boundary layer with a velocity shear. In addition, we found that the X-ray spectrum of the diffuse component is almost uniform across and along the jet, with an X-ray energy spectral index of αX ≈ 1, similar to those observed in the compact knots. We discuss this spectral behavior within a framework of shock and stochastic particle acceleration processes, connected with the turbulent, supersonic, and nonsteady nature of the relativistic outflow. We note some evidence for a possible spectral hardening at the outer sheath of the jet, and manifesting itself in observed X-ray spectra of αX < 0.5 in the most extreme cases. Due to the limited photon statistics of the present data, further deep observations of Centaurus A are required to determine the reality of this finding; however, we note that the existence of the hard X-ray features at outer jet boundaries would provide an important challenge to theories for the evolution of ultrarelativistic particles within extragalactic jets.
The Astrophysical Journal 12/2008; 641(1):158. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the variable X-ray emission from BL Lacertae detected in the ASCA ToO observation conducted during the EGRET and RXTE pointings, coincident with the 1997 July outburst. The source showed a historically high state of X-ray, optical, and γ-ray emission, with its 2-10 keV flux peaking at ~3.3 × 10-11 ergs cm-2 s-1. This is more than 3 times higher than the value measured by ASCA in 1995. We detected two rapid flares that occurred only in the soft X-ray band, while the hard X-ray flux also increased, but decayed with a much longer timescale. Together with the requirement of a very steep and varying power law dominating the soft X-ray band in addition to the hard power law, we suggest that both the high-energy end of the synchrotron spectrum and the hard inverse Compton spectrum were visible in this source during the outburst. We discuss the possible origins of the observed variability timescales, and interpret the short timescales of the soft X-ray variability as reflecting the size of the emission region.
The Astrophysical Journal 12/2008; 543(1):124. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Three uninterrupted, long (lasting respectively 7, 10, and 10 days) ASCA observations of the well-studied TeV-bright blazars Mrk 421, Mrk 501, and PKS 2155-304 all show continuous strong X-ray flaring. Despite the relatively faint intensity states in two of the three sources, there was no identifiable quiescent period in any of the observations. Structure function analysis shows that all blazars have a characteristic timescale of ~1 day, comparable to the recurrence time and to the timescale of the stronger flares. On the other hand, examination of these flares in more detail reveals that each of the strong flares is not a smooth increase and decrease but exhibits substructures of shorter flares having timescales of ~10 ks. We verify via simulations that in order to explain the observed structure function, these shorter flares ("shots") are unlikely to be fully random, but in some way are correlated with each other. The energy dependent cross-correlation analysis shows that interband lags are not universal in TeV blazars. This is important since in the past only positive detections of lags were reported. In this work, we determine that the sign of a lag may differ from flare to flare; significant lags of both signs were detected from several flares, while no significant lag was detected from others. However, we also argue that the nature of the underlying component can affect these values. The facts that all flares are nearly symmetric and that fast variability shorter than the characteristic timescale is strongly suppressed, support the scenario where the light crossing time dominates the variability timescales of the day-scale flares.
The Astrophysical Journal 12/2008; 563(2):569. · 6.02 Impact Factor
-
Jun Kataoka,
Tadayuki Takahashi,
Stefan J. Wagner,
Naoko Iyomoto,
Philip G. Edwards,
Kiyoshi Hayashida,
Susumu Inoue,
Greg M. Madejski,
Fumio Takahara,
Chiharu Tanihata,
and Nobuyuki Kawai
[show abstract]
[hide abstract]
ABSTRACT: We have studied the rapid X-ray variability of three extragalactic TeV γ-ray sources: Mrk 421, Mrk 501, and PKS 2155-304. Analyzing the X-ray light curves obtained from ASCA and/or Rossi X-Ray Timing Explorer observations between 1993 and 1998, we have investigated the variability in the time domain from 103 to 108 s. For all three sources, both the power spectrum density (PSD) and the structure function (SF) show a rollover with a timescale of the order of 1 day or longer, which may be interpreted as the typical timescale of successive flare events. Although the exact shape of turnover is not well constrained and the low-frequency (long timescale) behavior is still unclear, the high-frequency (short timescale) behavior is clearly resolved. We found that, on timescales shorter than 1 day, there is only small power in the variability, as indicated by a steep power spectrum density of f-2~-3. This is very different from other types of mass-accreting black hole systems, for which the short-timescale variability is well characterized by a fractal, flickering-noise PSD (f-1~-2). The steep PSD index and the characteristic timescale of flares imply that the X-ray-emitting site in the jet is of limited spatial extent: D ≥ 1017 cm distant from the base of the jet, which corresponds to ≥102 Schwarzschild radii for 107-10 M☉ black hole systems.
The Astrophysical Journal 12/2008; 560(2):659. · 6.02 Impact Factor
-
Takaaki Tanaka,
Yasunobu Uchiyama,
Felix A. Aharonian,
Tadayuki Takahashi,
Aya Bamba,
Junko S. Hiraga, Jun Kataoka,
Tetsuichi Kishishita,
Motohide Kokubun,
Koji Mori,
Kazuhiro Nakazawa,
Robert Petre,
Hiroyasu Tajima,
and Shin Watanabe
[show abstract]
[hide abstract]
ABSTRACT: We present results obtained from a series of observations of the supernova remnant RX J1713.7–3946 by Suzaku. Hard X-rays have been detected up to ~40 keV. The hard X-ray spectra are described by a power law with photon indices of ~3.0, which is larger than those below 10 keV. The combination of the spatially integrated XIS and HXD spectra clearly reveals a spectral cutoff which is linked to the maximum energy of accelerated electrons. The broadband coverage of Suzaku allows us to derive, for the first time, the energy spectrum of parent electrons in the cutoff region. The cutoff energy in the X-ray spectrum indicates that the electron acceleration in the remnant proceeds close to the Bohm diffusion limit. We discuss the implications of the spectral and morphological properties of the Suzaku data in the context of the origin of nonthermal emission. The Suzaku X-ray and H.E.S.S. gamma-ray data together hardly can be explained within a pure leptonic scenario. Moreover, the leptonic models require a weak magnetic field, which is inconsistent with the recently discovered X-ray filamentary structures and their short-term variability. The hadronic models with strong magnetic fields provide reasonable fits to the observed spectra, but require special arrangements of parameters to explain the lack of thermal X-ray emission. For morphology studies, we compare the X-ray and TeV gamma-ray surface brightness. We confirm the previously reported strong correlation between X-rays and TeV gamma rays. At the same time, the Suzaku data reveal a deviation from the general tendency, namely, the X-ray emission in the western rims appears brighter than expected from the average X-ray to gamma-ray ratio.
The Astrophysical Journal 12/2008; 685(2):988. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The recent launch of Fermi / GLAST - coinciding with the MAXI workshop - opens a new era for studies of jet-dominated active galaxies, known as blazars. While the emission processes operating in various spectral bands in blazars are reasonably well understood, the knowledge of the details of the structure of the jet, location of the dissipation region with respect to the accreting black hole, and coupling of the jet to the accretion process are known only at a rudimentary level. Blazars are variable, and this provides an opportunity to use the variability in various bands - and in particular, the relationship of respective time series to each other - to explore the relative location of regions responsible for emission in the respective bands. Observationally, this requires well-sampled time series in as many spectral bands as possible. To this end, with its all-sky, sensitive monitoring capability, the recently launched GLAST, and MAXI, to be deployed in 2009, are the most promising instruments bound to provide good sampling in respectively the energetic gamma-ray, and the soft X-ray band. This paper highlights the inferences regarding blazar jets that can be gleaned from such joint observations.
11/2008;
-
Takaaki Tanaka,
Yasunobu Uchiyama,
Felix A. Aharonian,
Tadayuki Takahashi,
Aya Bamba,
Junko S. Hiraga, Jun Kataoka,
Tetsuichi Kishishita,
Motohide Kokubun,
Koji Mori,
Kazuhiro Nakazawa,
Robert Petre,
Hiroyasu Tajima,
Shin Watanabe
[show abstract]
[hide abstract]
ABSTRACT: We present results obtained from a series of observations of the supernova remnant RX J1713.7-3946 by the Suzaku satellite. The observations cover about two-thirds of the remnant surface. We successfully detected hard X-rays up to ~ 40 keV from each pointing. The hard X-ray spectra are described by power-law functions with photon indices of ~ 3.0, which are larger than those in the energy region below 10 keV. Connection of the spatially-integrated XIS and HXD spectra clearly reveals a spectral cutoff in the 0.4--40 keV X-ray spectrum. This cutoff is interpreted to correspond to the maximum acceleration energy of electrons emitting synchrotron radiation. The wide-band coverage of Suzaku for the first time allows us to derive the parent electron spectrum in the cutoff region, which shows good agreement with theoretical predictions. The inferred cutoff energy in the spatially-integrated X-ray spectrum indicates that particle acceleration in the remnant is so efficient that it is almost at the theoretical limit, the so-called Bohm limit. Based on the Suzaku data, we present results of multi-wavelength studies from spectral and morphological points of view. The spectral energy distribution favors the hadronic scenario rather than the leptonic scenario. For the morphology studies, we compare the surface brightness maps from the Suzaku XIS and the H.E.S.S. telescope. We confirm the strong correlation between X-ray and TeV gamma-ray emission. In addition to the correlation, we found that in the bright western rim regions the X-ray emission is brighter than expected from the general X-ray to gamma-ray correlation. Comment: 16 pages, 22 figures, accepted for publication in ApJ
06/2008;
-
Tadayuki Takahashi,
Takaaki Tanaka,
Yasunobu Uchiyama,
Junko S. Hiraga,
Kazuhiro Nakazawa,
Shin Watanabe,
Aya Bamba,
John P. Hughes,
Hideaki Katagiri, Jun Kataoka,
Motohide Kokubun,
Katsuji Koyama,
Koji Mori,
Robert Petre,
Hiromitsu Takahashi,
Yoko Tsuboi
[show abstract]
[hide abstract]
ABSTRACT: We report on results from Suzaku broadband X-ray observations of the southwest part of the Galactic supernova remnant (SNR) RX J1713.7-3946 with an energy coverage of 0.4-40 keV. The X-ray spectrum, presumably of synchrotron origin, is known to be completely lineless, making this SNR ideally suited for a detailed study of the X-ray spectral shape formed through efficient particle acceleration at high speed shocks. With a sensitive hard X-ray measurement from the HXD PIN on board Suzaku, we determine the hard X-ray spectrum in the 12--40 keV range to be described by a power law with photon index Gamma = 3.2+/- 0.2, significantly steeper than the soft X-ray index of Gamma = 2.4+/- 0.05 measured previously with ASCA and other missions. We find that a simple power law fails to describe the full spectral range of 0.4-40 keV and instead a power-law with an exponential cutoff with hard index Gamma = 1.50+/- 0.09 and high-energy cutoff epsilon_c = 1.2+/- 0.3 keV formally provides an excellent fit over the full bandpass. If we use the so-called SRCUT model, as an alternative model, it gives the best-fit rolloff energy of epsilon_{roll} = 0.95+/- 0.04 keV. Together with the TeV gamma-ray spectrum ranging from 0.3 to 100 TeV obtained recently by HESS observations, our Suzaku observations of RX J1713.7-3946 provide stringent constraints on the highest energy particles accelerated in a supernova shock.
09/2007;
-
Jun Kataoka,
James N. Reeves,
Kazushi Iwasawa,
Alex G. Markowitz,
Richard F. Mushotzky,
Makoto Arimoto,
Tadayuki Takahashi,
Yoshihiro Tsubuku,
Masayoshi Ushio,
Shin Watanabe,
Luigi C. Gallo,
Greg M. Madejski,
Yuichi Terashima,
Naoki Isobe,
Makoto S. Tashiro,
Takayoshi Kohmura
[show abstract]
[hide abstract]
ABSTRACT: Broad line radio galaxies (BLRGs) are a rare type of radio-loud AGN, in which the broad optical permitted emission lines have been detected in addition to the extended jet emission. Here we report on deep (40ksec x4) observations of the bright BLRG 3C~120 using Suzaku. The observations were spaced a week apart, and sample a range of continuum fluxes. An excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50 keV) within each 40 ksec exposure. We clearly resolved the iron K emission line complex, finding that it consists of a narrow K_a core (sigma ~ 110 eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broad line is iron K line emission from a face-on accretion disk which is truncated at ~10 r_g. Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of R ~ 0.6), superposed on the primary X-ray continuum of Gamma ~ 1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of Gamma ~2.7, possibly related to the non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects.
01/2007;
