Context. As a result of the numerous missions dedicated to the detection of Gamma-ray bursts (GRBs), the observed properties of these events are now well known. However, studying their parameters in ...the source frame is not simple since it requires having measurements of both the bursts' parameters and of their distances. Aims. Taking advantage of the forthcoming Catalog of the High Energy Transient Explorer 2 (HETE-2) mission, the aim of this paper is to evaluate the main properties of HETE-2 GRBs-the peak energy (E_{peak}), the duration (T sub(90)) and the isotropic energy (E_{iso})-in their source frames and to derive their unbiased distribution. Methods. We first construct a complete sample containing all the bursts localized by the Wide-Field X-ray Monitor (WXM) on-board HETE-2, which are selected with a uniform criterion and whose observed parameters can be constrained. We then derive the intrinsic E_{peak}, T sub(90) and E_{iso} distributions using their redshift when it is available, or their pseudo- redshift otherwise. We finally compute the "volume of detectability" V_{max} of each GRB, i.e. the volume of the universe in which the burst is bright enough to be part of our sample, and the corresponding number of GRB within their visibility volume N_{V{max}}, in order to derive a weight for each detected burst accounting both for the detection significance and the star formation history of the universe. Results. We obtain unbiased distributions of three intrinsic properties of HETE-2 GRBs: E_{peak}{intr}, T_{intr} and the isotropic energy of the burst. These distributions clearly show the predominence of X-ray flashes (XRFs) in the global GRB population. We also derive the rate of local GRBs: R_{0}{H2} ga 11 Gpc super(-3) yr super(-1), which is intermediate between the local rate obtained by considering only the "high-luminosity" bursts ( similar to 1 Gpc super(-3) yr super(-1)) and that obtained by including the "low-luminosity" bursts (\ga200 Gpc super(-3) yr super(-1)). Conclusions. This study shows that the XRFs are predominent in the GRB population and are closely linked to the "classical" GRBs. We show that HETE- 2 detected no low-luminosity GRB like GRB 980425 or XRF 060218, due to the small size of its detectors, excluding this type of burst from our statistical analysis. The comparison of the GRB rate derived in this study with the known rate of type Ib/c supernovae clearly shows that the progenitors of SNe Ib/c must have some special characteristics in order to produce a gamma-ray burst or an X-ray flash.
Context. We report on new modeling results based on the mm- to X-ray emission of the SgrA* counterpart associated with the massive ~4$\times$106 $M_{\odot}$ black hole at the Galactic Center. Aims. ...We investigate the physical processes responsible for the variable emission from SgrA*. Methods. Our modeling is based on simultaneous observations carried out on 07 July, 2004, using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory as well as the Submillimeter Array SMA on Mauna Kea, Hawaii, and the Very Large Array in New Mexico. Results. The observations revealed several flare events in all wavelength domains. Here we show that the flare emission can be described with a combination of a synchrotron self-Compton (SSC) model followed by an adiabatic expansion of the source components. The SSC emission at NIR and X-ray wavelengths involves up-scattered sub-millimeter photons from a compact source component. At the start of the flare, spectra of these components peak at frequencies between several 100 GHz and 2 THz. The adiabatic expansion then accounts for the variable emission observed at sub-mm/mm wavelengths. The derived physical quantities that describe the flare emission give a blob expansion speed of vexp ~ 0.005 c, magnetic field of B around 60 G or less and spectral indices of α = 0.8 to 1.4, corresponding to a particle spectral index p ~ 2.6 to 3.8. Conclusions. A combined SSC and adiabatic expansion model can fully account for the observed flare flux densities and delay times covering the spectral range from the X-ray to the mm-radio domain. The derived model parameters suggest that the adiabatic expansion takes place in source components that have a bulk motion larger than vexp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*.
ABSTRACT
We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an ...intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11 d, and a mass and radius of 0.73 ± 0.02 M⊙ and 0.65 ± 0.02 R⊙, respectively. HD 73583 b (Pb = $6.3980420 _{ - 0.0000062 } ^ { + 0.0000067 }$ d) has a mass and radius of $10.2 _{ - 3.1 } ^ { + 3.4 }$ M⊕ and 2.79 ± 0.10 R⊕, respectively, which gives a density of $2.58 _{ - 0.81 } ^ { + 0.95 }$ ${\rm g\, cm^{-3}}$. HD 73583 c (Pc = $18.87974 _{ - 0.00074 } ^ { + 0.00086 }$ d) has a mass and radius of $9.7 _{ - 1.7 } ^ { + 1.8 }$ M⊕ and $2.39 _{ - 0.09 } ^ { + 0.10 }$ R⊕, respectively, which translates to a density of $3.88 _{ - 0.80 } ^ { + 0.91 }$ ${\rm g\, cm^{-3}}$. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
An exceptionally intense gamma-ray burst, GRB 030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 2003 March 29. The ...burst consisted of two similar to 10 s pulses of roughly equal brightness and an X-ray tail lasting more than 100 s. The energy fluence in the 30-400 keV energy band was S sub( gamma ) = 1.2 x 10 super(-4) ergs cm super(-2), making GRB 030329 one of the brightest GRBs ever detected. Communication of a 2' error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, and radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst light curves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB; the 2-10 keV fluence of this component is similar to 7 x 10 super(-6) ergs cm super(-2). The main pulses of GRB 030329 were preceded by two soft, faint, nonthermal bumps. We present details of the HETE observations of GRB 030329.
We report the discovery of a multiplanetary system transiting the M0 V dwarf HD 260655 (GJ 239, TOI-4599). The system consists of at least two transiting planets, namely HD 260655 b, with a period of ...2.77 d, a radius of
R
b
= 1.240 ± 0.023
R
⊕
, a mass of
M
b
= 2.14 ± 0.34
M
⊕
, and a bulk density of
ρ
b
= 6.2 ± 1.0 g cm
−3
, and HD 260655 c, with a period of 5.71 d, a radius of ${R_c} = 1.533_{ - 0.046}^{ + 0.051}{R_ \oplus }$, a mass of
M
c
= 3.09 ± 0.48
M
⊕
, and a bulk density of ${\rho _c} = 4.7_{ - 0.8}^{ + 0.9}{\rm{g}}$ g cm
−3
. The planets have been detected in transit by the Transiting Exoplanet Survey Satellite (TESS) mission and confirmed independently with archival and new precise radial velocities obtained with the HIRES and CARMENES instruments since 1998 and 2016, respectively. At a distance of 10 pc, HD 260655 has become the fourth closest known multitransiting planet system after HD 219134, LTT 1445 A, and AU Mic. Due to the apparent brightness of the host star (
J
= 6.7 mag), both planets are among the most suitable rocky worlds known today for atmospheric studies with the
James Webb
Space Telescope, both in transmission and emission.
We report the discovery of TOI-1268b, a transiting Saturn-mass planet from the TESS space mission. With an age of less than 1 Gyr, derived from various age indicators, TOI-1268b is the youngest ...Saturn-mass planet known to date; it contributes to the small sample of well-characterised young planets. It has an orbital period of
P
= 8.1577080 ± 0.0000044 days, and transits an early K-dwarf star with a mass of
M
*
= 0.96 ± 0.04
M
⊙
, a radius of
R
*
= 0.92 ± 0.06
R
⊙
, an effective temperature of
T
eff
= 5300 ± 100 K, and a metallicity of 0.36 ± 0.06 dex. By combining TESS photometry with high-resolution spectra acquired with the Tull spectrograph at the McDonald Observatory, and the high-resolution spectrographs at the Tautenburg and Ondřejov Observatories, we measured a planetary mass of
M
p
= 96.4 ± 8.3
M
⊕
and a radius of
R
p
= 9.1 ± 0.6
R
⊕
. TOI-1268 is an ideal system for studying the role of star-planet tidal interactions for non-inflated Saturn-mass planets. We used system parameters derived in this paper to constrain the planet’s tidal quality factor to the range of 10
4.5–5.3
. When compared with the sample of other non-inflated Saturn-mass planets, TOI-1268b is one of the best candidates for transmission spectroscopy studies.
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