We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes (
$\vert b\vert$
$>$
10
$^{\circ}$
), produced from the first 7-month data ...(2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4–10 keV band. We have developed an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above the 7
$\sigma$
significance level with a limiting sensitivity of
$\sim\ $
1.5
$\times$
10
$^{-11}\ $
erg cm
$^{-2}\ $
s
$^{-1}$
(1.2 mCrab) in the 4–10 keV band. Among them, we have identified 38 Galactic/LMC/SMC objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Four other sources are confused with multiple objects, and one remains unidentified. The log
$\ N$
–log
$\ S$
relation of extragalactic objects is in good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly changed since that produced 30 yr ago.
We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar, LS V
$+$
44 17/ RX J0440.9
$+$
4431, and the discovery of an absorption dip structure in the pulse profile. An ...outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of transient activity of LS V
$+$
44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of a follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile, which was clearer in the lower-energy bands. The pulse-phase-averaged energy spectra in the 3–100 keV band could be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron K
$\alpha$
emission line was also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column.
Possible X-ray cocoon emission from GRB 050709 Ogino, Naoki; Arimoto, Makoto; Hamidani, Hamid ...
Publications of the Astronomical Society of Japan,
06/2024, Letnik:
76, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract The detection of the short gamma-ray burst (SGRB) 050709 by the HETE-2 satellite opened the door to understanding the nature of SGRBs, offering clues about their emission mechanism and ...progenitors, with the crucial aid of optical follow-up observations. Here, we revisit the prompt emission of GRB 050709. Our analysis reveals an initial hard spike ∼200 ms long, followed by a subsequent soft-tail emission lasting ∼300 ms. These components could be common among other SGRBs originating from binary neutron merger events, such as GW 170817 and GRB 170817A. Detailed temporal and spectral analyses indicate that the soft-tail emission might be attributed to the cocoon formed by the relativistic jet depositing energy into the surrounding material. We find the necessary cocoon parameters at the breakout, as consistent with numerical simulation results. We compared the physical parameters of this cocoon with those of other SGRBs. The relatively higher cocoon pressure and temperature in GRB 050709 may indicate a more on-axis jet compared with GRB 170817A and GRB 150101B.
We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from ...TWA-7 with a flux of 3
$\times$
10
$^{-9}\ $
erg cm
$^{-2}\ $
s
$^{-1}$
in 2–20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3
$\times$
10
$^{32}\ $
erg s
$^{-1}$
, indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log
$\ L_{\rm X}/L_{\rm bol}$
$=$
$-$
0.1
$^{+0.2}_{-0.3}$
; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.
Abstract
We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image, ...and Neutron Star Interior Composition Explorer Mission. This energetic GRB was located relatively nearby (
z
= 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (
b
= 4.°3) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography, we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (≳10 kpc). We present analysis of the light curves and spectra at X-ray and UV–optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at
T
0
+ 4.5 ks than that from any previous GRB observed by Swift. In its rest frame, GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 10
4
long GRBs were as energetic as GRB 221009A; such a large
E
γ
,iso
implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ≲1 per 1000 yr—making this a truly remarkable opportunity unlikely to be repeated in our lifetime.
We report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare for the period of 2010 September 18–24 (MJD 55457
$-$
55463), detected by AGILE and Fermi-LAT. ...There were no significant variations on the pulse phase averaged and pulsed fluxes during the gamma-ray flare on time scales from 0.5 to 5 days. The pulse profile also showed no significant change during this period. The upper limits on the variations of the pulse phase averaged and pulsed fluxes for the period MJD 55457.5
$-$
55462.5 in the 4–10 keV band were derived to be 1% and 19%, respectively, at the 90% confidence limit of the statistical uncertainty. The lack of variations in the pulsed component over the multi-wavelength range (radio, X-ray, hard X-ray, and gamma-ray) supports not a pulsar, but a nebular origin for the gamma-ray flare.
The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB 090926B. This GRB had ...extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be
$r_0$
$=$
(4.3
$\ \pm\ $
0.9)
$\times$
10
$^{9}\ Y'^{-3/2}\ $
cm, the Lorentz factor of the plasma is
$\Gamma$
$=$
(110
$\ \pm\ $
10)
$\ Y'^{\ 1/4}$
, where
$Y'$
is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This
$r_0$
is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.
X-ray upper limits of GW150914 with MAXI Kawai, Nobuyuki; Negoro, Hitoshi; Serino, Motoko ...
Publications of the Astronomical Society of Japan,
12/2017, Letnik:
69, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
We searched for X-ray candidates for the gravitational wave (GW) event GW150914 with Monitor of All-sky X-ray Image (MAXI). MAXI observed the error region of the GW event GW150914 from 4 min ...after the event and covered about 90% of the error region in 25 min. No significant time variations on timescales of 1 s to 4 d were found in the GW error region. The 3 σ upper limits for the X-ray emission associated with the GW event in 2–20 keV were 9.5 × 10−10, 2.3 × 10−10, and 0.8 × 10−10 erg cm−2 s−1 for the time scales of ∼1000 s, 1 d, and 10 d, respectively. If GW events are associated with short gamma-ray bursts like GRB 050709, MAXI will be able to detect X-ray emissions from the source.
Abstract
We report on the discovery of a new supergiant fast X-ray transient (SFXT), MAXI J0709−159, and its identification with LY CMa (also known as HD 54786). On 2022 January 25, a new flaring ...X-ray object, named MAXI J0709−159, was detected by the Monitor of All-sky X-ray Image (MAXI). Two flaring activities were observed in two scans ∼3 hr apart, where the 2–10 keV flux reached 5 × 10−9 erg cm−2 s−1. During the period, the source exhibited a large spectral change, suggesting that the absorption column density NH increased from 1022 to 1023 cm−2. A NuSTAR follow-up observation on January 29 identified a new X-ray source with a flux of 6 × 10−13 erg cm−2 s−1 at a position consistent with LY CMa, which has been identified as a B supergiant as well as a Be star, located at a 3 kpc distance. The observed X-ray activity, characterized by short (≲several hours) duration, rapid (≲ a few seconds) variabilities accompanied by spectral changes, and a large luminosity swing (1032–1037 erg s−1), agree with those of SFXTs. On the other hand, optical spectroscopic observations of LY CMa reveal a broad Hα emission line, which may indicate the existence of a Be circumstellar disk. These results suggest that the optical companion, LY CMa, certainly has a complex circumstellar medium including dense clumps.
PDF
