The gamma-ray burst (GRB) 060218 has a luminosity similar to 10 super(5) times lower than that of typical long GRBs and is associated with a supernova (SN). The radio afterglow displays no jet break, ...so this burst might arise from a mildly relativistic spherical outflow produced by the SN shock sweeping the stellar surface. Since this model is energetically difficult, we propose that the radio afterglow is produced by a nonrelativistic phase of an initially collimated outflow (jet). Our jet model is supported by the detection of optical linear polarization in the SN component. We also show analytically that the jet can penetrate a progenitor star. We analyzed the observational data of the prompt emission of this burst and obtained a smooth power-law light curve which might last longer than 10 super(6) s. This behavior contrasts with the long intermittent activities of the X-ray flares of typical GRBs, implying that the central engine of this burst is different from those of typical GRBs. This argument is consistent with the analysis of the SN component of this burst, which suggests that the progenitor star was less massive and collapsed to a neutron star instead of a black hole. The collimatlon-corrected event rate of such low-luminosity GRBs is estimated to be similar to 10 times higher than that of typical long GRBs, and they might form a different GRB population: low-luminosity GRBs are produced by mildly relativistic jets from neutron stars at the collapses of massive stars, while typical long GRBs are produced by highly relativistic jets from black holes. We suggest that the central engine of GRB 060218 is a pulsar (or a magnetar) with initial rotation period P unk similar to 10 ms and magnetic field B similar to 10 super(16) G. A giant flare from the magnetar might be observed in future.
We present a catalog of 525 sprites detected over the Sea of Japan and a northeast part of the Pacific Ocean from Sagamihara between September 2016 and March 2021. We analyze the morphology of 525, ...estimate the location of 441, and calculate the accurate top height of 15 sprites. More than half of our samples occurred in winter, while only 11% were in summer. In terms of morphology, 52% to 60% column type sprites took place in spring, autumn, and winter, while only 15.5% in summer. Therefore, summer thunderstorms are more likely to produce sprites with complex structures like carrots. Furthermore, sprites in summer are almost all located on the main island of Japan, and their spatial distributions are significantly different from the other seasons. Finally, from the perspective of the time distribution, the number of sprites is the largest at 1:00 JST. In addition, the morphology of sprites tends to be simple (e.g., a column type) at midnight JST.
Abstract
The soft gamma-ray repeater Swift J1555.2−5402 was discovered by means of a short burst detected with Swift BAT on 2021 June 3. Then, 1.6 hr after the burst, the Neutron star Interior ...Composition Explorer (NICER) started daily monitoring of this target for a month. The absorbed 2–10 keV flux stayed nearly constant at around 4 × 10
−11
erg s
−1
cm
−2
during the monitoring, showing only a slight gradual decline. An absorbed blackbody with a temperature of 1.1 keV approximates the soft X-ray spectrum. A 3.86 s periodicity is detected, and the period derivative is measured to be 3.05(7) × 10
−11
s s
−1
. The soft X-ray pulse shows a single sinusoidal shape with an rms pulsed fraction that increases as a function of energy from 15% at 1.5 keV to 39% at 7 keV. The equatorial surface magnetic field, characteristic age, and spin-down luminosity are derived under the dipole field approximation to be 3.5 × 10
14
G, 2.0 kyr, and 2.1 × 10
34
erg s
−1
, respectively. We detect 5 and 45 bursts with Swift/BAT and NICER, respectively. Based on these properties, this new source is classified as a magnetar. A hard X-ray power-law component that extends up to at least 40 keV is detected with the Nuclear Spectroscopic Telescope Array (NuSTAR). The 10–60 keV flux is ∼9 × 10
−12
erg s
−1
cm
−2
with a photon index of ∼1.2. The pulsed fraction has a sharp cutoff at around 10 keV with an upper limit (≲10%) in the hard-tail band. No radio pulsations are detected during the DSN or VERA observations. The 7
σ
upper limits of the flux density are 0.043 and 0.026 mJy at the
S
and
X
bands, respectively.
MAXI observations of long X-ray bursts Serino, Motoko; Iwakiri, Wataru; Tamagawa, Toru ...
Publications of the Astronomical Society of Japan,
12/2016, Volume:
68, Issue:
6
Journal Article
Peer reviewed
Open access
Abstract
We report nine long X-ray bursts from neutron stars, detected with the Monitor of All-sky X-ray Image (MAXI). Some of these bursts lasted for hours, and hence are qualified as superbursts, ...which are prolonged thermonuclear flashes on neutron stars and are relatively rare events. MAXI observes roughly 85% of the whole sky every 92 minutes in the 2–20 keV energy band, and has detected nine bursts with a long e-folding decay time, ranging from 0.27 to 5.2 hr, since its launch in 2009 August until 2015 August. The majority of the nine events were found to originate from transient X-ray sources. The persistent luminosities of the sources, when these prolonged bursts were observed, were lower than 1% of the Eddington luminosity for five of them and lower than 20% for the rest. This trend is contrastive to the 18 superbursts observed before MAXI, all but two of which originated from bright persistent sources. The distribution of the total emitted energy, i.e., the product of e-folding time and luminosity, of these bursts clusters around 1041–1042 erg, whereas both the e-folding time and luminosity ranges for an order of magnitude. Among the nine events, two were from 4U 1850−086 during phases of relatively low persistent flux, whereas it usually exhibits standard short X-ray bursts during outbursts.
We present the earliest available soft X-ray observations of XTE J1810−197, the prototypical transient magnetar, obtained 75-84 days after its 2018 outburst with the Neutron Star Interior Composition ...Explorer. Using a series of observations covering eight days we find that its decreasing X-ray flux is well described by either a blackbody plus power law or a two-blackbody spectral model. The 2-10 keV flux of the source varied from (1.206 0.007) × 10−10 to , a decrease of about 7% within our observations and 44% from that measured 7-14 days after the outburst with NuSTAR. We confirm that the pulsed fraction and spin pulse phase of the neutron star are energy dependent up to at least 8 keV. Phase-resolved spectroscopy of the pulsar suggests magnetospheric variations relative to the line of sight.
We investigated the spectral properties of the prompt emission for short- and long-duration gamma-ray bursts (GRBs) using the Fermi Gamma-ray Burst Monitor data. In particular, we focused on ...comparing the spectral properties of short GRBs and the initial 2 s of long GRBs, motivated by the previous study of Ghirlanda et al. (2009). We confirmed the similarity in the low energy photon index α between short GRBs and the initial 2 s of long GRBs. Since about a quarter of our spectra of both short GRBs and the initial 2 s of long GRBs show α to be shallower than - 2 / 3 , it is difficult to understand in the context standard synchrotron emission.
Endometrial cytology by direct intrauterine sampling is the most common test for an initial evaluation of the endometrium in Japan. However, its diagnostic value for endometrial cancer remains ...unknown. Here, we assess the correlation between cytopathology and histopathology to evaluate the diagnostic value of cytology for endometrial cancer.
Patients with histologically confirmed endometrial cancer and controls with a normal endometrium confirmed by hysterectomy had all undergone preoperative endometrial cytology between 2001 and 2010 at our eight institutions and were retrospectively analyzed. The cytological results were compared by clinical stage, histological type, differentiation, and sampling instrument.
We analyzed 1,441 endometrial cancer and 1,361 control cases. Endometrial cytology detected cancer in 1,279 (916 positive and 363 suspicious) cases with a sensitivity (positive plus suspicious cases) of 88.8% and a specificity of 98.5%. The positive rate was high in advanced-stage, nonendometrioid, and undifferentiated cases, but there was no significant difference in sensitivity between these clinical conditions.
Endometrial cytology shows a relatively high sensitivity and specificity for endometrial cancer, and neither statistical measure is significantly affected by clinical stage, histological type, differentiation, sample numbers, or sampling instrument. These findings form a superior dataset for evaluating the efficacy of endometrial cytology.
Detection of the thermal component in GRB 160107A Kawakubo, Yuta; Sakamoto, Takanori; Nakahira, Satoshi ...
Publications of the Astronomical Society of Japan,
01/2018, Volume:
70, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
We present the detection of a blackbody component in gamma-ray burst GRB 160107A emission by using the combined spectral data of the CALET Gamma-ray Burst Monitor (CGBM) and the MAXI Gas ...Slit Camera (GSC). MAXI/GSC detected the emission ∼45 s prior to the main burst episode observed by the CGBM. The MAXI/GSC and the CGBM spectrum of this prior emission period is fitted well by a blackbody with temperature $1.0^{+0.3}_{-0.2}$ keV plus a power law with a photon index of −1.6 ± 0.3. We discuss the radius of the photospheric emission and the main burst emission based on the observational properties. We stress the importance of coordinated observations via various instruments collecting high-quality data over a broad energy coverage in order to understand the GRB prompt emission mechanism.
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