摘要 It has been argued that the long gamma-ray burst (GRB) of GRB 060614 without an associated supernova (SN) has challenged the current classification and fuel model for long GRBs, and thus a tidal disruption model has been proposed to account for such an event. Since it is difficult to detect SNe for long GRBs at high redshift, the absence of an SN association cannot be regarded as the solid criterion for a new classification of long GRBs similar to GRB 060614, called GRB 060614-type bursts. Fortunately, we now know that there is an obvious periodic substructure observed in the prompt light curve of GRB 060614. We thus use such periodic substructure as a potential criterion to categorize some long GRBs into a new class of bursts, which might have been fueled by an intermediate-mass black hole (IMBH) gulping a star, rather than a massive star collapsing to form a black hole. Therefore, the second criterion to recognize for this new class of bursts is whether they fit the tidal disruption model. From a total of 328 Swift GRBs with accurately measured durations and without SN association, we find 25 GRBs satisfying the criteria for GRB 060614-type bursts: seven of them are with known redshifts and 18 with unknown redshifts. These new bursts are similar to 6% of the total Swift GRBs, which are clustered into two subclasses: Type I and Type II with considerably different viscous parameters of accretion disks formed by tidally disrupting their different progenitor stars. We suggest that the two different kinds of progenitors are solar-type stars and white dwarfs: the progenitors for four Type I bursts with viscous parameter of around 0.1 are solar-type stars, and the progenitors for 21 Type II bursts with viscous parameter of around 0.3 are white dwarfs. The potential applications of this new class of GRBs as cosmic standard candles are discussed briefly.
摘要 Rapid magnetic changes in the course of the X7.1 solar flare on 2005 January 20 at the photosphere in the host active region (AR), NOAA AR 10720, are diagnosed. The database for this study consists of Huairou vector magnetograms, Transition Region and Coronal Explorer (TRACE) white light and UV/EUV images, RHESSI hard X-ray, and Solar and Heliospheric Observatory EUV observations. For such an event that is close to but not on the solar west limb (N12 W58), the projection effects in the observed vector magnetograms are untangled by combining an intuitive geometric analysis and a transformation of the magnetograms into the heliographic coordination system. The magnetic changes in the horizontal magnetic fields are emphasized. We find definitive evidence of weakening in the horizontal magnetic fields in a few isolated patches in the outskirts of this delta-sunspot group and strengthening in the horizontal fields (HFs) in an extended area centralized at the magnetic neutral line between major sunspots of opposite polarities. The rapid magnetic changes take place at the level of 100-300 G, several factors of ten of the noise level. The identified HF changes are consistent with the darkening of inner penumbrae and weakening of outer penumbrae in this delta-sunspot group. The enhanced HFs spatially coincide with the TRACE 1550 angstrom rope-like structures lying low above the magnetic neutral line. Unexpectedly, during the flare, the lower lying rope-like structures remain in place, though they exhibit episodic disturbance and brightening, while the outer EUV loops are impulsively expanding. The rapid magnetic changes manifest an impulsive input of free magnetic energy in the photosphere, resulting from an impulsive growth of a new emerging flux region (EFR) along the magnetic neutral line. The facts of the increasing core fields in magnetic nonpotentiality, the continued disturbance of the inner rope-like structures, and the breakout of the outer loops during the major flare cannot be interpreted by any single flare model. However, the nature of magnetohydrodynamical catastrophe is clearly implied for the flare triggering.
alpha-Adrenoceptor agonists for the treatment of vasovagal syncope: a meta-analysis of worldwide published data
The present study was aimed at evaluating present randomized controlled trials (RCTs) regarding the effect of alpha-adrenoceptor agonists on vasovagal syncope (VVS).
According to inclusion and exclusion criteria, articles were selected from medical electronic databases. RCTs were then assessed based on the Juni assessment, and meta-analysis was completed using the Review Manager 4.2 software. Indication to further evaluate effects was the recurrence of syncope during follow-up treatment or a response in the head-up tilt test (HUT) after treatment. The results were stated as odd ratio (OR), with a 95% confidence interval (CI) and a p < 0.05 significant level.
In total, six RCTs were selected. Funnel plot analysis showed possible publication bias. Meta-analysis of the six RCTs, including all 165 patients in the treatment group and 164 patients in the control group, indicated that alpha-adrenoceptor agonists were more effective than placebos in treating VVS (OR = 0.21, 95% CI: 0.06-0.77, p = 0.02). The further, weighted independent t-test disclosed that the weighted mean percentage of responders for midodrine (76.3% +/- 7.7%) was significantly higher than that for etilefrine (65.5% +/- 15.4%) (t = 5.863, p < 0.001).
The currently published RCTs support that alpha-adrenoceptor agonists might be effective for VVS. Midodrine can be regarded as a better choice compared with etilefrine.