DISPLAYING THE HETEROGENEITY OF THE SN 2002cx-LIKE SUBCLASS OF TYPE Ia SUPERNOVAE WITH OBSERVATIONS OF THE Pan-STARRS-1 DISCOVERED SN 2009ku

SN 2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SN Ia), and a member of the distinct SN 2002cx-like class of SNe Ia. Its light curves are similar to the prototypical SN 2002cx, but are slightly broader and have a later rise to maximum in g. SN 2009ku is brighter (similar to 0.6 mag) than other SN 2002cx-like objects, peaking at M-V = -18.4 mag, which is still significantly fainter than typical SNe Ia. SN 2009ku, which had an ejecta velocity of similar to 2000 km s(-1) at 18 days after maximum brightness, is spectroscopically most similar to SN 2008ha, which also had extremely low-velocity ejecta. However, SN 2008ha had an exceedingly low luminosity, peaking at M-V = -14.2 mag, similar to 4 mag fainter than SN 2009ku. The contrast of high luminosity and low ejecta velocity for SN 2009ku is contrary to an emerging trend seen for the SN 2002cx class. SN 2009ku is a counterexample of a previously held belief that the class was more homogeneous than typical SNe Ia, indicating that the class has a diverse progenitor population and/or complicated explosion physics. As the first example of a member of this class of objects from the new generation of transient surveys, SN 2009ku is an indication of the potential for these surveys to find rare and interesting objects.

Cotranscriptional role for Arabidopsis DICER-LIKE 4 in transcription termination.

Transcription termination is emerging as an important component of gene regulation necessary to partition the genome and minimize transcriptional interference. We have discovered a role for the Arabidopsis RNA silencing enzyme DICER-LIKE 4 (DCL4) in transcription termination of an endogenous Arabidopsis gene, FCA. DCL4 directly associates with FCA chromatin in the 3' region and promotes cleavage of the nascent transcript in a domain downstream of the canonical polyA site. In a dcl4 mutant, the resulting transcriptional read-through triggers an RNA interference–mediated gene silencing of a transgene containing the same 3' region. We conclude that DCL4 promotes transcription termination of the Arabidopsis FCA gene, reducing the amount of aberrant RNA produced from the locus.

A review of Ni-like X-ray laser experiments undertaken using the VULCAN laser at the Rutherford Appleton Laboratory

Recent progress using the VULCAN laser at the Rutherford Appleton Laboratory to pump X-ray lasing in nickel-like ions is reviewed. Double pulse pumping with similar to 100 ps pulses has been shown to produce significantly greater X-ray laser output than single pulses of duration 0.1-1 ns. With double pulse pumping, the main pumping pulse interacts with a pre-formed plasma created by a pre-pulse. The efficiency of lasing increases as there is a reduced effect of refraction of the X-ray laser beam due to smaller density gradients and larger gain volumes, which enable propagation of the X-ray laser beam along the full length of the target. The record shortest wavelength saturated laser at 5.9 nm has been achieved in Ni-like dysprosium using double pulse pumping of 75 ps duration from the VULCAN laser. A variant of the double pulse pumping using a single similar to 100 ps laser pulse and a superimposed short similar to 1 ps pulse has been found to further increase the efficiency of lasing by reducing the effects of over-ionisation during the gain period. The record shortest wavelength saturated laser pumped by a short similar to 1 ps pulse has been achieved in Ni-like samarium using the VULCAN laser operating in chirped pulse amplified (CPA) mode. Ni-like samarium lases at 7.3 nm. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

Transient pumping of a Ni-like Ag x-ray laser with a subpicosecond pump pulse in a traveling-wave irradiation geometry

We report what is to our knowledge the first demonstration of a transient x-ray laser pumped by a 350-fs pulse in a traveling-wave irradiation geometry. For a 500-fs pump pulse the traveling-wave irradiation was found to have a strong effect on enhancing the Ni-like silver 4d-4p lasing emission at 13.9 nm. The signal enhancement was significantly less when the pulse duration was lengthened to 1.7 ps. The experimental observations are well reproduced by a simple model when the duration of gain is taken of the order of 15-20 ps. For the 500-fs pulse a gain coefficient of 14.5 cm(-1) was measured for plasma lengths up to 7 mm. Refraction of the amplified photons is believed to be the main cause of the limitation of the effective amplification length. (C) 2000 Optical Society of America.

Gain saturation of the Ni-like X-ray lasers

Driven by a double 75 ps pulse with 2.2 ns separation, saturated operation of nickel-like Ag, In, Sn, and Sm X-ray lasers have been demonstrated with only 75 J drive energy on target. The variation of X-ray laser output with target length is found to fit well to a simple model for an amplified spontaneous emission (ASE) laser including saturation. Small signal gains of similar to 10 cm(-1), effective gain length products of similar to 18, and saturation irradiance of (1-5)x 10(10) W/cm(2) are measured for these lasers using a fitting procedure. (C) 1998 Elsevier Science B.V. All rights reserved.

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9].

Demonstration of saturation in a Ni-like Ag x-ray laser at 14 nm

We report the first demonstration of saturation in a Ni-like x-ray laser, specifically Ni-like Ag x-ray laser at 14 nm. Using high-resolution spatial imaging and angularly resolved streaking techniques, the output source size as well as the time history, divergence, energy, and spatial profile of the output beam have been fully characterized. The output intensity of the Ag laser was measured to be about 70 GWcm(-2) The narrow divergence, short pulse duration, high efficiency, and high brightness of the Ag laser make it an ideal candidate for many x-ray laser applications.