Wednesday, January 14, 2015

Exciting times in NGC 4666

I missed this when it happened in December, but a new Type Ia supernova was discovered in the "nearby" starburst galaxy NGC 4666 by the  Automated Sky Survey for SuperNovae (ASAS-SN) project on December 9th. Bob King at Universe Today has a nice short article with a finding chart for NGC 4666, and some background information and images of the galaxy. A more recent, early January, amateur observation showing the supernova by Justin Ng can be found at EarthSky.org.

More on this topic some time later...

Tuesday, December 23, 2014

High Energy Astronomy News

Two items of note:

  1. Scientific American has a nice article on why the threat to life on Earth from Gamma Ray Bursts, in particular from the dying start Eta Carinae, is not something you need to worry about. (I've discussed putative GRB-caused events here and here).
  2. NuSTAR, an orbitting hard X-ry telescope, has captured some cool images of hard X-ray emission from the Sun (not a target NuSTAR was expected to look at, being designed for the study of Active Galactic Nuclei millions to billions of light years from Earth).
The NuSTAR data, seen in green and blue, reveal solar high-energy emission (green shows energies between 2 and 3 kiloelectron volts, and blue shows energies between 3 and 5 kiloelectron volts). The high-energy X-rays come from gas heated to above 3 million degrees. The red channel represents ultraviolet light captured by SDO at wavelengths of 171 angstroms, and shows the presence of lower-temperature material in the solar atmosphere at 1 million degrees. [Image and caption from NASA/JPL]

Thursday, October 16, 2014

Hooray, Octave supports numpy-style boolean array indexing operations

I've only just discovered that Gnu Octave (the Gnu version of Matlab) supports numpy-style boolean array indexing operations, in particular

  • logical operations on vectors to return boolean true/false vectors
  • array indexing using vectors on vectors
An example, using a simple vector a.
octave:2> a=[1 2 3 4 1 2 3 4]
a =

   1   2   3   4   1   2   3   4

Create a boolean mask called b with all elements of a greater than 2.
octave:3> b=a > 2
b =

   0   0   1   1   0   0   1   1
Now use b to access only those elements of a that are true in the mask array b.
octave:4> a(b)
ans =

   3   4   3   4
Why use Octave when we have python/numpy/scipy? Sometimes its just faster to fire up octave to get a look at data, and matlab/octave syntax is much less verbose than python.

Tuesday, August 26, 2014

More on the possible AD 774/775 hit on the Earth by a nearby GRB

I hadn't heard of either the odd AD 774/775 values of the C12/C14 and increased B10 ratios or the hypothesized casue: a nearby (within the Milky Way) Gamma Ray Burst before reading a blog post by Greg Laden related to climate change a while ago.

It turns out the GRB hypothesis was only recently advanced: Hambaryan & Neuhäuser, 2013, MNRAS, 430, 32 [full article text available online here]. Back at the time Phil Plait actually covered the story in his blog, which has a nice write up of the idea and why other explanations (Solar Flare, Magnetar, nearby Supernova) are claimed to be less likely than a "short" (neutron-star merger induced) GRB.

It somewhat surprises me that an event of the magnitude necessary to alter the isotopic composition of the Earth's atmosphere in less than a few seconds could occur without (a) anyone seeing anything and recording it, and more over (b) not causing any significant biological events (e.g. animal, plant or human deaths). Still, reality often runs counter to naive expectation (i.e. "common sense") so I'm not too put off the idea by that.

For now I'd view this idea of the Earth getting hit by a short GRB as a plausible hypothesis rather than concrete fact, at least until several more studies come to the same conclusion. Still, it is a rather fun and exciting idea.