Dark Matter Damping

May 8, 2009

There is an interesting discussion over at Sarah’s blog, about astronomers being driven by ambition and greed just like everybody else. I remember this concept shocking Donald Pettie, the ex Chief Engineer at ROE, who moved there from Ferranti back in the eighties. He thought academics would be gentle, polite people. In some ways this was true, but he told me that he soon learned that the average astronomer would be prepared to sell his grandmother for an extra night on a big telescope.

There was something of an unseemly stampede last year when the ATIC results were announced – a claim of a hump in the cosmic ray electron energy spectrum, that could be a feature caused by the decay of dark matter particles. Gold !!!!!!! At a conference where the pre-publication results were presented, someone apparently photographed the screen, measured the points, and rushed a paper out. Of course this was only one of a gazillion papers with different interpretations. But now Fermi has made this all seem a bit daft : a paper just out in Phys Rev Lett has made an absolutely exquisite measurement of the CR energy spectrum from ten to a thousand GeV, which slides neatly underneath the ATIC data. Bump not there. See below.

Cosmic Ray electron energy spectrum measured by Fermi satellite

Cosmic Ray electron energy spectrum measured by Fermi satellite

Well this result has already caused a splash in the popular press and astroblogs (here is Sean Carrol’s take), but I had it in mind because I just attended a SLAC seminar explaining the result, given by Luca Patronico. The particle physicists are still seeing the glitter of gold in the river; the beautiful Fermi data disagree not only with the ATIC hump, but also with the “conventional diffusive model” … there are already papers out on ArXiv with revised DM fits…

However I am glad to report that the astronomers in the audience were somewhat saner. Not only is it possible that nearby pulsars could produce this “excess”,  at least one older wiser head said “errr… you aren’t taking that conventional diffusive model too seriously are you ? We don’t really understand the transport of cosmic rays through the ISM in that level of detail. Its kinda tricky. I can give you any curve you want”.

Maybe its relevant that the person who said this is already mature and respected … no need to grab at every chance of fame….


Gamma Rays coming at you

February 6, 2009

Just came back from a coffee time talk by David Paneque, showing the GeV light curve of blazar MKN 421 over 3 months, as measured by the Large Area Telescope (LAT) on Fermi. In the middle of his talk he got everybody excited because he just mentioned in passing that the LAT team are today submitting a paper to astro-ph describing the first public LAT catalog. This is a 10 sigma cut after 3 months data and has about a couple hundred sources. (This is what I remember from reading a slide, so treat with caution !). A few highlights… There as many gamma-ray only pulsars as previously known radio pulsars. There a hundred blazars, and two radio galaxies – Cen A and Perseus A, but NOT M87, and none of the bright Seyferts. There is a smattering of X-ray binaries. There are 37 unassociated objects : mostly at low latitude, so maybe more pulsars, but half a dozen high latitude mysteries.

Just on the off-chance, I fired up VODesktop and Topcat to see if HEASARC have already published the catalog. They haven’t, but there is already other Fermi stuff there. For example, you can get a table of 145 bursts seen by the GBM. Try this :

  • start up VODesktop and Topcat
  • click “New Smartlist”
  • search for waveband=gamma-ray and any-field=Fermi
  • this gives four resources available at HEASARC
  • select GBM burst catalog
  • click “query” which launches the Astroscope window
  • search 180 degree radius at any position
  • this returns a  VOTable with 145 results – the whole catalog of course
  • click “send to Topcat”
  • look at the table, plot stuff etc..

For example, if you now simply plot RA vs Dec, you can see there’s a whole clump of bursts around ra=235 dec =-55. Wossat ?


Spooky Space News

October 23, 2008

I am getting emails that are telling me that HST, Chandra and XMM were all down at the same time ..

Mike Watson tells me contact was lost with XMM on Saturday… but it has been regained today.

Martin Elvis said :

“I was working Saturday night for a Monday talk & Pat Slane was doing the same, when he got paged (as Top Mission Planner) that Chandra had gone into Sun Normal Mode (ie perpendicular to sun)….

Hubble we all knew about, but I saw Rodger Doxsey at STScI (which is where I was going Monday), and he told me about the 24h of good side B ops, followed by a glitch that they are still debugging. Incremental start-up of side B systems going well; options of cross-patching sides A,B exist; >15yr old spare undergoing check-out at GSFC for SM-4 (=major reason for delaying launch).”

Martin later said, noting the closeness to Halloween :

“Cue Twilight Zone music.”

To which Mike’s response was :

“probably due to LHC switch-on, which also precipitated major global financial instability as we all know”

Hey, is Fermi ok ????