Tuesday, 13 October 2015

CosPA 2015 Liveblog: Day Two Session One

Second day, I was still a little gate so I missed the first couple of minutes of the first talk.  The slides for today are not online, but unlike a certain conference I was at this summer, yesterday's talks are already posted.
09:00 am: Cosmic Infrared Background, Asantha Cooray

Talking about the CIBER experiment, a telescope to look at the CIR.  I thought he said it was a space observatory, but it seems like actually it is not based in space but does short (15 minute) flights on rockets to take data.  Or is this just for callibration using solar absorption lines?  This is the problem of missing the start...

 CIBER-1 is complete and published.  CIVER-2 has been approved, for its first flight next year.

Maybe I'm just tired but none of this talk is making sense to me.

Looking for faint galaxies responsible for reionisation of the universe at high redshift.  Uses HST.  Biggest problem is that Hubble has small field of view, search for fluctuations requires combining images.  This will introduce fake fluctuations for ... reasons.

Proposed experiment SPHEREx, in final stages of proposal.    Will do ... something.  Something based on spectral analysis; looking at the sky through different filters.  Cosmic variance limited up to z ~ 1.  Constrains non-Gaussianity.

09:45 am: Searching for dark matter with gamma rays, Simona Murgia

There's a lot of review material here that I am very familiar with, so I'm not commenting on it.

Discussion of the Fermi GCE.  Using old statement that bbbar is required as final state, plus low mass ~ 50 GeV.

Fermi collaboration approach to model the complicated interstellar emission in the inner galaxy.  Use GALPROP models; tune baseline parameters to fit Fermi data outside central 15 x 15 degree square of data.  Use pulsar and OB star distributions as proxies for cosmic ray sources.  Scale contributions from pion decay and inverse compton in different annular regions of the galaxy as a whole.  This lets us fit the contribution of rings from observational regions outside the galactic center, then this determines its contribution along the GC line of sight.  Ultimately end with four different signal predictions based on different choices of parameterisation and scaling.  None stands out as better than any other.  However, discrepancy from observations reduced from 10-20% to <10%.

Point sources in signal region also important.  Modelling requires care.  Use data only, not pre-existing catalogues.  All models a little too bright below 2 GeV, and a little too dim above that energy; there remains a systematic excess at higher energies.

All models feature very bright IC from the GC.  Might point to more intense ISRF and/or CR electron density at the inner galaxy than expected.

Try seeing if excess can be modelled by a DM-like signal.  Also try other possible morphologies for the excess, but the DM signal is best.  However, the best-fit DM spectrum is strongly dependent on the foreground/background models.  While the excess is persistent, the problems in modelling the IEM are a cause for some concern and likely why we're still waiting for the official Fermi statement on the GCE.

Other main promising source for gamma rays, after GC, is dwarf spheroidals.  Benefit from large mass-to-light ratio, so low backgrounds.  Can infer the DM distribution (to some degree) by measuring stellar motion.  A study of 25 dSphs over 6 years of data.  No significant emission is found.  This begins to put the DM explanation of the GCE under pressure.  However, uncertainties in DM profile let some allowed regions remain.

20 new dSph candidates recently found.  Not yet confirmed that they are dSphs.  If they are, can use non-observation of gamma rays to place further constraints.

Summary of current and future status.  Now rule out thermal WIMP cross sections to ~ 10 GeV from Fermi.  with 10 years plus CTA, can exclude up to 10 TeV, and most of GCE parameter space.

Question: claims about Reticulum 2?  Fermi collaboration does not find any excess.  Another group claimed an excess, but they used different and less correct data analysis.

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