Friday, November 30, 2007

running xspec as a shell

John Baker just came up with a way of running xspec which hadn't occurred to me. Create a file of xspec commands with the first line as


This has the advantage that arguments can be used eg

cat > testscript.xcm
data $argv

chmod +x testscript.xcm

testscript.xcm file.pha

Thursday, November 29, 2007

model.dat entry for refsch in xspec v12

The refsch model.dat entry has a unit on one parameter of "erg cm/s". This is not interpreted correctly by xspec v12 with the result that the default input parameter values end up strange. The fix is to change the unit definition to ergcm/s.

Monday, November 26, 2007

bad error in gabs model

Takao Kitaguchi and colleagues at the University of Tokyo point out that the gabs, gaussian absorption, model gives a result dependent on the energy bin size. This has been fixed in v11.3.2aj and v12.4.0.

Wednesday, November 14, 2007


Wrote a handy XSPEC Tcl procedure to multiply the covariance matrix used in an MCMC chain proposal distribution by a factor. Use after defining a proposal distribution by eg
 XSPEC12>chain proposal cauchy fit
XSPEC12>source rescalecov.tcl
XSPEC12>rescalecov 0.5
which divides all elements in the covariance matrix by 2.


Created a new ftool to correct the XMM RGS response for an extended source. This uses Andy Rasmussen's code included in the xspec v11 model rgsxsrc. Since that model has no free parameters it seems easier just to modify the response matrix before reading it into xspec and that is what this new tool does. This replaces the need to add rgsxsrc to xspec v12.


Flegal et al. discuss error estimation methods for MCMC computations.

Clifford Will notes that if there are stars in highly eccentric short period orbits (<~0.1 year) around Sgr A* they could be used to test the no-hair theorem. Cen & Fang show that GRBs may be biased tracers of star formation.

Eckert et al. use Integral IBIS imaging of the Coma cluster to find a hard X-ray source extending in the direction of the sub-cluster and co-incident with 1.4 GHz emission.

Ajith et al. construct a template bank for the GW signal from coalescing non-spinning BHs.

Ishak et al. show that gravitational lensing has a dependence on the cosmological constant and that current observations place an upper limit which is competitive with values determined from cosmology.

Davison & Sartori present their approach to the "Banff Challenge" of finding a signal in noisy particle physics data.

Dimopoulos et al. propose GW detection using atom interferometry which has the potential to be more sensitive than LIGO from the ground and LISA from space.

Tuesday, November 13, 2007

xspec plot contour

The contour information being passed from xspec to PLT was not at a high enough precision leading to problems when there are many (>10000) data channels and hence a large value of chi-squared. Fixed this for the 12.4 release.

Thursday, November 08, 2007

fluxerror and linked parameters

Robert Dunn pointed out that fluxerror.tcl doesn't work correctly if there are linked parameters. I made a simple fix to correct that. It does require the xspec 12.3.1an patch.

Friday, November 02, 2007


Jasra et al. present a population-based Reversible Jump MCMC method and argue that it works better than other MCMC methods on high dimension problems.

Hardcastle et al. report on an accumulated 700ksec observation of the Cen A jet which shows that the outer part of the jet requires an as yet unknown distributed acceleration mechanism.

Gierlinski et al. argue that the high frequency end of the power density spectrum in the hard states of BH sources is invariant in shape and the amplitude provides an estimate of the mass.

Snowden et al. present a catolog of 70 XMM cluster observations with a detailed description of their handling of background.

Lang & Hughes investigate the ability of GW observations to localize a SMBH-SMBH merger.

Narayan et al. fit Novikov-Thorne thin disk models to X-ray transients in the thermal state and estimate black hole rotation rates.

Mahdavi et al. compare weak lensing and X-ray measures of mass and find evidence for non-thermal pressure support.

Bianchi et al. use XMM and optical observations of NGC3147 to show that it has no intrinsic X-ray absorption but also no optical broad lines.

Thursday, November 01, 2007

XSPEC bug fixes for tclout plink and fakeit

A couple of recent minor bug fixes...

12.3.1an For the tclout plink option, it is more useful to output the link string in a format which can be used as input for other parameter commands, such as newpar. Our thanks to Jeremy Sanders for pointing this out. Report added on Oct 15, 2007.

The fix is to replace headas/Xspec/src/XSUser/Handler/xsTclout.cxx, and rebuild xspec.

12.3.1ao When a fakeit run is using a response with first legal channel number (TLMIN4) = 0, and is NOT based on an already existing spectrum, the last channel is erroneously ignored and always ends up with 0 counts. Our thanks to David Morris for pointing this out. Report added on Oct 31, 2007.

The fix is to replace headas/Xspec/src/XSModel/Data/SpectralData.cxx, and rebuild xspec.