QDP Input Files

They must be files written according to the QDP/PLT specifications. They consist of a header and a number of ``vectors", each written as a column. To use QDP files as input to XRONOS applications it is essential that these have 2 header lines at least:

• QDP HEADER LINE containing the READ command according to the QDP specifications. This is essential to let XRONOS know which vector have errors associated to them. Note that in case a QDP file contains asymmetric errors (READ TERR ....) only the first error column of a vector is used by Xronos.

• XRONOS HEADER LINE starting with !!H and followed by 5 numbers: (1) the first number represents the bin integration time of the file expressed in seconds: a negative number indicates an arrival time file in which times represent the arrival times of individual photons; (2-3) the second and third numbers give the center times of the first and last bin in the file expressed in days; (4) the fourth number is a file format flag and should be specified as follows: =0 if the Y-values are in counts/s (or any equivalent), =1 if Y-values are in counts; (5) the fifth number specifies the units of the time axis (X-axis): if =0 the units are seconds from the start time given by the 2nd number in the header; if =1 units are seconds from the beginning of the hour specified by the 2nd number; if =2 units are hours from the beginning of the day specified by the 2nd number; if =3 units are days. The fourth and fifth numbers might not be specified in the Xronos header line in which case they are taken =0 by default.

XRONOS applications include the input file options vx, vy and ve to specify which vector should be assigned, respectively, to the X-axis (i.e. time axis), which to the Y-axis and which to the bin exposure. By default vector 1 is assigned to the X-axis (i.e. time axis) and vector 2 to the Y-axis (i.e. the input series). Then if the input file contains more than 2 vectors the last vector is assigned by default to the bin exposure (note that this is the convention used in Xronos QDP Output Files). If the input file contains only 2 vectors the bin exposure will be =1 by default. If a negative number is specified after the input file option ve, then the bin exposure is forced to be =1, even if more the input file contains more than 2 vectors. Note that bin exposure, if present in a file in which Y-axis values are in counts (i.e. 4th number of the XRONOS header line is =4), are used to rescale Y-axis values and errors to counts/s.

The error on the X-axis points (i.e. the semiwidth of time bins) is not used by XRONOS applications. Errors on the Y-axis points are instead necessary. If the QDP file does not contain Y-axis errors, XRONOS applications calculate the error by using Poisson statistics (i.e. sqrt(Yvalue*bintime)/bintime, if the 4th number of the Xronos header line is =0, or sqrt(Yvalue), if the 4th number of the Xronos header line is =1). Note that in this case Y-axis bins should not be background subtracted. If the QDP file contains 1 vector only this is assigned to the Y-axis by default and X-axis values are stepped according to the content of the XRONOS header line. If an arrival time QDP file is indicated the Y-axis values and errors are always set =1.

Gaps in the vector(s) are indicated by the (QDP/PLT) value =-1.2e-34.

Note that XRONOS QDP files produced by XRONOS applications can be used as QDP input files.