HXD PIN Background

Summay table of the recommended background

Observation date	Directory	METHOD *	METHODV **	Description
Before 2006-03-23	pinnxb_ver1.2	PINUDLC	1.2	link
2006-03-23 - 2006-05-13	pinnxb_ver1.2_d	LCFIT (bgd_d)	1.2ver0611	link
2006-05-14 - 2006-05-23	pinnxb_ver1.2	PINUDLC	1.2	link
2006-05-24 - 2006-10-02	pinnxb_ver1.2_w123	PINUDLC	1.2w123	link
After 2006-10-3	pinnxb_ver1.2_w23	PINUDLC	1.2w23	link

*: FITS header keyword to distinguish the background modeling methods.
**: FITS header keyword to distinguish the minor revisions of the same model.

Release of the PIN background (bgd_d) for observations from 2006 March to May

Dear Suzaku users,

As described in Suzaku memo 2006-42, the reproducibility of the current PIN background model becomes significantly worse during the period of 2006 March-May, probably due to the operational change of the lower discrimination level of HXD-GSO (see HXD event log page). Since the discrepancy (~5%) between the background model and actual night earth data implies the "over-subtraction" during the source observation, this will significantly affects the scientific result, especially in case of faint sources. Although the HXD team has been extensively working to improve the reproducibility, it is difficult to immediately release a complete new set of background data, due to the "epoch fragmentation" caused by the high-voltage operations and long-term degradations of the PIN diodes. Therefore, to temporarily solve this situation, we release an development version of the PIN background, only for observations which suffer from the low GSO-LD level effect. Please note that these files are not dead-time corrected, differntly from the current background, and you need to correct the dead time exactly in the same manner as that for the cleaned event files. The new background files can be obtained from this page. The reproducibility of them is still under investigation, but will be soon reported as an appendix of Suzaku memo 2006-42. To distinguish new background files from old ones, you should check the "METHOD" keyword in the FITS header as follows:

unix% fkeyprint aeXXXX_hxd_pinbgd.evt.gz METHOD

Documents on the current PIN background model

We have summarized the method and reproducibility of the PIN background modeling in the following two documents:

Suzaku memo 2007-01
"The Method of the HXD-PIN Non X-ray Background Modeling"

Suzaku memo 2006-42
"Reproducibility of the HXD-PIN Non X-ray Background"

Release of the PIN response/background for W123/23-only analysis

Dear Suzaku users,

As noticed on the "HXD event log" page , on 2006 May 24, bias voltages for 16 out of 64 PIN diodes were reduced from 500 V to 400 V, to suppress the rapid increase of noise events, possibly caused by the in-orbit radiation damage. Since the thickness of depletion layer depends on the bias, this change slightly affected the energy response of the 16 PIN diodes especially at higher energy band than 20 keV. The comparison of Crab spectra obtained before and after the voltage reduction is shown below (see also the PDF version), in which filled circles (labeled "W0") indicate data from the 16 PIN diodes while open circles ("W123") denote spectra from other 48 diodes. While the effective area stayed almost the same below 15 keV, it decreased about 10% above 20 keV which corresponds to a few percent decline of the "total" effective area of HXD-PIN. In the current PIN response matrices (ver.20060814), this effect is not yet implemented. In addition, the level and shape of PIN-NXB are also expected to be different between two bias voltages, as a consequence of the loss of effective area. Therefore, especially in case of the faint source observations, the "standard" PIN analysis, which treat all the 64 diodes with no distinction, might draw an improper conclusion.

Until the calibration progress solves this situation, the HXD team temporarily recommend the observers to exclude data from the "diodes biased with 400 V", and to use the corresponding modified response matrices, together with the PIN-NXB event files for the W123-only analysis. A column named "UNITID" in the PIN event files is available to select the specified PIN diodes. There are 16 well-type phoswich units in the HXD and each of them consists of four PIN diodes, thus the UNITID ranges from 0 to 15, and the units biased with 400 V corresponds "UNITID=0,1,2,3". Therefore, the condition of "UNITID>3" should be applied with the "fselect" as follows (XXXX is your sequence ID):

unix% fselect aeXXXXhxd_0_pinno_cl.evt aeXXXXhxd_0_pinno_w123.evt 'UNITID>3'

Please note that you MUST NOT extract W123 data from "the background for 64 PIN diodes", since the UNITID column is meaningless in the background event files. Instead of extracting, you have to download and use another background files from this page.
The current reproducibility of the PIN background is described in this document (Suzaku memo 2006-42).

On 2006 October 3, another PIN high-voltage was also changed from 500 to 400 V, and the observational data after this date contain 32 PIN diodes biased with 400 V, and the other 32 diodes biased with 500 V. In these cases, the 'UNITID>7' condition should be applied, and the response matrices and background files for "W23-only analysis" should be used. The response matrices are listed here. The background files can be obtained from this page.

Release of HXD-PIN background files for version 1.2 process

These files are "background HXD-PIN event files" prepared by the HXD team. If you need urgent help, please contact the suzaku help web site.

General Notes:

1. The event rate of BGD event file is 10 times as high as the real so that the poisson error can be ignored. Therefore, users should change the exposure of derived spectra and light curve by yourself, by using fmodhead, and so on.
2. The BGD event files have the extension of GTI. The background estimation is performed inside the GTI. If you filter the data with your GTI, you should make a new GTI by ANDing the two GTIs.
3. You should correct the dead time of the observation spectral file to apply the background file correctly. On the other hand, there is no need to correct dead times for estimated PIN BGD files. The dead time correction tool (hxddtcor) is included in the latest version of the Suzaku ftools.
4. The BGD event file does not include the CXB. Since the CXB flux is about 5% of BGD for PIN, you should take it into account after subtracting the BGD. We will provide the simulated CXB spectrum for the HXD PIN, but please keep in mind that it is yet to be confirmed using actual observational data.
5. The accuracy of model is expected to reach as good as 5-10 % of the averaged background. However, since May 24, 2006, one of four high voltages has been reduced to 400 V from the nominal bias of 500 V, due to the in-orbit degradation, and this effect on the detector background has not yet been taken into account. Guest observers are strongly recommended to verify the reliability of background, by comparing the model spectrum with the "earth occultated spectrum" which can be obtained on the condition of "ELV<-5".
6. The BGD modeling is still under development, and the evaluation of the systematic errors of this BGD event files has not been done yet. Users should compare light curves of the observation and the BGD model. We also encourage users to compare the earth occultation data of your data that of BGD event files, to examine the accuracy of BGD model for your data.

Please find a PIN BGD event file for your observation from this page.

Note on PIN CXB

The HXD-PIN BGD event files do not contain the CXB component, and thus you should estimate it by yourself. One method is to estimate the CXB level by using the response for the flat emission distribution. This response file prepared by the HXD team is available from the link below. This response assumes that the uniform emission is from the region of 2 deg x 2 deg. Typical CXB spectrum is reported as follows, based on the HEAO-1 (Boldt 1987 IAUS..124..611B)

9.0e-9 * (E/3keV)**(-0.29) * exp(-E/40keV) erg/cm2/s/str/keV

Everyone should notice that the level and scatter of CXB level is one of important sciences and thus we cannot say how much level is correct.

• ae_hxd_pinflat_20060809.rsp.gz (For all 64 PINs)
• ae_hxd_pinflat_20060809_w123.rsp.gz (For W123-only)
• ae_hxd_pinflat_20060809_w23.rsp.gz (For W23-only)

If you have any questions, please contact Suzaku Help Desk.

ISAS/JAXA Department of High Energy Astrophysics