2009A&A...494..775G


C.D.S. - SIMBAD4 rel 1.7 - 2020.03.28CET09:35:25

2009A&A...494..775G - Astronomy and Astrophysics, volume 494, 775-797 (2009/2-1)

Modelling the spectral response of the Swift-XRT CCD camera: experience learnt from in-flight calibration.

GODET O., BEARDMORE A.P., ABBEY A.F., OSBORNE J.P., CUSUMANO G., PAGANI C., CAPALBI M., PERRI M., PAGE K.L., BURROWS D.N., CAMPANA S., HILL J.E., KENNEA J.A. and MORETTI A.

Abstract (from CDS):

Since its launch in November 2004, Swift has revolutionised our understanding of gamma-ray bursts. The X-ray telescope (XRT), one of the three instruments on board Swift, has played a key role in providing essential positions, timing, and spectroscopy of more than 300 GRB afterglows to date. Although Swift was designed to observe GRB afterglows with power-law spectra, Swift is spending an increasing fraction of its time observing more traditional X-ray sources, which have more complex spectra. The aim of this paper is a detailed description of the CCD response model used to compute the XRT RMFs (redistribution matrix files), the changes implemented to it based on measurements of celestial and on-board calibration sources, and current caveats in the RMFs for the spectral analysis of XRT data. The RMFs are computed via Monte-Carlo simulations based on a physical model describing the interaction of photons within the silicon bulk of the CCD detector. We show that the XRT spectral response calibration was complicated by various energy offsets in photon counting (PC) and windowed timing (WT) modes related to the way the CCD is operated in orbit (variation in temperature during observations, contamination by optical light from the sunlit Earth and increase in charge transfer inefficiency). We describe how these effects can be corrected for in the ground processing software. We show that the low-energy response, the redistribution in spectra of absorbed sources, and the modelling of the line profile have been significantly improved since launch by introducing empirical corrections in our code when it was not possible to use a physical description. We note that the increase in CTI became noticeable in June 2006 (i.e. 14 months after launch), but the evidence of a more serious degradation in spectroscopic performance (line broadening and change in the low-energy response) due to large charge traps (i.e. faults in the Si crystal) became more significant after March 2007. We describe efforts to handle such changes in the spectral response. Finally, we show that the commanded increase in the substrate voltage from 0 to 6V on 2007 August 30 reduced the dark current, enabling the collection of useful science data at higher CCD temperature (up to -50°C). We also briefly describe the plan to recalibrate the XRT response files at this new voltage. We show that the XRT spectral response is described well by the public response files for line and continuum spectra in the 0.3-10keV band in both PC and WT modes.

Abstract Copyright:

Journal keyword(s): gamma rays: bursts - X-rays: general - instrumentation: detectors - methods: numerical

Status at CDS:  

Simbad objects: 21

goto Full paper

goto View the reference in ADS

Number of rows : 21

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 GRB 050904 gB 00 54 50.794 +14 05 09.42           ~ 428 1
2 SNR B0102-72.3 SNR 01 04 01.2 -72 01 52           ~ 342 1
3 SN 2006aj SN* 03 21 39.670 +16 52 02.27 17.96 19.11 17.40     SNIc-BL 817 1
4 GRB 050822 gB 03 24 27.240 -46 01 59.20     20.82     ~ 92 0
5 V* CM Tau Psr 05 34 31.93830 +22 00 52.1758           ~ 4762 1
6 M 1 SNR 05 34 31.94 +22 00 52.2           ~ 5543 4
7 PSR B0540-69 Psr 05 40 10.84 -69 19 54.2           ~ 792 3
8 2MASX J07473129-1917403 BiC 07 47 31.296 -19 17 40.34   19.60       ~ 393 1
9 ClG 0745-19 ClG 07 47 31.3 -19 17 40           ~ 363 0
10 Mrk 421 BLL 11 04 27.3139210166 +38 12 31.798324828   13.50 12.90 8.31   ~ 2356 1
11 3C 273 BLL 12 29 06.6996828061 +02 03 08.598846466   13.05 14.830 14.11   ~ 5279 1
12 GRB 051117A gB 15 13 34.020 +30 52 12.30 18.66 19.81       ~ 61 0
13 V* QX Nor LXB 16 12 43.0 -52 25 23           ~ 820 1
14 V* V818 Sco LXB 16 19 55.0688745859 -15 38 25.019920749 11.60 12.40 11.1     Oev 1523 0
15 V* V1033 Sco HXB 16 54 00.137 -39 50 44.90   15.20 14.2 16.14   F5IV 1689 1
16 V* RS Oph No* 17 50 13.1592776879 -06 42 28.481553668   12.29 4.30     OB+M2ep 918 0
17 PSR J1833-1034 Psr 18 33 33.612 -10 34 07.69           ~ 381 1
18 RX J1856.6-3754 N* 18 56 35.11 -37 54 30.5     25.7     ~ 387 0
19 QSO B2155-304 BLL 21 58 52.0651817803 -30 13 32.120657891   13.36 13.09 12.62   ~ 1542 1
20 NGC 7172 Sy2 22 02 01.897 -31 52 11.60   12.72 13.61 11.15   ~ 460 1
21 NAME Cas A SNR 23 23 24.000 +58 48 54.00           ~ 2375 1

    Equat.    Gal    SGal    Ecl

To bookmark this query, right click on this link: simbad:objects in 2009A&A...494..775G and select 'bookmark this link' or equivalent in the popup menu


2020.03.28-09:35:25

© Université de Strasbourg/CNRS

    • Contact