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Chandra Electronic Bulletin No. 44
             |                                            |
             |              CCC  XX   XX    OOO           |
Chandra      |             CC     XX XX    OO OO          | CXC
Electronic   |            CC       XXX    OO   OO         | Number 44
Bulletin     |             CC     XX XX    OO OO          | October
             |              CCC  XX   XX    OOO           | 2005
             |                                            |

Welcome to the Chandra X-ray Center's Electronic News Bulletin Number 44.

CXC Web site: cxc.harvard.edu

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1.  Anomalous shutdown of DEA-A power supply, 15 Sept 2005

2.  HETG Calibration Update 

3.  Chandra Data Archive Mirror in India Operational

4.  Chandra Calibration Workshop Program and Presentations


Item 1.  Anomalous shutdown of DEA-A power supply, 15 Sept 2005  

An anomaly occurred on Sept 15th 2005 (DOY258) in which the DEA-A 
(Detector Electronics Assembly) power supply shut down. This shutdown 
had two consequences:

1) For observations made during the period Sept 16 - Oct 16 (DOY 259 - 289):
the reported value (as shown in data header files) of the ACIS Focal 
Plane (FP) temperature was ~1.3 degrees warmer than the actual temperature.  
GOs should subtract 1.3 degrees from the reported temperature to determine 
the true temperature.  

2) For observations made during Sep 16 - Oct 6th (DOY 259- DOY 279):
The FP temperature was not regulated during this period.  The FP temperature 
fluctuated between -121.3 C and -118.8 C during this time. For analysis of 
line-dominated spectra from the FI CCDs, GOs might notice a systematic gain 
shift, either towards higher/lower energies depending on if the FP temperature 
was colder/warmer than -119.7 C.  Analysis of line-dominated spectra
on S3 are mostly unaffected.  Analysis of continuum-dominated spectra on
both the FI and BI CCDs are mostly unaffected.  Imaging analysis on both
the FI and BI CCDs are mostly unaffected.

We have taken steps to ensure that the FP temperature and readout will not 
be left in an uncertain state should this unlikely event occur again.

The V&V reports for the observations affected by this anomaly will
provide information on the correct FP temperature. The data file headers 
will not be updated as this would provide inconsistencies within our data 
system and archive. Note that, for data analysis with CIAO, the temperature-
dependent calibrations are retrieved from the CALDB based on observation 
date/time. CIAO users will automatically get the "correct" calibration files 
when re-running acis_process_events regardless of the actual temperature 
value recorded in the headers.


Item 2.  HETG Calibration Update

There's a new calibration report that would be of interest to all  
users and HETGS users especially.  It is available from the HETGS  
calibration web pages, http://space.mit.edu/ASC/calib/hetg_user.html 
and http://space.mit.edu/ASC/calib/hetgcal.html.  The latter page has  
been updated significantly.  The report itself is available at 
http://space.mit.edu/ASC/calib/heg_meg/meg_heg_report.pdf.  Here's is the  
abstract of the report:

I present updates to the HETGS grating efficiencies.  When combined  
with other effective area updates, such as correcting the HRMA Ir-M  
edge, accounting for contamination, and correcting for a residual Si- 
K edge, I obtain very good residuals for simple fits to the spectra  
of many blazars. The updates are somewhat ad hoc and the  
apportionment of the mismatch of the MEG and HEG spectra is  
determined empirically. The result is that relative uncertainties  
should now be less than 5% across the HETGS band from 0.5 to 8 keV.

Calibration files incorporating all these effects will be available  
in the caldb soon.

Herman Marshall


Item 3.  Chandra Data Archive Mirror in India Operational

Since early October users in south Asia are being served public
Chandra data from a mirror at IUCAA in Pune, India.  All browse
functions in WebChaser and QuickImage still go through our servers at
CfA/CXC, but when users request the retrieval of data, their
geographic location is determined and, if in southern Asia, the data
are prepared at the Pune mirror, rather than in Cambridge, MA.
Note that this only applies to primary and secondary products for
public data; proprietary data are still exclusively retrieved from the
archive at CfA/CXC.
We hope that this will speed data transfers for our users in the
region and encourage them to give it a try, especially if they have
been reluctant in the past due to low transmission speeds.
We gratefully acknowledge the efforts of the staff at IUCAA to make
this possible.

Chandra Data Archive Operations


Item 4.  Chandra Calibration Workshop Program and Presentations

The Chandra Calibration Workshop is taking place on Oct 31 and Nov 1
at the Royal Sonesta Hotel.  If you missed previous announcements,
the agenda is at http://cxc.harvard.edu/ccw/agenda/program.html
Presentations will be put online after the end of the Workshop.

Vinay Kashyap


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Last modified: 12/03/10

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