MTA Monitoring Report 03/21/25 - 03/27/25

Archive of all weekly reports
Archive of monthly reports

Radiation

Auto SCS107 run due to minor trip from ACIS TXings.
ACIS Radiation Monitor Trip Update (Mar 28, 2025):
--------------------------------------------------
After some sleuthing, ACIS has determined the cause of Monday's unintended radiation trip of the ACIS radiation monitor, txings. Txings includes a check for monotonically increasing threshold-crossing events in each active chip. The bottom line is that this is a result of the newer (as of 2022) longer-period, larger amplitude dither having moved the bright source and its dispersed spectrum off of and back onto the subarray, leading to a large-amplitude oscillation of threshold crossing events. Although dozens such observations have been carried out in the past, the Cyg X-2 observations which resulted in Monday's shutdown were the first to use the larger dither, with the associated longer period that can lead to a txings trigger.

The observation in question used a 134-row subarray ACIS-S/HETG observation of a 0.5 Crab-bright source. The 0th order image and dispersed emission dithered off of and then onto the S3-subarray with the 2000s z-axis dither period making it relatively likely for a txings trip from the monotonically-increasing threshold-crossing rates during the increasing portion of the sinusoidal dither variation.

As you likely recall, the present baseline rule is to use reduced dither (in this case 8" semi-amplitude and 1000s period along the z-axis) only for <=128-row subarrays. If ACA finds this agreeable, ACIS requests that all future observations like this (SI-mode TE_00C82, with its 134-row subarray) make use of the reduced dither-amplitude in the z-direction. I.e., as if they were 128-row subarrays instead of 134.

Furthermore, we want to make sure that Norbert and Herman as HETG USINT leads are aware of this issue. (Also noting that it appears that over the last few years, the MIT/HETG group are the primary observers for this kind of study.) While the 134-row subarray is likely to be the most problematic case for this, any HETG observation with the full z-direction dither moving a bright source off of the chip or subarray could lead to this kind of unintended txings trigger. ACIS has other workarounds available if similar observations with different SI-modes fit this mold, but those workarounds will require SARs and so should be planned in coordination with ACIS

Detrended CTI

Although we prefer to quote CTI values of the cleanest data (FT <= -119.7 C, int time > 7000sec), the data that fulfills these conditions are getting rare. We now quote CTI based on temperature corrected data for Focal plane temperature <= -118.5 C).

The unit is now CTI/year not CTI/day.

ACIS Warm Pixels

We display all bad pixels that have showed up in past, and, if any, previously unknown bad pixels appeared in the last 14 days. We also list hot pixels (defined as 1000 above the average of bias background). Warm columns 509-514 are probably due to boundaries.

New definitions of warm pixels and flickering pixels (May 15, 2014). If a pixel displays the level beyond a threshold for more than 70% of the time in the past two weeks, the pixel is categorized as a "warm" pixel. If a pixel is above the threshold more than 30% of time but less than 70% of the time in the past two weeks, the pixel is categorized as a "flickering" pixel.

ACIS Focal Plane Temperature

For this period, 4 peaks are observed.

Day (DOY)	Temp (C)	Width (Days)
079.16	-95.05	1.99
081.94	-107.33	2.08
083.91	-107.91	1.24
084.82	-100.23	0.56

Weekly focal plane temperature with sun angle, earth angle, and altitude overplotted. Sun angle is the solar array angle, that is the angle between the sun and the optical axis (+X axis). The earth angle is the angle between earth and the ACIS radiator (+Z axis). Altitude varies from 34 kkm to 128 kkm.

SIM Movements

16 TSC moves this period

weekly average time/step	0.00130 s
mission average time/step	0.00132 s

Telemetry

New violations or new extrema are shown in blue cells.

IRUs

Gyro Bias Drift	Gyro Bias Drift Histogram

Recent Observations

Trending

This week's focus is ACIS

Last reported on Jan 09.

Only the most interesting or representative msids are shown below. For a full listing choose the bulletted link.

• ACIS Thermal

• DEA/DPA Thermal

• DEA/DPA Electronics

If you have any questions, please contact: swolk@head.cfa.harvard.edu