ACIS Bright-Source ToO/DDT Review

When does ACIS need to do a ToO / DDT H&S review?

The two proposal categories containing potentially bright source in which ACIS dosing assessment is required are:
1. BH AND NS BINARIES
2. SN, SNR AND ISOLATED NS

Of the second topic, only isolated NSs are of potential concern (particularly magnetars or SGRs).

Conducting the review

When a matching proposal comes along, the ToO / DDT email notice will include information like the following example: 
------------------------------
Emission Probability: 0.05000
Maximum Potential Flux: 1.00000
Maximum Exposure Time In Maximum Flux: 10.00000
Comment: No nearby bright sources.
==============================

These quantities are answers to the following questions:
1 - Probability of having either flaring or steady emission exceeding 100 mCrab intensity (3e-9 erg/s/cm2 from 0.5-10 keV) across all requested observations)
2 - Maximum potential flux (in units of Crab intensity)
3 - Maximum potential exposure time spent at that maximum flux (in ks)
4 - Additional comments on source brightness (justification for estimate)

If the first entry is identically 0, then there should be no concern for ACIS under most circumstances (i.e., unless dither is disabled). Otherwise, given a nonzero probability entry, the other quantities should be inputted in the dose_in_crabs script, e.g., here: 

/home/acisdude/bin/dose_in_crabs.pl
Please enter the estimated flux in terms of crab (.5 for half crab) 1
What is the exposure time in ksec? 10
Is the dither reduced/small-subarray (enter 0) or standard (1)? 1


AIMPT	GRATING	DITHER	Max Counts	Dose(krad)	% MD
------	-------	------	----------	----------	-----
ACIS-I	NONE	ON	 9614.00	0.07		0.28
ACIS-I	NONE	OFF	698042.00	5.17		20.68
ACIS-I	HETG	ON	 1610.00	0.01		0.05
ACIS-I	HETG	OFF	114501.00	0.84		0.21
ACIS-S	NONE	ON	 8748.00	0.09		0.01
ACIS-S	NONE	OFF	496955.50	4.97		0.79
ACIS-S	HETG	ON	 1475.50	0.15		0.00
ACIS-S	HETG	OFF	79602.00	0.80		0.12

Here, standard dither has been assumed, but be sure to check for a 128-row subarray or nonstandard dither in the DDT/ToO request. Let's assume this is a proposal for a standard ACIS-I/NONE observation. In this case, the maximum projected dose is 0.28%, but the probability of reaching a concerning brightness is low, only 5%, so the conservative probability-weighted dosing is 0.014%.

Assessment Guidelines

If either of the peak predicted per-pixel dosing is above **1%** OR the probability-weighted peak-pixel dosing is above **0.1%**, we should note the potential dosing risk and depending on the value may suggest mitigating options or a rejection of the proposal.

Note that for exceptional cases such as a very short-duration and intense flares (e.g., a magnetar exceeding 100 Crab for 1s), standard dither assumptions about the dosing being spread over the Lissajous pattern will not apply and the team should discuss such cases.

Distributing the Review

The results of the assessment should be entered in the associated ToO/DDT manager page available here. Near the bottom of the DDT/ToO manager entry is a box for "Bright-Source Comments". Enter a concise summary of the review results (e.g., "ACIS has no H&S concerns.") and when ready update and distribute by clicking on the "Email-Only Comments (no pager)" link unless the information is urgent.