3.1     Who May Propose

Participation in this program is open to the following categories of institutions and organizations:

• Educational Institutions – Universities or two- and four-year colleges accredited to confer degrees beyond that of the K-12 grade levels.
• Nonprofit, Nonacademic Organizations – Private or Government supported research laboratories, universities consortia, museums, observatories, professional societies, educational organizations, or similar institutions that directly support advanced research activities but whose principal charter is not for the training of students for academic degrees.
• NASA Centers – Any NASA Field Center and the Jet Propulsion Laboratory.
• Other Federal Agencies – Any non-NASA, U.S. Federal Executive agency or Federally Funded Research and Development Center (FFRDC) sponsored by a Federal agency.
• Commercial Organizations – Organizations of any size that operate for profit or fee and that have appropriate capabilities, facilities, and interests to conduct the proposed effort.
• Non-U.S. Organizations – Institutions outside the United States that propose on the basis of a policy of no-exchange-of-funds. See Section 3.3 for additional information.

Each proposal must have one, and only one, Principal Investigator (PI). Any other individuals who are actively involved in the program should be listed as Co-Investigators (Co-Is). The PI is responsible for the scientific and administrative conduct of the project and is the formal contact for all communications with the CXC.

Proposals by non-U.S. PIs that have one or more U.S. Co-Is who require funding must designate one of the U.S. Co-Is as the “Administrative PI”. (Note: U.S. is defined as the 50 states and the District of Columbia.) This person will have general oversight and responsibility for the budget submissions by the U.S. Co-Is in Stage 2.

3.2     Observing Policy

3.2.1     Chandra Observing Policy

3.2.1.1     Introduction and Scope

This section establishes the observing policy for Chandra. This policy reviews and confirms the distribution of observing time among the Guaranteed Time Observers (GTOs) and General Observers (GOs), establishes guidelines for the resolution of conflicts between and within these groups, and sets guidelines for the distribution of observing time.

3.2.1.2     Distribution of Data

Proprietary Data

With certain exceptions, all General Observing data awarded either to GTOs or to GOs will be proprietary for one year beginning when the data are made available to the observer. For fragmented “Long Duration” observations, the one-year period for each target begins when 90% of the data have been made available to the observer.

Data from unanticipated Targets Of Opportunity (TOO) and other use of Director’s Discretionary Time may be proprietary for limited periods – no more than three months – before they are placed in the public archive. Calibration data scheduled and obtained by the Chandra X-ray Center will not be proprietary and will be placed directly into the public archive.

Data from Very Large Projects (VLP) will not be proprietary.

Distribution of Observing Time

Distribution between GO and GTO - Scientific observations commenced approximately 2 months after launch. X-ray data obtained during these first two months were considered calibration data and were placed directly into the public archive. Subsequent to 22 months after launch, and exclusive of Calibration Time and Director’s Discretionary Times, 85% of observing time is provided to GOs and 15% to GTOs.

Distribution among GTOs - In Cycle 10, the GTOs comprise the following: Four Instrument Principal Investigators (IPIs) for the Advanced Imaging Spectrometer (ACIS), for the High-Resolution Camera (HRC), for the Low-Energy Transmission Grating (LETG), and for the High-Energy Transmission Grating (HETG). Their observing time is based on a distribution of 3.5 “shares” as follows:

LETG IPI	0.5 share	0.5 share total
HETG, ACIS, and HRC IPIs	1.0 share each	3.0 shares total

3.2.1.3     Target Selection and Phasing

Target selection will be carried out in a sequence phased with the timing of the CXC Call for Proposals. Target selection begins with the GTOs specifying targets that over-subscribe the GTO time available. Any GTO-GTO conflict at this point shall be resolved by the GTOs. In the event that a resolution is not achieved, the GTOs shall write proposals in accordance with the CfP. After the GO proposals are received, GO-GTO conflicts are identified. In response, GTOs may either (i) replace a conflicted target with an unconflicted backup target or (ii) write a proposal and let the peer review decide the conflict. Targets resulting from peer review of the responses to the CfP will be added to the set of unconflicted GTO targets to form the complete approved target list

3.2.1.4     GTO Proposals

GTOs must submit proposals for observing time if there are GO or other GTO proposals for the same target. GTOs are guaranteed to receive their observing time in accordance with Section 3.2.1.3 but cannot reserve targets in advance of the CfP.

3.2.1.5     Conflict Resolution

All conflicts (GO-GO, GO-GTO, or GTO-GTO) are decided as part of the peer review process with selection based on scientific merit.

3.2.1.6     Large Projects

Large Projects (see Section 4.2) are those that are designated as such by the proposer and that require more than 300 ksec observing time, whether long-duration observations of single targets or shorter duration observations of multiple targets. Large Projects are encouraged. Up to 6 Msec of observing time will be allocated for Large Projects and Very Large Projects in this cycle. The allocation of time to each type will be determined through peer review.

Large Projects must be proposed to be completed within the time span covered by the CfP and cannot reserve targets beyond that time.

3.2.1.7     Very Large Projects

Very Large Projects (see Section 4.3) are those that are designated as such by the proposer and that require 1 Msec or more of observing time. Very Large Projects are encouraged. Up to 6 Msec of observing time will be allocated for Large Projects and Very Large Projects in this cycle. The allocation of time to each type will be determined through peer review. Apart from the minimum amount of observing time and the restriction that data obtained under a Very Large Project enter the public data archive immediately, the approach to, and selection procedures for Large Projects are applicable (Section 3.2.1.6).

3.2.1.8     Targets of Opportunity (TOOs)

There are two categories of Targets of Opportunity: Those that are proposed and selected through peer review (Pre-Approved); and those that simply occur and have been brought to the attention of the Director of the CXC, who may reschedule Chandra to obtain the appropriate observations in the best interest of the scientific community.

Pre-Approved TOOs

A proposed TOO may be reserved for a single proposal cycle. The proposer may propose to renew the opportunity in subsequent cycles.

Unanticipated TOOs

Data obtained from an unanticipated TOO are considered Director’s Discretionary Time. These data may be kept proprietary for a period not to exceed three months.

3.2.1.9     GO Time Allocation

All GO time allocations will be subject to peer review.

3.2.1.10     GTO Time Allocation

All GTO targets with conflicts will be subject to peer review, consistent with the provisions of Sections 3.2.1.3 and 3.2.1.4.

3.2.1.11     Director’s Discretionary Time (DDT)

For this Cycle, 700 ksec of observing time is reserved for Director’s Discretionary Time. This allocation includes unanticipated TOOs.

3.2.1.12     Time-Critical Targets

The number of time-constrained observations accepted in any Cycle will be limited to 15% of the total with quotas for the various classes of constraints (section 5.2.8). New or additional constraints may not be imposed by the observer after the proposal deadline. Please note that an observation is defined as a single observation of a target. Monitoring observations are counted based on the number of repeat visits.  Long observations (>80 ksec) will be divided into several 80 ksec-long observations for the purpose of counting constraints. 

3.2.2     Procedures Concerning TOOs and DDTs

The deep orbit of Chandra permits reasonable access to any TOO. The minimum planned response time for a TOO is approximately 24 hours. The total number of TOOs performed is limited by operational and manpower constraints.

Requests either to initiate a Pre-Approved TOO or to propose a new one are made to the CXC Director, who decides whether to interrupt the timeline and conduct the observation. The investigator is required to submit the appropriate web-based form. The form, a Request for Observation (RfO), can be found at the CXC home page (http://cxc.harvard.edu/) and submitted via the WWW.

The response to a TOO will be classified according to the time delay between trigger and observation. The faster the Chandra response, the more difficult and the more limited the number of TOOs allowed. TOO follow-up observations (observations following a TOO within a few weeks) will also count as TOOs.

3.2.2.1     Pre-Approved TOOs

TOOs generated by a peer review-approved proposal are similar in spirit to the IUE or RXTE in that time is allocated to the proposal, but the time is unscheduled. To initiate the scheduling process, the investigator is required to specify in the RfO how the trigger condition has been met.

TOOs disrupt the timeline, and it is possible that the TOO conflicts with a time-critical observation or with another TOO. In such situations, the CXC Director will determine priorities. Any disrupted preplanned observation will, however, ultimately be accomplished if feasible.

3.2.2.2     Unanticipated TOOs

A request for an unanticipated TOO observation is made directly to the CXC Director as part of the DDT program. A RfO must be submitted. The procedure is as follows:

• The proposer must determine whether the target falls within the portion of the sky visible to Chandra. The ObsVis tool can generate such information.
• The proposer must establish whether the target can be detected using Chandra. The proposal planning tools can be used for this purpose.
• The proposer must address the following questions:
  • Why is the science from the observation important, and why not simply propose during the next Chandra CfP?
  • Is there an impending, previously approved, Chandra observation that can accomplish the objectives?
  • How urgent is the TOO? Must the observation be done immediately?
  • If relevant, what is the likelihood of additional transient behavior (i.e., does the phenomenon recur?)? If recurrence is likely, what is the consequence if the target is not observed until the next occurrence?
  • If data already exist in the archive, why is another observation with Chandra necessary?
  • What is the proposed or suggested detector configuration?

If the proposed observation is accepted, the CXC will create a new timeline as soon as possible. Some negotiation between the observer and the CXC may be necessary to achieve the optimum blend of response time and minimum impact on the rest of the schedule.

3.2.2.3     Director’s Discretionary Time (DDT)

General requests for DDT must follow the same procedure as required for an unanticipated TOO. The procedure is described in Section 3.2.2.2.

The proposer may apply for a short period of time (at most 3 months) during which the data are considered proprietary.

A limited amount of funding is available to support US-based PIs/Co-Is of DDT observations. This funding may be requested using the standard cost proposal form on the CXC website (http://cxc.harvard.edu/).

3.2.3     Criteria for Completeness and Data Quality

3.2.3.1     Completeness

In general, an observation, defined as corresponding to a unique sequence number, will be considered complete when 90% or more of the requested time has been observed, as determined by the Good Time Interval (GTI) in the processed data relative to the approved time. (Previous policy set this threshold at 80%).

The following 4 exceptions are identified:

1. TOO and DDT observations with GTI less than 90% of the requested time may be declared complete by the CXC Director or his representative when constraints due to competing targets and/or observatory restrictions do not allow the full time (or 90% of it) to be achieved and when a subsequent observation would no longer meet the objectives. Such cases will be tracked and closed by adjusting the approved observing time in the Observing Catalog (OBSCAT) after final scheduling is completed.
2. For observations (unique sequence number) greater than 200 ksec, any remaining time exceeding 20 ksec will be scheduled even if the GTI to approved time ratio exceeds 90%, provided constraints allow.
3. For observations less than 5 ksec, targets will be observed only once and will be considered complete regardless of the GTI achieved unless a spacecraft anomaly causes the entire observation to be missed.
4. For observations with less than 2 ks remaining, no additional time will be scheduled even if the 90% GTI to requested time has not been achieved.

Items 3 and 4 are intended to avoid additional short exposures with their relatively high fractional overhead (inefficient use of Chandra). Item 4 assures that observations between 5 and 20 ks get at least 60% of their approved time (for 5 ksec approved) with a sliding scale assuring that at least 90% is achieved at 20 ksec approved time.

Note: The proprietary time begins when the observation is “complete” according to the above rules.

3.2.3.2     Data Quality Due to High Background

Data can be lost (or overwhelmed) because of occasional episodes of very high background. If the principal target was a point source and the background is ≥ 10 times nominal for ≥ 50% of the observation, the target may be observed again for a period of time equal to the amount of time lost due to the high background. If the target is extended and the background increase is ≥ 5 times nominal for ≥ 50% of the observation, then another observation may be scheduled to replace the amount of time lost due to the high background. We realize that application of these limits is somewhat arbitrary. The intent is to only schedule additional observations if the scientific objectives were not achieved due to the high background. If “space weather” causes only some deterioration in data quality, the observation is considered complete.

Although the CXC monitors space weather, there is no real-time contact with the Chandra Observatory so high background periods cannot be avoided. Ultimately, it is the observer’s responsibility to determine if the data require another observation according to the criteria above. An application for an additional amount of time on target should be made to the CXC Director. Providing a plot of the background counting rate vs. time and a short table with the integration time at different background levels is required.

3.2.3.3     Data Quality - Telemetry Saturation Due to X-ray Sources

Telemetry saturation produced by the target and/or other sources in the field-of-view are the responsibility of the observer. The unique case of a previously unknown transient appearing in the field-of-view will be handled case-by-case.

3.3     Non-U.S. Participation

Science proposals from outside the United States are welcome. However, research conducted by non-U.S. Institutions cannot be funded by NASA; therefore, non-U.S. researchers who propose investigations requiring new Chandra observations must seek support through their own national funding agencies.

The Chandra data archive is open to the public; to obtain data of interest to his/her project, an interested researcher need only access the CXC website (http://cxc.harvard.edu)  or contact the Chandra X-ray Center for assistance. U.S. researchers who wish to analyze archival data or undertake theoretical investigations may apply for funding for their research through this CfP. The PI of an archive/theory proposal must be affiliated with a U.S.-based Institution. Non-U.S. researchers should not propose to this CfP for funding unless their proposal includes U.S. Co-Investigators who are eligible for funding.

Non-U.S. Principal Investigators are not eligible to submit an EPO supplementary proposal.

3.4     Proposal Confidentiality

Proposals submitted to the CXC will be kept confidential to the extent allowed by the review process. For accepted proposals, the scientific justification section of the proposal remains confidential but other sections become publicly accessible, including PI names, project titles, abstracts, and all observational details.  The remainder of the approved proposals, and the entirety of proposals not selected, will remain confidential.

All CXC and visiting personnel who will be handling or reviewing the proposals as part of the review process will be fully informed of the confidential nature of the proposals. They will be required to sign a non-disclosure agreement, agreeing to treat information in the proposals as confidential and not to disclose it or use it in any way beyond that needed for the review process itself. All copies (electronic and hardcopy) of the proposals distributed as part of the review process will be destroyed once the process is complete.

3.5     Chandra Observation Catalog: Checking for Duplicate Targets

Proposals for new observations that duplicate existing Chandra observations will not be accepted unless scientifically justified. It is the proposer’s responsibility to ensure that he or she does not propose for observations of the same target with the same instrument and comparable observing time to one already in the Chandra Observing Catalog or that such a request is justified. For targets previously observed in the X-ray band, particularly those observed by XMM-Newton, the proposal should address the specific need for the addition of Chandra data to accomplish the proposed scientific investigation. Previous observations may be checked using, for example, HEASARC W3Browse (http://heasarc.gsfc.nasa.gov/docs/HHP_heasarc_info.html).

The review panels will be provided with a list of previous X-ray observations of proposed targets. Information on the various ways to access the Chandra Observation Catalog may be found in Chapter 6.

3.6     Supporting Ground-Based Observations

As part of the proposal and corresponding budget for a Chandra investigation, proposers may request funding support for correlative observations at other wavelengths beyond the joint observations described in this solicitation (Section 4.5). Funding for such correlative studies will be considered only when they directly support a specific investigation using Chandra. Unless there are exceptional circumstances, such as a CXO/NOAO joint proposal or some archive or survey proposals, funding for ground-based supporting observations should not exceed 10% of the total request.