Director's Log

Patrick Slane

I don’t know about you, but I’m feeling really close to Chandra these days. But it’s not just because I’m sentimental. It’s more…

As its orbit continually evolves, Chandra’s perigee altitude waxes and wanes. At launch, that altitude was 9651 km. This reached a maximum value of over 29000 km in 2005, followed by a decline to a minimum of 3408 km in mid 2012. As Chandra raced around this low point of its orbit, the time spent in the radiation zones decreased; the resulting increase in science time prompted the creation of an X-ray Visionary Project proposal category that solicited programs up to 6 Ms in duration, leading to significant breakthroughs in studies of galaxy clusters, pulsar winds, star-forming complexes, and the Galactic Center, and through legacy surveys of the COSMOS, CDS-S, and UDS fields.

Following a subsequent increase, we have entered another low-perigee epoch, heading toward a low value of just over 1000 km in mid 2023. In late May of this year, Chandra crossed its previous low altitude; at perigee, Chandra is currently closer to us than it has been since launch! (Technical point: the perigee point is in the southern hemisphere; it is actually our Australian colleagues who are experiencing the closest fly-by passes.)

The resulting low perigee has again increased the amount of available observing time, but by considerably less than at its previous minimum. Thus, the XVP program will not be renewed, but we can look forward to increases of about 1.5-2 Ms per year for Chandra studies over the course of the next few years.

The last six months of Chandra operations have been marked by continued successful operation of the Observatory, albeit with one significant anomaly with the HRC detector experienced in early February. As described in the article by Grant Tremblay, the most likely candidate for the source of the anomaly is the +/-15V power supply on the B-side electronics chain that has been in use since a similar anomaly was experienced with the A-side +/-15V power supply in 2020, and a series of investigations are underway to identify potential approaches by which the HRC might be enabled again for science observations.

At present, approved HRC observations are on hold pending results of these investigations. Proposals submitted to the upcoming Cycle 24 peer review that request use of the HRC will be evaluated under the assumption of eventual return to science for HRC observations.

February also marked the submission of Chandra’s Senior Review proposal to NASA — the culmination of a massive effort by a large fraction of the team. Subsequent presentations were made to Chandra Senior Review panelists who, over the course of several days, provided important recommendations and insights for future consideration. The panel report will be integrated into a single set of recommendations to the NASA Astrophysics Advisory Committee.

Chandra’s users were busy in March, submitting proposals that over-subscribed the available observing time by a factor of about 4.5. Panels have now been arranged for the Cycle 24 peer review, which will be carried out fully remotely in June.

The Chandra Time Domain Working Group, expertly co-chaired by Jon Miller and Rudy Montez, carried out a review of Chandra’s support to this important and growing area. The team provided a very positive overall assessment along with a series of important recommendations in its report. The CXC began discussing these recommendations with the Chandra Users’ Committee and is working on further assessment and implementation plans.

NASA announced its 2021 Agency Awards earlier this year, and there are several that recognize contributions from our CXC colleagues. Former CXC Director Belinda Wilkes was awarded a NASA Outstanding Public Leadership Medal. In addition, NASA Group Achievement Awards were presented to the Chandra Gyroscope Reconfiguration Team and the Chandra 20^th Anniversary Communications Team.

This year has finally begun to see a return to in-person meetings. The Chandra team supported a booth at the April APS meeting and had engaging and productive visits from many attendees. Chandra will have its usual booth at the upcoming AAS meeting in Pasadena, along with an Exhibitor Theater presentation on “Proposing Tips for Chandra Time Domain Studies.” We look forward to having people drop by!

Finally, as summarized by the accompanying Newsletter article by Martin Weisskopf, this year marks Martin’s retirement after a long and impressive career in X-ray astronomy. Martin had been the NASA Chandra Project Scientist for Chandra for the entire duration of the mission to date. His contributions have been huge, and his leadership has had an indelible mark on the great success of the Observatory. Working in partnership with Martin for over 30 years — both on Chandra and, more recently, on IXPE — has been a tremendous experience for me, and I look forward to continued collaborations upon his retirement. Steve O’Dell will become the new Project Scientist, with Steven Ehlert becoming Deputy. On behalf of the entire Chandra community, many thanks Martin!