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Invaluable web site, this has saved me a huge amount of time in data reduction and makes scoping out papers and proposals very quick and easy. Very much hoping to see a continuation of HotGAS to include more datasets.

Prof. Tracey Jane Turner, UMBC


Tahir, I have found your page to be incredibly useful ! Its made the proposal possible. Thanks a lot !!!

RICH M

Richard Mushotzky, NASA/GSFC, Adjunct Prof. JHU


This is a great resource for X-ray astronomers. Good-to-go spectra, ready to analyze are perfect if you're interested in collective properties of AGN. Iron lines from accretion disks; warm absorbers; local, hot gas; IGM are all much easier to study if you have a large sample of uniformly analyzed data with which to work. HotGas is easy to work with & facilitates such sample studies.

Prof. Barry McKernan, CUNY (BMCC) & AMNH


Great webpage. It's quite helpful not only to astronomers who are not familar with grating X-ray spectra, but also to X-ray specialists. Including more data will significantly increase its value.

Dr. Junxian Wang, University of Science and Technology of China


Chandra and XMM high spectral resolution archival data are some of the most important resources for understanding AGN and X-ray binaries. Working on such data is naturally a two step process: evaluating the quality and suitability for the purpose and a deeper more detailed analysis for those spectra where the first step results look promising. Going through data without becoming a real expert is crucial since not everybody can spare the time to learn all secrets of the rather complex full data reduction process. My understanding is that HotGas provides exactly this. it makes Chandra high-resolution grating spectra accessible to scientists who may be non-experts in X-ray astronomy, or X-ray astronomers who want to quickly examine spectra without having to go through the process of downloading the entire set of observation files. I consider it an extremely useful facility and, in fact, would make more effort to announce and advertise it to the entire community. I came across it by chance and would like to make sure that other astronomers do not miss this tool that can greatly improve their productivity.

Prof. Hagai Netzer, School of Physics and Astronomy, Tel Aviv University


The database and its products are very useful, especially if you are analyzing Chandra HETG data for the first time. It would also be useful to include more recent observations. I would also suggest allowing the spectra and responses for any of the four available binsizes to be downloaded separately.

Dr. Valentina Braito, Johns Hopkins University - NASA/GSFC


I found the HotGAS to be very useful database since I work on modeling of the warm absorber in Active Galactic Nuclei. The modeling of hot, illuminated gas is very time consuming, so it is very important for me that I don't have to reduce the data from X-ray satellites by myself. The data reduction itself is very laborious process and I would never finish my work without help of specialists knowing Chandra satellite very well. Especially observations from gratings need separate treatment. Since observations for many AGN are collected on one website it is very easy to compare them, especially regions from 0.3 up to 7 keV, where the most important lines are situated, and also using HotGAS it is very easy to download fits files for spectra and responses and to fit the date by my own model. I will definitely do it soon.

Dr. Agata Rozanska, Nicolaus Copernicus Astronomical Center Polish Academy of Sciences


Overall this is a very nice, well-documented and well-organized set up. Since in many cases it seems that the continuum is fit fairly well, it would be nice to see a plot of the residuals to bring out the lines more clearly. Another nice feature would be to mark the positions of prominent lines in the plots, which would be especially useful for those who are not experts in X-ray astronomy. This would also fit in well with the Virtual Observatory, particularly if some search functionality could be added (e.g., find all sources with significant Si Kalpha emission, etc.).

Dr. Andrew Ptak, Johns Hopkins University


This has the potential to be an extremely useful tool, especially for non-experts who want to get their feet wet on real X-ray gratings data. It's hard to do astrophysics without spectra!

Dr. S. C. Gallagher, UCLA


great to see the data so easily available. one small thing that would make it even easier for non-expert users if there were a downloadable .xcm file for inputing the data into xspec including recommended ignore channels as well!

Dr. Chris Done, University of Durham, U.K.


HotGAS is an extremely useful archive providing reduced spectra for the most relevant AGN targets observed with Chandra. It allows the user to have a quick preview of the data without going through the time-consuming process of full data reduction, being therefore a precious ally in the preparation of observing proposals. I'm specially looking forward to use this valuable data collection in the framework of my Warm Absorber modelling studies. I suggest HotGAS could provide a link to any theoretical spectra/photoionization models available for specific objects in the list. This would definitely be an added value to HotGAS, as it would be making it compatible with Virtual Observatory facilities. I hope this archive will keep on growing and that more recent observations can be added soon!

Dr. Anabela C. Goncalves, Paris Observatory, France


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