Telescope

In order to further our understanding of the nature of neutron stars and black holes by studying their variable X-ray emission, Colibrì needs to be very sensitive and fast. For this reason, we set some goals for the concept of  Colibrì. If you would like detailed resources to simulate observations with Colibrì, please go to our resources page.

 

Initial baseline mission concept parameters:

 

  • Energy range: 0.5 -10 keV including the iron K-alpha emission line at 6.4 keV.

Accreting neutron stars and black holes shine bright in the 0.5-10 keV range. Moreover, the reflected emission used in reverberation mapping presents a strong feature at 6.4 keV: the iron fluorescence line.

 

  • Energy resolution: finer than 1 eV at 2 keV (3 eV at 6 keV) with count rates up to 10 kHz.

We want to be able to determine the energy of the incoming photons with a precision better than one in a thousand.

 

  • Timing capabilities: better than 1 μs.

We want to probe the region very close to the black hole or neutron stars and the dynamical  timescales of that region are of the order of microseconds.

 

  • Throughput: count rates up to 10 kHz.

We want to be able to look at bright sources, with a high photon count rate.

 

  • Type of optics: collector optics as for NICER, total effective area of at least 2000 cm2 at 6.4 keV.

Colibrì will not have just one mirror, but many different collectors similar to the ones employed by the NASA mission NICER. We need many collectors, each pointing on different arrays, to be able to look at bright sources without overwhelming the detectors with the incoming photons.

 

 

For scientists: you can download resources here.

Transition edge sensors

Colibrì will bear in its heart one of the coldest human-made devices: an array of superconducting transition-edge sensors (TES). Such ultracold sensors work at a temperature of about 0.1 K, which is 3,000 times colder than the human body temperature! Working at such low temperatures is crucial to achieve a high-resolution in energy and timing, and that is what Colibrì is all about. Indeed, using TESs will enable Colibrì to measure X-ray photons energy with a precision of about 1 eV, and its time of arrival to within a millionth of a second.

 

A TES is made of a superconducting metal film functioning near its transition temperature (typically 0.1 K, as mentioned above). While electrons manoeuvre freely in a superconducting metal, they encounter some significant resistance when the metal switches to its normal phase. The transition from superconductor to normal metal occurs within about 1 mK change in the temperature but results in a much larger change in resistance.

 

An array of TES made by people at NIST, Colorado. In the back a penny coin for scale.

 

A section of a TES: the superconductor (a film of molybdenum Mo) is in thermal contact with the absorber (copper Cu and bismuth Bi)

When an X-ray photon hits a TES, the provided energy provokes the needed rise in temperature for the transition to happen, electrons move more slowly in the TES, the measured electric current drops, and the X-ray photon is detected. Indeed, measuring how much the current diminishes and for how long enables us to determine the energy of that photon. Finally, after the absorption of a photon, a TES needs to be cooled down to its initial temperature by using a cooling bath, so as to be able to detect the next photon.

Colibrì would be able to detect over 250,000 X-rays each second, and using such accurate devices as TESs would enable Colibrì to perform unprecedented precision X-ray timing and spectroscopy over the widest range of photon energies (100 eV to 15 keV).

 

Taking the pulse of neutron stars and black holes

© Her Majesty the Queen in Right of Canada (2019)

Image credit banner: NASA/SOFIA/Lynette Cook

Image credit TES: Dan Schmidt/NIST, Hays-Wehle et al/NIST