INDAM · DATA MINING USING THE INTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY (INTEGRAL) OBSERVATORY

Final Activity Report Summary - INDAM (DATA MINING USING THE INTERNATIONAL GAMMA-RAY ASTROPHYSICS LABORATORY (INTEGRAL) OBSERVATORY)

As the name implies, the project was about using the large archive of the INTEGRAL data to research subjects that are not mainstream. Instead of working on bright point sources, we tried to analyse data from weak extended sources. Instead of spectral analysis, we attempted polarization measurements. We searched for nuclear lines with unknown energy and width. With this project, we wanted to achieve very important scientific goals like understanding the central engine of gamma-ray bursts, understanding the inner structure of neutron stars through gravitationally red-shifted nuclear lines, characterising the high energy emission of neutron stars with ultra-high magnetic fields (1000 times higher than regular neutron star magnetic fields). The analysis was very difficult, but the International Reintegration Grant provided opportunities for close collaboration with instrument and software people to achieve these goals. With the support, portions of the research was distributed to graduate students, and necessary computer resources were purchased. At the end, not all of the big objectives set at the beginning of the project could be achieved. The biggest accomplishment of the project was obtaining the polarization fraction of a bright gamma-ray burst. We obtained a very high polarisation fraction of 96%. However, the error in the fraction was so large that we could not constrain the emission models strongly. Our search for red-shifted nuclear lines from the surface of neutron stars were fruitless, only producing upper limits. We put these upper limits to good use by trying to constrain the production rate of nuclear line photons while comparing results from two different instruments. We have searched for high energy emission from special kind of neutron stars located at the centres of supernova remnants (central compact objects, CCO) with the major objection of comparing their properties to that of anomolous X-ray pulsars (AXPs), neutron stars with ultra-high surface magnetic fields that emit persistent hard X-ray emission. There was no significant detection of high energy emission from CCOs, with flux upper limits an order of magnitude lower than the measured fluxes of AXPs. Along with other observational support we believe that CCOs are not high magnetic field sources, but rather have low magnetic fields. AXPs, CCOs, and other isolated neutron star systems may still be linked through a presence of fall-back disks around them. We have imaged SN 1006 with JEM-X at energies below 8 keV, the first image of an extended object with the INTEGRAL observatory. We could not detect the source at higher energies. The initial prediction for the flux estimates changed during the project implementation, and it was not surprising that we did not detect the source. We were able to place the strongest constraints on the hard X-ray emission from the source, and also constrained some synchrotron emission models. We have also searched for positron (anti-electron) annihilation line from the source as young supernova remnants are good candidates for the source of positrons in the galaxy. This search also resulted in no detection, and with the upper limits we could only constrain the escape fraction of positrons from the supernova remnant. Finally we tried to investigate the effects of cosmic particles on the semiconductor detectors operating on SPI detector. Even though all the required software was written for the project, it could not be implemented thoroughly because of the faulty data. In summary, we were able to achieve most of our secondary objectives which resulted in several publications and conference proceedings, but some of the major objectives eluded us (mostly due to sensitivity issues of INTEGRAL instruments).

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