REQUERIMIENTOS ALIMENTARIOS DE LOS NIÑOS MENORES DE 5 AÑOS

Quick processing of 41% of the HTRU-North mid-lat data taken within this thesis project has resulted in detection of six new pulsars (see Fig. 3.9 for pulse profiles and Table 3.4for measured parameters). One of them, PSR J2327+6241, also showed up in the 350-MHz data of the GBNCC survey (Stovall et al., 2014), nearly at the same time as it was detected in HTRU-North (from priv. com.). Also, when looking at the results produced by the FAST PIPELINE, we found a number of pulsars (see Table3.5) that have been discovered and published by other surveys since the beginning of the HRTU-North. Though these sources were first discovered by other surveys and we did not follow them up, we include them in the overall HTRU-North yield to obtain a more complete picture of the survey’s performance, giving a total of 15 newly and co-discovered pulsars.

Upon the discovery, the six “brand-new” pulsars were confirmed with the Effels- berg telescope. PSR J2045+3633 and PSR J2053+4650, appeared to be in binary systems (see Chapter4for a detailed study of these pulsars), while the other four were isolated. Further, to measure their spin and astrometric parameters more precisely, we performed follow-up timing observations using different telescopes: Effelsberg and Lovell – for all six pulsars, additionally Nan¸cay and Arecibo – for the binaries. The results of timing are presented in Table 3.4 which contains the spin and astrometric parameters of new discoveries, as well as DM values and DM-derived distances calcu- lated according to both the NE2001Galactic electron density model (Cordes & Lazio, 2002) and a newerYMW16model (Yao et al.,2017). As can be seen, all new discoveries

3.6. New discoveries and detection rate 67

have high DMs, thus, confirming that the survey meets our original goal – to use the high frequency resolution to probe deeper into the Galaxy.

Out of six, two pulsars, PSR J0100+6427 and PSR J2053+4650 have profiles with interpulses. Follow-up of these pulsars with full polarisation observations may yield information about their spin geometry, thus, contributing to our understanding of the emission mechanism. PSR J1951+4721 has a relatively high ˙P indicating that it is reasonably young (τc < 100 kyr) and energetic ( ˙E = 4.4×1033erg s−1). A fold of

Fermi LAT data at this position did not show any γ-ray counterpart. However, the large estimated distance of 6–9 kpc (depending on the Galactic electron density model) and modest ˙E make the detection at these high energies hard, thus, a non-detection is not constraining.

The results of the quick processing show that the survey is less sensitive than expected. The initial estimates obtained by Barr et al.(2013) withPSRPOP16 software suggested that as many as 71 new non-MSPs and 20 MSPs would be discovered in a 50% mid-lat run17. The overall (including co-detections) HTRU-North yield to-date number 27 non-MSPs and 3 MSPs, with 50% of the mid-lat covered. Though the lack of MSP discoveries is expected for the case of “quick-only” processing, i.e. on down- sampled data and without performing proper acceleration search, the lower number of non-MSP discoveries can be probably explained by several factors: the lower survey sensitivity, RFI or/and incorrect initial model assumptions.

The calculations described in Section 3.5.1 already demonstrate that the survey sensitivity is lower by a factor of_∼1.3. In order to overcome this deficit the integration time for future mid-lat observations will need to be increased from 3 minutes to 5 minutes. Considering the overall remaining observing time, it will take 2232 hours instead of previously planned 1340 hours to finish the rest 50% of mid-lat. To reduce the load on the Effelsberg telescope, some unobserved regions can be shared (within a recently established collaboration) with the newly commissioned 500-meter FAST telescope18_{. Due to its large collecting area, it has a much higher gain allowing for much}

shorter integrations. The HTRU-North mid-lat will prioritize the pointings beyond the FAST’s visibility.

RFI also plays a significant role in the survey’s detection rate. Not only does it increase theTsysof the telescope, reduce the effective bandwidth and integration time,

it also causes confusion. The number of spurious candidates and their harmonics can overwhelm the number of astronomical signals pushing them down in the candidate list. The results of the quicklook can be leveraged to provide a catalogue of likely present RFI that will enable future processing to determine if similar periodicities are seen in multiple locations on the sky – ruling them out as an astronomical signal. The variable nature of RFI periodicities makes this tricky to implement but the extensive statistics gathered with the FAST PIPELINE should allow such signals to be characterised, for

16_{Lorimer et al.(2006), http://psrpop.phys.wvu.edu/}

17_{At the same time it should be noticed that the issue of potential discrepancy between the observed} and simulated pulsar populations has already been mentioned at the previous stage of the HTRU-North survey by E. Barr.

example, using more advanced machine learning algorithms.

Finally, since the survey was designed, a new model of the electron content of the Galaxy, YMW16, has been published (Yao et al.,2017). It is based on the numerous surveys that have taken place sinceNE2001was originally developed. TheYMW16model tends to place pulsars further away from the Earth than NE2001. This directly affects the number of potential HTRU-North discoveries and generally reduces the overall expected yield. New discoveries and independent distance measurements will determine whether this trend portrays the overall Galactic population.

With an increased integration time and more effective RFI mitigation further survey observations will be able to show if the reduced discovery rate reflects the underlying pulsar population or the telescope sensitivity. Future processing will also include a full acceleration search due to the newly available high performance computing resources. Although the number of systems that need such a search to be discovered is low, they are likely to be the most interesting.