PROCESOS PRODUCTIVOS MERCADO DE ELECTRODOMESTICOS.

In fig.3.7 it is shown the discovery plot of the pulsar J1832₋0835, found with the acceleration search and having a spin period of only 2.7 ms, no orbital acceleration and an interesting integrated profile made up of three peaks.

Since in the context of timing (section 1.2 and subsections) usually MSPs are very stable (except for those very few examples with timing noise), and furthermore this pulsar shows a sharp profile with several components that makes more efficient the cross-correlation from which we obtain the TOAs of the pulses, J1832₋0835 could turn out to be a good timer for the PTA project.

Figure 3.8: Standard profile used for the timing of the 2.7 ms pulsar J1832₋0835.

Moreover, since this pulsar typically has a S/N of about 10-15 for an observing time of 15-20 mins (the variation of the S/N with the observations is due to the fact that the pulsar scintillates slightly, which confirms that the

DM value is quite low), it is bright enough to allow to obtain quite small TOAs uncertainties with a reasonable integration time; hence, although it is slightly fainter than the average of the pulsars of the Parkes PTA, owing to these features it would be suitable for being part of a timing array. Due to its position in the sky, it could be a candidate to be observed with the Sardinia Radio Telescope (SRT), which is part of the European PTA.

The timing of this pulsar started at the Parkes Radio Telescope and is being performed now at Jodrell Bank, by using the 76-m Lovell Telescope. In fig.3.8 the standard profile used for the timing is shown. To date, we have only 7 months of timing observations, that are not enough to be sure about its actual intrinsic stability.

However, so far that seems to be quite good: the timing solution in fig.3.9 has a root mean square of the post-fit residuals between measured and model arrival times of _∼ 1.8 µs over 7 months of observation (the TOA uncertainties

σi in eq. (1.35) are ∼ 2.5 µs on average over an observation 15-20 min long),

that corresponds to a rotational stability7 _{of 9.4 ×10}−14_.

7

This value of the stability has been obtained as the ratio between the RMS and the time span, and is a figure of merit, that is a good estimate since the time span is short. With a longer time span we will be able to calculate it more precisely by using theσz parameter from Matsakis et al.

Figure 3.9: Present timing residuals of the 2.7 ms pulsar J1832₋0835 for a data span of 7 months. The green points correspond to timing observations carried out by using the Parkes Radio Telescope, while the blue points by using the Lovell Radio Telescope at Jodrell Bank.

The question now is if it will maintain such a good stability over longer data span (of the order of years).

In table 3.4 the values of the pulsar parameters obtained through the timing are summarised; since the data span is shorter than one year, the errors (at 2σ) in the determination of right ascension, declination and frequency derivative, which co-vary, are underestimated.

This pulsar will be published soon in a paper of the HTRU collaboration currently in preparation at the Cagliari Astronomical Observatory, together with 4 binary MSPs: J1431₋5736, J1546₋4552, J1825₋0322 and J2236₋5526, as soon as we have one year of timing data for all the 5 pulsars.

The timing of these binary pulsars is mainly being performed at the Parkes Radio Telescope, except for J1825₋0322, for which it is mainly being performed at Jodrell Bank. In fig.3.10 they are shown the standard profiles used for the timing of the 4 binary pulsars. Their timing solutions are illustrated in figures 3.11 (J1431₋5736), 3.12 (J1546₋4552), 3.13 (J1825₋0322), and 3.14 (J2236₋5526), while in table 3.5 a summary of the values of the parameters obtained through the timing (with errors at 2σ), for all the four pulsars, is reported. For the pulsar for which we do not have approximately one year of timing data, no value is reported for the first period derivative because it is

Parameter Value Right ascension (J2000) 18h32m27s.5949(8) Declination (J2000) -08◦₃₆′₅₄′′_.99(5) Spin frequency (ν) 367.767115561(1) Hz Frequency derivative ( ˙ν) -8(4)_×10−16 Hz s−1 Epoch MJD 55759 Dispersion measure (DM) 28.185(1) pc cm−3 Number of TOAs 27 RMS of fit 1.751 µs TOA range MJD 55670-55885

Table 3.4: Positional and rotational parameter values of J1832₋0835 obtained for a data span of 7 months. The two-sigma errors on the last digit of each parameter are reported in parentheses. The last three rows report the number of TOAs, the root mean square of the timing residuals and the time span covered by the timing data used to obtain the reported ephemerides.

Figure 3.10: Standard profiles used for the timing of the 4 binary MSPs J1431₋5736, J1546₋4552, J1825₋0322 and J2236₋5526.

Figure 3.11: Present timing residuals of the 4.1 ms pulsar J1431₋5736 for a data span of 325 days.

Figure 3.12: Present timing residuals of the 3.6 ms pulsar J1546₋4552 for a data span of 257 days. The green points correspond to timing observations carried out by using the Parkes Radio Telescope, while the blue point by using the Lovell Radio Telescope at Jodrell Bank.

Figure 3.13: Present timing residuals of the 4.6 ms pulsar J1825₋0322 for a data span of 599 days. The green points correspond to timing observations carried out by using the Parkes Radio Telescope, while the blue points by using the Lovell Radio Telescope at Jodrell Bank.

Figure 3.14: Present timing residuals of the 6.9 ms pulsar J2236₋5526 for a data span of 458 days.

PSRJ J1431-5736 J1546-4552 J1825-0322 J2236-5526 RAJ 14:31:03.4959(4) 15:45:55.948(3) 18:25:55.9523(5) 22:36:51.8515(6) DECJ -57:40:11.657(9) -45:50:37.52(7) -03:19:57.55(3) -

55:27:48.837(7) P0 (ms) 4.1105439566762(17) 3.57528861788(6) 4.553527919749(13) 6.90754939267(2)

P1 5.7(11)E-21 – 7.0(7)E-21 9.5(15)E-21

EPOCH (MJD) 55702.00000 55737.00000 55800.82910 55460.19044 DM (pc/cm3) 131.39(3) 68.390(8) 119.47(4) 20.09(4) PB (days) 2.726855837(18) 6.20306488(13) 52.6305024(15) 12.6891870(3) A1 (lt-s) 2.2698868(13) 3.846905(5) 18.266400(12) 8.775870(8) T0 (MJD) 55461.0699555(10) 55611.38(16) 55805.06(5) 55472.56(7)

ECC – 1.1(2)E-05 0.000194(1) 4.91(18)E-05

OM (deg) – 220(9) 93.2(3) 351(2)

SPAN (days) 325.128 257.172 599.195 457.666

RMS (µs) 2.134 6.295 28.389 9.753

Table 3.5: Positional, rotational and orbital parameters for the four binary millisecond pulsars soon to be published together with the isolated MSP J1832-0835 discovered in this work. The two-sigma errors on the last digit(s) of each parameter are reported in parentheses. For the pulsar for which we do not have approximately one year of timing data, no value is reported for the first period derivative because it is either unconstrained and/or covaries with the positional parameters. The last two rows report the time span covered by the timing data used to obtain the reported ephemerides and the root mean square of the timing residuals.

Figure 3.15: P ₋P˙ diagram showing four of the five MSPs described in the text, represented by the stars. The grey points are the Galactic radio-pulsars in the pulsar catalogue, while the circles represent the binary pulsars. The only star not surrounded by a circle, since isolated, is J1832₋0835, for which the determination of the period derivative is still uncertain due to the fact that the data span is much less than one year.

either unconstrained and/or covaries with the positional parameters.

The rotational stabilities of the 4 binary MSPs are respectively 7.6_×10−14

(J1431₋5736), 2.8 _×10−13 _{(J1546−4552), 5.5 ×10}−13 _{(J1825−0322) and 2.5}

×10−13 _{(J2236−5526). Hence J1431−5736 seems to be slightly better than}

J1832₋0835, whose stability is 9.4 _×10−14_{, but this is due to the fact that we}

have more data for J1431₋5736 than for J1832₋0835 and therefore we could obtain a timing solution for the former by using only the most recent data, and of the highest quality.

Fig.3.15 shows the P ₋P˙ diagram with four of the five mentioned MSPs (those for which the period derivative has been estimated).