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Radio Searches of Fermi LAT Sources and Blind Search Pulsars: the Fermi Pulsar Search Consortium P 2011 Fermi Symposium, Roma, May. 9{12 1 Radio Searches of Fermi LAT Sources and Blind Search Pulsars: The Fermi Pulsar Search Consortium P. S. Ray∗ Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA A. A. Abdo and D. Parent George Mason University, Fairfax, VA, resident at Naval Research Laboratory, Washington, DC, USA D. Bhattacharya and B. Bhattacharyya Inter-University Centre for Astronomy and Astrophysics, Pune 411 007, India F. Camilo Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA I. Cognard and G. Theureau LP2CE, CNRS, and Orleans´ University, F-45071 Orleans´ Cedex 02, and Station de radioastronomie de Nanc¸ay, Observatoire de Paris et CNRS/INSU, F-18330 Nanc¸ay, France E. C. Ferrara, A. K. Harding, and D. J. Thompson NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA P. C. C. Freire and L. Guillemot Max-Planck-Institut fur¨ Radioastronomie, Auf dem Hugel¨ 69, 53121 Bonn, Germany Y. Gupta and J. Roy National Centre for Radio Astrophysics, TIFR, Pune 411 007, India J. W. T. Hessels ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands S. Johnston, M. Keith, and R. Shannon CSIRO, Australia Telescope National Facility, Epping NSW 1710, Australia M. Kerr, P. F. Michelson, and R. W. Romani Stanford University, Stanford, CA, USA M. Kramer Jodrell Bank Centre for Astrophysics, University of Manchester, UK and Max-Planck-Institut fur¨ Radioastronomie, Auf dem Hugel¨ 69, 53121 Bonn, Germany M. A. McLaughlin Department of Physics, West Virginia University, Morgantown, WV 26506, USA S. M. Ransom National Radio Astronomy Observatory (NRAO), Charlottesville, VA 22903, USA M. S. E. Roberts Eureka Scientific, Oakland, CA 94602, USA P. M. Saz Parkinson and M. Ziegler University of California at Santa Cruz, Santa Cruz, CA 95064, USA D. A. Smith Universite´ Bordeaux 1, CNRS/IN2p3, Centre d’Etudes´ Nucleaires´ de Bordeaux Gradignan, France B. W. Stappers and P. Weltevrede Jodrell Bank Centre for Astrophysics,The University of Manchester, UK K. S. Wood Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA We present a summary of the Fermi Pulsar Search Consortium (PSC), an international collaboration of radio astronomers and members of the Large Area Telescope (LAT) collaboration, whose goal is to organize radio arXiv:1205.3089v1 [astro-ph.HE] 14 May 2012 follow-up observations of Fermi pulsars and pulsar candidates among the LAT γ-ray source population. The PSC includes pulsar observers with expertise using the world's largest radio telescopes that together cover the full sky. We have performed very deep observations of all 35 pulsars discovered in blind frequency searches of the LAT data, resulting in the discovery of radio pulsations from four of them. We have also searched over 300 LAT γ-ray sources that do not have strong associations with known γ-ray emitting source classes and have pulsar-like spectra and variability characteristics. These searches have led to the discovery of a total of 43 new radio millisecond pulsars (MSPs) and four normal pulsars. These discoveries greatly increase the known population of MSPs in the Galactic disk, more than double the known population of so-called `black widow' pulsars, and contain many promising candidates for inclusion in pulsar timing arrays. ∗Electronic address: [email protected] eConf C110509 2 2011 Fermi Symposium, Roma, May. 9{12 1. The Fermi Pulsar Search Consortium 107 The Fermi Pulsar Search Consortium (PSC) was es- tablished as a collaborative effort between the Fermi 106 LAT team and an international group of radio pulsar observers with expertise using radio telescopes around 105 the world. The two goals of the PSC are: (1) to ob- ) y 104 J tain radio observations of γ-ray pulsars discovered in µ ( 0 blind searches of LAT data, (2) to search for radio 0 4 3 1 10 pulsars in the directions of unassociated LAT sources S that have pulsar-like characteristics. This collabora- 2 tion has proven extremely successful, as we describe 10 below. Members of the PSC have used the following J0106+4855 101 radio telescopes for these observations: Green Bank J1907+0602 Telescope (GBT), Parkes, Effelsberg, Nan¸cay Radio 100 Telescope (NRT), Arecibo Telescope, the Lovell Tele- 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 E˙ (erg/s) scope at Jodrell Bank, and the Giant Metrewave Ra- dio Telescope (GMRT). Figure 1: Radio flux density upper limits (red arrows) and detections (green circles) for the 35 LAT blind search pulsars, scaled to 1400 MHz using a spectral index of 2. Radio Searches of Blind Search −1:6. The 1400 MHz flux densities of young pulsars in the ATNF catalog are plotted as black dots, for Pulsars comparison. One of the great successes of the Fermi LAT has been the discovery of 35 pulsars in blind searches of been reported at 34.5 MHz [15] and so additional the γ-ray data alone [1, 24, 32, 33]. Although these searches at low frequency are certainly warranted. discoveries were made using the γ-ray data alone, be- The vast majority of these pulsars are so faint in the fore these new pulsars can be dubbed \radio quiet", radio that without Fermi they would have remained they must first be searched deeply for radio pulsa- undetected for decades or longer. In fact, several tions. In addition, any radio detections provide im- of them resolved the mystery of what was powering portant new information on each pulsar including a unidentified TeV sources. distance determination from the dispersion measure For the 4 radio detections we have DM dis- (DM), which is critical for converting measured γ-ray tances and can thus convert the fluxes into pseudo- fluxes into luminosities and thus determining the γ- luminosities (in units of mJy-kpc2) and these are ray efficiency of the pulsar. A radio pulse detection shown in Figure 2. Here we find that one of our pul- also yields information on the location of the emission sars (J2032+4127) is a modestly low luminosity radio region from the radio to γ-ray offset [31]. Radio po- pulsar while the other three have luminosities of a few larization studies also provide potentially important ×10−2 mJy-kpc2, far less luminous than any other information on the pulsar geometry (e.g. the angles normal pulsar. This forces us to consider what \radio between the rotation and magnetic axes [α] and be- quiet" really means and how pulsars could have such tween the rotation axis and the line-of-sight [ζ]) [25]. a low luminosity. Could we be just scraping the edge Radio limits and detections also provide critical input of the beam or is there some other effect at work? To for population models, where the blind search pulsars really answer these questions, we will need more ex- give a much more complete sample of the young pulsar amples of this low luminosity population and detailed population, owing to the broad γ-ray beams [35, 36]. modeling of the emission region incorporating geomet- The PSC has made extremely deep radio observa- ric information from polarization measurements. tions of all of the LAT-discovered blind search pul- sars and detected radio pulsations from four of them [3, 8, 24]. Now, with 4 detections and 31 upper lim- its, it is appropriate to take a look at our progress so 3. Searching for Radio Pulsars in LAT far. In Figure 1, we show the flux limits and detections Unassociated Sources (scaled to 1400 MHz using a typical pulsar spectral in- dex of −1:6) from our observations. It is clear that we With known pulsars being such a prevalent class of are achieving flux limits competitive with the faintest GeV γ-ray sources, a complementary strategy is to use known radio pulsars (all well under 0.1 mJy) and two radio telescopes to search for pulsars powering sources of our detections (PSR J1907+0602 and J0106+4855) discovered in the LAT sky survey. A significant effort are very faint indeed! We also note that a possible was put into searches like these during the EGRET (non-PSC) radio detection of PSR J1732−3131 has era, with only modest success [11]. However, the sen- eConf C110509 2011 Fermi Symposium, Roma, May. 9{12 3 confirmed γ-ray emitting MSPs. Shortly after launch, 104 the LAT demonstrated that MSPs were indeed γ-ray emitters, much like their young pulsar brethren [2]. 103 Our radio searches of high-latitude LAT sources that are non-variable and have curved spectra character- istic of pulsars have yielded 43 new MSPs (42 were 102 discovered by the PSC and one by a non-PSC group also targeting LAT source; see Table II and Figure 5). 1 10 Also, in contrast to the situation for young pulsars in the plane, the sky at high latitudes has mostly 100 not been surveyed with good sensitivity to millisec- ond pulsars. This is changing with several new radio Pseudo-Luminosity (mJy-kpc**2) 10-1 surveys designed to detect MSPs (e.g. HTRU, GBT Drift, GBNCC). In several cases, new MSPs discov- 10-2 ered in these surveys have turned out to be LAT pul- 103 104 105 106 107 Characteristic Age (years) sars as well [19], and more are sure to come. As the newly-discovered pulsars are timed over a 2 Figure 2: Pseudo luminosities (S1400d ) for the four LAT year or so after discovery, we obtain orbital parame- blind search pulsars with detected radio pulsations, ters and precise positions enabling us to fold the LAT compared to the population of young pulsars in the γ-ray data to look for pulsations that confirm the asso- ATNF catalog (blue dots).
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