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Prompt survey for pulsars in globular clusters
Adv. Space Ret. Vol. 8. No. —3. pp. (2)353—(2)354, 1988 Printed in Great Britain. All rights reserved.
0273—1177/88 $0.00 + .51) Copyright © COSPAR
PROMPT SURVEY FOR PULSARS IN GLOBULAR CLUSTERS D. C. Backer and A. Dey Astronomy Department, University of California, Berkeley, CA 94720, U.S.A.
ABSTRACT A search for pulsars has been conducted in a sample of 31 globular clusters. A preliminary analysis has revealed no new pulsars. INTRODUCTION The recent discovery of a fast pulsar at the center of the globular cluster M28 suggests that the pulsar phenomenon may be common in globular clusters with dense cores. Searches for pulsars in globular clusters have been done in the past. Hamilton et al. /1/ surveyed twelve globular clusters with the VLA at 1.4 GHZ. They found a steep—spectrum source in M28 that was recently detected as a 3—ms pulsar /2,3/. Seiradakis and Graham /4/ surveyed fifteen clusters with the Effelsberg telescope at 1.4 GHz. They reported no detections for slow pulse periods between 0.3 s and 3 s, with a sensitivity of 0.4 — 2.0 mJy. METHOD AND RESULTS We have surveyed 31 of the 43 Galactic globular clusters above the declination limit of the NRAO 300—ft telescope ( —190 ) at 1400 MHz using the U. C. Berkeley Fast Pulsar Search Machine. Our detection limit is around 2 mjy with 132—s integration and 40—MHz bandwidth. This limit applies to periods in excess of about 1/4 the Nyquist rate, 8 ms. For shorter periods out to the Nyquist period of 2 ms, the limit is larger. Our survey covers more than twice the number of clusters that have been studied previously, and is the first effort to search for millisecond periods in this class of objects. No new pulsars have been detected in this prompt survey. The list of objects observed is given in Table 1 along with their distances and core densities. Observations of known pulsars confirm our estimated sensitivity: we detected all objects with 1400—MHz flux densities above 3 mJy and with 400—MHz flux densities above 15 mjy. We are pursuing one candidate, and several other high core density clusters with data written to magnetic tape for off—line analysis. These observations were made at 850 MHz. REFERENCES 1. Hamilton, T.T., Helfand, D.J. and Becker, R.H., A Search For Millisecond Pulsars In Globular Clusters, Astron. J., 90, 606 (1985) 2. Lyne, A.G., Brinklow, A., Middleditch, J.M., Kulkarni, S.R., Backer, D.C., and Clifton, T.R., The discovery of a millisecond pulsar in the globular cluster M28, Nature, 328, 399 (1987) 3. Middleditch, J.M., Lyne, A.G., Brinklow,A., Backer, D.C., Clifton, T.R. and Kulkarni, S.R., Millisecond Pulsar in M28, IAU Circ. 4401 (1987) 4. Seiradakis, J.H. and Graham, D.A., A 21—cm Search for Periodicities in Objects of Special Interest, Astron. Astrophys, 85, 353 (1980) (2)353
(2)354
D. C. Backer and A. Dey
TABLE 1. Globular Clusters with Dec > —19°
No.
*
Coordinates
Name
Longitude
Latitude
Distance (kpc)
Log(central dens) *
1 2 3 4 5
1126+292 1207+188 1310+184 1339+286 1403+287
Pal 4 NGC 4147 NGC 5024 NGC 5272 NGC 5466
202.293 252.848 332.965 042.218 042.137
+71.801 +77.189 +79.764 +78.707 +73.593
93.3 17.3 18.5 10.4 15.8
0.081 3.536 3.175 3.856 1.253
6 7 8 9 10
1427—057 1516+022 1629—129 1639+365 1644—018
NGC NGC NGC NGC NGC
5634 5904 6171 6205 6218
342.210 003.860 003.371 059.006 015.715
+49.260 +46.797 +23.012 +40.914 +26.313
25.0 7.6 6.2 7.1 5.3
3.200 4.109 3.272 3.556 3.173
11 12 13 14 15
1654—040 1657—004 1715+432 1720—177 1725—050
NGC 6254 Pal 15 NGC 6341 NGC 6356 NGC 6366
015.138 018.873 068.339 006.723 018.411
+23.074 +24.293 +34.858 +10.220 +16.041
4.5 69.7 7.7 16.7 4.0
3.765 —0.625 4.381 3.838 2.402
16 17 18 19 20
1735—032 1742+031 1759—089 1801—003 1802—075
NGC NGC NGC NGC NGC
6402 6426 6517 6535 6539
021.322 028.088 019.225 027.176 020.795
+14.803 +16.233 +06.762 +10.435 +06.775
10.2 17.5 6.1 6.9 3.1
3.496 2.435 5.416 3.629 4.189
21 22 23 24 25
1812—121 1850—087 1908+009 1914+300 1916+184
Kod 1 NGC 6712 NGC 6760 NGC 6779 Pal 10
018.072 025.353 036.108 062.659 052.437
+02.415 —04.318 —03.924 +08.336 +02.726
6.2 4.1 9.8 10.6
3.641 4.319 3.351 3.157
26 27 28 29 30
1942—081 2031+072 2050—127 2059+160 2130—010
Pal 11 NGC 6934 NGC 6981 NGC 7006 NGC 7089
031.806 052.105 035.163 063.769 053.371
—15.577 —18.894 —32.683 —19.407 —35.770
13.8 14.9 17.0 39.1 11.9
1.947 3.790 2.744 2.908 4.001
31
2305—159
NGC 7492
053.392
—63.479
19.1
1.065
Units are M
3.
pc
—
—
0273—1177/88 $0.00 + .51) Copyright © COSPAR
PROMPT SURVEY FOR PULSARS IN GLOBULAR CLUSTERS D. C. Backer and A. Dey Astronomy Department, University of California, Berkeley, CA 94720, U.S.A.
ABSTRACT A search for pulsars has been conducted in a sample of 31 globular clusters. A preliminary analysis has revealed no new pulsars. INTRODUCTION The recent discovery of a fast pulsar at the center of the globular cluster M28 suggests that the pulsar phenomenon may be common in globular clusters with dense cores. Searches for pulsars in globular clusters have been done in the past. Hamilton et al. /1/ surveyed twelve globular clusters with the VLA at 1.4 GHZ. They found a steep—spectrum source in M28 that was recently detected as a 3—ms pulsar /2,3/. Seiradakis and Graham /4/ surveyed fifteen clusters with the Effelsberg telescope at 1.4 GHz. They reported no detections for slow pulse periods between 0.3 s and 3 s, with a sensitivity of 0.4 — 2.0 mJy. METHOD AND RESULTS We have surveyed 31 of the 43 Galactic globular clusters above the declination limit of the NRAO 300—ft telescope ( —190 ) at 1400 MHz using the U. C. Berkeley Fast Pulsar Search Machine. Our detection limit is around 2 mjy with 132—s integration and 40—MHz bandwidth. This limit applies to periods in excess of about 1/4 the Nyquist rate, 8 ms. For shorter periods out to the Nyquist period of 2 ms, the limit is larger. Our survey covers more than twice the number of clusters that have been studied previously, and is the first effort to search for millisecond periods in this class of objects. No new pulsars have been detected in this prompt survey. The list of objects observed is given in Table 1 along with their distances and core densities. Observations of known pulsars confirm our estimated sensitivity: we detected all objects with 1400—MHz flux densities above 3 mJy and with 400—MHz flux densities above 15 mjy. We are pursuing one candidate, and several other high core density clusters with data written to magnetic tape for off—line analysis. These observations were made at 850 MHz. REFERENCES 1. Hamilton, T.T., Helfand, D.J. and Becker, R.H., A Search For Millisecond Pulsars In Globular Clusters, Astron. J., 90, 606 (1985) 2. Lyne, A.G., Brinklow, A., Middleditch, J.M., Kulkarni, S.R., Backer, D.C., and Clifton, T.R., The discovery of a millisecond pulsar in the globular cluster M28, Nature, 328, 399 (1987) 3. Middleditch, J.M., Lyne, A.G., Brinklow,A., Backer, D.C., Clifton, T.R. and Kulkarni, S.R., Millisecond Pulsar in M28, IAU Circ. 4401 (1987) 4. Seiradakis, J.H. and Graham, D.A., A 21—cm Search for Periodicities in Objects of Special Interest, Astron. Astrophys, 85, 353 (1980) (2)353
(2)354
D. C. Backer and A. Dey
TABLE 1. Globular Clusters with Dec > —19°
No.
*
Coordinates
Name
Longitude
Latitude
Distance (kpc)
Log(central dens) *
1 2 3 4 5
1126+292 1207+188 1310+184 1339+286 1403+287
Pal 4 NGC 4147 NGC 5024 NGC 5272 NGC 5466
202.293 252.848 332.965 042.218 042.137
+71.801 +77.189 +79.764 +78.707 +73.593
93.3 17.3 18.5 10.4 15.8
0.081 3.536 3.175 3.856 1.253
6 7 8 9 10
1427—057 1516+022 1629—129 1639+365 1644—018
NGC NGC NGC NGC NGC
5634 5904 6171 6205 6218
342.210 003.860 003.371 059.006 015.715
+49.260 +46.797 +23.012 +40.914 +26.313
25.0 7.6 6.2 7.1 5.3
3.200 4.109 3.272 3.556 3.173
11 12 13 14 15
1654—040 1657—004 1715+432 1720—177 1725—050
NGC 6254 Pal 15 NGC 6341 NGC 6356 NGC 6366
015.138 018.873 068.339 006.723 018.411
+23.074 +24.293 +34.858 +10.220 +16.041
4.5 69.7 7.7 16.7 4.0
3.765 —0.625 4.381 3.838 2.402
16 17 18 19 20
1735—032 1742+031 1759—089 1801—003 1802—075
NGC NGC NGC NGC NGC
6402 6426 6517 6535 6539
021.322 028.088 019.225 027.176 020.795
+14.803 +16.233 +06.762 +10.435 +06.775
10.2 17.5 6.1 6.9 3.1
3.496 2.435 5.416 3.629 4.189
21 22 23 24 25
1812—121 1850—087 1908+009 1914+300 1916+184
Kod 1 NGC 6712 NGC 6760 NGC 6779 Pal 10
018.072 025.353 036.108 062.659 052.437
+02.415 —04.318 —03.924 +08.336 +02.726
6.2 4.1 9.8 10.6
3.641 4.319 3.351 3.157
26 27 28 29 30
1942—081 2031+072 2050—127 2059+160 2130—010
Pal 11 NGC 6934 NGC 6981 NGC 7006 NGC 7089
031.806 052.105 035.163 063.769 053.371
—15.577 —18.894 —32.683 —19.407 —35.770
13.8 14.9 17.0 39.1 11.9
1.947 3.790 2.744 2.908 4.001
31
2305—159
NGC 7492
053.392
—63.479
19.1
1.065
Units are M
3.
pc
—
—