Abstract
We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radio-quiet quasar (RQQ) at z ≈ 4.1-4.4. These observations cover a representative sample of RLQs with moderate radio loudness (R ≈ 40-400), filling the X-ray observational gap between optically selected RQQs (predominantly R ≲ 2-10) and the five known blazars at z > 4(R ≈ 800-27,000), where R = f 5GHz/f 4400Å (rest frame). We study the relationship between X-ray luminosity and radio loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic N H, with a best-fit neutral intrinsic column density of N H = 2.4 -1.8 +2.0 × 10 22 cm -2, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low to moderate redshifts. Overall, the z ≈ 4-5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 523-533 |
| Number of pages | 11 |
| Journal | Astronomical Journal |
| Volume | 128 |
| Issue number | 2 1784 |
| DOIs | |
| State | Published - Aug 1 2004 |
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All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
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Chandra observations of radio-loud quasars at z > 4 : X-rays from the radio beacons of the early universe. / Bassett, L. C.; Brandt, William Nielsen; Schneider, Donald P.; Vignali, C.; Chartas, G.; Garmire, G. P.
In: Astronomical Journal, Vol. 128, No. 2 1784, 01.08.2004, p. 523-533.Research output: Contribution to journal › Article
TY - JOUR
T1 - Chandra observations of radio-loud quasars at z > 4
T2 - X-rays from the radio beacons of the early universe
AU - Bassett, L. C.
AU - Brandt, William Nielsen
AU - Schneider, Donald P.
AU - Vignali, C.
AU - Chartas, G.
AU - Garmire, G. P.
PY - 2004/8/1
Y1 - 2004/8/1
N2 - We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radio-quiet quasar (RQQ) at z ≈ 4.1-4.4. These observations cover a representative sample of RLQs with moderate radio loudness (R ≈ 40-400), filling the X-ray observational gap between optically selected RQQs (predominantly R ≲ 2-10) and the five known blazars at z > 4(R ≈ 800-27,000), where R = f 5GHz/f 4400Å (rest frame). We study the relationship between X-ray luminosity and radio loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic N H, with a best-fit neutral intrinsic column density of N H = 2.4 -1.8 +2.0 × 10 22 cm -2, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low to moderate redshifts. Overall, the z ≈ 4-5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well.
AB - We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radio-quiet quasar (RQQ) at z ≈ 4.1-4.4. These observations cover a representative sample of RLQs with moderate radio loudness (R ≈ 40-400), filling the X-ray observational gap between optically selected RQQs (predominantly R ≲ 2-10) and the five known blazars at z > 4(R ≈ 800-27,000), where R = f 5GHz/f 4400Å (rest frame). We study the relationship between X-ray luminosity and radio loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic N H, with a best-fit neutral intrinsic column density of N H = 2.4 -1.8 +2.0 × 10 22 cm -2, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low to moderate redshifts. Overall, the z ≈ 4-5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well.
UR - http://www.scopus.com/inward/record.url?scp=4544284741&partnerID=8YFLogxK
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U2 - 10.1086/422019
DO - 10.1086/422019
M3 - Article
AN - SCOPUS:4544284741
VL - 128
SP - 523
EP - 533
JO - Astronomical Journal
JF - Astronomical Journal
SN - 0004-6256
IS - 2 1784
ER -