Ultraviolet, X-ray, and optical radiation from the Geminga pulsar

O. Y. Kargaltsev, G. G. Pavlov, V. E. Zavlin, R. W. Romani

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

We observed the γ-ray pulsar Geminga with the FUV-MAMA and NUV-MAMA detectors of the Space Telescope Imaging Spectrometer to measure Geminga's spectrum and pulsations in the ultraviolet. The slope of the far-ultraviolet (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, FFUV = (3.7 ± 0.2) × 10-15 ergs cm-2 s-1 in the 1155-1702 Å band, corresponds to a brightness temperature TRJ ≈ (0.3-0.4)(d200/R13)2 MK, depending on the interstellar extinction (d = 200d200 pc and R = 13R13 km are the distance and the NS radius, respectively). The soft thermal component of Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature Ts = 0.49 ± 0.01 MK and radius Rs = (12.9 ± 1.0)d200 km. Contrary to other NSs detected in the UV-optical, for which the extrapolation of the X-ray thermal component into the optical underpredicts the observed flux of thermal radiation, the FUV spectrum of Geminga lies slightly below the extrapolation of the soft thermal component, which might be associated with Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast to the FUV spectrum, the near-infrared (NIR) through near-ultraviolet (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, Fν ∞ ν -Γ+1, with a photon index Γ = 1.43 ± 0.15, close to the slope Γ = 1.56 ± 0.24 of the hard X-ray (E > 2.5 keV) magnetospheric component. The extrapolation of the X-ray magnetospheric spectrum into the optical is marginally consistent with (or perhaps lies slightly above) the observed NIR-optical-NUV spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.

Original languageEnglish (US)
Pages (from-to)307-323
Number of pages17
JournalAstrophysical Journal
Volume625
Issue number1 I
DOIs
StatePublished - May 20 2005

Fingerprint

pulsars
ultraviolet spectra
radiation
far ultraviolet radiation
extrapolation
x rays
neutron stars
ultraviolet detectors
ultraviolet radiation
slopes
electron-positron plasmas
interstellar extinction
radii
near infrared
brightness temperature
imaging spectrometers
occultation
thermal radiation
thermal emission
XMM-Newton telescope

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kargaltsev, O. Y. ; Pavlov, G. G. ; Zavlin, V. E. ; Romani, R. W. / Ultraviolet, X-ray, and optical radiation from the Geminga pulsar. In: Astrophysical Journal. 2005 ; Vol. 625, No. 1 I. pp. 307-323.
@article{cd5a1df8a63749a2a91ba62c18e2a813,
title = "Ultraviolet, X-ray, and optical radiation from the Geminga pulsar",
abstract = "We observed the γ-ray pulsar Geminga with the FUV-MAMA and NUV-MAMA detectors of the Space Telescope Imaging Spectrometer to measure Geminga's spectrum and pulsations in the ultraviolet. The slope of the far-ultraviolet (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, FFUV = (3.7 ± 0.2) × 10-15 ergs cm-2 s-1 in the 1155-1702 {\AA} band, corresponds to a brightness temperature TRJ ≈ (0.3-0.4)(d200/R13)2 MK, depending on the interstellar extinction (d = 200d200 pc and R = 13R13 km are the distance and the NS radius, respectively). The soft thermal component of Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature Ts = 0.49 ± 0.01 MK and radius Rs = (12.9 ± 1.0)d200 km. Contrary to other NSs detected in the UV-optical, for which the extrapolation of the X-ray thermal component into the optical underpredicts the observed flux of thermal radiation, the FUV spectrum of Geminga lies slightly below the extrapolation of the soft thermal component, which might be associated with Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast to the FUV spectrum, the near-infrared (NIR) through near-ultraviolet (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, Fν ∞ ν -Γ+1, with a photon index Γ = 1.43 ± 0.15, close to the slope Γ = 1.56 ± 0.24 of the hard X-ray (E > 2.5 keV) magnetospheric component. The extrapolation of the X-ray magnetospheric spectrum into the optical is marginally consistent with (or perhaps lies slightly above) the observed NIR-optical-NUV spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.",
author = "Kargaltsev, {O. Y.} and Pavlov, {G. G.} and Zavlin, {V. E.} and Romani, {R. W.}",
year = "2005",
month = "5",
day = "20",
doi = "10.1086/429368",
language = "English (US)",
volume = "625",
pages = "307--323",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 I",

}

Ultraviolet, X-ray, and optical radiation from the Geminga pulsar. / Kargaltsev, O. Y.; Pavlov, G. G.; Zavlin, V. E.; Romani, R. W.

In: Astrophysical Journal, Vol. 625, No. 1 I, 20.05.2005, p. 307-323.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Ultraviolet, X-ray, and optical radiation from the Geminga pulsar

AU - Kargaltsev, O. Y.

AU - Pavlov, G. G.

AU - Zavlin, V. E.

AU - Romani, R. W.

PY - 2005/5/20

Y1 - 2005/5/20

N2 - We observed the γ-ray pulsar Geminga with the FUV-MAMA and NUV-MAMA detectors of the Space Telescope Imaging Spectrometer to measure Geminga's spectrum and pulsations in the ultraviolet. The slope of the far-ultraviolet (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, FFUV = (3.7 ± 0.2) × 10-15 ergs cm-2 s-1 in the 1155-1702 Å band, corresponds to a brightness temperature TRJ ≈ (0.3-0.4)(d200/R13)2 MK, depending on the interstellar extinction (d = 200d200 pc and R = 13R13 km are the distance and the NS radius, respectively). The soft thermal component of Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature Ts = 0.49 ± 0.01 MK and radius Rs = (12.9 ± 1.0)d200 km. Contrary to other NSs detected in the UV-optical, for which the extrapolation of the X-ray thermal component into the optical underpredicts the observed flux of thermal radiation, the FUV spectrum of Geminga lies slightly below the extrapolation of the soft thermal component, which might be associated with Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast to the FUV spectrum, the near-infrared (NIR) through near-ultraviolet (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, Fν ∞ ν -Γ+1, with a photon index Γ = 1.43 ± 0.15, close to the slope Γ = 1.56 ± 0.24 of the hard X-ray (E > 2.5 keV) magnetospheric component. The extrapolation of the X-ray magnetospheric spectrum into the optical is marginally consistent with (or perhaps lies slightly above) the observed NIR-optical-NUV spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.

AB - We observed the γ-ray pulsar Geminga with the FUV-MAMA and NUV-MAMA detectors of the Space Telescope Imaging Spectrometer to measure Geminga's spectrum and pulsations in the ultraviolet. The slope of the far-ultraviolet (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, FFUV = (3.7 ± 0.2) × 10-15 ergs cm-2 s-1 in the 1155-1702 Å band, corresponds to a brightness temperature TRJ ≈ (0.3-0.4)(d200/R13)2 MK, depending on the interstellar extinction (d = 200d200 pc and R = 13R13 km are the distance and the NS radius, respectively). The soft thermal component of Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature Ts = 0.49 ± 0.01 MK and radius Rs = (12.9 ± 1.0)d200 km. Contrary to other NSs detected in the UV-optical, for which the extrapolation of the X-ray thermal component into the optical underpredicts the observed flux of thermal radiation, the FUV spectrum of Geminga lies slightly below the extrapolation of the soft thermal component, which might be associated with Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast to the FUV spectrum, the near-infrared (NIR) through near-ultraviolet (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, Fν ∞ ν -Γ+1, with a photon index Γ = 1.43 ± 0.15, close to the slope Γ = 1.56 ± 0.24 of the hard X-ray (E > 2.5 keV) magnetospheric component. The extrapolation of the X-ray magnetospheric spectrum into the optical is marginally consistent with (or perhaps lies slightly above) the observed NIR-optical-NUV spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.

UR - http://www.scopus.com/inward/record.url?scp=22144471246&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=22144471246&partnerID=8YFLogxK

U2 - 10.1086/429368

DO - 10.1086/429368

M3 - Article

AN - SCOPUS:22144471246

VL - 625

SP - 307

EP - 323

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 I

ER -