Abstract
We report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk421) during the first 1.5years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3GeV can be well described by a power-law function with photon index Γ = 1.78 0.02 and average photon flux F(> 0.3GeV) = (7.23 0.16) × 10-8phcm-2s -1. Over this time period, the Fermi-LAT spectrum above 0.3GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor 3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk421 showed a low activity at all wavebands. The extensive multi-instrument (radio toTeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.
Original language | English (US) |
---|---|
Article number | 131 |
Journal | Astrophysical Journal |
Volume | 736 |
Issue number | 2 |
DOIs | |
State | Published - Aug 1 2011 |
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
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In: Astrophysical Journal, Vol. 736, No. 2, 131, 01.08.2011.
Research output: Contribution to journal › Article › peer-review
TY - JOUR
T1 - Fermi large area telescope observations of Markarian 421
T2 - The missing piece of its spectral energy distribution
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PY - 2011/8/1
Y1 - 2011/8/1
N2 - We report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk421) during the first 1.5years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3GeV can be well described by a power-law function with photon index Γ = 1.78 0.02 and average photon flux F(> 0.3GeV) = (7.23 0.16) × 10-8phcm-2s -1. Over this time period, the Fermi-LAT spectrum above 0.3GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor 3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk421 showed a low activity at all wavebands. The extensive multi-instrument (radio toTeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.
AB - We report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk421) during the first 1.5years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3GeV can be well described by a power-law function with photon index Γ = 1.78 0.02 and average photon flux F(> 0.3GeV) = (7.23 0.16) × 10-8phcm-2s -1. Over this time period, the Fermi-LAT spectrum above 0.3GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor 3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk421 showed a low activity at all wavebands. The extensive multi-instrument (radio toTeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.
UR - http://www.scopus.com/inward/record.url?scp=80051535196&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=80051535196&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/736/2/131
DO - 10.1088/0004-637X/736/2/131
M3 - Article
AN - SCOPUS:80051535196
SN - 0004-637X
VL - 736
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 131
ER -