Title: The missing GeV γ-ray binary: Searching for HESS J0632+057 with Fermi-LAT

Abstract

The very high energy (VHE; >100 GeV) source HESS J0632+057 has been recently confirmed as a γ-ray binary, a subclass of the high-mass X-ray binary population, through the detection of an orbital period of 321 d. We performed a deep search for the emission of HESS J0632+057 in the GeV energy range using data from the Fermi Large Area Telescope (LAT). The analysis was challenging due to the source being located in close proximity to the bright γ-ray pulsar PSR J0633+0632 and lying in a crowded region of the Galactic plane where there is prominent diffuse emission. We formulated a Bayesian block algorithm adapted to work with weighted photon counts, in order to define the off-pulse phases of PSR J0633+0632. A detailed spectral-spatial model of a 5° circular region centred on the known location of HESS J0632+057 was generated to accurately model the LAT data. No significant emission from the location of HESS J0632+057 was detected in the 0.1–100 GeV energy range integrating over ~3.5 yr of data, with a 95 per cent flux upper limit of F0.1-100 GeV < 3 × 10^–8 ph cm^–2 s^–1. A search for emission over different phases of the orbit also yielded no significantmore » detection. A search for source emission on shorter time-scales (days–months) did not yield any significant detections. We also report the results of a search for radio pulsations using the 100-m Green Bank Telescope. No periodic signals or individual dispersed bursts of a likely astronomical origin were detected. We estimated the flux density limit of < 90/40 μJy at 2/9 GHz. Furthermore, the LAT flux upper limits combined with the detection of HESS J0632+057 in the 136–400 TeV energy band by the MAGIC collaboration imply that the VHE spectrum must turn over at energies <136 GeV placing constraints on any theoretical models invoked to explain the γ-ray emission.« less

Authors:

Caliandro, G. A. ^[1]; Hill, A. B. ^[2]; Torres, D. F. ^[3]; Hadasch, D. ^[1]; Ray, P. ^[4]; Abdo, A. ^[5]; Hessels, J. W. T. ^[6]; Ridolfi, A. ^[7]; Possenti, A. ^[7]; Burgay, M. ^[7]; Rea, N. ^[1]; Tam, P. H. T. ^[8]; Dubois, R. ^[9]; Dubus, G. ^[10]; Glanzman, T. ^[9]; Jogler, T. ^[9]

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+ Show Author Affiliations

1. Institut de Ciencies de l'Espai (IEEC-CSIC), Barcelona (Spain)
2. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.; Univ. of Southampton, Southampton (United Kingdom)
3. Institut de Ciencies de l'Espai (IEEC-CSIC), Barcelona (Spain); Institucio Catalana de Recerca i Estudis Avancats (ICREA), Barcelona (Spain)
4. Naval Research Lab., Washington, D. C. (United States)
5. George Mason Univ., Fairfax, VA (United States)
6. ASTRON, the Netherlands Institute for Radio Astronomy, Dwingeloo (The Netherlands); Univ. of Amsterdam, Amsterdam (The Netherlands)
7. INAF Osservatorio Astronomico di Cagliari, Capoterra (CA) (Italy)
8. National Tsing Hua Univ., Hsinchu (Taiwan)
9. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
10. Institut de Planetologie et d'Astrophysique de Grenoble (IPAG), Grenoble (France)

Publication Date:

Wed Sep 25 00:00:00 EDT 2013

Research Org.:

SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1356556

Grant/Contract Number:  

AC02-76SF00515

Resource Type:

Accepted Manuscript

Journal Name:

Monthly Notices of the Royal Astronomical Society

Additional Journal Information:

Journal Volume: 436; Journal Issue: 1; Journal ID: ISSN 0035-8711

Publisher:

Royal Astronomical Society

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; gamma-rays: general; X-rays: binaries