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Title: Associating long-term γ-ray variability with the superorbital period of LS I +61°303

Gamma-ray binaries are stellar systems for which the spectral energy distribution (discounting the thermal stellar emission) peaks at high energies. Detected from radio to TeV gamma rays, the γ-ray binary LS I +61°303 is highly variable across all frequencies. One aspect of this system's variability is the modulation of its emission with the timescale set by the ~26.4960 day orbital period. Here we show that, during the time of our observations, the γ-ray emission of LS I +61°303 also presents a sinusoidal variability consistent with the previously known superorbital period of 1667 days. This modulation is more prominently seen at orbital phases around apastron, whereas it does not introduce a visible change close to periastron. It is also found in the appearance and disappearance of variability at the orbital period in the power spectrum of the data. This behavior could be explained by a quasi-cyclical evolution of the equatorial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. Furthermore, these findings open the possibility to use γ-ray observations to study the outflows of massive stars in eccentric binary systems.
Authors:
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Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 773; Journal Issue: 2; Journal ID: ISSN 2041-8205
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; gamma rays: general; gamma rays: stars; stars: emission-line; Be
OSTI Identifier:
1356568

Ackermann, M., Ajello, M., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bonamente, E., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Casandjian, J. M., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Cutini, S., Dalton, M., D'Ammando, F., de Angelis, A., den Hartog, P. R., de Palma, F., Dermer, C. D., Digel, S. W., Di Venere, L., Drell, P. S., Dubois, R., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hays, E., Hill, A. B., Horan, D., Hughes, R. E., Jogler, T., Jóhannesson, G., Johnson, A. S., Johnson, T. J., Kawano, T., Kerr, M., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Longo, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohsugi, T., Okumura, A., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Papitto, A., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Rea, N., Reimer, A., Reimer, O., Scargle, J. D., Schulz, A., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. G., Thayer, J. B., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Werner, M., Winer, B. L., and Wood, K. S.. Associating long-term γ-ray variability with the superorbital period of LS I +61°303. United States: N. p., Web. doi:10.1088/2041-8205/773/2/L35.
Ackermann, M., Ajello, M., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bonamente, E., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Casandjian, J. M., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Cutini, S., Dalton, M., D'Ammando, F., de Angelis, A., den Hartog, P. R., de Palma, F., Dermer, C. D., Digel, S. W., Di Venere, L., Drell, P. S., Dubois, R., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hays, E., Hill, A. B., Horan, D., Hughes, R. E., Jogler, T., Jóhannesson, G., Johnson, A. S., Johnson, T. J., Kawano, T., Kerr, M., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Longo, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohsugi, T., Okumura, A., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Papitto, A., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Rea, N., Reimer, A., Reimer, O., Scargle, J. D., Schulz, A., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. G., Thayer, J. B., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Werner, M., Winer, B. L., & Wood, K. S.. Associating long-term γ-ray variability with the superorbital period of LS I +61°303. United States. doi:10.1088/2041-8205/773/2/L35.
Ackermann, M., Ajello, M., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bonamente, E., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Casandjian, J. M., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Cutini, S., Dalton, M., D'Ammando, F., de Angelis, A., den Hartog, P. R., de Palma, F., Dermer, C. D., Digel, S. W., Di Venere, L., Drell, P. S., Dubois, R., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hays, E., Hill, A. B., Horan, D., Hughes, R. E., Jogler, T., Jóhannesson, G., Johnson, A. S., Johnson, T. J., Kawano, T., Kerr, M., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Longo, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohsugi, T., Okumura, A., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Papitto, A., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Rea, N., Reimer, A., Reimer, O., Scargle, J. D., Schulz, A., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. G., Thayer, J. B., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Werner, M., Winer, B. L., and Wood, K. S.. 2013. "Associating long-term γ-ray variability with the superorbital period of LS I +61°303". United States. doi:10.1088/2041-8205/773/2/L35. https://www.osti.gov/servlets/purl/1356568.
@article{osti_1356568,
title = {Associating long-term γ-ray variability with the superorbital period of LS I +61°303},
author = {Ackermann, M. and Ajello, M. and Ballet, J. and Barbiellini, G. and Bastieri, D. and Bellazzini, R. and Bonamente, E. and Brandt, T. J. and Bregeon, J. and Brigida, M. and Bruel, P. and Buehler, R. and Buson, S. and Caliandro, G. A. and Cameron, R. A. and Caraveo, P. A. and Casandjian, J. M. and Cavazzuti, E. and Cecchi, C. and Chekhtman, A. and Chiang, J. and Chiaro, G. and Ciprini, S. and Claus, R. and Cohen-Tanugi, J. and Cominsky, L. R. and Conrad, J. and Cutini, S. and Dalton, M. and D'Ammando, F. and de Angelis, A. and den Hartog, P. R. and de Palma, F. and Dermer, C. D. and Digel, S. W. and Di Venere, L. and Drell, P. S. and Dubois, R. and Favuzzi, C. and Fegan, S. J. and Ferrara, E. C. and Focke, W. B. and Franckowiak, A. and Funk, S. and Fusco, P. and Gargano, F. and Gasparrini, D. and Germani, S. and Giglietto, N. and Giordano, F. and Giroletti, M. and Glanzman, T. and Godfrey, G. and Grenier, I. A. and Guiriec, S. and Hadasch, D. and Hanabata, Y. and Harding, A. K. and Hayashida, M. and Hays, E. and Hill, A. B. and Horan, D. and Hughes, R. E. and Jogler, T. and Jóhannesson, G. and Johnson, A. S. and Johnson, T. J. and Kawano, T. and Kerr, M. and Knödlseder, J. and Kuss, M. and Lande, J. and Larsson, S. and Latronico, L. and Lemoine-Goumard, M. and Li, J. and Longo, F. and Lovellette, M. N. and Lubrano, P. and Mayer, M. and Mazziotta, M. N. and McEnery, J. E. and Michelson, P. F. and Mizuno, T. and Monzani, M. E. and Morselli, A. and Moskalenko, I. V. and Murgia, S. and Nemmen, R. and Nuss, E. and Ohsugi, T. and Okumura, A. and Orienti, M. and Orlando, E. and Ormes, J. F. and Paneque, D. and Papitto, A. and Perkins, J. S. and Pesce-Rollins, M. and Piron, F. and Pivato, G. and Rainò, S. and Rando, R. and Razzano, M. and Rea, N. and Reimer, A. and Reimer, O. and Scargle, J. D. and Schulz, A. and Sgrò, C. and Siskind, E. J. and Spandre, G. and Spinelli, P. and Takahashi, H. and Thayer, J. G. and Thayer, J. B. and Tinivella, M. and Torres, D. F. and Tosti, G. and Troja, E. and Uchiyama, Y. and Usher, T. L. and Vandenbroucke, J. and Vasileiou, V. and Vianello, G. and Vitale, V. and Werner, M. and Winer, B. L. and Wood, K. S.},
abstractNote = {Gamma-ray binaries are stellar systems for which the spectral energy distribution (discounting the thermal stellar emission) peaks at high energies. Detected from radio to TeV gamma rays, the γ-ray binary LS I +61°303 is highly variable across all frequencies. One aspect of this system's variability is the modulation of its emission with the timescale set by the ~26.4960 day orbital period. Here we show that, during the time of our observations, the γ-ray emission of LS I +61°303 also presents a sinusoidal variability consistent with the previously known superorbital period of 1667 days. This modulation is more prominently seen at orbital phases around apastron, whereas it does not introduce a visible change close to periastron. It is also found in the appearance and disappearance of variability at the orbital period in the power spectrum of the data. This behavior could be explained by a quasi-cyclical evolution of the equatorial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. Furthermore, these findings open the possibility to use γ-ray observations to study the outflows of massive stars in eccentric binary systems.},
doi = {10.1088/2041-8205/773/2/L35},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 773,
place = {United States},
year = {2013},
month = {8}
}