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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. Fermi GRB 250217A: Global MASTER-Net observations report
  2. GRANDMA/OPD observations of GRB250215A
  3. GRB 250217B: Fermi GBM Final Real-time Localization
  4. The EP-WXT trigger 01709131775 is likely a flaring star
  5. GRB 250217A: Fermi GBM Final Real-time Localization
  6. Fermi GRB 250216A: Global MASTER-Net observations report
  7. GRB 250215A / EP250215a: LCO detection of the afterglow
  8. GRB 250216A: Fermi GBM Final Real-time Localization
  9. EP250212a: FTW optical and NIR upper limits
  10. GRB 250215A: Swift/UVOT Upper Limits
  11. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  12. EP250215a / GRB 250215A : GTC redshift z = 4.61
  13. GRB 250215A: Fermi GBM Observation
  14. EP250215a / GRB 250215A : NOT optical observations
  15. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  16. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  17. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  18. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  19. GRB 250215A: Swift-XRT refined Analysis
  20. GRB 250215A: SVOM/GRM observation
  21. EP250215a / GRB 250215A: AstroSat CZTI detection
  22. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  23. EP250215a: Global MASTER-Net observations report
  24. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  25. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  26. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  27. Fermi GRB 250215A: Global MASTER-Net observations report
  28. GRB 250215A: Fermi GBM Final Real-time Localization
  29. Fermi trigger No 761206993: Global MASTER-Net observations report
  30. GRB 250213A：SVOM/VT optical candidate
  31. Fermi Gamma-ray Burst Monitor trigger 761206993/250214266 is not a GRB
  32. EP250207b: Xinglong optical upper limit
  33. Fermi GRB 250214A: Global MASTER-Net observations report
  34. GRB 250213A: Swift ToO observations
  35. GRB 250214A: Fermi GBM Final Real-time Localization
  36. EP250212a: Xinglong optical upper limit
  37. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  38. GRB 250213A: SVOM detection of a burst
  39. EP250212a: Global MASTER-Net observations report
  40. GRB 250205A: VIRT Optical Upper Limit
  41. GRB 250205A: Leavitt Observatory optical upper limit
  42. GRB 250210A: GRBAlpha detection
  43. EP250207B: Chandra localization of the X-ray counterpart
  44. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  45. EP250207b: VLA radio upper limits
  46. EP250212a: Liverpool Telescope optical upper limits
  47. EP250212a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  48. GRB250101A: Radio upper limits from GMRT observations
  49. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  50. EP250207B: GTC z-band Observations
  51. Fermi GRB 250212A: Global MASTER-Net observations report
  52. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  53. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  54. Fermi trigger No 760945500: Global MASTER-Net observations report
  55. EP250207b: NOT optical counterpart candidate
  56. GRB 250211A: SVOM trigger sb25021103 is not a GRB
  57. GRB 250211B: A long GRB detected by INTEGRAL
  58. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  59. GRB 250211A: Swift ToO observations
  60. Integral GRB250211.89: Global MASTER-Net observations report
  61. GRB 250212A: Fermi GBM Final Real-time Localization
  62. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  63. LIGO/Virgo/KAGRA S250211be: Updated Sky localization
  64. GRB 250207A: Fermi GBM Observation
  65. GRB 250206A: Fermi GBM Observation
  66. GRB 250205A / EP250205A: radio detection with the VLA
  67. IceCube-250207A: One candidate from the Zwicky Transient Facility
  68. EP250207b: Tentative z-band brightening source
  69. LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
  70. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  71. Konus-Wind detection of GRB 250207A
  72. Konus-Wind detection of GRB 250206A
  73. GRB 250210A: SVOM/GRM observation of a long burst
  74. EP250207b: Liverpool Telescope possible optical counterpart
  75. EP250207b: Global MASTER-Net observations report
  76. Fermi Gamma-ray Burst Monitor trigger 760945500/250211240 is not a GRB
  77. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  78. LIGO/Virgo/KAGRA S250211be: Identification of a GW compact binary merger candidate
  79. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  80. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  81. GRB 250207A: Skynet optical afterglow observations
  82. LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II
  83. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  84. GRB 241128A: VIRT Optical Upper Limit
  85. EP250207b: Gemini GMOS-N z-band observations
  86. EP250207A: Upper limits from Fermi-GBM Observations
  87. GRB 250210A: INTEGRAL SPI-ACS detection
  88. GRB 250210A: AstroSat CZTI detection
  89. EP250207b: a new X-ray transient detected by Einstein Probe
  90. LIGO/Virgo/KAGRA S250206dm: MASTER detection AT2025bbo
  91. GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
  92. Fermi GRB 250210A: Global MASTER-Net observations report
  93. GRB 250210A: Fermi GBM Final Real-time Localization
  94. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  95. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube
  96. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report
  97. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  98. IceCube Alert 250207.09: Global MASTER-Net observations report
  99. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER
  100. GRB 250204B: GRBAlpha detection

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