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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. GRB 250217C: AstroSat CZTI detection of a short burst
  2. Fermi GRB 250217C: Global MASTER-Net observations report
  3. GRB 250217C: Fermi GBM Final Real-time Localization
  4. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  5. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  6. Fermi GRB 250217A: Global MASTER-Net observations report
  7. GRANDMA/OPD observations of GRB250215A
  8. GRB 250217B: Fermi GBM Final Real-time Localization
  9. The EP-WXT trigger 01709131775 is likely a flaring star
  10. GRB 250217A: Fermi GBM Final Real-time Localization
  11. Fermi GRB 250216A: Global MASTER-Net observations report
  12. GRB 250215A / EP250215a: LCO detection of the afterglow
  13. GRB 250216A: Fermi GBM Final Real-time Localization
  14. EP250212a: FTW optical and NIR upper limits
  15. GRB 250215A: Swift/UVOT Upper Limits
  16. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  17. EP250215a / GRB 250215A : GTC redshift z = 4.61
  18. GRB 250215A: Fermi GBM Observation
  19. EP250215a / GRB 250215A : NOT optical observations
  20. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  21. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  22. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  23. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  24. GRB 250215A: Swift-XRT refined Analysis
  25. GRB 250215A: SVOM/GRM observation
  26. EP250215a / GRB 250215A: AstroSat CZTI detection
  27. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  28. EP250215a: Global MASTER-Net observations report
  29. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  30. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  31. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  32. Fermi GRB 250215A: Global MASTER-Net observations report
  33. GRB 250215A: Fermi GBM Final Real-time Localization
  34. Fermi trigger No 761206993: Global MASTER-Net observations report
  35. GRB 250213A：SVOM/VT optical candidate
  36. Fermi Gamma-ray Burst Monitor trigger 761206993/250214266 is not a GRB
  37. EP250207b: Xinglong optical upper limit
  38. Fermi GRB 250214A: Global MASTER-Net observations report
  39. GRB 250213A: Swift ToO observations
  40. GRB 250214A: Fermi GBM Final Real-time Localization
  41. EP250212a: Xinglong optical upper limit
  42. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  43. GRB 250213A: SVOM detection of a burst
  44. EP250212a: Global MASTER-Net observations report
  45. GRB 250205A: VIRT Optical Upper Limit
  46. GRB 250205A: Leavitt Observatory optical upper limit
  47. GRB 250210A: GRBAlpha detection
  48. EP250207B: Chandra localization of the X-ray counterpart
  49. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  50. EP250207b: VLA radio upper limits
  51. EP250212a: Liverpool Telescope optical upper limits
  52. EP250212a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  53. GRB250101A: Radio upper limits from GMRT observations
  54. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  55. EP250207B: GTC z-band Observations
  56. Fermi GRB 250212A: Global MASTER-Net observations report
  57. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  58. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  59. Fermi trigger No 760945500: Global MASTER-Net observations report
  60. EP250207b: NOT optical counterpart candidate
  61. GRB 250211A: SVOM trigger sb25021103 is not a GRB
  62. GRB 250211B: A long GRB detected by INTEGRAL
  63. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  64. GRB 250211A: Swift ToO observations
  65. Integral GRB250211.89: Global MASTER-Net observations report
  66. GRB 250212A: Fermi GBM Final Real-time Localization
  67. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  68. LIGO/Virgo/KAGRA S250211be: Updated Sky localization
  69. GRB 250207A: Fermi GBM Observation
  70. GRB 250206A: Fermi GBM Observation
  71. GRB 250205A / EP250205A: radio detection with the VLA
  72. IceCube-250207A: One candidate from the Zwicky Transient Facility
  73. EP250207b: Tentative z-band brightening source
  74. LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
  75. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  76. Konus-Wind detection of GRB 250207A
  77. Konus-Wind detection of GRB 250206A
  78. GRB 250210A: SVOM/GRM observation of a long burst
  79. EP250207b: Liverpool Telescope possible optical counterpart
  80. EP250207b: Global MASTER-Net observations report
  81. Fermi Gamma-ray Burst Monitor trigger 760945500/250211240 is not a GRB
  82. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  83. LIGO/Virgo/KAGRA S250211be: Identification of a GW compact binary merger candidate
  84. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  85. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  86. GRB 250207A: Skynet optical afterglow observations
  87. LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II
  88. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  89. GRB 241128A: VIRT Optical Upper Limit
  90. EP250207b: Gemini GMOS-N z-band observations
  91. EP250207A: Upper limits from Fermi-GBM Observations
  92. GRB 250210A: INTEGRAL SPI-ACS detection
  93. GRB 250210A: AstroSat CZTI detection
  94. EP250207b: a new X-ray transient detected by Einstein Probe
  95. LIGO/Virgo/KAGRA S250206dm: MASTER detection AT2025bbo
  96. GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
  97. Fermi GRB 250210A: Global MASTER-Net observations report
  98. GRB 250210A: Fermi GBM Final Real-time Localization
  99. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  100. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube

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